Skull Base Bones and Anatomy

Normal skull base
• Concept of fossa does not work well for the
skull base, because the bony anatomy spills
over from one fossa to the next.
• Perspective of individual bones
– Components
– Apertures
– Transmitted structures

Normal skull base
• Extend
– root of nose anteriorly to the superior nuchal line
posteriorly

Normal skull base
• 5 bones:
– Frontal
– Ethmoid
– Sphenoid
– Temporal
– Occipital

Normal skull base
• Most important part:
– Basisphenoid (anterior aspect of sella)
– Basiocciput (posterior lip of the foramen magnum)
• The cranial nerves and cerebral vasculature traverse
the skull base here.

Occipital bone
• Floor of the posterior
fossa
• 3 distinct areas:
– Basiocciput (clivus and
jugulare tubercles)
– Condylar (lateral)
portion
– Squamous (posterior)
portion

Occipital bone
• Apertures:
– Foramen magnum
– Posterior condylar canal
– Hypoglossal canal

Temporal bone
• Petrous pyramid and mastoid
process form most of the skull
base between the posterior and
middle skull base.
• Apex of the petrous pyramid joins
the anterolateral margin of the
clivus (i.e., basiocciput) and the
posteromedial aspect of the
greater wing of sphenoid along
the basisphenoid synchondrosis.

• Apertures:
– Jugular foramen
– Internal auditory canal
– Facial nerve canal
– Petrous carotid canal
– Eustachian tube

Sphenoid bone
• Mid section of the skull base
• Anterior wall of middle cranial fossa

Sphenoid bone
• 3 compartments:
– Basisphenoid:
• Dorsum sella, posterior
clinoids, sella turcica,
tuberculum sella, sphenoid
sinus
• Fused to clivus in adult
– Greater wing of sphenoid
• Medial two-thirds and anterior
wall of the middle cranial fossa
floor
– Lesser wing of sphenoid
• Medial and superior aspects of
the anterior wall of the middle
cranial fossa and the anterior
clinoids
• Superior and medial edges of
the superior orbital fissure

Sphenoid bone
• Apertures:
– Foramen ovale
– Foramen spinosum
– Foramen rotundum
– Optic canal
– Superior orbital fissure
– Precavernous carotid canal
– Foramen lacerum
• Not a true foramen
• Thinning of skull base, filled with fibrocartilage in life

Frontal bone
• Anterior cranial fossa is
anteriorly and laterally
bound by frontal bone;
majority by orbital plate
of frontal bone

• Foramen caecum
– Indentation in the medial
anterior frontal bone
– Normal (should not be
confused with
cephalocoele)
– Complete bony floor
(protrude through a gap in
the frontal bone)
– Prominent at birth and
gradually shrinks over first
10 years of life
Frontal bone

Ethmoid bone
• 2 distinct pieces:
– Cribriform plate
– Crista galli

Ethmoid bone
• Cribriform plate is
perforated by approx 20
holes on each side of the
crista galli
• Nerve fibres of olfactory
nerve (CN I) pass from nasal
mucosa to olfactory bulb
• Crista galli serves as the
anchor for anterior margin
of the falx cerebri

Development of the skull base
• Development of the skull base begins only
after the spinal cord, cranial nerves, and blood
vessels have formed.
• The cranial base is relatively stable during
development as compared with the rapid
growth and expansion of the calvaria.
• Study of fetal developmental anatomy may
lead to a better understanding of congenital
skull base disorders.

The skull base originates predominately from cartilaginous
precursors with a small contribution from membranous bone.

The components of the skull base are derived from neural crest cells
and mesoderm during the fourth week of fetal life to form the
cartilaginous and bony components of the cranial base.

Ossification of the skull base progresses in an
orderly pattern from posterior to anterior.

Submento-vertical
• Position of patient and cassette
– The patient may be imaged erect or supine.
If the patient is unsteady, then a supine
technique is advisable.
• Supine
– The patient’s shoulders are raised and the
neck is hyperextended to bring the vertex of
the skull in contact with the grid cassette or
table.
– The head is adjusted to bring the external
auditory meatuses equidistant from the
cassette.
– The median sagittal plane should be at right-
angles to the cassette along its midline.
– The orbito-meatal plane should be as near as
possible parallel to the cassette.
• Erect
– The patient sits a short distance away from a vertical Bucky.
– The neck is hyperextended to allow the head to fall back
until the vertex of the skull makes contact with the centre
of the vertical Bucky.

Submento-vertical
• Direction and centring of the
X-ray beam
– The central ray is directed at
right-angles to the orbito-meatal
plane and centred midway
between the external auditory
meatuses.

Essential image characteristics
• A correct projection will
show the angles of the
mandible clear of the
petrous portions of the
temporal bone.
• The foramina of the
middle cranial fossa
should be seen
symmetrically either
side of the midline.

Essential image characteristics
POSITIONING
• No rotation is evidenced by
 The lateral borders of the foramen
magnum are equidistant from the
lateral borders of the skull.
• No tilt is evidenced by
• The vomer and the bony nasal
septum are aligned with the long
axis of the film.

Jugular foramina:
Submento-vertical 20 degrees caudad
• The jugular foramina lie in
the posterior cranial fossa
between the petrous
temporal and occipital
bones on each side of the
foramen magnum.
• Both sides are imaged
simultaneously on a -
single image by
undertaking a submento-
vertical (SMV) 20 degrees
caudad projection.

Jugular foramina:
• Position of patient and
cassette
– As per the SMV
projection described
previously.

Jugular foramina:
• Direction and centring
of the X-ray beam
– Using a well-collimated
beam, the central ray is
angled caudally so that
it makes an angle of 70
degrees to the
orbitomeatal plane and
centred in the midline to
pass midway between
the external auditory
meatuses.

Notes: Alternative Technique
• With the patient’s neck
less extended, the head
can be positioned with
the orbito-meatal plane
at an angle of 20
degrees to the Bucky, in
which case a horizontal
central ray will make
the required angle of 70
degrees to the base
plane (see photograph).

Jugular foramina:

Role of imaging
• Diagnosis
• Extend of disease – criteria of surgical
resectability
• Treatment planning – surgical approach
• Follow up – recurrence vs post ttreatment
changes

Anterior skull base lesions
• Bones:
– Orbital plates of frontal
bones
– Cribriform plate of
ethmoid bone
– Planum sphenoidale

Anterior Skull Base Lesions
Common:
Malignant sinonasal tumor (eg., SCC,
RMS)
Meningioma
Metastases
Uncommon
Mucocoele
Osteoma
Polyposis
Inverted papilloma
Esthesioneuroblastoma
Lymphoma
Complicated sinusitis (bacterial,
fungal, granulomatous)
Rare
Cephalocoele
Dermoid cyst

• Lesions arise:
– Extracranially
• From the nasal vault, frontal and ethmoid sinuses
– Intrinsically
• From the skull base itself
– Intracranially
• From the brain, meninges and CSF spaces

Extra cranial lesions
• Most arise from the nose and paranasal
sinuses
Common Benign Lesions
Mucocoele
Polyposis
Inverted papilloma
Osteoma
Common Malignant Lesions
Squamous cell carcinoma
Rhabdomyosarcoma
Adenoid cystic carcinoma

Mucocoele
• Accumulation of
impacted mucus behind
an occluded draining
sinus ostium.
• Obstruction -
Inflammatory > post
traumatic, neoplastic
• Frontal > Ethmoid >
Maxillary > Sphenoid

Mucocoele - Imaging
• Well delineated soft tissue mass with bony
expansion and remodelling.
• Low density on NECT; inspissated secretions
may appear hyperdense.
• MR signal is variable.
• Aggressive bone erosion seen in 10 – 12% of
cases.

Mucocele
A: Coronal T1 magnetic resonance image. The sphenoid sinus is enlarged and its contents are of high signal. Mucocele also
involves the left anterior clinoid (arrow), which is markedly expanded and filled with the same high-signal contents as the
rest of the sinus.
B: Sagittal T1 magnetic resonance image again shows marked enlargement of the left anterior clinoid (large arrow).

Mucopyocoele
• Mucocoeles when
infected
Axial T1 C+ MR shows left frontal mucopyocoele with thick, peripheral enhancement.
Note linear enhancement of the anterior fossa dura (arrows) consistent with meningitis.

Inverted Papilloma
• Benign slow growing
epithelial neoplasm.
• 1 to 4% of sinonasal
neoplasms
• Arise near the nasal vault
near the junction of
ethmoid and maxillary
sinuses.
• The surface epithelium
proliferates by inverting
into underlying stroma
rather than growing
outward.

Inverted Papilloma
• Benign slow growing
epithelial neoplasm.
• 1 to 4% of sinonasal
neoplasms
• Arise near the nasal vault
near the junction of
ethmoid and maxillary
sinuses.
• The surface epithelium
proliferates by inverting
into underlying stroma
rather than growing
outward.
Inverted sinonasal or Schneiderian papilloma shows
endophytic or “inverted” growth pattern. These nests of
squamous epithelial cells grow down into the myxomatous
to fibrous stroma with chronic inflammatory cells and
vascularity

Inverted Papilloma - Imaging
• A unilateral, polypoid nasal
fossa soft tissue mass
• widens the nasal vault
• sometimes destroying bone
and extending into the
adjacent ethmoid and
maxillary sinuses
• Focal erosion of the cribriform
plate with cephalad extension
occassionally occurs. (DD:
sinonasal malignancies)
• No definitive MR findings to
differentiate from various
malignant tumors.

Osteoma
• Benign bony tumor
• Mature well delineated
cortical bone as their
primary component.
• Most common site:
frontal sinus
• Expands and erodes the
posterior and superior
frontal sinus walls

Malignant Sinonasal Tumors
• Intracranial extension
occurs in upto one-third of
cases
• Squamous cell carcinoma
• Esthesioneuroblastoma
• Adenocarcinoma
• Melanoma
• Non-Hodgkin Lymphoma

Rhabdomyosarcoma
• In children the most common extracranial
malignancy that affects the skull base is
Rhabdomyosarcoma.
• It is the most common soft tissue sarcoma in
children.
• Head and neck is the most common site.
• Orbit & nasopharynx > PNS & middle ear

• Anterior skull base invasion or cavernous sinus
invasion - approx. 35% of nasopharyngeal
RMS.
• Bulky soft tissue mass with areas of bone
destruction.
• Isointense to muscle on T1, hyperintense on
T2; some contrast enhancement.
• Meningeal and perineural spread are common

Nasal cavity RMS with extension through
sinonasal roof, along the anterior cranial fossa

Intracranial extension of masticator
fossa RMS through foramen ovale

Other Malignancies
• 98% of nasopharyngeal tumors in adults are
carcinomas.
• Squamous cell carcinoma accounts for 80% of
these tumors, and adenocarcinoma (most
commonly from minor salivary glands) represent
18%.
• Nasopharyngeal carcinomas spread directly into
skull base as well as along muscles and their
tendinous insertions.
• They extend intracranially along neural and
vascular bundles via osseous foramina.

• A nasopharyngeal mass
with obliterated soft
tisssue planes and
adjacent bone
destruction are the
typical imaging findings
with direct tumor
invasion.
• Serous otitis media can
be seen because the
eustachian tube is
frequently obstructed. T1C+ : NP Ca has destroyed large area of skull base
bone (arrows) surrounding the foramen ovale.
Opposite foramen ovale has V3 traversing it (open
arrow).

• Perineural tumor spread most commonly
involves the second and third divisions of
trigeminal nerve and facial nerve.
• Sometimes no dominant mass is present.
• Enhancement of the affected nerve or
denervation atrophy of the muscles of
mastication and face may be the only
detectable abnormalities.

• Olfactory
neuroblastoma
• Bipolar sensory
receptor cells in the
olfactory mucosa.
(neural crest origin)
• Any age – bimodal peak
(2nd and 4th/5th decade)

Esthesioneuroblastoma - imaging
• Often confined to nasal
cavity; may extend to PNS
or anterior cranial fossa
(through cribriform plate)
• High nasal vault with focal
bone destruction
• Variable signal intensity on
MR
• Moderate but
inhomogenous
enhancement
• CNS dissemination as a late
manifestation
CECT - right nasal cavity ENB with destruction
of the cribriform plate (arrow) and lamina
papyracea (open arrow).

Esthesioneuroblastoma - imaging
• Often confined to nasal
cavity; may extend to PNS
or anterior cranial fossa
(through cribriform plate)
• High nasal vault with focal
bone destruction
• Variable signal intensity on
MR
• Moderate but
inhomogenous
enhancement
• CNS dissemination as a late
manifestation

Miscellaneous
• Bacterial or fungal
sinusitis

Misc
• Cocaine granulomatosis
– History of coccaine
abuse
– Septal perforation with
nasal inflammatory
changes

Misc
• Wegner granulomatosis
– Soft tissue mass in nose
with septal and non-
septal bone destruction
Enhancing soft tissue in maxillary sinuses
extending into nasopharynx (arrows) with
large septal perforation.

Intrinsic anterior skull base lesions
Intrinsic anterior skull base lesions
Fibrous dysplasia
Paget disease
Osteopetrosis

Intracranial lesions
• Arise from:
– Meninges
– CSF spaces
– Brain

Meningioma
• Most common meningeal lesion to involve anterior skull
base
• Planum sphenoidale and olfactory groove – 10-15% of all
meningiomas
• Broad based, anterior basal subfrontal mass that enhances
strongly and relatively uniformly after contrast
administration is typical.
• Presence of tumor-brain interface or cleft with compressed
cortex and white matter buckling indicate extraaxial
location.
• Blistering and hyperostosis of the adjacent bone.
• Enlargement of the air-containing ethmoid sinus
(pneumosinus dilatans) or even frank bone destruction is
sometimes observed.

Figure. (A) Enlarged, air-filled ethmoid sinus extending into an isointense intracranial mass on T1-
weighted MRI, which enhances uniformly on contrast agent administration (B). (C) Axial CT shows
expansion of sinus beyond its normal boundaries into the meningioma, where the plate of bone
lining the pneumosinus dilatans is preserved
Mai A et al. Neurology 2003;60:1861-1861
©2003 by Lippincott Williams & Wilkins

Cephalocoele
• The most common
anterior skull base
lesion that arises from
the brain is
nasoethmoidal
cephalocoele.
• 15% of basal
cephalocoeles occur in
the frontonasal area.

Misc
• Nasal dermoid sinuses and nasal cerebral
heterotopias (nasal gliomas) are less common
congenital lesions that occur in this location.
• Occasionally, a slow growing peripherally located
primary brain neoplasms such as
ganglioneuroma cause pressure erosion of the
adjacent skull.
• Frank dural invasion or calvarial destruction can
occur with anaplastic astrocytoma and
glioblastoma multiforme, but uncommon.

Destructive Central Skull Base Lesions
Common
Metastases
Nasopharyngeal malignancy
Haematogenous
Uncommon
Osteomyelitis
Fungal sinusitis
Non fungal granulomas
Wegner granulomatosis
Cocaine abuse
Midline granuloma (probably a lymphoma variant)
Aggressive pituitary adenoma
Lymphoma
Myeloma
Meningioma
Juvenile nasopharyngeal angiofibroma
Chordoma
Rare
Leprosy
Rhinoscleroma
Syphilis
Sarcoidosis

Central skull base
• It includes:
– Upper clivus
– Sella turcica
– Cavernous sinuses
– Sphenoid alae

Central Skull Base Lesions
• Lesions affecting the central skull base
originate from:
– Cavernous sinus
– Pituitary gland
– Basisphenoid bone
– Nasopharynx

Cavernous sinus
• Multiseptated, extradural venous spaces that
lie on both sides of the sella turcica.
• They communicate extensively with each
other, the intracranial dural sinuses, and deep
facial venous plexuses.

• Lateral wall is composed of
2 layers:
– Thick outer dural layer
– Thin inner membranous layer
• The inner layer is formed by
the perineurium of CNs III,
IV, V1 and sometimes V2.
These nerves lie within the
lateral wall, whereas the
internal carotid artery and
CN VI are inside the
cavernous sinus proper.

• Medially, a thin poorly
delineated medial dural
wall separates the
cavernous sinus from
sella turcica.
• Meckel’s cave and its
contents, the trigeminal
ganglion, CSF, and
investing arachnoid,
invaginate into the
cavernous sinus
posteriorly.

Cavernous Sinus Masses
Unilateral Bilateral
Common Common
Schwannoma Invasive pituitary adenoma
Meningioma Meningioma
Metastasis Metastases
Aneurysm (Cavernous ICA)
Carotid-cavernous fistula
Uncommon Uncommon
Chordoma Lymphoma
Lymphoma Cavernous sinus thrombosis
Rare
Lipoma
Epidermoid
Cavernous haemangioma
Osteocartilagiomnous tumors
Plexiform neurofibroma (NF 1)

Congenital/Developmental lesions Neoplasms
Cephalocoele Benign
Encephalocoele Pituitary adenoma
Meningocoele Meningioma
Trauma Nerve sheath tumors
Fractures Juvenile nasopharyngeal angiofibroma
CSF fistula Chordoma
Infection and Inflammatory disease Osteocartilaginous tumors
Osteomyelitis Tumor like lesions
Bacteral sinusitis Epidermoid tumor
Fungal sinusitis Lipoma
Wegner granulomatosis Malignant tumors
Leishmaniasis Nasopharyngeal carcinoma
Sarcoidosis Rhabdomyosarcoma
Leprosy, Treponemes, Mycobacteria,
Rhinoscleroma
Multiple myeloma or Solitary
plasmocytoma
Cocaine abuse Osteosarcoma
Midline lethal granuloma (T-cell
lymphoma)
Chondrosarcoma
Miscellaneous Metastatic disease
Paget disease, Fibrous dyspasia Prostate, lung and breast carcinomas
Radiation necrosis Lymphoma – primary / secondary

Cephalocoele
• Axial CT scan (b) photographed
with bone window and coronal
CT scan (c) photographed with
soft-tissue window reveal the
presence of a persistent
craniopharyngeal canal (arrow)
in the sphenoid bone.
• Coronal (d) and midsagittal (e) Ti -
weighted MR images through the
central skull base demonstrate
herniation of the pituitary gland
into the craniopharyngeal canal
through the sphenoidal defect
(arrow) . Note the proximity of
the pituitary gland to the roof of
the nasopharynx.

Fractures
• Most commonly occur
as extensions of cranial-
vault fractures.
• Petrous temporal bone
> orbital surface of the
frontal bone >
basiocciput.
Multiple skull-base fractures in a 23-year-old
man after an automobile accident.

CSF fistula
• The most common cause of CSF fistula is skull-base trauma
– Fractures through the frontoethmoidal complex and middle cranial
fossa.
• Nontraumatic cause of leakage:
– Tumors, especially those arising from the pituitary gland
– congenital anomalies, such as encephaloceles
Coronal CT scans through the sphenoid sinus
were obtained before (a) and after (b) the
intrathecal instillation of water-soluble
contrast material. A mass with attenuation
values of soft tissue (arrow in a) is seen
involving the right lateral floor of the
sphenoid sinus. After contrast enhancement
increased attenuation is seen in this region,
consistent with the accumulation of contrast
material (curved arrow in b) . This finding
confirms the presence of a CSF fistula.

Osteomyelitis
• Potentially lethal complication of:
– Immunocompromised states
– Diabetes
– Chronic mastoiditis
– Paranasal sinus inection
– Trauma
– Necrotising otitis externa
• Occasionally in the absence of predisposing
factors

Bacterial sinusitis complicating
Osteomyelitis
• Infection can extend :
– Directly from frontal, ethmoid or sphenoid sinuses
– Intracranially via emissary veins and the cavernous
sinus.
• May result in:
– Cerebral infarct
– Meningitis
– Subdural empyema
– Brain abscess

Left frontal SDE with leptomeningeal enhancement in a
patient with left pansinusitis

Paranasal sinus fungal infections
• 4 different patterns:
– Extramucosal disease with cavitating mycetoma
(fungus ball)
– Allergic fungal sinusitis
– Mucosal thickening from indolent, penetrating
fungal sinusitis
– Fulminant invasive mycosis

• Manifestations include:
– Multiple cranial nerve palsies
– Septic cavernous sinus thrombosis
– Internal carotid occlusion
– Brain infarction
– Brain abscess

Fungal sinusitis - Imaging
• Multisinus nodular mucoperiosteal thickening
• High attenuation foci in soft tissue masses on
CT

17-year-old boy with allergic fungal sinusitis complicated by compression of right optic nerve. Painless decreased
vision had been present in the right eye for 2 months. Coronal (A–C) and axial (D) CT images show high-attenuation
opacification of left maxillary, left ethmoidal, and bilateral sphenoidal sinuses with bone expansion and thinning.
Compression of right optic nerve (straight arrow, B and D) is caused by expanded right anterior clinoid process
(asterisk, B and D). Bone dehiscence is present at left lamina papyracea (curved arrow,A and D) and around left
optic nerve (arrowhead, B and D), and internal carotid arteries (arrows, C). These structures are at risk of injury
during functional endoscopic sinus surgery.

Mycetomas
• Best diagnostic clue: single PNS contains high density
mass with fine round to linear matrix calcifications
• Very hypointense on MR with a high signal rim
surrounding the fungal ball.

Aggressive mycosis
• Extensive skull base destruction
• Cavernous sinus thrombosis, blood vessel
invasion and rapid intracranial dissemination
can occur
• CEMR / CECT – multiple filling defects within
the cavernous sinus.
• Extensive skull base erosion is
indistinguishable from nasopharyngeal
malignancy

• Biopsy-proved aspergillosis in a 23- year
oId black woman with right-sided facial
pain.
• Axial (a) and coronal (b, c) non-contrast-
enhanced CT scans show a large soft-
tissue mass (*) with extensive bone
destruction of the right maxillary sinus (m),
nasopharynx (n), pterygoid plate (p), and
sphenoid sinus (s) . The central high
attenatuation may represent calcium
deposits in mycetoma.
• T1-weighted MR images obtained before
(d) and after (e) administration of
gadopentetate dimeglumine show the
extent of skull base and sinus ivolvement.
• The central low-signal-intensity areas
within the sinus may represent inspissated
secretions or fungal mycetoma containing
metals.

Sarcoidosis
• Due to its propensity for leptomeningeal invasion,
sinus and nasopharyngeal sarcoidosis is recognized as a
more common cause of cranial nerve neuropathy.
• Central nervous system involvement occurs in 3%-8%
of patients with sarcoidosis.
• The most frequent problem is cranial neuropathy
secondary to facial, acoustic, optic, or trigeminal nerve
involvement.
• Sarcoidosis should be considered when both the
meninges and the cranial nerves are involved in a
pathologic process.

Other granulomatous diseases
• Wegner granulomatosis
• Leishmaniasis
• Leprosy
• Rhinoscleroma
• Mycobacteria
• Treponemes
• Cocaine abuse
• Midline lethal granuloma (T-cell lymphoma)

Pituitary Adenoma
• Usually indolent, non agresssive tumors that
expand and slowly erode the bony sella
turcica.
• Typically extend superorly through the
diaphragma sellae and laterlally into the
cavernous sinus.
• Occasionally, some variants behave more
aggressively and may cause extensive
destruction of the central skull base.

Meningioma
• Meningiomas of the central skull base are located
along
– the sphenoid wing,
– diaphragma sellae,
– clivus and
– cavernous sinus
• Focal, globose or flat, en-plaque lesions
• Occasionally, bony destruction or hyperostosis.
• Cavernous sinus meningiomas cause multiple
cranial nerve palsies.

Medial sphenoid wing meningioma

Nerve Sheath Tumors
• Those involving the central skull base often
affects the cavernous sinus and Meckel’s cave.
– Plexiform neurofibromas
– Schwanommas

Plexiform neurofibromas
• Unencapsulated diffusely infiltrating masses
that originate along peripheral nerve, usually
ophthalmic division of trigeminal nerve, and
involve BOS by central extension.
• Extension along mandibular and maxillary
divisions of trigeminal nerve is also common.

Schwannoma
• Encapsulated, well delineated tumors.
• Most are quite vascular
• Haemorrhage or necrosis may occur

Trigeminal Schwannoma
• Most common schwannoma to involve the central BOS and
cavernous sinus is a trigeminal schwannoma.
• Its symptoms, signs, and imaging appearance varies with
the part of the nerve involved, direction and extent of
tumor growth.
– Meckel’s cave – extend into skull base
– Cisternal – CP angle mass
• Cisternal and ganglion – “dumbbell” configuration
• Circumscribed, rounded or lobulated soft tissue masses
that enhance strongly but heterogenously.
• Most are isodense with brain on CT
• Isointense on T1WI, hyperintense on T2WI

On an axial T1-weighted image, a normal nonenhancing Meckel’s cave is seen on the
right side (arrow). In the left Meckel’s cave, a heterogeneous enhancing mass
arrowheads) is depicted, extending in the cavernous sinus: trigeminal schwannoma.

Juvenile Angiofibroma
• Highly vascular, locally
invasive lesion
• Originates near
sphenopalatine foramen
• Adolescent males
• Most common benign
nasopharyngeal tumor
• Typically spread along
natural foramina and
fissures into
pterygopalatine fossa, orbit,
middle cranial fossa,
sphenoid sinus, and
cavernous sinus.

• Imaging – strongly
enhancing, highly
vascular
nasopharyngeal soft
tissue mass.

Chordoma
• Slowly growing
destructive tumor
• Histologically benign,
but locally invasive
• One-third in
sphenooccipital region
– Most in midline;
primarily involve clivus
– Other – petrous apex
and Meckel’s cave

Destructive lesion in the central skull base
– T1 hypontense and T2 hyperintense

Osteocartilaginous neoplasms
• Clivus and skull base – cartilaginous
neurocranium by endochondral ossification
vs
• Calvarium – mesenchymal membranous
neurocranium by intramembranous ossification
• Therefore, a spectrum of benign and malignant
osteocartilaginous neoplasms can arise in the
central skull base.

Enchondroma
• The most common benign osteocartilaginous
tumor in this location.
• CT
– Expansile lobulated soft tissue mass with scalloped
endosteal bone resorption and curvilinear matrix
mineralisation
• MRI
– isointense on T1; hyperintense on T2
– Post contrast – enhancement of scalloped margins
and curvilinear septae (ring-and-arc pattern)

Multiple myeloma
• Diffuse skull vault and calvarial vault
destruction.
• Solitary plasmacytoma
– Focal destructive sphenoid sinus or calvarial vault
mass is typical, though nonspecific
– Best diagnostic clue:
• CT shows solitary intraosseous osteolytic soft tissue
mass with nonsclerotic margins

Osteosarcoma
• Craniofacial osteosarcomas are uncommon - when
present, present in older patients, and commonly
affect the maxilla or mandible.
• Skull base osteosarcomas are rare.
– May occur spontaneously or
– In association with Paget disease or previous radiation
therapy.
• A soft tissue mass with tumor matrix mineralisation
and aggressive bone destruction is characteristic.
• DD:
– Radiation osteitis, metastatic carcinoma, myeloma

MRIs of a radiation–induced osteosarcoma in a patient with severe fibrous dysplasia of the skull
and skull base.
(A)Gadolinium–enhanced, T1–weighted axial image with fat suppression shows a large tumor in
the region of the sphenoid and sella.
(B)T2–weighted fast spin–echo, axial and (C) gadolinium–enhanced, T1–weighted coronal image
with fat suppression of the same lesion.

Chondrosarcoma
• Rare in skull base
• Slow growing, locally invasive tumors
• Soft tissue mass with focal bone destruction is
typical.
• Matrix mineralisation in half of cases.
• MR:
– low to intermediate signal on T1
– Hyperintense on T2
– Strong but heterogeneous enhancement

• Chondrosarcoma in a 65-year-
old man with epistaxis and facial
pain.
• (a) Axial CT scan with bone
windows reveals the presence of
a midline destructive lesion
involving the sphenoid body and
extending anteriorly to the
ethmoid bones and nasal fossa
with tumor calcification (arrow),
within the mass.
• (b) Axial T1 -weighted MR image
a relatively homogeneous
midline mass (*) that is slightly
less intense than brain and
associated destruction of the
clivus (arrows) .
• (c) Midsagittal T1-weighted MR
image shows a destructive mass
in the midline of the ethmoid
bones and nasal fossa extending
posteriorly and causing
destruction of the sphenoid
body and clivus(*).

Metastatic disease
• Central skull base metastases are more
common than primary bone neoplasms.
• Arise via
– regional extension of head and neck malignancies
or
– perineural spread from regional or remote
malignancies or
– haematogenous spread from extracranial sites

• Prostate, lung and breast
carcinomas are the most
common.
• Lung and breast – focal or
diffuse lytic destructive
lesions
• Prostate – mixed
hyperostoses and bone
destruction with an
associated soft tissue mass
(resembles meningioma).
– Lateral orbital wall – favourite
site

Lymphoma
• CNS involvement – primary or secondary
• Leptomeningeal involvement (most common type)
• Cranial nerve palsies (most common presenting signs)
• Focal masses or perineural tumor can occur
• MR:
– Replacement of normal high signal marrow with infiltrating
soft tissue that has decreased signal intensity
• Cavernous sinus lymphoma can be unilateral or
bilateral.

Unenhanced (A) and contrast-enhanced (B) axial T1-weighted images reveal
homogeneous infiltrating lesions (arrow) in cavernous sinus, which exhibits
homogeneous, intense enhancement.

Posterior Cranial Fossa
• Largest and the deepest
of the 3 cranial fossae.
• Roughly two-fifths of
the base of skull.
• Surrounds the foramen
magnum

• Includes:
– clivus below the
sphenooccipital
synchondrosis
– petrous temporal bone
– pars lateralis and
– squamae of occipital
bone

NOTE!!!
• MR signal of normal clivus and posterior skull base depends
on the amount and nature of the marrow elements the
comprise the cancellous bone.
• Red marrow (haematopoetic tissue) predominates upto
approximately 3 years of age and results in low and high
intensity portions mixed in various proportions on T1WI.
• Enhancement of normal clivus marrow sometimes follows
contrast administration.
• This is mild and infrequent in adults, but is common and
may even be quite striking in young children.
• The skull base in children normally has signal irregularity
and patchy enhancement.

Posterior Skull Base Lesions - location
• CP Angle – IAC cistern
• Temporal bone
• Clival and paraclival
• Jugular foramen
• Foramen magnum

CEREBELLO PONTINE ANGLE –
INTENAL AUDITORY CANAL CISTERN

Normal anatomy
• CPA cistern lies between
the anterolateral surface
of pons & cerebellum
and the posterior surface
of the petrous temporal
bone.
• Important structures:
– Nerves – CNs V, VII and VIII
– Arteries – SCA, AICA
– Tributaries of superior
petrosal veins
– Others – Flocculus, choroid
plexus

Normal variants in CPA-lAC
• Normal structures, when unusually prominent, trouble radiologist
evaluating CPA – lAC.
• AICA loop flow void on high-resolution T2 MR
– Will not prominently enhance on Tl1C+ MR
– Subtle enhancement in lAC on TI C+ MR may be mistaken for small acoustic
schwannoma
• Choroid plexus protruding through lateral recess of 4th ventricle
– T1 C+ MR shows enhancing bilateral tear-shaped masses of CPA cistern
– Symmetry &. characteristic appearance make diagnosis
• Cerebellar flocculus is a lobule of cerebellum projecting into
posterolateral aspect of CPA cistern
– Signal follows intensity of cerebellum on all MR sequences
• Marrow space foci in walls of lAC can mimic lAC tumor on Tl C+ MR
images
– Correlate location of foci with lAC cistern
– Bone CT of T-bone may be necessary to identify this normal variant
• High jugular bulb
• Prominent jugular tubercles

Cerebellopontine angle cistern masses
• Uncommon in children; very common in adults
Cerebellopontine angle cistern masses
Common Uncommon
Acoustic schwannoma (75%) Arachnoid cyst
Meningioma (8 to 10%) Lipoma
Epidermoid (5%) Demoid
Other schwannomas Exophytic cerebellar/brainstem
astrostoma
Vascular (VB ectasia, aneurysm, VM) Chordoma
Metastases Osteocartilaginous tumors
Paraganglioma
Ependymoma
Choroid plexus papilloma

Internal Auditory Canal Masses
Internal Auditory Canal Masses
Common Uncommon
Intracanalicular acoustic
schwannoma
Neuritis (eg., Bell’s palsy, Ramsay
Hunt syndrome)
Post operative fibrosis Haemangioma
Lymphoma
Metastases
Sarcoidosis
Meningioma

• Primary temporal bone lesions:
– Gradenigo’s syndrome
– Malignant otitis externa
– Cholesterol granulomas
– Paraganglioma (glomus tympanicum)

Gradenigo’s Syndrome
• Osteomyelitis of
petrous apex with sixth
nerve palsy, otorrhea,
and retroorbital pain.
• NECT:
– Destructive lesion of the
petrous apex with fliud
in the adjacent middle
ear and mastoid.

Malignant otitis externa
• Uncommon but fulminant
form of temporal bone
osteomyelitis
• Typical in insulin-
dependent diabetics and
immunocompromised
patients
• Extension into parotid
and masticator spaces,
skull base, and
occassionally the CPA
cistern may occur.

Cholesterol granulomas
• Expansile cystic lesions
of petrous apex that
contain haemorrhage
and cholesterol crystals.
• Hyperintense on T1 and
T2

Paragangliomas
• Slow growing
hypervascular tumors
• Arise from neural crest
cells
• Locaised to cochlear
promontory in the
middle ear cavity –
glomus tympanicum
tumors

Paragangliomas
• Glomus
jugulotympanicum
tumors extend from the
jugular foramen into
middle ear cavity.
• Large masses also
extend into CPA cistern.
The axial post-gadolinium T1-weighted image above shows an enhancing lesion involving almost
the entire petrous temporal bone and extending through the external auditory canal to
protrude from the external ear (green arrow). The tumour extended beyond the skull base into
the carotid sheath, and bulged into the posterior fossa

Clival and Paraclival Lesions
• Chordoma and Metastasis are the most common
causes of destructive clival masses.
• The same infectious and inflammatory processes
and primary and metastatic tumors that affect
the anterior and central skull base can also
involve the clivus.
• Replacement of the normal marrow that forms
the cancellous clival bone by soft tissue masses is
easily identified on MR studies in these cases.
• Compared to brain, most abnormalities exhibit
low signal on T1 and high signal on T2WI.

Axial computed tomography shows a large midline
chordoma involving the petrous apex bilaterally.

Jugular foramen
• Jugular foramen:
– Located in the floor of
the posterior fossa,
between the petrous
temporal bone
anterolaterally and the
occipital bone
posteromedially.
– Anterior and inferior to it
is the hypoglossal canal
• Hypoglossal nerve

Divided into:
• Pars nervosa
• (smaller anteromedial
compartment)
• CN IX
• Pars vascularis
• (larger posterolateral
compartment)
• CN X and XI
• Jugular vein

Jugular Foramen Masses
Non Neoplastic Masses
Common
Large jugular bulb (normal variant)
Jugular vein thrombosis
Uncommon
Osteomyelitis
Malignant otitis external
Neoplasms
Common
Paraganglioma
Metastasis
Nasopharyngeal carcinoma
Haematogenous
Uncommon
Scwannoma
neurofibroma
Epidermoid tumor

Prominent jugular bulb
• Normal variant
• Most common “pseudomass” in the jugular
foramen.

Glomus Jugulare
• The glomus jugulare is
situated in the jugular
bulb adventitia
immediately below the
middle ear.
• .

Glomus Jugulare
• Expand the jugular
foramen, eroding the
jugular spine and
surrounding cortex.

Glomus Jugulare
• T1 : low signal
• T2 : high signal
• T1 C+ (Gd) : marked intense
enhancement
• Salt and pepper appearance
is seen on both T1 and T2
weighted sequences; the
salt representing blood
products from haemorrhage
or slow flow and the pepper
representing flow voids due
to high vascularity.

Glomus Jugulare
• Carotid arteriography
is necessary for
preoperative
evaluation and/or
embolization

Nerve Sheath Tumors
• Jugular foramen is uncommon
location for nerve sheath
tumors.
• Schwannomas of CNs IX to XI
• smooth well delineated
rounded or lobulated soft
tissue masses that expand the
jugular foramen.
• Pressure erosion is common
(frank invasion is rare; c.f.
paragangliomas)
• Isointense to brain on T1;
hyperintense on T2
• Strong homogenous contrast
enhancement

Normal Aantomy
• Large aperture in the occipital
bone though which posterior
fossa communicates with the
cervical spinal canal.
• It transmits:
– Medulla and its meninges
– Spinal segment of CN XI
– 2 vertebral arteries
– Anterior and posterior spinal
arteries
– Vertebral veins
• Bony elements that contain
these structures are
collectively termed the
craniovertebral junction (CVJ).

CVJ
• Formed by the occiput
and the C1 and C2
vertebrae.
• 4 joints are present here:
– Atlanto occipital
– Anterior median atlanto
axial
– Posterior median atlanto
axial
– Lateral atlanto axial joints

Pathology
• Intraaxial
(cervicomedullary)
masses
• Extramedullary
intradural masses
– Anterior
– Posterior
• Extradural masses
– CVJ
– Clivus & Skull base

Cervicomedullary masses Extradural masses
Common Craniovertbral junction
Syringohydromyelia Trauma
Demyelinating disease Arthropathies
Glioma Congenital anomalies
Fourth ventricle tumor Clivus and skull base
Uncommon Metastases
Haemangioblastoma Chordoma
Anterior extramedullary intradural masses Posterior extramedullary intradural masses
Common Common
Vertebrobasilar dolichoectasia Tonsillar herniation
Meningioma Ependymoma/subependymoma
Aneurysm (VA, PICA) Medulloblastoma
Uncommon
Schwannoma
Epidermoid tumor
Paraganglioma
Metastases
Arachnoid cyst

Intraaxial (cervicomedullary) masses
• Non neoplastic
intraaxial lesions
– Syringohydromyelia
• 25% of patients with
Chiari I malformation
• Acquired syrinxes –
trauma, cystic neoplasms
– Demyelinating diseases
• Including multiple
sclerosis
• In medulla and upper
cervical spinal cord
Cervicothoracic ganglioneuroblastoma

• Non neoplastic
intraaxial lesions
– Syringohydromyelia
• 25% of patients with
Chiari I malformation
• Acquired syrinxes –
trauma, cystic neoplasms
– Demyelinating diseases
• Including multiple
sclerosis
• In medulla and upper
cervical spinal cord
Demyelination extends from the cervicomedullary
junction to the T2 vertebral level. ADEM post liver
transplantation

• Neoplasms
– Half of brain stem gliomas
occur here
– Cephalad extension of cervical
spinal cord tumors into distal
medulla is also common
– Most are low grade
astrocytomas
– Inferior extension of
medulloblastoma in children
and haemangioblastoma in
adults are common are the
common nonglial neoplasms of
the cervicomedullary junction.
– Intraaxial metastases are rare
in this location.

Extramedullary Intradural Masses
• Anterior foramen
magnum masses
– Most arise anterior to
cervicomedullary
junction.
• Posterior foramen
magnum masses

Anterior foramen magnum masses
• Vascular lesions
– Ectatic Vertebral Artery
– Aneurysms
• Neoplasms
– Meningioma
– Schwannoma
– Epidermoid tumors
– Paragangliomas
– Metastases
• Non-vascular Non-neoplastic lesions
– Arachnoid, inflammatory and neurenteric cysts
– Extraosseous intradural chordomas
– Intradural rheumatiod nodules

Anterior foramen magnum masses –
vascular lesions
• Ectatic vertebral artery
– Most common intradural
mass anterior to the medulla
– There is no correlation
between neurologic deficit
and the presence of vascular
grooves along the brainstem,
regardless of their size.
• Aneurysms
– Vertebral artery
– Posterior inferior cerebellar
artery
PICA aneurysm

Anterior foramen magnum masses -
neoplasms
• Meningioma:
– The most common primary intradural extramedullary
neoplasm in this location.
• Nerve sheath tumors
– Second most frequently encountered neoplasms
– Schwannomas of CNs IX to XI
– Neurofibromas from exiting spinal nerve segments
• Misc:
– Epidermoid tumors
– Paragangliomas
– Metastases – cistenal, perineural and skull base

Left: Sagittal T2-weighted MR image obtained in a 48-year-old man, demonstrating an anteriorly situated foramen magnum
meningioma (long arrow) causing compression and displacement of the rostral spinal cord (short arrow).
Right: Axial T1-weighted Gd-enhanced MR image obtained at the level of the foramen magnum. The homogeneously
enhancing tumor arises predominantly in an anterior location with some left lateral contribution. The large tumor occupies
slightly more than half of the transverse diameter of the foramen magnum and affords an adequate surgical corridor of
approximately 1 cm. The rostral spinal cord (arrow) is compressed and displaced posteriorly.

Anterior foramen magnum masses -
Non-vascular Non-neoplastic lesions
• They are uncommon.
– Arachnoid, inflammatory and neurenteric cysts
– Extraosseous intradural chordomas or
notochordal remnants
– Intradural rheumatoid nodules

Posterior Foramen Magnum Masses
• Herniated tonsils
– 5 to 10% of all foramen
magnum masses
– Most frequent
extramedullary
intradural mass posterior
to the cervicomedullary
junction.

• Herniated tonsils
– Congenital
• Occur with Chiari I
malformations
– Acquired
• Causd by increased
intracranial pressure or
posterior fossa masses.
• After lumboperitoneal
shunting of subarachnoid
spinal space.
• Reported with multiple
traumatic lumbar
punctures

• Ependymoma
• Subependymoma
• Medulloblastoma
– Are intraaxial neoplastic
masses that sometimes
extend posteroinferiorly
behind the medulla

Cervicomedullary masses Extradural masses
Common Craniovertebral junction
Syringohydromyelia Trauma
Demyelinating disease Arthropathies
Glioma Congenital anomalies
Fourth ventricle tumor Clivus and skull base
Uncommon Metastases
Haemangioblastoma Chordoma
Anterior extramedullary intradural masses Posterior extramedullary intradural masses
Common Common
Vertebrobasilar dolichoectasia Tonsillar herniation
Meningioma Ependymoma/subependymoma
Aneurysm (VA, PICA) Medulloblastoma
Uncommon
Schwannoma
Epidermoid tumor
Paraganglioma
Metastases
Arachnoid cyst

Extradural Masses
• Most extradural masses at the
foramen magnum are osseous
lesions.
– Trauma
– Arthropathies
– Congenital malformations
– Tumors
• High resolution MR delineates
relationship between the osseous
abnormalities, neural canal, and
spinal cord in CVJ malformations.
• Plain film tomography and CT
with multiplanar 3D
reconstruction are helpful for
detailing the complicated osseous
abnormalities seen in these
disorders.

Trauma
• Odontoid fractures
– Relatively common
– 20% of all cervical fractures
– 25 to 40% cause death at
the site of accident.
– Survivors do not
experience immediate
neurologic impairment.
– Late-onset myelopathy
secondary to non united
dens fracture may occur.
– Chronic instability can lead
to spinal stenosis and
irreversible cord damage.
The Anderson and D’Alonzo classification of odontoid fracture. Type I fractures involve
avulsion near the tip of the dens. Type II fractures occur at the base of the odontoid
process. Type III fracture lines extend into the body of the axis.

Trauma
• Odontoid fractures
– CT – delineates the
osseous abnormalities.
– MR – best delineates the
relation to the spinal
subarachnoid space and
cord itself.

Arthropathies
• True synovial joints
– Full spectrum of degenerative and inflammatory arthropathies
occur.
• Rheumatoid arthritis of spine is second in incidence only to
that of hands and feet.
• Cervical spine is affected in 80% of patients.
• Prominent pannus and atlantoaxial subluxation may cause
severe CVJ narrowing with spinal cord compression.
• Occasionally, rheumatoid nodules may be present within
the dura and perineurium.
• Less common CVJ lesions include:
– Osteoarthritis, Paget disease, CPPD disorders, osteomyelitis with
or without epidural abscess.

MRI of rheumatoid arthritis of the cervical spine.
A sagittal spin-echo T1-weighted MR image shows inflammatory pannus eroding
odontoid (arrow), and cranial settling with cephalad migration of C-2 impinging on the
medulla oblongata (open arrow).

Congenital anomalies
• Congenital CVJ anomalies are relatively uncommon,
and include:
– Vertrabralisation of occipital condyles
– Arch hypoplasias and aplasias
– Os odontoideum
– Odontoid hypoplasia
– Assimilations and
– Ligament laxity
• Occur in isolation or with basilar invagination.
• May be associated with other congenital abnormalities
like Down syndrome, Chiari I malformations, or
syringohydromyelia.

Neoplasms
• Primary and metastatic tumors
• Most extradural tumors affect clivus and are therfore anterior to
medulla.
• Primary neoplasms include:
– Chordoma
– Osteocartilaginous tumors (chondroma, chondrosarcoma)
• Metastases
– Haematogenous
– Local extensions (nasopharyngeal or skull base tumors)
• All lesions replace normal fatty marrow
– Hypointense on T1; hyperintense on T2 (regardless of etiology)
• Exception is Chordoma:
– Very high, but heterogenous signal intensity on T2

Metastasis from a renal cell carcinoma
at the jugular foramen and FM region
Contrast-enhanced computed tomographyshows an
enhancing mass at the base of the left posterior fossa
destroying the lower clivus, occipital squama, and lateral mass
of C1.
MRI shows large enhancing soft tissue mass in the region
of the left jugular foramen and lateral to the foramen
magnum.

• Lesions that can occur
in any or all BOS
locations
Diffuse Skull Base Lesions
Non Neoplastic Masses
Uncommon
Fibrous dysplasia
Paget’s disease
Langerhans’ cell histiocytosis
Neoplastic Masses
Common
Metastasis
Uncommon
Myeloma
Anaemias
Meningioma
Meningioma
Lymphoma
Rhabdomyosarcoma

Fibrous dysplasia
• Among the most common
skeletal disorders.
• Adolescents and young
adults
• Monoostotic (70%) or
polyostotic
• Skull and facial bone
involvement:
– 25% of patients with
monoostotic FD
– 40 to 60% of patients with
polyostotic FD

• Expands and replaces the normal
bone medullary spaces with
vascular fibrocellular tissue.
• Varying degrees of ossification
may be seen.
• CT:
– Thickened sclerotic bone with a
“ground-glass” appearance.
• Cystic components may be
present in the early active stage.
• MR:
– Low to intermediate signal on T1
and T2; scattered hyperintense
regions may be present.
• Variable contrast enhancement.

• Expands and replaces the normal
bone medullary spaces with
vascular fibrocellular tissue.
• Varying degrees of ossification
may be sen.
• CT:
– Thickened sclerotic bone with a
“ground-glass” appearance.
• Cystic components may be
present in the early active stage.
• MR:
– Low to intermediate signal on T1
and T2; scattered hyperintense
regions may be present.
• Variable contrast enhancement.

Paget disease
• Osseous lesion of
unknown etiology
• Monoostotic or
polyostotic
• Focal or diffuse
• 3 phases are identified:
– Early destructive phase
– Intermediate phase with
combined destruction
and healing
– Late sclerotic phase.

• Imaging findings vary with
stage.
• Both CT and MRI scans show
expanded bone of the skull
base associated with calvarial
involvement.
• MRI better demonstrates the
basilar invagination often
seen because of bone
softening.
CT scan of the skull included an axial view at midcranial level (bone window), which confirmed the
asymmetric broadening of the skull, increased density of the calvarium, and disturbance of the trabecular
architecture due to diffuse mineralisation of the diploe with corticomedullary dedifferentiation.

• Imaging findings vary with
stage.
• Both CT and MRI scans show
expanded bone of the skull
base associated with calvarial
involvement.
• MRI better demonstrates the
basilar invagination often
seen because of bone
softening.
MRI of the skullshows on the axial T2- weighted MR-
image of the posterior fossa showing thickening of the
skull with corticomedullary dedifferentiation and non-
homogeneous, low to intermediate signal intensity of
the diploe.

Langerhan Cell Histiocytosis
• Solitary or monoostotic Eosinophilic
Granuloma is the most common
presentation.
• Children between 5 and 15 years;
occassionally in young to middle-
aged adults.
• Typically affects skull vault
• However, striking diffuse osteolytic
skull base and calvarial lesions can
occur.
• Single or multiple areas of pure
osteolysis are seen in the skull base
and calvarium of children (i.e.,
eosinophilic granuloma).
• A soft tissue mass may be associated
(i.e., Hand-Schuller-Christian or
Letterer-Siwe disease)

Metastases
• Most common malignancy
of skull base
• Direct or haematogenous
spread
• MC primary – lung, breast
and prostate
• CT – destructive mass
infiltrating the skull base
• MRI – T1WI show a
“muscle” intensity mass
within the skull base with
loss of normal, low intensity
cortical bone signal Metastasis to the sphenoid triangle (greater wing of
sphenoid). The tumor (T) expands in all directions,
pushing the temporalis muscle laterally, extending
into the middle cranial fossa, and impinging on the
orbit causing proptosis.

Myeloma
• Multiple myeloma or
solitary plasmacytoma
is possible
• Indistinguishable from
osteolytic metastases
on CT or MRI
• In the diffuse form, all
bones of the skull base
are involved, with
permeative changes.
Bone window images demonstrates
destruction of clivus, petrous apex,
sphenoid bone, lateral mass of C1, and the
pedicle of C2 on left side

Anemias
CT of the 6 years old with thalassemia showing extensive hypertrophy of the diploic spaces
mostly in the maxillary walls, skull base and frontal bones. Note obliteration of the maxillary,
sphenoid and frontal sinuses. Also note increased trabeculation in the diploë. This results from
bone marrow hypertrophy due to ineffective erythropoiesis.

Interventional Neuroradiology in
Skull Base

Interventional Neuroradiology in Skull Base
• Image guided biopsy
• Radio-frequency Ablation and Cryoablation for Tumors
• Percutaneous Sclerotherapy – venous malformations
• Preoperative Tumor Embolization
• Management of Bleeding from the Head and Neck
– Transarterial Embolization for Epistaxis
– Bleeding from Carcinoma of the Head and Neck
– Carotid Blowout Syndrome
• Other lesions of vascular etiology
– AVF
– Dural AVF – Transverse, Sigmoid
– CCF
– Aneurysms
• Intra-Arterial Chemotherapy for Head and Neck Carcinoma

Image-Guided Biopsies
• A, Paramaxillary approach to the left
parapharyngeal space mass, proven to
be an oncocytoma. Slight turning of
the head to the opposite side simplifies
the approach to this parapharyngeal
space lesion.
• B, Subzygomatic approach to the
masticator space mass via the
intercondylar notch. The core
specimens in this patient with
previously treated squamous cell
carcinoma revealed scar tissue with no
evidence of malignant cells.
• C, CT image in a patient with a mass at
the C2 level reveals a subtle left-sided
epidural soft-tissue (arrow) and
cortical irregularity of the vertebral
body (arrowhead). This image was
acquired with contrast to map the
location of the adjacent vertebral A.
• D, A posterolateral approach to the
epidural mass was planned. A 22-gauge
Franseen needle is advanced through a
guiding needle, and aspiration biopsy is
performed. Aspiration biopsy was
consistent with a diagnosis of
chordoma

Radio-frequency Ablation and
Cryoablation for Tumors
• A 59-year-old man with severe
dyspnea and dysphagia secondary
to a large squamous cell
carcinoma treated with radio-
frequency ablation.
• A, Axial contrast-enhanced CT scan
demonstrates a large necrotic
tumor (arrows) in the floor of the
mouth and hypopharynx.
• B, 3D volume-rendered
reconstruction demonstrates the
radio-frequency probe and
electrode deployment within the
tumor by means of a submental
approach.
• Note that the tumor anterior and
posterior to the hyoid bone could
be ablated simultaneously.

Left cheek venous
vascular malformation
(A)Clinical picture before treatment
showing left cheek mass.
(B)T2-weighted, fat-saturated axial MR
image showing a mass with
heterogeneous signal intensity in the
left masseter muscle extending to the
masticator space.
(C)Injection of 75% ethanol mixed with
Ethiodol under live subtraction mode
showing accumulation of the sclerosing
agent in the lesion.
(D)Further injection of the sclerosing
agent with compression of the venous
outflow of the lesion.
(E)Non-subtracted image of the head
after sclerotherapy showing stasis of
the sclerosing agent within the lesion.
(F)Clinical picture 5 months after
treatment showing decreased size of
the left cheek mass.

Preoperative Tumor Embolization
• The tumors that require embolization in the head and neck most
commonly include
– glomus tumors,
– angiofibromas, and
– meningiomas.
• Many other types of tumors that may also require preoperative
embolization include the following:
– hypervascular metastases,
– esthesioneuroblastomas,
– schwannomas,
– rhabdomyosarcomas,
– plasmacytomas,
– chordomas, and
– hemangiopericytomas.

Preoperative Tumor Embolization
• The embolic agents in common use are:
– polyvinyl alcohol (PVA),
– Embospheres (Bio- Sphere Medical, Rockland, Mass),
– liquid embolic agents (glue, ethylvinyl alcohol copolymer, or Onyx),
– gelatin sponge (Gelfoam), and
– coils.

Glomus jugulare tumor.
• (A) Contrast-enhanced head CT shows an enhancing
mass extending into right temporal bone at cerebellar
pontine angle level (arrow).
• (B) Bony expansion and destruction at jugular fossa
level (arrow) is seen on thin section temporal bone CT.
• (C) Axial and (D) coronal contrast-enhanced MRI shows
a corresponding intensely enhancing mass (arrows),
consistent with glomus jugulare paraganglioma tumor.
• Diagnostic angiography confirms dense tumor blush,
consistent with glomus tumor.
• Multiple feeding arteries were found, indicating a
multicompartmental tumor, and these feeding
pedicles were embolized to stasis with polyvinyl
alcohol particles.
• (E) Lateral view during injection of a common trunk of
the right occipital artery and ascending pharyngeal
shows dense stain from ascending pharyngeal artery.
AP, ascending pharyngeal artery; Occ, occipital artery.
• (F) Tumor blush seen on selective catheterization of a
feeding pedicle from posterior division of the right
ascending pharyngeal artery.

Juvenile nasal angiofibroma
• (A) Axial and (B) coronal T1-weighted
MRI with contrast confirms the
intensely enhancing mucosal mass in
left nasal cavity, with rightward
displacement of the nasal septum
(arrows).
• (C) Unsubtracted and (D) subtracted
cerebral angiogram demonstrates
intense tumor blush in nasal cavity
during internal maxillary artery.
• (E) Postembolization angiogram of
the sphenopalatine artery shows no
residual tumor blush.
• The tumor subsequently was
resected endoscopically, with an
estimated total blood loss of 75 cm3.

Bleeding from Carcinoma of the Head
and Neck
• An elderly man with a recurrent head and neck cancer presenting with pulsatile bleeding
through the oral cavity.
• A, CT angiogram of the neck shows an ulcerated left oropharyngeal mass (arrowheads) that
encases the left ECA (arrow).
• B, Common carotid angiogram reveals a long-segment tumor encasement of the left ECA. C,
The ECA is embolized with fibered and detachable platinum coils. The patient did not have
additional episodes of bleeding after the embolization.

Maxillary arteriovenous
malformation
• (A) Clinical picture before treatment
showing a soft tissue pulsatile mass in
the left gingiva and palate.
• (B, C) Early (B) and late (C) phases of the
left external carotid artery angiogram in
the lateral projection showing a left
maxillary arteriovenous malformation
with large draining venous channel inside
the maxilla.
• (D) Lateral view of the superselective
angiogram of the left descending
palatine artery showing arteriovenous
shunts to the intraosseous vein.
• (E) N-butyl cyanoacrylate (NBCA) cast
injected from the same microcatheter
position as in (D), showing penetration of
NBCA into the vein.
• (F) Lateral view of the external carotid
artery angiogram after multiple
embolization showing disappearance of
the arteriovenous malformation.
• (G) Clinical picture after embolization
showing ulceration of the left palate. No
further hemorrhagic episodes were
experienced.

Lower-grade dural arteriovenous
fistula of the left sigmoid sinus
• Study confirms low-grade dural arteriovenous
fistula of the left sigmoid sinus, with multiple
feeding arteries, including (A) occipital artery,
(B) ascending pharyngeal artery, (C) middle
meningeal artery, and (D), and left vertebral
artery.
• Each of these feeding arteries was embolized to
stasis using polyvinyl alcohol particles. Coils
were placed in the distal occipital artery to
protect the cutaneous branches from the effects
of the proximal embolization (∗, seen in B).
• Following transarterial embolization of the
feeding arteries, transvenous embolization was
performed for a combined transarterial-
transvenous approach, resulting in complete
obliteration of the fistula.
• This combined transarterial and transvenous
treatment results in durable cure of this fistula
without open surgery.

Higher-grade dural arteriovenous
fistula of the torcular region
• Diagnostic angiogram confirms
DAVF of the torcular region, with
supply from multiple arteries
including the middle meningeal
artery and opacification of
multiple cerebellar veins.
• Transvenous embolization of this
fistula is not practical.
• After transarterial embolization
with NBCA tissue adhesive,
resulting in a glue cast of the
distal feeding arteries and
proximal recipient veins, the
fistula is obliterated.
• CV, cerebellar veins; MC,
microcatheter in middle
meningeal artery; MMA, middle
meningeal artery.

Direct (high-flow) carotid cavernous
fistula – post traumatic
• (A) Coronal T1-weighted MRI
shows dilated superior
ophthalmic vein (SOV).
• (B) Axial image from MR
angiogram also shows a dilated
superior ophthalmic vein (SOV).
• (C) Angiogram of left internal
carotid artery (IAC) (lateral
projection) confirms a fistula
(CCF) with opacification of
cavernous sinus and retrograde
flow in superior ophthalmic vein
(SOV), draining to facial veins
(FV).
• (D) After embolization with
detachable balloons, the fistula is
closed.

Symptomatic mid-basilar aneurysm
• (A) 3-D reconstructions from
magnetic resonance
angiography.
• (B) Diagnostic cerebral
angiogram, anteroposterior
projection from
• (C) 3-D rotational angiography.
(D) Lateral projection from
cerebral angiogram obtained
after endovascular treatment
with a combination of
endovascular stents for
reconstruction of the arterial
lumen, followed by coiling.
• Patient's symptoms resolved
following this treatment.

Intra-Arterial Chemotherapy for Head
and Neck Carcinoma

Advances in Skull Base Imaging
• Advances in the areas of diagnostic imaging,
interventional radiology, surgical approaches
and techniques, as well as electrophysiological
monitoring, have all advanced the treatment
of skull base tumors and disorders.

Advances in CT & MR technologies
• Better and precise diagnosis
• Facilitated aggressive skull base surgery by
allowing precise preoperative delineation of
the extent of lesions
• Post operative follow-up

Advanced image-guided skull base surgery.

Advanced image-guided skull base surgery.
The early localization of the major vessels or neural structures during transtumoral
decompression is beneficial. A: Instrument points to the petrous portion of the internal carotid
artery (ICA) during decompression of a cavernous sinus meningioma.
B: Instrument points to the basilar artery (BA) during removal of a craniopharyngioma

CT/MR Fusion For Skull Base Imaging

CT/MR Fusion For Skull Base Imaging
• A: Axial CT visualized at bone window
settings demonstrates lytic lesion with well-
defined margins in left petrous apex (M).
Note extent of bone erosion involving cortex
of the posterior petrous portion of the
temporal bone (curved arrow) and bony
covering (straight arrows) of the petrous
segment of the internal carotid artery (C).
• B: Axial T1-weighted noncontrast- enhanced
MR imaging performed in same patient
shows a high signal intensity mass located
within the left petrous apex (curved arrow)
which is characteristic of a cholesterol
granuloma. Note relationship of the mass to
the basilar artery (straight arrow).
• There is excellent visualization of the soft
tissues of the brain and masticator spaces
(M); however, the relationship of the mass to
the carotid artery (c) and the extent of bone
erosion is better seen on CT than on MR
imaging.

Conclusion
• The central skull base is a highly complex
region.
• Knowledge of the normal development and
anatomic relationships will lead to more
accurate diagnoses.
• This in turn helps in decision making,
especially regarding challenging surgical
procedures.

Skull Base Bones and Anatomy

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