skullbase imaging

1. Skull Base: Review of Anatomy, Imaging Technique,
and Illustration of Common Benign and Malignant
Tumors at the Skull Base
Dr. Nasr M.Osman,MD
Lecturer of Radiology

2. Introduction
• Skull base is a complex and challenging
imaging area for most radiologists because of
the complex anatomy.
• Purpose of this exhibit:
a. Briefly discuss the embryology
b. Discuss the imaging technique
c. Illustrate the anatomy and common variants
e. Discuss and illustrate some common benign
and malignant tumors of the skull base

3. Embryologic Development
• Bones of skull base – cartilaginous precursors:
chondrocranium
• Calvarial bones – membranous bone
• Membranous bone components of skull base
a. Frontal bone, nasal bone
• Chrondrocranial components
a. Alisphenoid, basioccipital, exoccipital, nasal capsule,
orbitosphenoid, preshenoid, postsphenoid,
supraoccipital.
b. Primordial foramina: foramen ovale, foramen
rotundum, optic canal, superior orbital fissure

4. CT Technique
• Axial and Coronal planes
• Section thickeness of 1.5 – 3mm commonly used
• Bone detail: high-resolution bone algorithm with
a wide window setting
• Axial study performed in plane of Reid baseline
(parallel to a line drawn from orbitomeatal line).
• Axial scans from foramen magnum to suprasellar
cistern
• Direct coronal images obtained perpendicular to
Reid baseline

5. MR Imaging Technique
• Standard head coil
• Axial, Coronal and mid sagittal planes
• Section thickness of 3-5 mm
• T1-weighted sequences
a. Midsagittal image
b. Axial images: suprasellar cistern to
nasopharynx
c. Coronal images: Anterior aspect of
sphenoid sinus to foramen magnum
• T2-weighted sequences (slightly of lesser value)

6. Yellow arrow: Optic canal
Contents: Optic nerve, Opthalmic
artery, Sympathetic fibers from
carotid plexus
Yellow arrow: Superior Orbital
Fissure
Contents: V1 branches, cranial
nerve III, cranial nerve IV, cranial
nerve VI, superior ophthalmic vein,
sympathetic roots of ciliary ganglion

7. Yellow arrow: Inferior Orbital
Fissure
Contents: V2 branches,
pterygopalatine ganglion nerve,
inferior ophthalmic vein
Yellow arrow: Foramen
rotundum
Contents: Cranial nerve V2

8. Blue arrow: Pterygopalatine fossa
Yellow arrow: Vidian canal
Blue arrow: Foramen Ovale
Contents: Cranial nerve V3
Yellow arrow: Foramen Spinosum
Contents: Middle meningeal artery &
vein, meningeal branch of mandibular
nerve

9. Yellow arrow: Optic canal
Green arrow: Foramen rotundum
Blue arrow: Vidian canal Yellow arrow: Foramen Ovale

10. Blue arrow: Carotid canal
Yellow arrow: Jugular Foramen
Contents: Jugular Vein, CN IX, X, & XI, inferior petrosal sinus,
branch of ascending pharyngeal artery
Green arrow: Jugular Spine
Pars Nervosa – CN IX
Pars Vascularis – CN X, CN XI

11. Yellow arrow: Hypoglossal canal
Contents: Cranial nerve X11
Yellow arrow: Jugular tubercle
Green arrow: Hypoglossal canal

12. Pediatric Skull
Blue arrow: Basisphenoid
Yellow arrow: Sphenooccipital
Synchondrosis
Green arrow: Basiocciput
Yellow arrow: Sphenooccipital
synchondrosis
Adult Skull
Yellow arrow: Clivus

13. Arrows: Cranial nerve V3

14. Absence of the carotid canal and
foramen lacerum on the right.
Normal carotid canal on the left
(yellow arrow)
Absence of foramen spinosum on the
right. Normal foramen spinosum on the
left (yellow arrow)

15. Craniopharyngeal Duct
Rare, rare congenital skull base defect.
Well-corticated defect through the midline
of the sphenoid bone from the sellar floor
to the anterosuperior nasopharyngeal roof.

17. Cranial Nerves: I - XII
• 12 Pairs
• Numbered Anterior to Posterior
• Attach to Ventral surface of brain
• Exit brain through foramina in skull
• I + II attach to Forebrain (cerebrum +
diencephalon)
• III-XII attach to Brainstem (midbrain, pons,
medulla)
• Only X goes beyond the head-neck

18. I Olfactory--------Sensory--smell
II Optic-------------Sensory--vision
III Oculomotor----Motor----extrinsic eye muscles
IV Trochlear-------Motor----extrinsic eye muscles
V Trigeminal
V1 Opthalmic-----Sensory-cornea, nasal mucosa, face skin
V2 Maxillary------Sensory-skin of face, oral cavity, teeth
V3 Mandibular---Motor-muscles of mastication
---Sensory-face skin, teeth, tongue (general)
Cranial Nerve Function

19. VI Abducens--------------Motor-----eye abduction muscles
VII Facial-------------------Sensory---part of tongue (taste)
-------------------Motor------muscles of facial
expression
VIII Vestibulocochlear---Sensory----hearing, equilibrium
IX Glossopharyngeal----Motor------stylopharyngeus muscle
----Sensory----tongue (gen & taste),
pharynx
X Vagus------------------Motor-------pharynx, larynx
-------------------Sensory----pharynx, larynx, abd.
organs
XI Accessory-------------Motor------trapezius,
sternocleidomastoid
XII Hypoglossal----------Motor-------tongue muscles

20. Skull base lesions

21. Benign tumors
• Some common intrinsic lesions
a. Intraosseous hemangioma
b. Fibrous dysplasia
c. Paget disease
• Some common benign tumors of the skull base
include:
a. Paraganglioma (glomus jugulare)
b. Neural sheath tumor
c. Meningioma
d. Chordoma

22. Clival IntraosseousHemangioma
CT scan demonstrates a fat containing
lesion with coarse trabeculae in the
clivus (arrow)

23. Fibrous Dysplasia
• Relatively common, benign, developmental skeletal
disorder
• 75% present before 30 years of age
• Medullary cavity of the affected bone fills and expands
with fibrous tissue
• CT: thickened, sclerotic bone usually uniform in density,
sometimes with cystic regions.
• MRI: expanded, low intensity areas seen as hypointense
on T1 and T2 images. Active lesions may have complex
high- and low signal areas on T1 and T2 weighted
sequences

24. Fibrous Dysplasia
Thickened, sclerotic bone with cystic
changes involving the anterior skull base
and extending to the clivus posteriorly.

25. Paraganglioma
• Glomus Jugulare
a. Adventitia of jugular bulb along
glossopharyngeal nerve
b. Complex cranial neuropathy-cranial nerves
IX, X, and XI in jugular foramen.
• Glomus Jugulotympanicum
a. Tumor extends into temporal bone
b. Usually presents with pulsatile tinnitus and
retrotympanic mass.

26. CT: enhancing mass in jugular foramen with erosion of jugular spine and adjacent
permeative bony changes (arrows).

27. MRI: T1-weighted scans show mixed intensity mass in jugular
foramen with serpiginous flow voids within mass. Appear as
black lines and dots (arrows). Post contrast images
demonstrate avid enhancement.

28. Juvenile Angiofibroma centered in the
posterior right nasal cavity, in the region of
the spenopalatine foramen and extending
posteriorly scalloping the Clivus and
laterally into the masticator space (arrows)

29. Neural sheath tumor
• Schwannoma
a. Solitary, encapsulated tumor
• Neurofibroma
a. Multiple or single
b. Unencapsulated and associated with
neurofibromatosis in about 50% of cases.

30. Nerve sheath tumor
• Any of cranial nerves exiting skull base may be
involved
a. Jugular foramen (most common site –
cranial nerves IX, X, and XI)
b. CT: smooth, scalloped enlargement of the
affected area with a fusiform soft tissue
mass
c. MRI: Fusiform mass with uniform intensity
and enhancement.

31. V3 Schwannoma involving V3
the region of foramen ovale
(arrows)

32. Left mastoid segment facial nerve
schwannoma (arrows)

33. Meningioma
• Can arise anywhere from leptomeninges
• When arising from entrance or within neural
foramen, may appear intrinsic to skull base
• CT
a. Uniformly enhancing, dural-based mass.
b. Partially calcified. Associated with
hyperostosis
• MRI
a. Brain intensity, dural-based mass
b. Calcification and skull base hyperostosis
c. Marked enhancement

34. Foramen Magnum Meningioma
Enhancing mass in the region of
foramen magnum resulting in mass
effect on the brainstem and upper
cervical cord (arrows)

35. Left Hypoglossal Canal Meningioma

36. Chordoma
• Rare bone tumor
• Arises from remnants of cranial end of
primitive notochord
• 35% intracranial, usually clivus
a. Principal location: sphenooccipital
synchondrosis
b. Other locations: basisphenoid and
basiocciput
• 50% sacrococcygeal
• 15% from vertebral body

37. Chordoma
- Destructive midline mass adjacent to
clivus (arrows).
- Bone destruction (95%) and tumor
calcification (50%).

38. Chordoma
- T1-weighed images:
isointense to hypointense to
brain
- T2-weighted images:
hyperintensity
- Post contrast:
variable enhancement

39. Malignant Tumors
• Metastatic tumor
• Non-Hodgkin lymphoma and leukemia
• Myeloma
• Malignant primary bone tumors
a. Chrondrosarcoma
b. Osteosarcoma

40. Metastatic tumor
• Most common malignant tumor of skull base
• Direct spread: orbit, sinonasal,
nasopharyngeal carcinoma
• Hematogenously: lung, breast, prostate gland
• CT: destructive mass infiltrating skull base
• MRI: T1-weighted mass “Muscle” intensity
mass with loss of normal, low intensity cortical
bone signal.

41. Nasopharyngeal carcinoma involving the carotid space, jugular space, hypoglossal canal, masticatory space, vidian
canal resulting in multiple cranial neuropathies

42. Undifferentiated Sinonasal tumor
extending to the clivus (arrows)

43. Undifferentiated Sinonasal
tumor extending to the clivus
(arrows)

44. Chondrosarcoma of the petroclival fissure
• Extremely rare
• Often in paramedian basisphenoid
synchrondrosis
• Slow-growing.
• CT: chondroid matrix mineralization in less
than 50% of cases
• MRI: heterogenous signal in about 60% cases
• Matrix mineralization, fibrocartilaginous
elements, or both

45. Chrondrosarcoma
Destructive mass in the paramedial location at the
basisphenoid synchondrosis
CT: chondroid matrix mineralization in less than 50%
of cases (arrows)

46. Skull base encephalocele initially mistaken
for a mass.
CT scan shows a lytic lesion at the right
skull base in the region of the petroclival
fissure (arrows).

47. Skull base encephalocele
initially mistaken for a mass.
MRI scan shows a non-
enhancing CSF isointense, T2
bright lesion at the right skull
base in the region of the
petroclival fissure (arrows).

48. Conclusion
• Due to complex anatomy, skull base is a
complex and challenging imaging area for most
radiologists.
• The purpose of this exhibit was to review skull
base anatomy, illustrate some normal variants,
and then describe and illustrate some common
benign and malignant skull base tumors.

49. 1. Harnsberger, Hand book of Head and Neck Imaging, 2nd
Edition, 1994
2. Laine FJ, Nadel L, Braun IF, “CT and MR Imaging of the
Central Skull Base”, Radiographics 1990;10: 591-602