lesions of the temporal bone & petrous apex ct & mri charecteristics

1. Lesions of the Temporal
Bone & Petrous Apex
DEBKUMAR BISWAS
JR2 MCH

2. • The anatomy of the temporal bone is complex
• It is further complicated by the small size and three-dimensional
orientation of associated structures.
• Computed tomography (CT) has revolutionized imaging of the
temporal bone.
• Recent advances in multisection CT scanners allow acquisition of
high-resolution volumetric data that enable image reformation in any
plane.

3. Technique
• Axial CT images are acquired through the temporal bones
• HIGH SPATIAL FREQUENCY BONE ALGORITHM
• 0.625-mm axial sections taken and are then reprocessed and
reformatted into magnified axial and coronal images and displayed at
0.3-mm intervals with overlap.
• In addition to the traditional axial and coronal views, it has become
routine to also perform reformation in the Stenvers and Pöschl
projections.
• Magnetic resonance (MR) imaging may be used to evaluate the eighth
cranial nerve, which is typically best seen on heavily T2-weighted
images in the axial and oblique projections.

5. Axial I to S

10. Coronal A to P

16. Anatomy of the Petrous Apex
• The petrous apex is a complex region of the central skull base that is
surrounded by a number of important vascular and neural structures
• Pyramid-shaped structure
• Formed by the medial portions of the temporal bone
• Obliquely positioned within the skull base, with its apex pointing
anteromedially and its base located posterolaterally.
• The petrous apex is bounded by :
laterally :the inner ear structures
medially : the petro-occipital fissure
anteriorly :the petrosphenoidal fissure and ICA
behind :the posterior cranial fossa
superior surface :Middle cranial fossa, Meckel cave, and ICA
inferior surface :the jugular bulb and inferior petrosal sinus

20. Pneumatisation of Petrous Apex
• The anterior portion of the petrous apex is filled with
marrow : 60 %
pneumatized : 33%
sclerotic : 7%
• Pneumatisation of the petrous apex results from extension of air
cells from he mastoid or middle ear cavity and provide direct
pathways for disease spread from the mastoid bone or middle ear
to the petrous apex.
• Pneumatisation is asymmetric in 5%–10% of individuals

21. Normal variants
• Variants which may simulate disease:
Cochlear cleft (otosclerosis)
Petromastoid canal (fracture)
Cochlear aqueduct (fracture)
• Variants which may pose a danger during
surgery:
High jugular bulb or jugular bulb diverticulum
Bulging sigmoid sinus

22. Cochlear cleft
• A cochlear cleft is a narrow curved lucency extending from the
cochlea towards the promontory.
• It is often visible in infants and children but can also be seen in adults.
• It can be mistaken for a fracture line or an otosclerotic focus.

24. Petromastoid canal /Sub arcuate canal

26. Cochlear aqueduct
• The cochlear aqueduct connects the perilymph with the subarachnoid
space.
• The cochlear aqueduct is a narrow canal which runs towards the cochlea in
almost the same direction as the inner auditory canal, but situated more
caudally.
• It is a point where infected cerebrospinal fluid can enter the inner ear.
• This can happen in patients with meningitis and cause labyrinthitis
ossificans.

28. High jugular bulb
• The jugular bulb is often asymmetric, with the right jugular bulb
usually being larger than the left.
• If it reaches above the posterior semi-circular canal it is called a high
jugular bulb.
• If the bony separation b/w jugular bulb & tympanic cavity is absent it
is called dehiscent jugular bulb.
• Rarely an outpouching is seen – this is known as a jugular bulb
diverticulum

31. Bulging sigmoid sinus

32. Congenital anomalies
Large vestibular aqueduct
• The vestibular aqueduct is a narrow bony canal (aqueduct) that connects the
endolymphatic sac with the inner ear (vestibule).
• Running through this bony canal is a tube called the endolymphatic duct.
• A large vestibular aqueduct is associated with progressive sensorineural hearing
loss. . A commonly accepted imaging criterion for an enlarged
vestibular aqueduct is a calibre of 1.5 mm or greater in
the midportion of the aqueduct
The large vestibular aqueduct is associated with an absence of the bony modiolus
in more than 90% of patients.

34. External auditory canal atresia
• In external ear atresia the external auditory canal is not developed and sound
cannot reach the tympanic membrane leading to a conductive hearing loss.
• It is important to note whether the atretic plate is composed of soft tissue or
bone.
• The extent of ossicular chain malformation can vary from a fusion of the mallear
head and incudal body to a small clump of malformed ossicles, which is often
fused to the wall of the tympanic cavity.
• The mastoid portion of the facial nerve canal can be located more anteriorly than
normal and this is important to report in order to avoid iatrogenic injury to the
nerve during surgery.

37. Congenital Inner Ear Malformations

38. • In cochlear aplasia, there is complete absence of the
cochlea. The vestibule is present but often dysplastic.
• In cochlear hypoplasia, the cochlea and vestibule are
separated but their dimensions are smaller than usual.
• Common cavity deformity is characterized by a single
featureless labyrinthine cavity with no distinct vestibule,
cochlea, or SCCs.
• Mondini’s malformation , more recently classified as incomplete
partition (IP) type II,has a cochlea with 1.5 turns. The
middle and apical turns of the cochlea fuse to form
one cavity
• Dilatation of the vestibular aqueduct and vestibule are
frequent associated anomalies

40. Semi-circular Canal Dehiscence Syndrome.

41. Inflammatory Conditions
• Acute Otomastoiditis.
• Themostcommoninflammatory conditionaffectingthetemporalbone
• appears as middle ear and mastoid air cell opacification with fluid
and nonspecific debris.
• Thefluid in serous otitis media cannot be distinguished from the pus
seen with purulent otitis.
• Subacute otitis media shows similar findingswith the additional
finding of focal or diffuse mucosal thickening
• Spread of infection to the bone with erosion of the mastoid,
lateral mastoid cortex, or cortex over the sigmoid plate is termed
coalescent mastoiditis

44. Chronic otitis media
• It results in nonspecific opacification of the middle ear
and mastoid air cells by granulation tissue and effusion.
• Reactive sclerosis results in thickening of the bony septa
of the mastoid.
• there will be a gradual reduction in the number of
mastoid air cells, resulting in poorly developed mastoids
• Hyalinization of cartilage (tympanosclerosis) will appear
as punctate, nodular, or web like calcifications in the
middle ear, often involving ossicular tendons or ligaments

45. • the differentiation between chronic otitis media and cholesteatoma is important.
• Both diseases often occur in poorly pneumatized mastoids.
• Differentiate the two conditions is bony erosion.
Erosion of the lateral wall of the epitympanum and of the ossicular chain is
common in cholesteatoma (around 75%).
Erosion can occur in chronic otitis, but reportedly in less than 10% of patients.
• Displacement of the ossicular chain can be seen in cholesteatoma, not in
chronic otitis
• Cholesteatoma can present with a non dependent mass while chronic otitis
shows thickened mucosal lining.
• However, in both diseases the middle ear cavity can be completely opacified,
obscuring a cholesteatoma.

49. Cholesteatoma
Primary acquired cholesteatomas
(80%)
• result from chronic infection
with development of granulation
tissue behind an apparently
intact TM,usually in the region
of the pars flaccida.
• On CT, primary acquired
cholesteatomas are usually seen
as a rounded, expansile, soft
tissue mass in Prussak’s space,
with erosion of the scutum
and medial displacement of
the ossicles.
Secondary acquired
cholesteatomas (18%)
• develop throughperforationinthe
TM, usually involving the
pars tensa and less often
the pars flaccida.
• On CT Secondary acquired
cholesteatomas are often
located in the facial
recess and sinus
tympani.

50. • It is important to note on imaging whether a cholesteatoma
occupies the sinus tympani or facial nerve recess of the
middle ear cavity.
• The sinus tympani and facial nerve recess are blind spots
during surgical resection of cholesteatomas
• are the most common and second most common sites of
recurrent cholesteatoma, respectively.
• The most affected structures are:
Auditory ossicles, especially the long process and lenticular processes of the
incus as well as the head of the stapes
Wall of the lateral semi-circular canal
Lateral epitympanic wall (the scutum)

51. CT signs of cholesteatoma
1. Soft tissue mass in the middle ear
• Especially if located in Prussak's
space
• In advanced cholesteatoma the
presence of aerated parts of the
middle ear denote a mass and not
an effusion
• Non-dependent soft tissue
particularly favours a mass
2. Bony erosion in the following predilection
sites:
• Scutum (lateral wall of the
epitympanum)
• Lateral semi-circular canal
• Tegmen tympani
• Long process of the incus and
stapes superstructure

57. • Congenital cholesteatomas (2%) develop from embryonic
epithelial rests that can occur anywhere in the
temporal bone, including the middle ear.
• In the middle ear, congenital cholesteatomas most
frequently originate in the anterior superior quadrant
of the middle ear at the eustachian tube orifice
near the anterior tympanic ring.
• A small nodular mass is usually seen on CT

60. Malignant External Otitis.
• most often associated with a Pseudomonas infection in older
diabetic or immunosuppressed patients.
• Presents with otalgia and pus in the EAC.
• The infection may affect just the soft tissues and cartilage.
• However, it can also lead to osteomyelitis of the adjacent
temporal bone structures or skull base, with resultant cranial
nerve palsies.
• Cranial nerve VII is the most common nerve to be involved
• CT : soft tissue thickening of the EAC, enhancement of canal
granulation tissue, and osseous erosions
• MRI is more useful to assess soft tissue spread of disease,
skull base osteomyelitis, and cranial nerve palsies.

62. Labyrinthitis
• An inflamatory process of the peri lymphatic space .
• Causes : infection, trauma, or autoimmune disease.
• Presents with sudden onset vertigo or hearing loss.
• Basal turn of the cochlea is most commonly affected.
• Acutely, inner ear enhancement is seen on MRI. Increased precontract
T1 signal can represent haemorrhage within the labyrinth.
• In intermediate stage, fibrosis results in loss of fluid signal in the affected inner ear
structures on heavily T2-weighted MRI images.
• Labyrinthitis ossificans
is a late stage of labyrinthitis that results in ossification with new bone
formation.
• It is only in the late stage when the CT becomes abnormal with
bony attenuation in the cochlea, vestibule, and/or SCCs

64. Petrous Apicitis
• an infectious osteitis resulting most often from adjacent spread
of otomastoiditis, usually in the setting of a pneumatized
petrous apex.
• The osteitis may cause Gradenigo’s syndrome, which manifests as
facial pain(Cranial nerves V ) or diplopia (Cranial nerves V I)
• CT findings of petrous Apicitis include opacification of a
pneumatized petrous apex and bone destruction
• On MRI the petrous apex is opacified and enhances
• MRI may also show enhancement of cranial nerves V and VI,
Meckel’s cave, and dura adjacent to the petrous apex and
cavernous sinus.
• Abscesses demonstrate ring enhancement and restricted diffusion on diffusion-
weighted images

67. Otosclerosis
• a genetically mediated metabolic bone disease of unknown etiology.
• The dense, ivory-like endochondral bone is replaced by more spongy,
highly vascular bone tissue.
• fenestral (stapedial): ~80%
• involves oval window
• the most common lesion of this type affects the bone just anterior to the oval
window, and can extend to involve the foot plate of the stapes resulting in thickening
and fixation
• hearing loss is often conductive
• retro-fenestral (cochlear): ~20%
• Cochlear involvement
• sensorineural hearing loss

68. The findings depend on the type of otosclerosis present.
Fenestral
• Typical findings depend on the phase of the disease.
• During active phases, there is bone loss or demineralization just anterior to the
oval window, involving a small cleft known as the fistula ante fenestram.
• During remission, the region becomes sclerotic. In severe cases, the oval window
is completely filled in by a dense bony plate (with complete fixation of
the stapes).
Retrofenestral
• Foci of lucency can be seen disrupting the normal sharply demarcated
homogeneously dense (although not homogeneously thick) border of the
cochlear otic capsule. It may be focal or may encircle the whole cochlea

71. Tumours

72. Exostoses
• osteomas are unilateral and solitary pedunculated hyper
dense masses on CT,
• exostoses present as multiple sessile, bilateral, hyper
dense masses on CT
• Exostoses are caused by contact with cold water and mostly seen in
swimmers and surfers.

74. • Cholesterol Granuloma
the most common lesions arising in the petrous apex
• occur in patients with a pneumatized petrous apex and a long-standing
history of otitis media.
• The cysts are filled with viscous brown fluid, granulation tissue, and
cholesterol crystals, & surrounded by a thick fibrous capsule that lacks
a true epithelial lining.
• cholesterol granulomas are usually hyperintense on both T1- and T2-
weighted image
• the presence of a highly pneumatized contralateral petrous apex also
supports the diagnosis of cholesterol granuloma.
• Cholesterol granulomas do not enhance with contrast material, and the
presence of enhancement should lead to an alternative diagnosis

77. Differential Diagnosis :
• asymmetric petrous apex pneumatisation.
• In these instances, fatty bone marrow also appears hyperintense on
T1-weighted images and may be mistaken for a lesion.
• Fat-suppressed imaging allows differentiation of the two entities, as
cholesterol granulomas will remain hyperintense after fat
suppression

78. Petrous Apex Mucoceles
• uncommon.
• caused by postinflammatory obstruction of a pneumatized petrous apex air
cell.
• CT shows a smoothly expansile bone lesion that may cause septal erosion
and can be difficult to distinguish from a cholesterol granuloma.
• MR imaging is particularly helpful in distinction between these two
entities,
• Mucoceles onT1-weighted images typically have low to intermediate signal
intensity & hyperintense on T2-weighted images
• Do not enhance after contrast material administration.

79. Petrous Apex Cephalocele
• Rare lesions representing protrusions of arachnoid or dura
mater,usually from the Meckel cave, into the petrous apex.
• Associated with empty sella and Usher syndrome,
• Usually bilateral, women >men
• At imaging, petrous apex cephaloceles are situated just above the
anterior petrous apex and are continuous with the Meckel cave.
• They are smoothly marginated and have the same signal intensity
characteristics as CSF with all MR imaging sequences.
• CT may show extensive nonaggressive erosion of the petrous apex
with a smooth or scalloped border.

81. Glomus tumour
• Glomus tumours (paraganglioma) arise from paraganglion cells present in
the jugular foramen and on the promontory of the cochlea around the
tympanic branch of the glossopharyngeal nerve.
• Elderly persons are most commonly affected with a female predominance.
• The presenting symptoms are conductive hearing loss, tinnitus, and pain.
• At otoscopy a blue ear drum is seen.
• Glomus tumours of the jugular foramen ( glomus jugulotympanicum
tumours) are more common than tumours which are confined to the
middle ear (glomus tympanicum tumour)

82. • On CT ,paragangliomas show typical moth-eaten or permeative bone
changes around the jugular foramen as a result of tumour infiltration.
• At MR imaging, large paragangliomas may have a characteristic salt-
and-pepper appearance on T1-weighted images. The hypo intense
“pepper” represents high-velocity flow voids of feeding arterial
branches in the tumour (also evident on T2-weighted images), while
the less commonly seen hyperintense “salt” represents underlying foci
of haemorrhage.
• These tumours usually enhance intensely at both CT and MR imaging
after contrast material administration .

86. ENDOLYMPHATIC SAC TUMOURS
• ELSTs are located along the posterior petrous temporal bone between the
internal auditory canal and the sigmoid sinus.
• The imaging hallmark of ELST is that of a retro labyrinthine mass associated
with osseous erosion.
• Bone CT shows an infiltrative, poorly circumscribed, lytic lesion with
central intratumoral bone spicules.
• MR demonstrates T1 hyperintense foci in 80% of cases. Signal intensity is
mixed hyper- and hypo intense on T2WI. Heterogeneous enhancement is
seen following contrast administration.
• ELSTs are vascular lesions that may demonstrate prominent "flow voids" on
MR and prolonged tumour "blush" on DSA.

90. Vestibular schwannoma
• VS is by far the most common
intracranial schwannoma.
• VS is also the most common
cerebellopontine cistern mass,(85-
90% )
• Peak presentation is 40-60 years of
age.
• There is no gender predilection
• slowly progressive unilateral
sensorineural hearing loss (SNHL)

93. Facial Nerve Schwannoma
• Almost 90% of FN schwannomas
involve more than one facial nerve
segment.
• The geniculate fossa is the most
common site ( 80%)
• indistinguishable from vestibular
schwannomas if do not demonstrate
extension into the labyrinthine
segment of the facial nerve
canal.
• Lesions that traverse the labyrinthine
segment often have a
"dumbbell"appearance

96. Meningioma
• meningiomas tend to be broad-based along the posterior petrous wall,
forming an obtuse angle at the bone-tumour interface, appearing either
hemispherical or plaque like .
• Dural enhancement extending outward from the margins of the tumour is
often seen.
• On CT , meningiomas are hyper- or isoattenuation to brain parenchyma and
may be calcified. Sclerosis or hyperostosis in the adjacent bone may be seen.
• At MR imaging, meningiomas are iso- or slightly hypo intense to gray matter
on T1-weightedimages and are iso- or hypo intense to gray matter on T2-
weighted images.
• Enhancement is usually homogeneous, unless there are calcific or cystic foci.

99. Chondrosarcoma
• Chondrosarcomas are malignant cartilaginous tumours
• typically manifest in the 2nd and 3rd decades of life.
• In the skull base, they are much more common than their benign
counterpart, the chondroma.
• Associated with a number of syndromes, including Ollier disease,
Maffucci syndrome, and Paget disease.
• chondrosarcomas involving the petrous apex typically originate at the
petroclival and petrosphenoidal synchondrosis

100. • CT demonstrates a destructive petrous apex mass containing arcs and rings
of calcification,( which reflect the chondroid nature of the tumour.)
• At MR imaging, the lesions have
on T1WI low to intermediate signal intensity
on T2WI high signal intensity .
• Signal heterogeneity can be seen and may be due to the presence of
mineralized chondroid matrix.
• variable degrees of enhancement after contrast material administration

102. Chordoma
• Chordomas are midline tumours that may arise anywhere along the
primitive notochord.
• The sacrum is the most common site (50%) followed by the
sphenooccipital (clival) region (35%) and spine (15%)
• NECT shows a relatively well-circumscribed, moderately hyper dense
midline clival mass with permeative lytic bony changes.
• Intratumoral calcifications generally represent sequestrations from
destroyed bone
• On T1WI intermediate to low SI and hyperintense on T2WI .
• On sagittal images, a "thumb" of tumour tissue is often seen extending
posteriorly through the cortex of the clivus and indenting the pons.
• Moderate to marked but heterogeneous enhancement is typical after
contrast administration.

104. Metastasis

107. Vascular Lesions
Petrous Carotid Aneurysm
• Most petrous ICA aneurysms are large and fusiform,
• CT shows expansion of the carotid canal in the anterior petrous apex.
The walls of the canal may be thin or even dehiscent, and the
aneurysms may mimic cholesterol granulomas at unenhanced CT.
• However, contrast-enhanced studies show marked enhancement in
the lumen of a nonthrombosed aneurysm.
• At MR imaging, mixed signal intensity or heterogeneous
enhancement can be seen in the aneurysm lumen due to turbulent
flow or mural thrombus

109. Intraosseous Dural
Arteriovenous Fistula

110. Aberrant internal carotid artery
• In patients with an aberrant internal carotid artery the cervical part of the
internal carotid artery is absent.
• It is replaced by the ascending pharyngeal artery which connects with the
horizontal part of the internal carotid artery.
• The actual intratympanic segment may be a collateral branch
that occurs from the anastomoses of the inferior tympanic
branch of the ascending pharyngeal artery (from the external
carotid artery) with the caroticotympanic artery of the internal
carotid artery.
• may be asymptomatic, but it can cause pulsatile tinnitus or
conductive hearing loss

112. Persistent stapedial artery
• If the artery does not regress the middle meningeal
artery does not develop the PSA will then supply
the structures normally supplied by the middle meningeal
artery.
• After branching from the petrous internal carotid artery, the
persistent stapedial artery runs with the facial nerve through the
tympanic cavity.
• A persistent stapedial artery may be asymptomatic but may also
cause tinnitus.
• It is important to be aware of persistent stapedial artery in
patients undergoing stapes surgery, because the artery courses
through the obturator foramen of the stapes and may be
injured.

115. Clinical Features and
Choice of Imaging Technique
• Often asymptomatic
• May present with nonspecific symptoms, such as headache,
retro-orbital pain, or ear pain.
• Large lesions or those close to cranial nerves(e.g., in the
Meckel cave, cavernous sinus, or IAC) may cause cranial
neuropathies, which can include sensorineural hearing loss,
tinnitus, or vertigo(cranial nerve VIII); diplopia (cranial
nerves III,IV, or VI); facial pain (cranial nerve V); or facial
weakness (cranial nerve VII).
• The trigeminal and abducens nerves are the most
commonly affected cranial nerves in the setting of petrous
apex disease, as they are separated from the petrous apex
by only a thin layer of dura mater and are therefore
particularly susceptible to compression by adjacent
disease processes .

117. • MR imaging is the first line study for evaluation of suspected petrous
apex disease
• Higher contrast resolution provides excellent delineation of the soft-tissue extent
of lesions, nicely demonstrates invasion of the cavernous sinus and marrow space
, and depicts the relationship of lesions to nearby cranial nerves and vessels.
• MR imaging may also allow definitive diagnosis of certain petrous apex
lesions that have unique signal intensity characteristics, such as cholesterol
granulomas and petrous apex cephaloceles (discussed later).
• CT is primarily a problem solving tool reserved for situations in which better
characterization of mineralization and osseous involvement is needed, as CT is
superior to MR imaging in this regard

124. The petrous apex
• .
• It can be home to a wide range of disease processes.
• Cross-sectional imaging with computed tomography and magnetic
resonance (MR) imaging plays an important role in diagnosis and
characterization of lesions occurring there.
• Besides one should also be familiar with anatomic variants or pseudo
lesions in the petrous apex that can be mistaken for pathologic
conditions

126. Cholesteatoma (Epidermoid)
• Cholesteatomas may be classifed as acquired or congenital
• Congenital cholesteatomas of the petrous apex being more common.
• Congenital cholesteatomas arise from aberrant ectoderm that
is trapped during embryogenesis
• These lesions classically occur in children and young adults.

127. • At CT, cholesteatomas appear as nonenhancing, expansile petrous apex
lesions that cause variable degrees of bone destruction.
• When no or minimal bone destruction is present, they cannot be
distinguished from cholesterol granulomas with CT alone.
• MR imaging, cholesteatomas
On T1-weighted images generally have intermediate to low signal intensity.
On T2-weighted and fluid-attenuated inversion-recovery images, they
generally have high signal intensity.
• Enhancement is not seen after contrast material administration.
• Diffusion-weighted imaging is useful in diagnosis of cholesteatomas, as the
lesions often show restricted diffusion