1. Lesions of the Skull Base
Candace E. Hobson
March 10, 2017

2. Lateral Skull Base Cerebellopontine angle Petrous Apex Intra-axial
Space between cerebellum and pons containing CSF, arachnoid tissue, cranial nerves, vessels
Petrous Apex
Pyramidal, medial projection of petrous temporal bone
Intra-axial
Within the brain parynchema or brainstem
Extra-axial
Outside of brain

3. CPA Lesions 10% of intracranial tumors originate in the CPA
Arise MC from:
cranial nerve sheath
meninges
blood vessels
congenital epithelial rests

4. CPA Lesions Most common presenting symptoms
Asymmetric SNHL with poor discrimination
Unilateral tinnitus
Imbalance (vertigo uncommon)
Facial numbness (large tumor w anterior extension)
(Rare facial weakness)

5. CPA Lesions Vestibular Schwannoma (60-90%) Meningioma (3-7%)
Epidermoid cyst (2-6%)]
Non-acoustic schwannoma (5, 7, 9-12)
arachnoid cyst (0.5 – 2%), melanoma (<1%), hemangioma (<1%), lipoma, dermoid teratoma (< 1%)
= 75-98%

6. 45 yo F with left SSNHL
WRS 96% AD, 42% AS

10. Vestibular Schwannoma
Aka acoustic neuroma
MC CPA/IAC tumor (60-90%)
Arise from superior or inferior vestibular nerve
Typically arise in IAC and enlarge into CPA
Rounded mass in CPA with cone-shaped stem in IAC
May arise in CPA with mass centered at porus

11. Vestibular Schwannoma MRI
T1 isointense (to brain)
T2 iso- or hypointense
Enhances with gadolinium
May contain micro or macrocystic components (non-ehanancing)

14. MRI Meningioma
Often arises from posterior petrous surface w broad base along petrous bone
Eccentric to the porus (unlike VS)
T1 iso or hypointense
T2 hypo or hyperintense
25% have calcifications (hypo on T1, T2)
Cysts rare

15. MRI Meningioma Surrounding dural thickening on gadolinium
Dural tail = meningeal sign = flare sign
Hypervascular dura
reactive, not neoplastic

17. Epidermoid Cyst Anterolateral or posterolateral to brainstem
Congenital rests of epithelium, symptomatic in adulthood
Expand to area of low resistance: pre-pontine or supracellar cistern
“dumbbell” in to contralateral cistern or MCF
May erode petrous apex
CT: isodense to CSF, rare hyperinense

18. Epidermoid Cyst MRI T1 hypointense T2 hyperintense
Non-enhancing (else, consider SCC within)

19. Other Schwannomas CN V CN VII Jugular Foramen schwannoma (IX – XII)
Often indistinguishable from VIII
Widening of canal on CT scan
Facial twitching
Jugular Foramen schwannoma (IX – XII)
Hoarseness, dysphagia, shoulder weakness, tongue weakness
Enlarged JF on CT scan
No flow void like paraganglioma, and less vascular (angio)
XII
Smooth enlargement of hypoglossal canal

20. Glomus Jugulare Paraganglioma of jugular foramen Arises from
Glomus bodies in adventitia of JB
Jacobson’s nerve (tympanic branch of IX)
Arnolds’s nerve (auricular branch of X)
Glomus body = cluster of chief cells (Zellballen) = paraganglia – neuromodulators/monitor of vascular activity

21. Glomus Jugulare MC in F, whites and on the left side
5-10% have multiple
50% in familial form (AD)
1-3% chemically active
Check 24h urine for VMA, metanephrine if concern

22. Glomus Jugulare Arise in jugular fossa Often large before symptoms
Lower cranial nerve neuropathy (IX, X, XI)
Jugular foramen syndrome (Vernet)
Villaret if also has Horner’s

23. Glomus Jugulare
CT:
Erodes bone of jugular bulb/fossa

24. Glomus Jugulare MRI MRA/MRV to det invlmt of ICA, IJV
T1: hypo, isointense
T2: hyperintense
Contrast enhancing
Flow voids (“salt & pepper”) T1-2
MRA/MRV to det invlmt of ICA, IJV

28. Petrous Apex Lesions Symptomatic lesions rare
Symptoms related to anatomy affected
Hearing loss
Vestibular dysfunction
Headache
Tinnitus
Facial twitching
Diplopia
Facial paralysis
Otorrhea
May be found incidentally

29. Petrous Apex: Imaging Basics
Marrow is T1-Bright because of its high fat content
Effusions T2-Bright (T1-hypointense)
CT can help differentiate normal anatomy from pathology
Neither asymmetric pneumatization nor effusion cause erosion or expansion of surrounding bone

30. Common PA Lesions Cystic Infectious Neoplastic Cholesterol Granuloma
Cholesteatoma (aka epidermoid cyst)
Mucocele
Infectious
Petrous Apicitis
Skull Base Osteomyelitis
Neoplastic
Chondrosarcoma
Chordoma
Meningioma

31. Cholesterol Granuloma
Not epithelial-lined, so not a true cyst
Fluid-filled expansile lesion with a fibrous capsule
Bleeding in PA air cells anaerobic metabolism of hemoglobin  cholesterol crystals  giant-cell foreign body reaction
Exposed marrow theory, obstructed air cell
Often in highly-pneumatized petrous apicies without ME disease

32. Cholesterol Granuloma: Presentation
Peak incidence yo
MC symptom is hearing loss (50%)
SNHL from compression of VIII
CHL from extension of mass into middle ear

33. Cholesterol Granuloma: Imaging
CT:
Isointense to brain
Expansile with smooth margins (older lesions)
Loss of bony trabeculae
Useful for surgical planning

34. Cholesterol Granuloma: Imaging
MRI: T1- and T2-bright
*some heterogeneity related to fibrosis and age of lesion
Early lesions may have contrast-enhancement of capsule

35. `
MRI: bright on T1 & T2
CT: isointense lesion with bony erosion

36. Cholesterol Granuloma: Management
Incidentally-discovered lesions may be observed
Consider surgical management for:
progressive symptoms
radiologic evidence of growth
Drainage or resection (decreases risk of recurrence)
Can be difficult to establish permanent drainage pathway
“Because it is difficult to establish a permanent path for drainage and aeration in these cases, an attempt at complete tumor resection is advocated to reduce the risk of recurrence.”
Surgical drainage has shown to improve/resolve:
Tinnitus
Imbalance
Hearing may stabilize or worsen
Cases of recurrence typically show closure of drainage pathway
Very rare recurrence with complete excision

37. Cholesteatoma aka epithelial inclusion cyst aka epidermoid
MC an extension of middle ear/mastoid cholesteatoma
Primary epidermoids may occur
Exfoliated keratin debris creates a slowly-expanding lesion erosive of petrous bone
Acquired cholesteatoma more likely to be c/b infection

38. Cholesteatoma: Presentation
More advanced symptoms than middle ear/mastoid cholesteatoma
50% p/w facial paralysis
80% p/w hearing loss
Vertigo, tinnitus, headache also common

39. Cholesteatoma: Imaging
CT provides the most detail about degree of PA involvement, and also status ME/mastoid
Non-enhancing lesion isointense to spinal fluid
Bony erosion w smooth or scalloped edges
MRI: T1-hypointense, T2-hyperintense

40. MRI: T1 isointense, T2-bright
CT: erosive lesion with scalloped margins

41. Cholesteatoma: Surgical Management
Epithelium-lined cyst (unlike CG)
Drainage is not curative
Required resection or exteriorization (not in PA)
Infralabyrinthine
Middle fossa
Translabyrinthine

42. 20 yo M with chronic AOM p/w
Left eye pain
Diplopia (left VI palsy)
Left otorrhea

46. Petrous Apicitis Rare in era antibiotics
Bacteriology similar to coalescent mastoiditis:
Pneumococcus, H. flu, β -hemolytic strep
Staphylococcus species causative in cases a/w SkB osteomyelitis
Pseudomonas in cases of chronic otitis media
Acute or chronic
Acute: unimpeded spread of infection in a pneumatized apex
Chronic: otitis media and limited air cell development.
Infectious

47. Petrous Apicitis: Imaging
CT:
Expansile lesion erosive of bony trabeculae
Acute: contralateral PA well- pneumatized
Chronic: evidence of chronic otitis media
Rim-enhancing

48. Petrous Apicitis: Imaging
MRI
T1-hypointense, T2-hyperintense
Gad: rim-enhancing

49. Petrous Apicitis: Treatment
IV antibiotics = cornerstone
Drainage in cases of intracranial complications or progression with medical mgmt
Translab if non-hearing
May follow existing air cell tracts to infection
Treat any concurrent middle ear/mastoid disease (mastoidectomy)

50. Chondrosarcoma Rare primary bony malignancy,
Accounts for ~1/3 all primary bone malignancies
Intracranial chondrosarc < 0.2% of all IC tumors
Thought to arise from persistent chondrocytes at petrosphenoid, petro-occipital, and spheno-occipital sutures

51. Chondrosarcoma
Typically develops at foramen lacerum or petroclival suture line
Off the midline (unlike chordoma)
MC initial symptoms:
headache
hearing loss
diplopia,
lower cranial neuropathy

52. Chondrosarcoma: ImagingCT
Contrast-enhancing, invasive lesion
May contain remnants of eroded bone (calcifications)

53. Chondrosarcoma: Imaging
MRI
T1-iso/hypointense, homogenous
T2-hyperintense, heterogenous
Contrast-enhancing (brighter than chordoma)

54. Chondrosarcoma: Treatment
Surgical excision
Complete resection may be limited by invlmt neurovascular structures (inc ICA, CN’s and brainstem)
May consider SRS for non-surgical candidates with small tumors
Adjuvant radio therapy has been shown to be of benefit
5-year control rate with multimodality therapy ~95%

55. Chordoma Rare, locally-aggressive primary bone malignancy
Aries from notochord remnant
Often originate at clivus
Spread laterally to involve petrous apex
May rarely originate in petrous apex
Presents in 40’s-50’s
Headache and diplopia MC symptoms

56. Chordoma: Imaging
CT:
Contrast enhancing, locally- destructive, lobulated lesion centered within the clivus in the midline
May retain calcifications from eroded bone

57. Chordoma: Imaging MRI T1-iso/hypointense, homogenous
T2-hyperintense, heterogenous
Contrast-enhancing (less bright than chondrosarc)

58. Chordoma Gross total excision (high rate of recurrence)
80% 5-year recurrence-free survival, 50% 10-y
Adjuvant radiation of little survival benefit

59. Meningioma
Benign neoplasm arising from the arachnoid villi of the meninges
Accounts for 10-20% of all intracranial tumors
Petroclival meningiomas arise from the dura in the region of the petroclival synchondrosis
May extend to involve petrous apex

60. Meningioma: Imaging CT MRI Iso/hyperintense lesion with calcifications
Contrast-enhancing
Hyperostosis of the adjacent bone
MRI
T1- and T2 iso/hyperintense
Contrast enhancing
Enhancement of adjacent dura = “dural tail”

61. Meningioma: Treatment
Observation
Surgical resection
Radiation
to improve exposure while minimizing
brain retraction

62. Metastatic Lesions
MC mets: breast, lung, prostate, melanoma, and renal.
Tendency for hematogenous spread of malig to PA b/c of the filtering effect of PA bone marrow
slow blood flow through the vascular channels within the marrow facilitate deposition of tumor cells
Imaging characteristics depend on primary tumor
Typically an contrast-enhancing erosive lesion

63. Adapted from Otolaryngol Clin North Am. 2007 Jun;40(3):479-519, viii

68. Mucocele
Slowly-expanding cystic lesion evolved from any pneumatized area of SkB
Occurs 2/2 obstxn of mucous-lined space
MC occurs in paranasal sinuses
Rare in petrous apex

69. Mucocele: Imaging CT MRI
Clearly-defined expansile lesion isodense to CSF
Loss of bony septations (unlike effusion)
Typically non-enhancing (except rim or case of infxn)
MRI
T1-intermediate, T2-bright
Non-ehnancing
Drainage is adequate

70. Petrous Apicitis: Presentation
Pain: temporal, occipital, or retro-orbital.
OM symptoms: hearing loss, otorrhea
Ipsilateral VI palsy (CN VI is susceptible to injury as it courses through Dorello’s canal)
Complications:
Intracranial: brain abscess, subdural empyema, meningitis, dural sinus thrombosis (including cavernous sinus)
Intratemporal: labyrinthitis or facial paralysis.
Neck: lateral pharyngeal or retropharyngeal abscess.

71. Skull Base Osteomyelitis
2/2 of extension of bacterial infection from (malignant) otitis externa to involve both the cortical and marrow spaces of the skull base
MC etiologic pathogen is Pseudomonas
CT and MR imaging often nonspecific, especially in the early stages
Advanced dz: bone demineralization & sequestration seen on CT
Technetium 99 sensitive to detect osteomyelitis
Gallium useful for both diagnosis of osteomyelitis and to evaluate for resolution of infection.

72. Skull Base Osteomyelitis
Treat with prolonged course of culture-directed antibiotics.
Surgical management reserved for cases of abscess, bony sequestra, or necrotic tissue