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

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

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

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)

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%

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

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

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

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

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

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

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

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

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

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

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

Glomus Jugulare CT: Erodes bone of jugular bulb/fossa

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

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

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

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

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

Cholesterol Granuloma: Presentation Peak incidence 30-60 yo MC symptom is hearing loss (50%) SNHL from compression of VIII CHL from extension of mass into middle ear

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

Chondrosarcoma: Imaging CT Contrast-enhancing, invasive lesion May contain remnants of eroded bone (calcifications)

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

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%

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

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

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

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

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

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”

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

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

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

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

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

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.

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.

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