Approach to Skull BaseTumors

Manohar BanceProfessor, Division of

Otolaryngology, Dept of SurgeryDalhousie University

Classification:

Where is it?• Intra-axial vs extra-axial (outside brain)• CPA vs Jugular Foramen Vs Petrous ApexImaging• T1 vs T2• Light up on contrast• Shape, boundaries• Sometimes CT findings

Quickly Getting BearingsIn bonePetrous Apex:Chol GranMucocoeleCholesteatoma(epidermoid)Chrondroma/ChondrosarcTG schwannMetastasis

In CPA:Vest SchwannMeningiomaEpidermoidArachnoid CystLipoma

In Jugular Foramen:Glomus, Vagus Schwannoma, Met

MRI Imaging Characteristics

BRIGHT T1

CG

BRIGHT T2

Acoustic (+C)Meningioma(+C)Lipoma (-C)

EpidermoidArachnoid Cyst

Cerebellopontine Angle

• Area of the lateral (quadrimenal) cisterncontaining CSF, arachnoid tissue, cranial nervesand their associated vessels.

• Borders– Medial – lateral surface of the brainstem– Lateral – petrous bone– Superior – middle cerebellar peduncle & cerebellum– Inferior – arachnoid tissue of lower cranial nerves– Posterior – cerbellar peduncle

Medial:Lat surfaceBrainstem

Lat:PetrousBone

Sup: Middle Cbllr Peduncleand Cbllm

Inf: Lower CN and arachnoid

Post:not shownCbllr peduncle

CPA

CPA tumors

• Vestibular Schwannoma: 70-90%• Meningioma: 5-10%• Epidermoids: 2-5%• Arachnoid Cysts: 1%• Others: Facial and TG Schwannoma,

Lipoma, ELS tumor, aneurysm AICA etc

AN Features•Centered on Porus Acousticus

•Acute angles to petrous bone

•Often involves the IAC

•Homogeneous enhancement

•No dural tail

•No calcifications

Meningioma Features•Arise from surface of petrous bone

•Obtuse angles to petrous bone

•Uncommonly involves the IAC

•Frequently with dural tail

•Calcifications common

Arachnoid Cyst

Main differential onT1 and T2: Epidermoid

Epidermoid brighton DWI and FLAIRACyst follows CSF

T1

T2

FLAIR

DWI

Treatment

Treatment for VS

• Observation• Surgery

– Translabrynthine– Retrosigmoid– Middle Fossa

• Radiotherapy– Conventional radiation therapy– Stereotactic radiosurgery

Choice of Surgical Approach

Hearing Preservation Wanted?

Large Tumor:Suboccipital

Yes

Small LateralTumor: Middle

Fossa

Any Size Tumor:Translabyrinthine

No

Large Tumor?Yes

No

SO

TL

TC/TO

MF

Views From Different Approaches

Trans-labyrinthine• Indications

– Non-serviceable hearing• Advantages:

– little cerebellar retraction– Good exposure of facial nerve laterally– Can do all size tumors

• Disadvantages:– Sacrifice hearing, slightly higher CSF leak rate

Middle Fossa• Indications

– Intracanallicular tumor (maybe 0.5cm into IAC)– Residual Hearing (50:50 or 70:30 rule)

• Contraindications– Large tumors– Older patients ( > 60 yrs. may have higher rate of bleeding or

stroke)

• Advantages:– Perhaps highest hearing preservation rate– Good access to lateral fundus

• Disadvantages:– Facial nerve first in line of exposure in IAC– Limited medial exposure– Risk of Seizure

Retrosigmoid• Indications

– Serviceable hearing– Any size tumor as long as not in lateral fundus only

• Contraindications– Lateral IAC tumor (cant get to fundus without risking hearing)

• Advantages– Good exposure superior-inferiorly– Familiar to most neurosurgeons

• Disadvantages– Cerebellar retraction– Limited access to lateral fundus

Observation

• Still relatively high chance of significanthearing loss, approx 40%

• Only about 30-50% of tumors requiretreatment

• Often used in elderly, medically unfit

Stereotactic Radiosurgery

• LINAC, Gamma Knife, Cyber-knife• Fractionated vs non-fractionated• Tumor control rates well over 90%• Risks:

– Tumor miss, hydrocephalus, facial pain, facialparalysis (under 5% and usually partial),malignant transformation

– Similar or increased risk of long term hearingloss to conservative treatment

Special Case: NF2

• Scan whole brain, not just IAC• Scan spine• Screen family• Counsel re family planning

Petrous Apex Masses

Petrous Apex MassesBeware petrous apex asymmetric pneumatization

Table 2. Petrous Apex Lesion Characteristics on MRI Scanning (Intensity Compared with Adjacent Brain)*

Lesion T1 Images T2 Images T1-Gadolinium

Cholesteatoma Hypo Hyper No enhancement

Cholesterol granuloma Hyper Markedly hyper No enhancement

Petrous apicitis Hypo Hyper Rim enhancement

Effusion Hypo Hyper Mucosal enhancement

Bone marrow asymmetry Hyper Hypo No enhancement

Neoplasia Hypo Hyper Enhancing

From Jackler RK and Parker D: The radiographic differential diagnosis of petrousapex lesions. AJO 1992;13:561-574

Approaches to Petrous Apex

• Translabyrinthine, Transcochlear/otic• Infracochlear• Infralabyrinthine , retrolabyrinthine and

other perilabyrinthine approaches• Transsphenoid• Middle Fossa• Partial labyrinthectomy

TranspenoidalTransphenoidal

Infralab

TL or TC

Infracochlear

Jugulotympanic Paragangliomas

• 2nd most common temporal bone tumor ( after AN)• 4:1 female to male ratio• Median age of presentation 50-60 yrs• No ethnic or racial predeliction• Sporadic and familial forms ( 25 – 50% multicentricity)• Functional secretion about 1-3%• Malignancy rate < 5%

Imaging: salt and pepper pattern

Jugulotympanic ParagangliomasClassification

• Glasscock-Jackson Classification– I. Small tumor involving jugular bulb, middle ear, and

mastoid– II. Tumor extending under internal auditory canal; may

have intracranial extension (ICE)– III. Tumor extending into petrous apex; may have ICE– Tumor extending beyond petrous apex into clivus or

infratemporal fossa; may have ICE

• Fisch Classification

Systemic Considerations

• Association with MEN IIA, MEN IIB, VHL• Paraganglioma neuropeptides

– Norepinephrine, serotonin, vasoactiveintestinal peptide, neuron specific enolase

• 1-3% functional• Symptoms

– HA, palpitations, flushing, perspiration

Fisch Type A approach

Treatment

• Surgical: Fisch Type A or extendedmastoidectomy– Mobilize facial nerve anteriorly– Isolate tumor between jugular vein in neck

and the sigmoid sinus• Stereotactic or conventional radiotherapy• Observation

Summary• Diagnosis:

– Where is it?– What are its imaging characteristics?

• Treatment similar for all common ones:– Surgery– Watch– Radiation (except epidermoid)

• Don’t forget about rehabilitation afterwards