CPA /posterior fossa

it's not a Tumor!

100

what are the most common tumors of the posterior fossa name 5

Acoustic neuroma – 80%, most common adult lesion Meningioma – 5%, 2nd most common adult lesion Epidermoid – 3%, 3rd most common adult lesion Arachnoid cyst – 1% Nonacoustic neuroma - Facial schwannoma most common, 1% Paraganglioma Hemangioma

200

Seven Uncommon CPA lesions name 4

A: Metastatic malignant tumor A: Lipoma A: Dermoid A: Teratoma A: Chordoma A: Chondrosarcoma A: Giant cell tumor

300

Ddx of Petrous Apex lesions (5) name 3

A: Cholesterol granuloma (20x more frequent than epidermoids in the petrous apex) A: Epidermoid A: Asymmetric pneumatization A: Retained mucus/mucocele A: Petrous apicitis +/- Osteomyelitis A: Petrous ICA aneurysm A: Meningioma A: Glomus tumors (Tympanicum, Jugulare) A: Chondrosarcoma

400

Ddx of Intraaxial tumors (4) name 2

A: Hemangioblastoma A: Medulloblastoma A: Brainstem Glioma (most common Pediatric CPA lesion) A: Malignant Choroids Plexus Papilloma & Ependymomas

500

From what cells do Meningiomas Arise?

Cap cells, around Tips of Arachnoid Villi

Surgical approaches

100

list approaches to the Posterior fossa (4/8)

Translabyrinthine Retrosigmoid (suboccipital)* Retrolabyrinthine* Transcochlear Transotic Middle fossa* Extended middle fossa* Petrosal*

200

Of the 3 approaches of AN surgery. order then in least to most likely to get a CSF leak

Retrosigmoid craniotomy has the highest CSF leak rate, followed by translabyrinthine craniotomy. Middle fossa craniotomy has the lowest leakage rate. (Bailey’s)

300

Discuss the 4 Advantages & 1 Disadvantage of the Translabyrinthine Approach for Acoustic Neuromas excision

A: Advantages – Safest for CN VII function Preservation; Direct approach to IAC; Wide Exposure not limited by Tumor Size; Minimal cerebellar Retraction A: Disadvantange – Total Hearing Eradication, Increased risk of CSF Leak

400

Discuss the 2 Advantages & 3 Disadvantages of the Middle Fossa Approach for Acoustic Neuromas excision

A: Advantages – CN VIII nerve preservation possible; Ideal for Small Intracanalicular tumors A: Disadvantages – Contraindicated if >1 cm or extension into CPA; Increased Risk to CN VII, significant Temporal Lobe Retraction, More technically Difficult

500

Discuss the 50:50 rule or 70:30 rule and how it would guide your surgical management

Hearing preservation 50:50 rule – not recommended if >50db HL, speech discrim <50% Hearing preservation recommended if <30db, >70% speech discrim, normal ABR

Acoustic neuroma

100

discuss Radiographic features of Acoustic Neuroma on mRI

A: MRI – T1 Isointense to brain, Hyperintense to CSF; T2 Hyperintense to brain, Iso/Hypointense to CSF; Gad Intense enhancement

200

Where do Acoustic Neuromas Originate historically?

At Schwann cell-Glial junction (Obersteiner-Redlich zone)

300

Audio findings most consistent with AN list 2

A: PTA – 65% will have HF SNHL; 10% present with SSNHL (but only 5% of SSNHL is due to AN); 5% have Normal hearing A: SDS – Poor scores out of proportion to PTA suspicious; Rollover present A: Stapedial Reflex – 88% will have Absent Reflex or Positive Reflex Decay

400

Average growth rate of AN

0.2 cm/ year

500

NF1 and NF2 list the chromosome and % chance of developing AN

NF 1 (17) NF2 (22) <5 vs 96% bilat

Radiology

100

Radiographic features of Meningoma on MRI

A: MRI – T1 Isointense to brain, larger lesions may be heterogeneous with central hypointensity; T2 Hyperintense to brain, Hypointense to CSF; Gad Intense enhancement (but less than AN)

200

Radiographic features of Epidermoid on MRI

A: MRI – T1 Hypointense to brain, Isointense to CSF; T2 Hyperintense to brain, Isointense to CSF;

300

Radiographic features of Arachnoid Cyst on MRI

A: MRI – T1 Isointense, T2 hyperintense to CSF, Homogeneous lesion, DWI suppressed

400

Six IAC lesions that light up with Gadolinium name 3

A: Neuromas – Acoustic or Facial nerve A: Meningiomas A: Inflammatory nerve lesions A: AVM’s A: Vascular loops A: Petrous bone metastasis

500

Eight Radiographic Differences between Meningiomas and Acoustic Neuromas name 4

A: Meningiomas more Dense & Homogenous A: Meningiomas cause More Hyperostosis of surrounding bone A: Meningiomas Sessile, Broad base, Obtuse Angle to Petrous bone A: Meningiomas Eccentric over IAC A: Meningiomas Uncommonly involve the IAC, whereas ANs have Intracanulicular component A: Meningiomas frequently have a Dural Tail A: Meningiomas frequently have Calcifications A: Acoustic Neuroma exhibit Greater, More Homogeneous Gadolinium Enhancement

Potpourri

100

Define Brown’s sign

A: Seen in Glomus Typmanicum tumors A: Reddish blush seen behind an intact TM which Blanches upon introducing Pneumatic Pressure that exceeds the Systolic BP

200

Define Aquino’s sign

A: Seen in Paragangliomas A: Pulsatile Tinnitus of paraganglioma Decreases with Carotid artery Compression

300

Draw me contents of the IAC

Seven up coch down

400

Describe Hitselberger’s sign

A: Numbness of Posterior EAC from Compression of Sensory branches of Facial Nerve

500

Most common primary lesion of Petrous Apex

Cholesterol Granuloma