Posterior Fossa Skull Base Lesions

Posted by e-Medical PPT
Acoustic Neuroma (AN)
Benign schwann cells in collagenous matrix and don’t invade (usually cause symptoms by encroaching)
Usually arise from vestibular (95%) nerve in IAC but if they arise medial then symptoms develop later
95% are unilateral and nonhereditary
Slow growing (0.2-4mm/yr)

Hereditary AN’s
Type I
Only 5% with AN’s and no bilateral AN’s
Intra and extra-cranial
Appear late
Chromosome 17

Type II
Bilateral AN’s in 96%
Cranial nerve schwannomas
Appear by 2nd decade
Chromosome 22

Signs and symptoms
Sensorineural Hearing Loss,NHL (95%),SSNHL (20%), tinnitus (56%)
Dysequilibrium (50%), vertigo, nystagmus
Facial hypesthesia and loss of corneal reflex
Long tract signs, ataxia
Headaches and nausea
Hitselberger sign

Originate cap cells near arachnoid villi which are more prominent near cranial nerve foramina and venous sinuses.
Grossly appear speckled due to psammoma bodies
25% Cause hyperostosis
Same symptoms as AN but arise from posterior surface of petrous bone so audiometric (75% HL) and vestibular testing is less sensitive.
Only 75% have abnl ABR

Originates from epithelial rests within temporal bone or CPA.
Stratified squamous epithelial cells lining desquamated keratin
Same symptoms as AN but facial tic and paresis more common
Expand along least resistance so irregular shapes and borders and discovered in 2nd-4th decades.


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