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Acoustic neuroma is by far the most common tumor of the cerebellopontine
angle. Acoustic neuromas
are benign encapsulated tumors that usually arise from the Schwann cells
of the superior division of the vestibular nerve.
Less frequently, they may arise from the inferior vestibular
nerve: rarely, they arise from the cochlear nerve.
The usual site of origin is within the internal auditory canal in
the region of Scarpa’s ganglion where the neurilemmal sheath
terminates. As the tumor
slowly enlarges, growth is toward the cerebellopontine angle with
widening of the canal and involvement of cranial nerve VIII by
compression.
Occasionally, the tumor may originate within the angle and may spare the
cranial nerve involvement until the tumor reaches large size.
Histologically, the tumor is composed of streams of elongated
spindle cells, with elongated nuclei, arranged in a parallel fashion.
Each group spreads in a different direction, so that the
appearance is that of latticework.
Tumors in which there is a thick concentration of cells are
called Atoni type A, whereas those with a loose arrangement are called
Atoni type B. Usually there
is a combination of the two types within a given tumor.
Jung TT and Nissen RL. Otologic manifestations of retrocochlear disease,
Pg 1762 in Otolaryngology Vol II 3rd edition, eds Paparella,
Shumerick, Gluckman, Meyerhoff. WB
Saunders, Phil, PA.
This
76 year old male had a history of bronchopneumonia and cardiac
insufficiency. Audiometric
evaluation revealed a severe left sensorineural hearing loss.
A history of dizziness was noted.
The left temporal bone shows a large schwannoma (S) filling the
internal auditory canal and eroding its posterior wall.
IAC = internal carotid artery, EAC = external auditory canal.
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At high magnification the schwannoma is seen to be an
Antoni type B schwannoma. The
pattern is a loose texture of cells with a honeycomb appearance.
The accumulation of lipids within the cells gives it its
characteristic look.
Areas of cells arranged in whorls as well as in
parallel alignment are characteristic of this Antoni type A schwannoma. |
