Brain Pathology Case of the Month - December 2012


Schwannoma with exuberant inflammatory infiltrate and intratumoral edema that may have caused the increase of mass effect and sudden clinical deterioration.


When an intracranial schwannoma presents acutely, the clinical manifestation is usually coincident with tumoral infarct, hemorrhagic degeneration or hydrocephalus (7,8). In cases of intratumoral hemorrhage, the acutely increased mass may compress the brain stem with a secondary obstructive hydrocephalus and a sudden decreased level of consciousness. Sixty percent of schwannomas measuring more than 2 cm present a marked increase in vascularity (5). The vascular abnormalities of schwannomas may cause spontaneous vessel obliteration, necrosis and focal hemorrhagic degeneration (2). These changes may lead to the formation of microcystic areas (13). Another factor contributing to microcyst formation is the degeneration of clear foamy cells that result in vacuolar formation (1). Coalescence of microcystic areas might result in unilocular cysts, sometimes responsible for increased tumor volume (3,10). Sudden increase in cyst volume may result from intracystic hemorrhage as previously described in the case of spinal schwannomas. (1,12). Indeed, intracystic hemorrhage may account for the sudden onset of paraparesis in a case of spinal schwannoma (9). Presumably, intracystic hemorrhage can also occur when these tumors are located intracranially although not described in the current English literature.

In the present case, no intratumoral or intracystic hemorrhage and no hydrocephalus that could have precipitated the acute loss of consciousness were documented on the cerebral CT. No acute hemorrhage was observed on macroscopic and microscopic examinations. Although the precise etiology of the acute brain stem dysfunction remains to be elucidated, the important inflammatory infiltrate might have contributed to this unusual clinical presentation. Inflammatory infiltrates representing the host's humoral and cellular response to brain tumors, including schwannomas, have been documented (9,11). However the finding of an exuberant lymphoplasmacytic infiltration is highly unusual for schwannomas (4,10). A subclinical hemorrhagic, ischemic and xanthomatous transformation contributing to cystic formation might have been responsible for a non-specific inflammatory reaction. This inflammatory infiltrate may have induced increased vessel permeability and resulted in an adjacent intratumoral edema. Therefore, the massive infiltration of inflammatory cells and/or the consequent oedema might have contributed to the enlargement of a tumor that grew to occupy the cerebellopontine angle and presumably rendered the adjacent neural elements of the brain stem susceptible to minor incremental change in tumor size (6). This phenomenon of microscopic tumoral enlargement has recently been proposed to explain sudden paraplegia due to a lumbar schwannoma without coincident hemorrhage (6). To the authors' knowledge, this is the first reported case of a similar sudden neurological deterioration due to a CPA schwannoma with no acute hemorrhage or hydrocephalus.


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Contributed by Nancy McLaughlin, MD, PhD, FRCS(C), France Berthelet, MD, MSc, Michel W. Bojanowski, MD, FRCS(C)

International Society of Neuropathology