Cerebellopontine angle and intracanalicular masses mimicking vestibular schwannomas.

OBJECTIVE: To describe the clinical and radiographic characteristics in a series of patients with non-vestibular schwannoma cerebellopontine angle (CPA) and intracanalicular (IAC) masses, who underwent microsurgery for presumed vestibular schwannoma (VS). STUDY DESIGN: Retrospective case series. SETTING: Tertiary neurotologic referral center. PATIENTS: One thousand five hundred ninety-three patients underwent microsurgery for apparent VS from 2002 to 2013. Of these, 53 patients (3%) were discovered to have a diagnosis other than VS. INTERVENTIONS: Middle fossa, translabyrinthine, and retrosigmoid craniotomy. MAIN OUTCOME MEASURES: Clinical presentation, radiologic analysis, and histopathology examination. RESULTS: There were 17 facial schwannomas, 15 meningiomas, 9 hemangiomas, 6 lipochoristomas, 3 inflammatory reactions, and one each of lymphoma, glial heterotopia, solitary fibrous tumor, ependymoma, and a non-diagnostic mass. Excluding facial schwannomas, 23 cases were misdiagnosed as VS in the first half of the study period, compared to only 15 cases in the latter half (p = 0.09). Ninety-six percent of patients presented with some combination of sensorineural hearing loss, balance disturbance, and tinnitus. In the subset of patients with available preoperative MRI scans for retrospective review, only 4 of 28 patients had radiologic findings suggestive of pathology other than VS. The most common missed radiologic diagnoses were facial schwannoma, lipochoristoma, and meningioma. CONCLUSION: A subgroup of patients with CPA and IAC masses who present with radiologic findings diagnostic of VS will have an alternative histopathologic diagnosis. Optimal radiologic imaging and experienced interpretation can improve diagnostic accuracy. The most common tumors that mimic VS despite ideal radiologic imaging are facial schwannomas, meningiomas, and hemangiomas.

Lipochoristomas (lipomatous tumors) of the acoustic nerve.

CONTEXT: Lipochoristomas (lipomatous choristomas) are rare tumors of the acoustic nerve (cranial nerve VIII/vestibulocochlear nerve) within the internal acoustic canal and sometimes the cerebellopontine angle, and are histogenetically believed to be congenital malformations. Their clinically indolent behavior has recently prompted a more conservative management protocol in a quest for maximal nerve/hearing preservation. This approach contrasts sharply with that for the common internal acoustic canal/cerebellopontine angle tumors, the neuroepithelial neoplasms (acoustic schwannomas and meningiomas), which behave more aggressively and have more prominent clinical manifestations. Owing to their rarity, the clinicopathologic features of cranial nerve VIII lipochoristomas have been obtained mainly through case reports. OBJECTIVE: We present the clinicopathologic features of 11 cases of lipochoristomas of cranial nerve VIII. DESIGN: The 11 cases were documented between 1992 and 2003. We performed complete clinical reviews with histologic, histochemical, and immunohistochemical analyses of formalin-fixed, paraffin-embedded tumor samples. RESULTS: The patients were 8 men and 3 women with hearing loss of the right ear (5 patients) or the left ear (6 patients). No patient had bilateral tumors. All lipochoristomas histologically possessed mature adipose tissue admixed with varied amounts of mature fibrous tissue, tortuous thick-walled vessels, smooth muscle bundles, and skeletal muscle fibers, the latter verified with immunohistochemistry. CONCLUSIONS: The histomorphologic and immunophenotypic evidence showed that these tumors are better characterized as choristomas than as simple "lipomas," as they have been labeled in the past. Their overall nonaggressive clinical nature in addition to the characteristic radiologic and histomorphologic findings are important clinicopathologic features for the pathologist to recognize and differentiate, especially during frozen section evaluations, in order to direct the neurosurgeon to a more appropriate conservative therapeutic intervention.