Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 4, 2011, pp. 642-645

Neurology India, Vol. 59, No. 4, July-August, 2011, pp. 642-645

Letter to Editor

Calcification in vestibular schwannoma: Report of two cases and review of the literature

CV Gopalakrishnan, Adesh Shrivastava, Suresh Nair
Department of Neurosurgery, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India
Correspondence Address: C V Gopalakrishnan, Department of Neurosurgery, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India, doc_gopal@yahoo.com

Date of Submission: 21-Mar-2011
Date of Decision: 21-Mar-2011
Date of Acceptance: 21-Mar-2011

Code Number: ni11197

PMID: 21891960

DOI: 10.4103/0028-3886.84364

Sir,

Calcification in vestibular schwannomas have been reported but infrequently. ^{[1],[2],[3],[4],[5]} Calcification in vestibular schwannoma causes some difficulty in the neuroradiological and histological differential diagnosis. Here we report two uncommon cases of vestibular schwannomas demonstrating peculiar radiological findings.

A 65-year-old man presented with gradually progressive left-sided hearing loss, facial numbness, and asymmetry of 3 years duration. On examination, he had hypoesthesia involving the left half of face with House-Brackmann Grade 3 facial palsy. He had Grade 4 Gardner and Robertson left sensorineural hearing loss and depressed gag reflex. Computed tomography (CT) of the head revealed a 3 cm left cerebellopontine (CP) angle mass with widening of the internal acoustic meatus (IAM). The lesion showed areas of significant calcification [Figure - 1]. Magnetic resonance imaging (MRI) of brain showed the lesion to be predominantly hypointense on T1-weighted imaging and heterogeneously hyperintense on T2-weighted imaging. On administration of intravenous gadolinium, there was inhomogeneous enhancement of the tumor. These signal characteristics, along with the CT appearance suggested the possibility of a vestibular schwannoma though calcification is extremely rare. The patient underwent a left retromastoid suboccipital craniectomy and total excision of the tumor. The presence of calcific deposits was confirmed intraoperatively. In the immediate postoperative period, the patient had an extensive anterior wall myocardial infarction and despite all resuscitative measures he could not be revived. The histopathology of the tumor was suggestive of schwannoma with foci of calcification.

A 31-year-old female presented with right-sided deafness and facial numbness of 6 months duration. On examination, she had right-sided Grade 5 Gardner and Robertson sensorineural hearing loss with decreased perception to touch and temperature involving the right half of face. CT of the head showed a large right CP angle lesion with two areas of peripheral calcification and erosion of the IAM [Figure - 2]. MRI brain revealed an approximately 5 cm right CP angle tumor with an arachnoid cap compressing the brainstem and cerebellum with extension into the IAM. The lesion showed heterogeneous signal characteristics with moderate contrast enhancement. With a preoperative diagnosis of vestibular schwannoma the patient underwent a right retromastoid subSoccipital craniotomy and excision of the tumor. Except for the presence of postoperative facial palsy, the patient had an uneventful recovery. Histopathology confirmed the preoperative diagnosis.

Vestibular schwannomas are benign tumors of schwann cell origin that originate predominantly from the transition zone between the schwann cells and oligodendrocytes of the vestibular division of the eighth nerve. Calcification is extremely uncommon in vestibular schwannomas and its presence on preoperative imaging warrants an alternate diagnosis. The differentiation of vestibular schwannoma and meningioma in the CP angle can be difficult with CT, in view of similar enhancement characteristics and extra-axial location. Calcification is common in meningiomas occurring in close to one-fourth, whereas none was detected in two large series of vestibular schwannoma. ^[6],[7] Although signal characteristics on MRI can often differentiate these two lesions, this may not always be possible. Extra-axial cavernous hemangiomas involving the 7-8 ^th nerve complex, though frequently associated with calcification, are rare lesions seen within the IAM. ^[8] In both our patients, the presence of hearing loss as the predominant symptom and widening of the IAM on CT strengthened the possibility of a vestibular schwannoma as the preoperative diagnosis. Changes in the internal auditory meatus are relatively rare with meningiomas or other calcified lesions in the CP angle.

Histopathologic examination in both our patients showed broad interlacing bundles of bipolar, spindle-shaped cells with both Antoni A and Antoni B tissue and extensive hyalinized blood vessels and microhemorrhages. Immunostaining for glial fibrillary acidic protein was negative, but was strongly positive for S100 protein. The areas of calcification were clearly identified in both the histology slides. The pathophysiology behind calcification is not clear but may be related to ischemic necrosis within the tumor or microhemorrhages within it. Atlas et al. ^[1] proposed that it may occur as one of the secondary changes in Antoni B areas. Necrosis may be the result of frequent intratumoral bleeding caused by abnormal vasculature which is often seen in large vestibular schwannomas; ^[9] the presence of heterogeneous signal intensities on MRI suggest its possibility in our report. Microscopic examination rarely detects foci of calcification in schwannomas. ^[6],[10] Large areas of calcification demonstrated on CT and encountered during tumor decompression in our cases, can be attributed to long standing dystrophic calcification over areas of intratumoral necrosis.

We report two rare cases of vestibular schwannoma with calcification. To our knowledge, only five cases have been previously reported in the literature, of which three showed small calcific deposits. The possibility of vestibular schwannoma should therefore be considered in the differential diagnosis of calcific lesions in the cerebellopontine angle on preoperative imaging. This is essential since preservation rates of the 7-8 ^th nerve complex needs to be addressed to the patient prior to surgery especially when the tumor is large.

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