Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 59, Num. 5, 2011, pp. 786-788

Neurology India, Vol. 59, No. 5, September-October, 2011, pp. 786-788

Letter to Editor

Greater superficial petrosal nerve schwannoma: Report of two cases and literature review

Alok Umredkar¹, Navneet Singla¹, Sunil Kumar Gupta¹, Bishan Radotra²

¹ Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India
² Department of Histopathology, Postgraduate Institute of Medical Education and Research, Chandigarh, India
Correspondence Address: Alok Umredkar, Department of Neurosurgery, Postgraduate Institute of Medical Education and Research, Chandigarh, India, alokumr@yahoo.co.in

Date of Submission: 19-Jul-2011
Date of Decision: 19-Jul-2011
Date of Acceptance: 25-Jul-2011

Code Number: ni11243

PMID: 22019683

DOI: 10.4103/0028-3886.86578

Sir,

Greater superficial petrosal nerve (GSPN) schwannomas are relatively uncommon tumors and involve the middle cranial fossa by anterior extension through the facial hiatus. ^[1],[2] We report two cases of GSPN schwannomas.

In the first case, a 51-year-female presented with headache and hearing loss in the left ear since 4 months. Neurological deficits included left-side lower motor facial palsy, decreased tear secretion, and sensori-neural hearing loss. Head computed tomography (CT) scan showed an iso- to hypodense mass in left middle cranial fossa abutting the petrous bone with erosion of the bone [Figure - 1]a. Magnetic resonance imaging (MRI) scan demonstrated an extra-axial mass iso- to hypointense on T1 [Figure - 1]b and iso- to hyperintense on T2-weighted images [Figure - 1]c, with heterogenous enhancement [Figure - 1]d and e. She underwent left temporal craniotomy and total excision. The tumor was totally extradural, eroding the anterosuperior surface of petrous bone. Histopathology showed a tumor composed of hypo- and hypercellular areas with focal areas of veroccay body formation, consistent with diagnosis of schwannoma [Figure - 2]a. Repeat MRI at 6 months did not show any evidence of tumor recurrence [Figure - 1]f. Her hearing improved but with no improvement in facial palsy at 1-year follow-up.

In the second case, a 45-year-female was admitted for decreased hearing in the left ear and left facial paresis for the last 2 years. She had left sensorineural hearing loss, left facial palsy, and conjunctival congestion. Cranial contrast CT scan showed left temporal heterogeneously enhancing mass along the superior surface of petrous bone with erosion [Figure - 3]a and b and MRI showed densely enhancing extraaxial mass occupying middle fossa suggestive of GSPN schwannoma [Figure - 3]c- e. Gross total removal of the tumor was achieved by an extradural subtemporal approach. Histopathology showed a schwannoma [Figure - 2]b. Postoperative CT scan showed complete excision [Figure - 3]f and MRI done at 6 months showed no residual or recurrent tumor. She had improvement in the facial paresis, but not in hearing loss.

A schwannoma originating from the GSPN is a rare type of facial nerve schwannoma comprising 0.8% of all petrous bone lesions. ^[1] It was first described by Woodruf et al. in 1981. ^[3] Only 13 patients with schwannomas originating from the GSPN had been reported in the literature [Table - 1]. ^{[1],[2],[3],[4],[5],[6],[7],[8],[9]} As GSPN contains the parasympathetic fibers to lacrimal gland, decreased tear secretion is major clue to the diagnosis of GSPN schwannoma. ^[2],[8] The common presenting symptoms of GSPN schwannoma were facial palsy, hearing disturbances due to inner ear destruction, headache, and burning pain and redness of eye [Table - 1]. In our report also, both patients had facial palsy, sensorineural hearing loss, and decreased tear secretions, and a Schirmer test was positive.

CT scan is valuable for showing bony details such as erosion of the petrous bone or enlargement of the internal auditory meatus; facial canal and facial hiatus are better delineated by CT scan. ^[1],[8] MRI is more useful in detecting GSPN schwannomas and their relation with the facial nerve. MRI characteristics include mildly hypo- or hyperintense to gray matter on T1-weighted images and hyperintense on T2-weighted images, with marked contrast enhancement. ^[3] Differential diagnosis includes facial nerve and trigeminal schwannomas, primary cholesteatoma, meningioma, and bony tumor of petrous bone. ^[2],[3] The surgical excision through the middle fossa approach remains the first line treatment. ^[1] In both our patients, as the tumor was restricted to GSPN, the continuity of facial nerve was not disturbed. In both the patients, total tumor excision was done with no intervening nerve graft.

Due to relative rarity of this tumor, preoperative diagnosis may be misleading unless one is aware of the clinical and radiological presentation. The clinical presentation depends on the size of the tumor. The early signs include decreased tear secretion followed by facial nerve palsy. The presence of an extra-axial enhancing mass on the anterior aspect of the middle part of petrous bone with underlying bony erosion along with the clinical presentation should help in the early diagnosis. Early diagnosis and surgical treatment of GSPN schwannoma may preserve the function of facial and acoustic nerves.

References

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