Purpose

Schwannoma is a rare tumour originating from Schwann cells in the peripheral nerve sheath. Most orbital schwannomas arise from the sensory branches of cranial nerve V and are more often found in superior orbital regions. This case report presents an unusual location of orbital schwannoma arising within medial rectus muscle in a healthy young man.

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Methods

In this case report, we present a 35-year-old healthy man with right eye proptosis and discomfort for 5 months with no diplopia symptom. Pre-operative MRI imaging revealed a well circumscribed T1 hypointense and T2 heterogenous mildly hyperintense oval mass within the right medial rectus with marked contrast enhancement, favouring a radiological diagnosis of a cavernous haemangioma. The patient underwent a right transcaruncular orbitotomy surgical resection of this intramuscular tumour.

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Results

The patient underwent a complete surgical resection of the intramuscular mass with no damage of the medial rectus muscle. Pathological and immunohistochemical evaluations confirmed the diagnosis of schwannoma. The patient had no visual loss and no diplopia problem after surgery. He has been followed up for 5 years with no recurrence.

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Conclusion

This report highlights that precise preoperative diagnosis of orbital schwannoma by imaging alone is not always possible, and requires histopathological evaluation. It also highlights the importance of including schwannoma in the differential diagnosis of tumours arising within extraocular muscles. Complete surgical excision of intramuscular schwannoma within medial rectus muscle can be achieved by orbitotomy through transcaruncular route.

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Additional Authors

First name	Last name	Base Hospital / Institution
Cheuk Yin Brian	Wong	LKS Faculty of Medicine, The University of Hong Kong, HKSAR, China
Chi On Andy	Cheng	Hong Kong Sanatorium & Hospital, HKSAR, China

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