An Eyelid Mass Revealing an Intraorbital Schwannoma: A Rare Case Report

Abstract

Introduction: Orbital schwannomas are rare benign tumors arising from Schwann cells of peripheral nerve sheaths and account for a small percentage of orbital masses. They are most commonly located within the intraconal space, while involvement of extraocular muscles is exceptional. We report a rare case of an isolated schwannoma originating from the inferior rectus muscle. Case Presentation: A 60-year-old woman with no significant medical history presented with a progressive left lower eyelid swelling evolving over three months, associated with binocular vertical diplopia. Ophthalmological examination revealed normal best-corrected visual acuity in both eyes, left hypertropia, a well-circumscribed inferior eyelid mass, and limitation of downgaze. Orbital magnetic resonance imaging demonstrated a well-defined lesion arising from the left inferior rectus muscle, measuring 21 × 13.5 × 12 mm, hypointense on T1-weighted images, hyperintense on T2-weighted images, with peripheral gadolinium enhancement. The lesion displaced the globe superiorly without intraocular extension. Histopathological examination following transconjunctival biopsy confirmed the diagnosis of schwannoma. Complete en bloc surgical excision was achieved via a subciliary approach. The postoperative course was uneventful, and no recurrence was observed after one year of follow-up. Discussion: Orbital schwannomas represent approximately 1–6.5% of orbital tumors and typically present with slowly progressive symptoms related to mass effect. Imaging, particularly MRI, plays a crucial role in lesion characterization and surgical planning, while histopathological analysis remains essential for definitive diagnosis. Complete surgical excision is the treatment of choice and is associated with excellent outcomes and a low recurrence rate. Conclusion: Although rare, intraorbital schwannoma should be considered in the differential diagnosis of atypical orbital masses presenting with diplopia. MRI findings are suggestive, but histological confirmation is necessary. Early and complete surgical excision offers a favorable prognosis.