Purpose

To report a rare case of orbital oncocytoma presenting as a cystic superolateral orbital mass with clinical and radiological concern for malignancy.

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Methods

Single-patient case report with review of the literature.

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Results

A 78-year-old man was referred with a 9-month history of left-sided globe displacement, limited elevation and abduction, and diplopia on left gaze and upgaze. Examination showed left proptosis with inferior dystopia and mild extraocular motility restriction. MRI demonstrated a cystic lesion in the superolateral orbit, with posterior enhancing tissue, raising concern for metastatic disease in view of a past history of bowel and renal malignancy. The patient underwent left lateral orbitotomy with removal of the lateral orbital wall and excision biopsy of the lesion. Intra-operatively, the mass appeared cystic and contained yellow turbid fluid with a greasy, liquefied-fat appearance. Histopathology showed fibrous cyst wall and well-circumscribed nests of large cells with distinct membranes and abundant eosinophilic granular cytoplasm, consistent with oncocytes. Immunohistochemistry demonstrated CK7 positivity and negativity for S100 and PAX8, supporting the diagnosis of oncocytoma. Early postoperative recovery was uncomplicated, with full ocular motility and only mild temporal swelling and minimal chemosis at follow-up.

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Conclusion

Reported only rarely in the literature, orbital oncocytoma is an unusual benign tumour that may closely simulate malignant orbital pathology on clinical and radiological assessment. This case adds to the limited body of evidence and emphasises the importance of biopsy in establishing the diagnosis of atypical superolateral orbital lesions.

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Additional Authors

First name	Last name	Base Hospital / Institution
Emma	Kerr	Cambridge University Hospitals NHS Foundation Trust
Felicity	Allen	Cambridge University Hospitals NHS Foundation Trust

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