We report a case of lacrimal gland oncocytic adenocarcinoma (OCA) whose initial presentation mimicked that of an isolated sixth nerve palsy rather than neoplastic tumour.

Case Report

A 76-year-old male was referred with diplopia and proptosis. He had been under review at his local hospital for an isolated sixth nerve palsy that had been well controlled with prismatic correction. His past medical history was unremarkable, with no history of diabetes, hypertension, or deranged thyroid function.

On right ocular examination, best-corrected visual acuity was 6/6 and optic nerve function was normal. A palpable mass was noted superotemporally, with a 2 mm proptosis. Slit lamp examination was unremarkable. MRI showed an enhancing extraconal mass involving the lacrimal gland and abutting the globe (Figure 1). There was no intracranial extension and systemic evaluation showed no metastasis.

Figure 1
figure 1

(a) T1 non-enhanced axial MR image showing an extraconal mass in the right orbit involving the lacrimal gland. There was no evidence of intracranial involvement. (b) T1 post-contrast axial MR image.

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An anterior orbitotomy was performed and the tumour was excised en-bloc. The tumour appeared as a solid, craggy lesion without attachments to lateral rectus muscle. Histolopathological examination demonstrated fibrous tissue and fat extensively infiltrated by carcinoma with multiple perineural, vascular, and perivascular invasion. The cells had oncocytic cytoplasm, enlarged nuclei, and numerous mitotic bodies. These features were consistent with OCA (Figure 2). Unfortunately, despite en-bloc removal of tumour, histological margins were not clear. Repeat CT scan showed residual tumour. The case was considered at a multidisciplinary meeting with exenteration being recommended.

Figure 2
figure 2

Histopathology slide showing an invasive OCA with perivascular and perineural invasion.

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Comment

OCA is a malignant epithelial tumour arising in the ductal cell lining of apocrine glandular structures.1 Prognosis is poor as it is a high-grade neoplasm with infiltrative growth pattern and tendency to recur and metastasize. OCA may involve the caruncle, the conjunctiva, the lacrimal sac, and more rarely, the lacrimal gland. To date, only four cases of lacrimal gland OCA have been reported.2, 3, 4, 5

One possible explanation as to why the presumed diagnosis of sixth nerve palsy was made initially instead of mechanical limitation, and therefore not prompting any further investigations, might be early direct neural invasion with no evident mass effect. Our patient has remained disease-free for 24 months, but careful follow-up is recommended as metastasis appears to be the most important prognostic factor. OCA should be considered in the differential diagnosis of lacrimal gland lesions and exenteration is the treatment of choice.