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Here, we describe a unique case of an SCCP presenting as a metastatic lesion to an extraocular muscle causing optic nerve compression.
A 51-year-old male presented with a 9-day history of progressively decreasing vision in the left eye and binocular diplopia in left gaze. His medical history was significant for HIV infection with a recent CD4 count of 850 cells/mm3 on antiretroviral therapy. His medical examination was otherwise negative.
Clinical examination showed a best-corrected visual acuity of 20/25 OD and 20/40 OS. Intraocular pressures were normal, and there was no significant axial proptosis by exophthalmometry. Examination of the left eye was notable for a relative afferent pupillary defect, dyschromatopsia with Ishihara colour plates, and limitation of extraocular motility in abduction. There was no resistance to retropulsion, and the posterior pole examination was otherwise unremarkable.
Magnetic resonance imaging with gadolinium showed an ill-defined, enhancing mass within the left lateral orbital apex causing optic nerve compression. The lesion appeared to arise from the lateral rectus muscle and was hypointense on T1-weighted imaging and isointense to brain parenchyma on T2-weighted imaging (Fig. 1).
Given the findings of an orbital lesion with compressive optic neuropathy, a lateral orbitotomy was performed. Intraoperatively, a friable lesion with ill-defined margins was found to be adherent to the apical portion of the belly of the left lateral rectus muscle. The remainder of the lesion was excised piecemeal, and histologic evaluation disclosed a tumour composed of basophilic cells and smudge nuclei that stained positively for cytokeratin, synaptophysin, TTF-1, and CK20 (Fig. 2). The findings were concerning for a diagnosis of metastatic small-cell cancer.
Postoperatively, the patient’s vision improved to 20/20 with resolution of compressive optic neuropathy. He continued to have limitation in abduction in his left eye. The patient was referred to the medical oncology service, where a systemic work-up revealed multiple liver lesions and a large pancreatic tail mass, suggestive of primary small-cell carcinoma of pancreatic origin. Notably, no lung foci were found on dedicated computed tomography imaging of the chest.
Metastases to the orbit represent 3%–7% of all orbital tumours, with breast, lung, and prostate carcinoma being the most prevalent.
Recently, a retrospective analysis of over 30 million records in the National Cancer Database from 1998 to 2011 yielded a total of 541 cases of SCCP compared to 156 733 cases of primary ductal adenocarcinoma, with SCCP representing only 0.2% of all pancreatic tumours.
No lesions were found on dedicated imaging to suggest a primary lung cancer. With these findings, the pancreas was deemed the primary origin, with metastases to the liver and the lateral rectus muscle causing the presenting symptoms of diplopia and decreased vision.
In cases in which there is pathologic evidence of small-cell carcinoma, prompt referral to an oncologist for systemic work-up is essential given the propensity for numerous distant metastases. It is interesting to speculate what effect our patient’s HIV status played as a predisposing factor for the development of SCCP, and indeed there has been a reported case of small-cell carcinoma of the anus in an HIV-positive patient.
Extensive discussion regarding the treatment of SCCP is beyond the scope of this case report, although recent evidence recommends combination chemotherapy with carboplatin and etoposide, with consideration of surgical resection in stage I/II disease.