Mediastinal small cell carcinoma with a metastasis to the orbit: A rare carcinoma with an unusual metastatic progression.

Extraocular muscle (EOM) is a rare site for orbital metastasis. We presented a case of solitary EOM metastasis from mediastinal small cell cancer (MSCC) for the first time. A 49-year-old man presented with hoarseness. Thorax computed tomography (CT) revealed a mediastinal mass. A fine-needle aspiration biopsy (FNAB) confirmed the diagnosis of MSCC. The patient staged as limited-stage MSCC with a positron emission computed tomography (PET-CT). The patient received radical chemo-radiotherapy (CRT). PET-CT showed a complete response after CRT. Afterward, the patient presented with double vision and a headache. Brain magnetic resonance imaging (MRI) demonstrated a 2 cm metastatic lesion at the left inferior rectus muscle. A 30 Gy palliative RT was applied. The full regression of the mass was achieved 3 months after the palliative RT. Although solitary EOM metastasis is rare, the timing of accurate diagnosis and appropriate treatment can help to preserve the patient's vision and relieve complaints related to the mass.