Rare Orbital Metastasis of Carcinoid Tumor Despite Long-Term Somatostatin Therapy: A Case Report

<b>Background and Clinical Significance</b>: Carcinoid tumors are rare, slow-growing neuroendocrine cell neoplasms that typically affect the gastrointestinal tract. While metastasis may occur, it most commonly occurs in the liver, and orbital metastasis is extremely rare, especially while on systemic somatostatin suppression. <b>Case Presentation</b>: A 57-year-old man with a history of gastrointestinal carcinoid tumor treated with lanreotide for 5 years presented with a left proptotic, red eye and double vision for several months. Clinical examination revealed left proptosis, supraduction deficit, lower lid retraction, and dilated episcleral vessels inferiorly. Magnetic resonance imaging demonstrated a 1.8 cm enhancing lesion centered within the left inferior rectus muscle. Left orbitotomy and biopsy were performed, which confirmed metastatic carcinoid tumor. He will undergo localized orbital radiation and substitution of lanreotide with systemic chemotherapy. <b>Conclusions</b>: Orbital metastasis of carcinoid tumor is extremely uncommon. Given its rarity, diagnosis may be challenging. In patients presenting with ocular complaints including chronic red eye, double vision, proptosis, and mass effect with a prior history of neuroendocrine cancer, a high index of suspicion for orbital metastasis is necessary with timely workup and treatment even if the disease has been otherwise well-controlled with somatostatin analogs.