131I MIBG/111In octreotide mismatch in a patient with liver metastases secondary to a carcinoid of unknown origin.

Carcinoids, tumors arising from enterochromaffin cells, represent the most common type of gastrointestinal endocrine neoplasm; they are often multiple and may appear anywhere in the gut. Carcinoid tumors may also occur in bronchi and ovaries. Classic symptomatology includes secretory diarrhea, flushing, edema, bronchospasm and cutaneous teleangectasias; however, over 30% of patients with demonstrably elevated serotonin levels may not exhibit any symptoms at all. The diagnosis of carcinoid tumor is typically made by measurement of 24-hour urinary excretion of 5-hydroxyindoloacetic acid. Commonly, tumor localisation is established with CT, US, NMR and arteriography. MIBG scintigraphy is also used to visualize tumors deriving from neuroendocrine cells as carcinoid. These tumors may express somatostatin receptors located on the cell surface. Therefore 111In Octreotide (Octreoscan), a somatostatin analogue, can be employed for tumor localisation. A 32-years-old man with liver metastases secondary to a carcinoid tumor of unknown origin is presented. Classic carcinoid symptoms were absent. Diagnosis was supported by elevated values of urinary 5-hydroxyindolocetic acid and liver fine-needle aspiration. Abdominal US and CT scan detected only liver masses but not the primary tumor. Arteriography was not performed. 131I MIBG and 111I octreotide scans both failed in locating the primary cancer too; only the second tracer showed marked uptake in liver metastases. Beside localization, these two tracers give also informations about the following therapy especially in malignant tumors where local resection isn't an adequate treatment.