Adrenocorticotropic Hormone-Secreting Neuroendocrine Tumor of the Rectum Demonstrated on 68Ga-DOTATATE and 18F-FDG PET Imaging.

An 81-year-old man with Cushing syndrome was referred for a Ga-DOTATATE PET/CT study to investigate for an ectopic source of adrenocorticotropic hormone. The scan demonstrated mildly increased octreopeptide uptake at a rectal mass and focal uptake at multiple regions throughout the bone marrow of the axial skeleton, consistent with metastases. A subsequent F-FDG PET/CT study was performed for further evaluation and demonstrated markedly increased metabolism at the previously identified rectal mass, in addition to the liver and multiple regions throughout the skeleton. Histopathology from biopsy of the rectal mass confirmed a small cell neuroendocrine carcinoma.