IMAGE IN ENDOCRINOLOGY: Localization of an Occult Adrenocorticotropin-Secreting Carcinoid Tumor with Somatostatin Receptor Scintigraphy Using Single-Photon Emission Computed Tomography/Computed Tomographic Image Scanning

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A 32-yr-old man was referred for evaluation of ACTH-dependent Cushing’s syndrome. Evidence for ectopic ACTH secretion included normal pituitary magnetic resonance imaging and lack of a central to peripheral gradient on bilateral inferior petrosal sinus sampling. The initial chest computed tomographic (CT) scan was interpreted as normal. The patient underwent somatostatin receptor scintigraphy (SRS) on a dual-head γ-camera (Millenium VG Hawkeye; General Electric Medical Systems, Milwaukee, WI), in which single-photon emission computed tomography (SPECT) and CT are recorded during the same examination, allowing the two images to be fused (SRS/SPECT/CT). A low-intensity uptake that was seen on SPECT acquisition only was located in the left posterior mediastinal area (Fig. 1). A second chest CT scan, centered on the cardiac area and with cardiac gating, clearly revealed an image compatible with a neuroendocrine tumor in the same position as seen in the SRS (Fig. 2). A left inferior lobectomy was performed, and a typical 2-cm carcinoid tumor with strong immunostaining for ACTH was resected. This scintigraphic approach may lead to promising progress in a condition where small neuroendocrine tumors are often difficult to localize. Since the initial reports (1), SRS has been proposed for the diagnosis of occult tumors with ectopic ACTH secretion. Although diagnostic performance of SRS in small series of patients with neuroendocrine neoplasms have reported contradictory results (2, 3), some clinical investigators have reported patients whose tumors were detected only by SRS (4, 5). Chest CT scan should be the first imaging approach in search of a source of ectopic ACTH secretion; yet no imaging technique with a possible result should be neglected in the diagnosis of these rare tumors, SRS/SPECT/CT should be systematically proposed in occult ectopic ACTH secretion.