Role of 68Ga-DOTATOC Positron Emission Tomography in Locating Pulmonary Neuroendocrine Tumor Presenting with ACTH-Dependent Cushing’s Syndrome: A Case Report

<b>Background:</b> In ectopic adrenocorticotropic hormone (ACTH) syndrome, locating the responsible lesion is often challenging. <b>Case Presentation</b>: A 68-year-old woman was transferred to Nara Medical University hospital for a detailed investigation of her ACTH-dependent Cushing's syndrome. Because of hypercortisolism-induced immunosuppression, she subsequently developed severe <i>Nocardia</i> pneumonia and was forced to temporarily depend on noninvasive positive pressure ventilation (NIPPV). Intravenous antifungal agents and antibiotics were administered, resulting in significant symptomatic improvement. Metyrapone was administered to suppress excessive cortisol. Contrast-enhanced magnetic resonance imaging of the pituitary revealed a 4 mm sized poorly enhanced area, and microadenoma was suspected. Although cavernous venous sampling was indispensable prior to trans-spheroidal surgery (TSS), this examination could not be performed because of the presence of deep vein thrombosis. TSS was performed for both diagnostic and therapeutic purposes, but hypercortisolism did not improve. Moreover, immunohistochemical findings of the specimen revealed nonfunctional pituitary tumor. <b>Methods:</b> We re-evaluated the responsible lesion causing ACTH-dependent Cushing's syndrome. Fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) revealed weak and abnormal FDG uptake in the right pericardium, but the possibility of nonspecific uptake could not be ruled out. However, gallium-68 1,4,7,10-tetraazacyclododecane-<i>N</i>,<i>N</i>',<i>N</i>'',<i>N</i>'''-tetraacetic-acid-D-Phe¹-Tyr³-octreotide (⁶⁸Ga-DOTATOC)-PET demonstrated the same degree of abnormal uptake; therefore, a functional pulmonary tumor was strongly suspected. <b>Results:</b> Video-Assisted Thoracic Surgery (VATS) was performed, and histopathological findings of the specimen revealed a neuroendocrine tumor with positive ACTH staining. After VATS, ACTH and cortisol levels were normalized. <b>Conclusions</b>: Here, we report a case of ACTH-dependent Cushing's syndrome caused by a lung neuroendocrine tumor, in which ⁶⁸Ga-DOTATOC PET was helpful in detecting the functional tumors.