Usefulness of Somatostatin Receptor Scintigraphy in Patients with Occult Ectopic Adrenocorticotropin Syndrome

Abstract

SRIF receptor scintigraphy (SRS) has been proposed for the localization of ectopic ACTH-secreting tumors responsible for Cushing's syndrome. However, in most cases reported, the tumors were also visible using conventional imaging. Therefore, the usefulness of SRS in localizing truly occult ectopic ACTH-secreting tumors remains unknown. We report the results of SRS in 12 patients with ectopic ACTH syndrome (EAS) and in whom the source of ACTH was occult at presentation despite carefully performed conventional imaging. The diagnosis of EAS was made by identification of an ACTH-secreting tumor during follow-up in 5 patients or given a pituitary-toperipheral ACTH ratio of 1.9 or less during petrosal sinus sampling combined with CRH injection and a negative pituitary magnetic resonance imaging (MRI). Whole-body planar SRS, using 111 In-pentetreotide, was performed 19 times in the 12 patients during initial workup and/or follow-up. Axial tomography imaging (single-photon emission-computed tomography) was performed in 7 of these. Conventional imaging was performed within a month of SRS, allowing comparison of the two approaches for the localization of the ACTHsecreting tumors. In addition, the response of plasma cortisol, after a single injection of 200 g octreotide, was studied in 6 patients.Five patients had negative SRS and conventional imaging studies. The source of ACTH secretion remains occult despite 10 -55 months of follow-up in four of these, whereas a 2-cm ileal carcinoid tumor, with liver micrometastases, was found at laparotomy in one patient, 14 months after presentation.SRS was positive in 4 of 12 patients. It was false-positive in 1 patient with follicular thyroid adenoma. Nineteen months after presentation, SRS identified liver metastasis that was also visible using MRI in one patient, but the primary tumor remains occult. SRS identified a 10-mm pancreatic tumor that became detectable, using computed tomography (CT) scanning 9 months later, in 1 patient; and 2 mediastinal lymph nodes of 10 mm, previously ignored by MRI, in another patient, whereas no tumor was detectable within the parenchymal lung. SRS had little influence on therapeutic options in these 2 patients, in whom no final diagnosis could be made. Repetition of SRS during the follow-up of patients with previously negative scintiscans was useless.Conventional imaging was positive in 6 of 12 patients. In the 2 patients with pancreatic tumor and isolated mediastinal lymph nodes, conventional imaging studies were interpreted as positive only after the results of SRS. One patient had liver metastasis that was also visible using SRS. Thin-section CT scanning visualized ACTHsecreting bronchial tumors and metastatic mediastinal lymph nodes of 10 -15 mm in diameter in 3 patients after 14 -72 months of followup, whereas SRS was negative.There was no evident relationship between the endocrine status (hyper-or eucortisolism) and the results of SRS. The in vivo response of plasma cortisol to octreotide correlated to the results of SRS in 4 of 6 c...

Dual bronchial carcinoids and Cushing's syndrome with a paradoxical response to dexamethasone and a false positive outcome of inferior petrosal sinus sampling

“…The present case, however, presented ambiguous results at further work-up; a paradoxical increase in cortisol in response to dexamethasone, a BIPSS pointing to a pituitary origin of ACTH, a normal MRI of the pituitary gland, and two oval-shaped lesions in the middle lobe of the lung at a CT scan. Both were positive at somatostatin receptor scintigraphy, a finding that is compatible with, but not diagnostic for tumors, since inflammatory processes may express somatostatin receptors (13). At this point we faced different and unusual scenarios, either a central origin of ACTH overproduction and two unrelated lesions in the lung, or ectopic ACTH production from two primary pulmonary tumors, or theoretically ectopic ACTH production of a pituitary metastasis from a neuroendocrine tumor, although it seems probable that a pituitary metastasis would have been visible on MRI.…”

Rare localization of an ACTH-producing tumour

“…Несмотря на очевидные успехи в диагностической визуализации и эндокри-нологическом тестировании, позволяющие диагно-стировать АКТГ-эктопический синдром, чрезвы-чайно трудно выявить локализацию около 15% опу-холей обычными методами, такими как КТ и МРТ и также методами с применением радиоактивных изотопов, таких как сцинтиграфия рецепторов со-матостатина и ПЭТ. Выбор того или иного метода визуализации зависит от подозрения на ту или иную опухоль, так как каждый из методов имеет свою специфичность и чувствительность для каждого конкретного новообразования с определенной ло-кализацией [25,26].…”

[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) positron emission tomography imaging of thymic carcinoid tumor presenting with recurrent Cushing’s syndrome

“…If this proves negative, or in cases with small ambiguous lesions where there is a need for confirming their neuroendocrine origin, functional imaging (i.e. 111 In-labelled octreotide and/or PET) can be extremely helpful in establishing the correct diagnosis (1).…”