Ectopic adrenocorticotropin secretion (EAS) accounts for 1015% of cases of Cushings syndrome and comprises a spectrum of lesions from highly malignant tumours to a variety of less aggressive neuroendocrine tumours. Selective removal of the primary lesion is the optimal management. It is therefore mandatory to localize the source of ectopic ACTH.
As no single test is accurate enough to distinguish the ectopic from the pituitary sources of ACTH, no single imaging technique can itself identify every tumour responsible for EAS.
We report on the use of Photon Emission Tomography (PET) scanning using 18F-fluoro-Dopa in the localization of an occult ACTH-secreting carcinoid tumour.
An 18-yr-old man was referred for evaluation of EAS. Evidence for EAS included: plasma ACTH and ß LPH levels above the normal reference range, no serum cortisol suppression after high-dose dexamethasone suppression test, normal pituitary MRI and lack of central to peripheral gradient on bilateral inferior petrosal sinus sampling. The patient had a history of post-infectious bronchiectasis since 6 years. The chest computed tomographic (CT) scan showed a widespread lobar disease already known and compatible with bronchiectasis. In-111 pentreotide scintigraphy was interpreted as normal. A low-intensity uptake was seen on 18FDG PET scanning located in the middle right pulmonary lobe. As the patient suffered from a respiratory infection, interpretation of this image was difficult. An 18F-fluoro-dopa PET scanning revealed a pathologic uptake localized in the right lung middle lobe.
The pulmonary lesion was surgically treated after adrenolytic medication. Histology revealed a bronchial carcinoid tumor. Hypercortisolism was replaced by prolonged corticotropic insufficiency. Until now, hypercortisolims did not relapse.
In conclusion, no imaging technique should be neglected in the localization of an occult EAS.