European Journal of Nuclear Medicine and Molecular Imaging | 2019
FDG-PET/CT in the detection of pituitary stalk ACTH-secreting adenoma
Abstract
A 50-year-old male diagnosed with an adrenocorticotropic hormone (ACTH)–dependent Cushing syndrome, and inferior petrosal sinus sampling displayed an ACTH concentration 4 times higher than that of peripheral blood. MRI demonstrated abnormal signal at posterior pituitary as well as thickening at pituitary stalk. The patient underwent transnasal endoscopic pituitary lesion resection, but immunohistochemistry demonstrated negative ACTH, and no significant clinical improvement was observed. The patient was admitted to our hospital and whole-body FDG-PET/CT was performed. Cranial FDGPET/CT showed a 0.5 × 0.5-cm lesion at pituitary stalk with radioactivity (SUVmax 3.2, arrow noted), and no abnormal FDG uptake was found in the chest cavity or other part of the body. The patient was considered having a pituitary stalk ACTH-secreting adenoma, and a craniotomy for pituitary stalk lesion was performed. Pathology confirmed ACTH-secreting adenoma (ACTH-positive for immunohistochemistry), and patient displayed significant clinical improvement. Ectopic ACTH-secreting lesions contribute to 5–10% of Cushing syndrome and remains a clinical challenge to differentiate [1]. ACTH-producing adenoma at pituitary stalk is extremely rare and difficult to localize due to the MRI characteristics of pituitary stalk thickening is non-specific [2, 3]. Remarkably, patient may also have a non-functional pituitary lesion that can be misrecognized as the source of ACTH. As a sensitive metabolic imaging technique, FDGPET/CT can be utilized in the detection ACTH-secreting lesions since they often display elevated FDG uptake [4, 5]. In our case, FDG-PET/CT did provide substantial evidence to identify the pituitary stalk ACTH-producing lesion when MRI alone is insufficient for localization. In addition, FDG-PET/CT also excluded alternative ectopic ACTH-secreting lesions and guided the surgical plan for the patient.