Evaluation of pituitary uptake incidentally identified on 18F-FDG PET/CT scan

The clinical significance of pituitary uptake on routine whole body 18F-fluorodeoxyglucose (FDG) positron emission tomography/computer tomography (PET/CT) is not completely characterized. We seek to assess the potential differential diagnosis/underlying etiology of pituitary FDG uptake incidentally identified on routine PET/CT scans. A total of 24,007 PET/CT whole body scans in recent 5 years were retrospectively reviewed. Patients with maximum standardized uptake value (SUVmax) > 4.1 in the pituitary glands were identified. Cases with a known history of pituitary disorders were excluded. Nineteen cases were identified with incidental pituitary FDG uptake which all had a final pathological diagnosis/clinical follow up. Among them, there were 9 primary pituitary tumors, with SUVmax ranging from 4.7 to 29.3 (13.6 ± 9.8); 3 metastatic malignancy with SUVmax ranging from 7.3 to 32.3 (16.0 ± 10.6); 3 Langerhans cell histiocytosis (LCH) with SUVmax ranging from 6.0 to 26.0 (15.0 ± 10.2); 1 pituitary lymphocytic hypophysitis with SUVmax of 4.7. Of note, 3 cases with SUVmax of 7.5,7.9 and 9.6 showed no relevant clinical symptoms with negative results on subsequent magnetic resonance (MR) and were counted as benign physiologic uptake. The most common differential diagnosis of incidental pituitary uptake on routine whole body PET/CT scans was primary pituitary tumors, followed by metastatic malignancy, Langerhans cell histiocytosis, and inflammatory lymphocytic hypophysitis. Of note, benign physiologic uptake without corresponding lesions could also occur in our population.