Diagnostic value of 18F-dihydroxyphenylalanine positron emission tomography for growth hormone-producing pituitary adenoma.

A 55-year-old woman with signs of acromegaly was referred to our hospital. Endocrinological examinations showed that she had high levels of growth hormone (GH; 5.54 ng ml(-1); normal range: 0.66-3.68 ng ml(-1)) and insulin-like growth factor-I (IGF-I; 508 ng ml(-1); normal range: 37-266 ng ml(-1)) levels, incomplete suppression of serum GH following a 75-gram oral glucose tolerance test (oGTT; trough GH 3.66 ng ml(-1)), and paradoxical GH responses to a TRH provocation test (peak GH 38.9 ng ml(-1)). Dynamic magnetic resonance imaging (MRI) suggested the presence of an intrasellar mass lesion (5.9 x 2.8 mm) in the left part of her pituitary gland (Fig. 1a, upper panel). F-18 fluorodeoxyglucose (FDG) positron emission tomographic (PET) imaging clearly showed focal but remarkable FDG uptake (Fig. 1a, lower panel), consistent with the localization of the tumor suspected on MRI. The tumor was removed by transsphenoidal surgery. Subsequent histological analysis confirmed the diagnosis of a GH-producing pituitary adenoma. After removal, serum IGF-I levels decreased to a normal range (178 ng ml(-1)), and serum GH was appropriately suppressed during oGTT (trough GH 0.30 ng ml(-1)), suggesting that complete resection was obtained [1]. While postsurgical changes made it difficult to detect any residual lesion on MRI (Fig. 1b, upper panel), abnormal FDG uptake was not seen on FDG-PET after surgery (Fig. 1b, lower panel). PET scans are reported to be a valuable tool for the detection of pituitary adenomas [2-4]. This case clearly showed that FDG-PET is also useful for re-evaluation of the disease after surgery. PET scans are recommended for patients with equivocal pituitary mass lesions on conventional MRI, and for follow-up examinations after surgery.