PET/MRI in the Diagnosis of Hormone-Producing Pituitary Microadenoma: A Prospective Pilot Study

This study was designed to evaluate the ability of PET/MRI, using 18F-FDG and 68Ga-DOTATATE as tracers, to detect hormone-producing pituitary microadenoma when diagnosis is difficult using MRI alone. Methods: We recruited 37 patients with elevated hormone levels, including 19 with undiagnosable primary pituitary adenoma and 18 with suspected recurrent pituitary adenoma. 18F-FDG PET/MRI and 68Ga-DOTATATE PET/MRI were performed within 1 wk of each other in all patients. Within 2 wk afterward, 27 of the 37 patients underwent transsphenoidal adenomectomy, 3 underwent sella region radiotherapy, 1 underwent somatostatin therapy, and 6 had only clinical follow-up. The image characteristics and uptake levels were correlated with the surgical findings and pathologic results. Receiver-operating-characteristic curves were analyzed to determine the optimal cutoff to differentiate adenoma from normal pituitary tissue. The area under the receiver-operating-characteristic curve was calculated to compare diagnostic performance. Results: The PET/MR images were of diagnostic quality and without obvious image artifacts. The high contrast of the PET images provided complementary information to the fine anatomic display of the MR images. Increased 18F-FDG uptake was clearly observed in all patients. MRI enhanced using a 0.05 mmol/kg dose of gadopentetate dimeglumine showed suggestive findings in only 47% of the patients with primary adenoma and 39% of those with recurrent adenoma; when a 0.1 mmol/kg dose was used, the respective percentages were 37% and 50%. The 18F-FDG SUVmax of the 16 primary adenomas that underwent transsphenoidal adenomectomy (6.8 ± 3.7) was significantly higher than that of normal pituitary tissue (3.2 ± 1.1, P < 0.01). The adenomas showed moderate 68Ga-DOTATATE uptake (SUVmax, 3.8 ± 2.6), but the 68Ga-DOTATATE uptake was generally lower than that of normal pituitary tissue (SUVmax, 6.2 ± 3.2, P < 0.05). In the 11 suspected recurrent pituitary adenomas that underwent transsphenoidal adenomectomy, the 18F-FDG SUVmax was 6.1 ± 3.5, significantly higher than that of normal pituitary tissue (2.5 ± 1.1, P < 0.01), and the 68Ga-DOTATATE SUVmax was 3.0 ± 1.1, significantly lower than that of normal pituitary tissue (5.5 ± 1.7, P < 0.01). The 18F-FDG/68Ga-DOTATATE SUVmax ratio of the adenomas (2.3 ± 1.5) was significantly higher than that of normal pituitary tissue (0.6 ± 0.3, P < 0.05). When the 18F-FDG SUVmax alone and the 18F-FDG/68Ga-DOTATATE SUVmax ratio were used as criteria to discriminate between adenoma and pituitary tissue, the best analysis came from the ratio, and that from 18F-FDG SUVmax alone was slightly less, with optimal diagnostic cutoffs of 1.04 and 3.88, respectively. Conclusion: PET/MRI provides an ideal tool for the detection of hormone-producing pituitary microadenoma. Dual-tracer 18F-FDG and 68Ga-DOTATATE PET/MRI was useful for distinguishing pituitary microadenoma from normal pituitary tissue.