High-resolution ¹⁸F-fluorodeoxyglucose positron emission tomography and magnetic resonance imaging for pituitary adenoma detection in Cushing disease

OBJECT: High-resolution PET (hrPET) performed using a high-resolution research tomograph is reported as having a resolution of 2 mm and could be used to detect corticotroph adenomas through uptake of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). To determine the sensitivity of this imaging modality, the authors compared ¹⁸F-FDG hrPET and MRI detection of pituitary adenomas in Cushing disease (CD). METHODS:Consecutive patients with CD who underwent preoperative ¹⁸F-FDG hrPET and MRI (spin echo [SE] and spoiled gradient recalled [SPGR] sequences) were prospectively analyzed. Standardized uptake values (SUVs) were calculated from hrPET and were compared with MRI findings. Imaging findings were correlated to operative and histological findings. RESULTS:Ten patients (7 females and 3 males) were included (mean age 30.8 ± 19.3 years; range 11-59 years). MRI revealed a pituitary adenoma in 4 patients (40% of patients) on SE and 7 patients (70%) on SPGR sequences. ¹⁸F-FDG hrPET demonstrated increased ¹⁸F-FDG uptake consistent with an adenoma in 4 patients (40%; adenoma size range 3-14 mm). Maximum SUV was significantly higher for ¹⁸F-FDG hrPET-positive tumors (difference=5.1, 95% CI 2.1-8.1; p=0.004) than for ¹⁸F-FDG hrPET-negative tumors. ¹⁸F-FDG hrPET positivity was not associated with tumor volume (p=0.2) or dural invasion (p=0.5). Midnight and morning ACTH levels were associated with ¹⁸F-FDG hrPET positivity (p=0.01 and 0.04, respectively) and correlated with the maximum SUV (R=0.9; p=0.001) and average SUV (R=0.8; p=0.01). All ¹⁸F-FDG hrPET-positive adenomas had a less than a 180% ACTH increase and ¹⁸F-FDG hrPET-negative adenomas had a greater than 180% ACTH increase after CRH stimulation (p=0.03). Three adenomas were detected on SPGR MRI sequences that were not detected by ¹⁸F-FDG hrPET imaging. Two adenomas not detected on SE (but no adenomas not detected on SPGR) were detected on ¹⁸F-FDG hrPET. CONCLUSIONS:While ¹⁸F-FDG hrPET imaging can detect small functioning corticotroph adenomas and is more sensitive than SE MRI, SPGR MRI is more sensitive than ¹⁸F-FDG hrPET and SE MRI in the detection of CD-associated pituitary adenomas. Response to CRH stimulation can predict ¹⁸F-FDG hrPET-positive adenomas in CD. Clinical trial registration no.: NCT01459237 (clinicaltrials.gov)