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 ¹⁸ F-fluorodeoxyglucose ( ¹⁸ F-FDG). To determine the sensitivity of this imaging modality, the authors compared ¹⁸ F-FDG hrPET and MRI detection of pituitary adenomas in Cushing disease (CD).

Consecutive patients with CD who underwent preoperative ¹⁸ F-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.

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. ¹⁸ F-FDG hrPET demonstrated increased ¹⁸ F-FDG uptake consistent with an adenoma in 4 patients (40%; adenoma size range 3–14 mm). Maximum SUV was significantly higher for ¹⁸ F-FDG hrPET–positive tumors (difference = 5.1, 95% CI 2.1–8.1; p = 0.004) than for ¹⁸ F-FDG hrPET–negative tumors. ¹⁸ F-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 ¹⁸ F-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 ¹⁸ F-FDG hrPET–positive adenomas had a less than a 180% ACTH increase and ¹⁸ F-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 ¹⁸ F-FDG hrPET imaging. Two adenomas not detected on SE (but no adenomas not detected on SPGR) were detected on ¹⁸ F-FDG hrPET.

While ¹⁸ F-FDG hrPET imaging can detect small functioning corticotroph adenomas and is more sensitive than SE MRI, SPGR MRI is more sensitive than ¹⁸ F-FDG hrPET and SE MRI in the detection of CD-associated pituitary adenomas. Response to CRH stimulation can predict ¹⁸ F-FDG hrPET–positive adenomas in CD.