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

Abstract

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(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). METHODS 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. 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.(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. CONCLUSIONS 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.

Trial registration: ClinicalTrials.gov NCT01459237.

Keywords: ACTH = adrenocorticotropic hormone; CD = Cushing disease; CRH = corticotropin-releasing hormone; Cushing disease; IPSS = inferior petrosal sinus sampling; SE = spin echo; SPGR = spoiled gradient recalled; SUV = standardized uptake value; SUVAvg = average SUV; SUVMax = maximum SUV; hrPET = high-resolution PET; magnetic resonance imaging; pituitary adenoma; pituitary surgery; positron emission tomography.

Figures

Fig. 1

Images obtained in a patient in whom a hypoenhancing adenoma (arrowheads) was detected on SPGR sequences (A and B), but not on SE sequences (C and D). Corresponding 18F-FDG hrPET images (E and F) revealed a focus of increased 18F-FDG uptake (arrowhead).

Fig. 2

A and B:18F-FDG hrPET findings were associated with biochemical data. Tumors detected on 18F-FDG hrPET had higher midnight (A) and morning (B) serum ACTH levels. C and D: Correlation between serum ACTH (black, midnight [MN]; red, morning [AM]) with both maximum SUV (SUV Max; C) and average SUV (SUV Avg; D) for the sella.

Fig. 3

18F-FDG hrPET–positive tumors had an attenuated response to CRH stimulation. All 18F-FDG hrPET–positive tumors had an attenuated response, specifically, less than 180% change in ACTH level during CRH stimulation test. The red line demonstrates cutoff at 180% change that separates the 18F-FDG hrPET–positive tumors from negative tumors.