Contrast Enhanced CISS/FIESTA Imaging for Increased Conspicuity of Pituitary Microadenomas in Cushing Disease.

Background and purpose: Pituitary microadenomas can be challenging to see on MRI, particularly when they are small. The detection of microadenomas commonly relies on contrast-enhanced sequences, highlighting the adenoma that demonstrates hypoenhancement relative to the native pituitary on T1-weighted sequences. Detecting adenomas in patients with Cushing disease is crucial, as surgery is the standard of care treatment. Accurate pre-operative lesion localization is directly associated with improved outcomes. The purpose of our study was to determine the utility of contrast-enhanced CISS/FIESTA-C for identifying pituitary microadenomas in patients with Cushing disease.

Materials and methods: This cross-sectional study retrospectively reviewed pituitary MR images in patients with Cushing disease who had post-contrast CISS/FIESTA-C. Images were evaluated for lesion conspicuity (well-defined margins), as well as the signal intensity of the adenoma and native pituitary. The normalized signal intensity difference (nSID) was calculated by subtracting the lesion signal intensity from the pituitary signal intensity, and dividing by the pituitary signal intensity. Patient age, sex, and diagnosis based on intraoperative findings, pathology results, and post-operative adrenal insufficiency were recorded.

Results: 17 patients (15 female) were included in this study. 16 (94%) adenomas were discrete on CISS/FIESTA-C compared to 11 (65%) on T1-weighted imaging. The mean adenoma nSID with CISS/FIESTA-C was 0.512 (SD 0.12), relative to 0.242 (SD 0.15) on T1-weighted imaging (p<0.001).

Conclusion: In comparison to MRI T1-weighted images, contrast-enhanced CISS/FIESTA-C imaging detects a higher number of pituitary microadenomas with superior conspicuity. As up to 50% of patients with Cushing disease present without a pituitary lesion detect on MRI, post contrast CISS/FIESTA-C may be especially valuable as an additional sequence in this population.

Abbreviations: CISS = Constructive interference in steady state; FIESTA-C = fast imaging employing steady-state acquisition with cycling; SI = Signal Intensity, nSID = normalized signal intensity difference.