Frequency of lipid-poor adrenal adenomas in magnetic resonance imaging examinations of the abdomen

Abstract

Objective: To estimate the frequency of lipid-poor adenomas (LPAs) in magnetic resonance imaging (MRI) examinations. Materials and Methods: We retrospectively investigated adrenal lesions on MRI examinations performed in a total of 2,014 patients between January 2016 and December 2017. After exclusions, the sample comprised 69 patients with 74 proven adenomas. Two readers (reader 1 and reader 2) evaluated lesion size, laterality, homogeneity, signal drop on out-of-phase (OP) images, and the signal intensity index (SII). An LPA was defined as a lesion with no signal drop on OP images and an SII < 16.5%. For 68 lesions, computed tomography (CT) scans (obtained within one year of the MRI) were also reviewed. Results: Of the 69 patients evaluated, 42 (60.8%) were women and 27 (39.2%) were men. The mean age was 59.2 ± 14.1 years. Among the 74 confirmed adrenal adenomas evaluated, the mean lesion size was 18.5 ± 7.7 mm (range, 7.0-56.0 mm) for reader 1 and 21.0 ± 8.3 mm (range, 7.0-55.0 mm) for reader 2 (p = 0.055). On the basis of the signal drop in OP MRI sequences, both readers identified five (6.8%) of the 74 lesions as being LPAs. When determined on the basis of the SII, that frequency was three (4.0%) for reader 1 and four (5.4%) for reader 2. On CT, 21 (30.8%) of the 68 lesions evaluated were classified as LPAs. Conclusion: The prevalence of LPA was significantly lower on MRI than on CT. That prevalence tends to be even lower when the definition of LPA relies on a quantitative analysis rather than on a qualitative (visual) analysis.

Prevalence of ‘Fat-Poor’ Adrenal Adenomas at Chemical-Shift MRI.

“…A signal intensity index threshold of 16.5% is also derived for use at 1.5 T and, although applied liberally at 3 T may require modification with a lower proposed threshold at higher field strength. 25 In another 2022 retrospective study by Martins et al, 26 only 4-5% (compared to 31% at NECT) adenomas were fat poor at chemical-shift MRI. Another factor which may influence performance of chemical shift MRI for depiction of microscopic fat when using the chemical shift signal intensity index is placement of ROI.…”

“…A signal intensity index threshold of 16.5% is also derived for use at 1.5 T and, although applied liberally at 3 T may require modification with a lower proposed threshold at higher field strength. 25 In another 2022 retrospective study by Martins et al, 26 only 4-5% (compared to 31% at NECT) adenomas were fat poor at chemical-shift MRI.…”