The role of magnetic resonance imaging (MRI) in the detection of intracellular lipid content in adrenal adenomas.

BACKGROUND

Accurate differentiation of adrenal adenomas from non-adenomatous lesions is critical for patient management. Chemical shift MRI (CSI) detects microscopic intracellular lipid in adenomas through quantitative metrics, including chemical shift ratio (CSR) and signal intensity index (SII). However, optimal cutoff values remain heterogeneous across populations, and confounding pathologies such as pheochromocytomas and non-suppressing adenomas challenge diagnostic reliability.

PURPOSE: To establish population-specific CSI thresholds and evaluate the incremental value of paraspinal muscle signal intensity in a histopathologically validated Turkish cohort, with particular attention to lipid-poor adenomas and diagnostic confounders.

MATERIALS AND

METHODS

This retrospective study included 67 consecutive patients (mean age 52.3 ± 14.8 years; 36 adenomas, 31 non-adenomas) with histopathologically confirmed adrenal lesions who underwent preoperative 3.0T CSI MRI. Chemical shift ratio (CSR), signal intensity index (SII), and paraspinal muscle in-phase and out-phase signal intensity (PM-IP & OP SI) were measured using standardized ROI protocols. Interobserver reproducibility was assessed in 25 lesions using intraclass correlation coefficients. ROC curve analysis determined optimal cutoffs, with diagnostic performance calculated at literature-recommended and population-optimized thresholds.

RESULTS

CSR demonstrated superior discriminative performance (AUC 0.822, 95% CI: 0.718-0.926, p < 0.001) with an optimal cutoff of ≤ 0.895 (sensitivity 83.3%, specificity 80.6%), significantly exceeding literature standards (≤ 0.71). SII exhibited suboptimal sensitivity (63.9%) at cutoff ≥ 15.1% due to a 13.9% prevalence of non-suppressing adenomas. Paraspinal muscle signal intensity emerged as an ancillary discriminator (AUC 0.729, cutoff ≤ 671.5 AU, p < 0.001), with significantly lower values in adenomas (452.5 vs. 768.0 AU). Interobserver agreement was excellent for all parameters (ICC > 0.84). Notably, 19.4% of non-adenomas (predominantly pheochromocytomas and myelolipomas) exhibited false-positive CSR patterns.

CONCLUSION

In surgical referral populations enriched with lipid-poor adenomas and confounding pathologies, higher CSR cutoffs (≤ 0.895) are required. The modest SII sensitivity highlights the challenge of non-suppressing adenomas, while paraspinal muscle signal intensity provides valuable ancillary discrimination. A multiparametric, population-aware diagnostic algorithm integrating CSR, SII, and PM-IP & OP SI is recommended to optimize adrenal mass characterization and reduce unnecessary interventions.