Iliopsoas muscle to visceral fat ratio on CT predicts Cushing’s syndrome in elderly females with adrenal tumors

There is no computed tomography (CT)-based numerical index for predicting Cushing’s syndrome (CS) in patients with adrenal incidentalomas. We tested the hypothesis that the iliopsoas muscle (Ip-M) to visceral fat (V-fat) ratio (IVR) on CT may predict CS in elderly female patients with adrenal tumors. We examined the V-fat area, subcutaneous fat (S-fat) area, Ip-M area, V-fat/S-fat ratio, and IVR at the third lumbar vertebra (L3) level using abdominal CT in female patients aged ≥50 years with cortisol-producing adrenal tumor diagnosed with CS or non-functioning adrenal tumor (NFT) in the derivation cohort. We performed receiver operating characteristic (ROC) analysis to evaluate the diagnostic value of the V-fat/S-fat ratio and IVR for predicting CS. We assessed the usefulness of the IVR in a separate validation cohort. In the derivation cohort, the IVR was significantly lower in the 9 patients with CS than in the 15 patients with NFT (p < 0.001). In ROC analysis with a cut-off value of 0.067, the IVR showed a sensitivity of 100%, specificity of 80.0%, positive likelihood ratio (PLR) of 5.000, and negative likelihood ratio (NLR) of 0.000. The area under the curve was significantly higher for the IVR than for the V-fat/S-fat ratio (0.933 vs. 0.704, respectively, p = 0.036). In 23 patients in the validation cohort, the IVR demonstrated a PLR of 5.714 and an NLR of 0.327. The novel IVR index, based on single-slice CT at the L3 level, predicted CS in elderly female patients with adrenal tumors.