Angiomyolipoma (AML) is the most common renal mesenchymal neoplasm. Most AMLs contain macroscopic adipose tissues that can be easily identified via computed tomography (CT) or magnetic resonance imaging. According to the 2016 World Health Organization (WHO) classification, renal epithelioid angiomyolipoma (EAML) is a rare variant of AML that consists predominantly of epithelioid cells (>80%). Unlike typical AMLs, EAMLs contain minimal or no fat that can be recognized, possibly leading to a misdiagnosis of renal cell carcinomas (RCCs) in histologic and imaging evaluations. When we encounter enhancing renal mass with no or minimal fat, differentiating EAML from RCC or fat-poor AML is challenging. However, because of the rarity of this disease, imaging findings of EAML have been less well reported. Additionally, to the best of our knowledge, there are no reliable image findings...

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Study cohort

 This retrospective case-control study was approved by the institutional review board, and the requirement for written informed consent was waived. We searched the pathology database of two tertiary care institutions for surgical specimens diagnosed with renal EAMLs between January 2006 and June 2021: We identified 31 patients (16 in center A and 15 in center B). We excluded three patients who did not have three-phase kidney protocol CT, including precontrast, corticomedullary, and excretory phases. Finally, a total of 28 patients (15 men and 13 women, mean age 45.6 ± 13.7 years) were included (Fig. 1).

For the comparison group, we collected data on 56 patients with a diagnosis of clear cell RCC (38 men and 18 women, mean age 61.2 ± 11.7 years) during the same study period in center A. We matched the average maximal diameter of...

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Baseline characteristics of EAMLs

 The mean size of the tumors was 6.2 ± 5.0 cm (range, 0.9–17.6 cm). Three patients (10.7%) had a history of tuberous sclerosis. One patient showed bone metastasis on diagnosis. Two patients were presented with lung metastases at 20 and 61 months after surgery, respectively. The remaining 25 patients had no evidence of tumor recurrence or distant metastasis during the median follow-up of 12.5 months (range, 1–137 months).

Comparison of CT findings between EAMLs and clear cell RCCs

 The patients with EAML were significantly younger than those with clear cell RCC (45.6 ± 13.7 vs. 61.2 ± 11.7 years, P < 0.001). The mean mass size was 6.2 ± 5.5 cm in the EAML group and 5.5 ± 3.4 cm in the clear cell RCC group, and did not show significant...

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 We analyzed the CT findings of EAMLs and developed a radiomics-based model to differentiate EAMLs from clear cell RCCs. A radiomics-based model was developed from the radiomics features and the subjective image findings, which could be achieved from the CT images. By using this noninvasive information, the radiomics-based model showed good performance in distinguishing EAMLs and clear cell RCCs (AUC 0.89), which was similar to that of genitourinary radiologists (AUC 0.81 and 0.78) and superior to that of a third-year resident (AUC 0.62).

 In conclusion, our study found that EAML has characteristic CT signs that can be distinguished from clear cell RCC. Furthermore, our radiomics-based model has the potential to differentiate EAML and clear cell RCC with better diagnostic performance compared with that of an inexperienced radiologist and could be useful when choosing...

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