Radiologically similar bilateral multifocal renal tumours with discordant pathology: a case report of fat-poor angiomyolipoma and contralateral chromophobe renal cell carcinoma

Background: Imaging-pathology discordance is well recognised in individual renal tumours, particularly when fat-poor angiomyolipoma (fp-AML) resembles renal cell carcinoma (RCC). However, the consequences of such discordance across lesions receive less attention. In bilateral or multifocal disease, the presumed diagnostic identity of one mass may be transferred to another, potentially compromising nephron preservation.

Case Description: An asymptomatic 37-year-old man with no family history of tumours was found to have small bilateral renal masses during a routine health examination at an outside hospital. The lesions were monitored, and follow-up imaging one year later showed marked progression of the left lesion, prompting referral to our institution. The patient presented with three renal tumours: a dominant left renal mass, a smaller left renal nodule, and a right renal mass. On computed tomography (CT) and magnetic resonance imaging (MRI), the dominant left mass and the right mass lacked visible fat, were heterogeneously hypointense on T2-weighted images and iso- to hypointense on in-phase T1-weighted images, showed no opposed-phase signal loss, and demonstrated marked diffusion restriction, low apparent diffusion coefficient values, and progressive enhancement; both lesions were considered RCC preoperatively. The smaller left nodule contained visible fat and was considered a classic angiomyolipoma. Staged treatment began with right partial nephrectomy, which unexpectedly revealed fp-AML. This benign diagnosis prompted lesion-specific reassessment rather than an assumption that the contralateral mass had identical pathology. CT-guided biopsy of the dominant left mass demonstrated chromophobe renal cell carcinoma (chRCC). Subsequent left radical nephrectomy confirmed chRCC and a separate angiomyolipoma. After left nephrectomy, estimated glomerular filtration rate (eGFR) declined from 113.28 to 63.58 mL/min/1.73 m². At the last documented follow-up, eGFR was 62.6 mL/min/1.73 m².

Conclusions: This unusual three-lesion pattern shows that radiological similarity does not establish pathological identity. In bilateral or multifocal renal tumours, each mass should therefore remain a separate diagnostic problem. Renal mass biopsy should be considered selectively when lesion-specific histology is likely to change management, particularly when a benign mimic is plausible and future renal reserve is at stake.