Invasive Renal Parenchymal Urothelial Carcinoma: A Case Report and Literature Review of Imaging Features and Spectrum of Infiltrative Renal Masses.

Upper tract urothelial carcinoma (UTUC) is a rare and aggressive malignancy. When UTUC invades the renal parenchyma, its imaging appearance may overlap with other infiltrative renal masses (IRMs), including renal cell carcinoma (RCC), renal lymphoma, metastases, and inflammatory or infectious lesions. A 58-year-old female patient presented with painless gross hematuria. Her medical history included a right renal cyst that was previously aspirated, with no further details available. An ultrasound was performed, but it was inconclusive. A contrast-enhanced CT demonstrated a large, diffusely hypoenhancing infiltrative tumor in the mid and upper poles of the right kidney, with largely preserved renal contour. The mass extended into the renal pelvis. The imaging findings were suggestive of an invasive renal parenchymal urothelial carcinoma (UC). A decision was made not to perform a biopsy, and the patient subsequently underwent a nephroureterectomy with extended lymph node dissection. Histopathological examination confirmed the diagnosis of UC. This case highlights the importance of recognizing invasive renal parenchymal UC as part of the spectrum of IRMs, which may represent an initial diagnostic clue. It also emphasizes the need to accurately distinguish UC from other IRMs, given the significant differences in management.