Papillary renal neoplasm with reverse polarity: A case report.

Papillary renal neoplasm with reverse polarity is a rare, newly identified subtype of papillary renal cell carcinoma believed to originate from the distal renal tubules. It is characterized by distinct histomorphological features and an associated immunophenotype. Contrast-enhanced scans usually do not exhibit a rapid wash-in and wash-out enhancement pattern, and this tumor is generally associated with a favorable overall prognosis. This study reports a case of papillary renal neoplasm with reverse polarity in a male patient in his 50 s who was admitted with recurrent left lumbar pain and discomfort. Computed tomography showed a quasi-circular, isodense lesion measuring 1.3 × 0.8 cm in the left kidney. The contrast-enhanced scan demonstrated a rapid wash-in and wash-out enhancement pattern. Following comprehensive evaluation, the patient underwent laparoscopic partial nephrectomy.Postoperative pathological examination with hematoxylin and eosin staining showed tumor cells forming papillary structures with eosinophilic cytoplasm and basally displaced nuclei. The tumor stroma exhibited focal proliferation of fibrous and adipose tissue along with thick-walled blood vessels. The pathological findings aligned with the classic characteristics of papillary renal neoplasm with reverse polarity. No tumor recurrence or distant metastasis was detected during an 18-month postoperative follow-up.This case report highlights an atypical imaging enhancement feature of papillary renal neoplasm with reverse polarity, thereby enriching the clinical and imaging spectrum of this tumor. It also confirms that pathological examination combined with immunohistochemistry remains the gold standard for diagnosing papillary renal neoplasm with reverse polarity, providing a valuable clinical reference for the identification and differential diagnosis of this rare neoplasm.