A Slippery Diagnosis: Primary Mucinous Adenocarcinoma of the Renal Pelvis in an Elderly Man

Introduction. Primary mucinous adenocarcinoma of the kidney is an exceedingly uncommon malignancy. It comprises a minority of renal malignancies and presents notable diagnostic complexities owing to its atypical manifestation and resemblance in clinical features to common urinary tract conditions. Surgical intervention is the preferred treatment modality, although the prognosis remains bleak, with high rates of recurrence. A definitive diagnosis is established through postoperative histopathological examination. Patient Presentation. Here, we present a 75-year-old man who reported complaints of a mass in the left flank with clinical findings suggestive of a nonfunctioning left kidney. Initial diagnostic imaging suggested a pelvi-uretric junction calculus-associated gross hydronephrosis. However, a subsequent nephrectomy was performed, and the specimen received was subjected to histopathological analysis, which revealed the diagnosis to be a primary mucinous adenocarcinoma involving the kidney. Conclusion. This clinical observation highlights the diagnostic challenge and importance of considering rare entities in patients with vague clinical presentations. Histopathological evaluation is crucial in accurately diagnosing and appropriately managing such rare malignancies. This report contributes to the limited literature on this entity, emphasising the need for awareness among clinicians.