Aggressive Clinical Course of Mucinous Tubular and Spindle Cell Renal Cell Carcinoma Following CT-Guided Ablation: A Case Report

Mucinous tubular and spindle cell renal cell carcinoma (MTSRCC) is an uncommon renal epithelial neoplasm historically regarded as indolent. We describe an 81-year-old woman with an incidentally detected 1.4 cm right interpolar renal mass, biopsied and ablated percutaneously, with histology confirming World Health Organization/International Society of Urological Pathology grade 2 (WHO/ISUP grade 2) MTSRCC. Within three months, she developed extensive right renal vein thrombosis with propagation to the inferior vena cava (IVC) and right atrium, initially considered treatment-related. Despite systemic anticoagulation, she demonstrated rapid progression with innumerable hepatic metastases on magnetic resonance cholangiopancreatography (MRCP) six months after ablation and died shortly thereafter. This report underscores that MTSRCC can behave aggressively, with venous tumor thrombus and an explosive metastatic dissemination. It also highlights the diagnostic challenges distinguishing bland from malignant thrombus, as well as the nuances of managing small renal masses in frail older adults.