Pathologic Findings and Management of Renal Mass in Horseshoe Kidneys.

OBJECTIVES: To evaluate the management, surgical outcomes, and pathological findings in patients with tumor in a horseshoe-kidney (HK). HK patients present unique challenges due to aberrant vascular anatomy and risk of renal insufficiency. We hypothesized that many tumors in this setting may be indolent or benign. MATERIALS AND METHODS: Patients managed for renal mass in HK at our center (1999-2021) were reviewed. Baseline characteristics, surgical approach, complications, functional outcomes, pathology, and survival were analyzed. RESULTS: Forty-three procedures were performed in 42 patients with HK including 24 nephron-sparing surgeries (NSS) and 19 radical nephrectomies (RN: splitting the isthmus and saving the contralateral moiety). NSS included 22 partial nephrectomy (PN) and 2 thermal ablations. Median tumor size was 4.3 cm. Eighteen cases (42%) were minimally-invasive, 17 open-midline, and 8 other open approaches. Ninety-day Clavien III-V complication rate was 12% with no mortalities. For PN, median warm/cold ischemia times were 26/31 minutes, respectively. On pathology, only 27 tumors (63%) were renal-cell-carcinoma (RCC), and 22 tumors (51%) were either benign (n = 10) or low grade, confined RCC (n = 12). Preoperative/new baseline/long-term eGFR were 82/83/78 mL/min/1.73 m2 after NSS vs 75/48/57 mL/min/1.73 m2 after RN, respectively. Long-term dialysis was required in 3 patients (7%). Median follow-up was 36 months. Five-year recurrence-free survival was 83% for NSS and 66% for RN. CONCLUSIONS: Management of renal masses in HK is challenging and requires versatility with multiple surgical approaches. Preservation of renal function was accomplished in most patients, with a functional advantage observed for NSS. RCC was less common than expected while benign and non-aggressive tumors were prevalent, suggesting consideration for preoperative renal-mass-biopsy when feasible.