Systematic Review and Case Report of a Left Gonadal Vein Anastomosing Hemangioma.

: Anastomosing hemangioma (AH) is a rare, benign vascular tumor predominantly found in the genitourinary tract and often associated with impaired renal function. Due to its nonspecific radiological features, AH is frequently misinterpreted as a malignant vascular neoplasm, particularly angiosarcoma (AS), leading to potentially unnecessary surgical interventions. This study presents a systematic review of AH cases and describes a rare instance of retroperitoneal AH arising from the left gonadal vein, which was resected due to diagnostic uncertainty. A 68-year-old man underwent imaging for benign prostatic hyperplasia, incidentally revealing a 15-mm hypervascular retroperitoneal nodule adjacent to the left psoas muscle. Imaging findings, including moderate metabolic uptake on 18FDG-PET/CT, raised suspicion for AS. Given the diagnostic uncertainty and high-risk location, the multidisciplinary team (MDT) recommended surgical resection. Laparoscopic excision was performed, and histopathological analysis confirmed AH. The patient remained asymptomatic at a 22 month follow-up. In addition, a systematic review of 159 cases from 64 studies (2009-2024) was conducted to analyze radiological features, treatment approaches, and outcomes. Among the reviewed cases, 68% were incidentally diagnosed, with AH occurring predominantly in the genitourinary system (70%), especially in the kidney, adrenal gland, and ovary. Chronic kidney disease (CKD) was present in 23.3% of cases, while 19.5% had a history of malignancy. Imaging was inconclusive in differentiating AH from malignancies: CT (71.9%) and MRI (6.1%) were the most used modalities, but none could reliably exclude AS. Management strategies included upfront surgical resection in 85%, while a growing proportion (9%) of cases underwent biopsy-based observation rather than immediate surgery. No cases were followed with imaging alone. AH remains a diagnostic challenge due to its overlap with malignant vascular tumors. While surgical excision is often performed, our review highlights an increasing trend toward conservative management with biopsy-based diagnosis. Improved awareness and the integration of histopathology, molecular markers, and MDT-based decision-making are crucial to prevent overtreatment in cases of suspected AH.