Undifferentiated Embryonal Sarcoma of the Liver in a 6 Years Old Male Patient: A Case Report.

Undifferentiated Embryonal Sarcoma of the Liver (UESL) is a rare, aggressive mesenchymal tumor predominantly affecting children. Its non-specific clinical presentation and variable imaging characteristics often lead to diagnostic delays and complex management. We report a 6-year-old male presenting with a 2-month history of progressive abdominal distension and pain. Initial investigations, including abdominal ultrasound and Computed Tomography (CT), revealed a large, complex intra-abdominal mass, initially raising suspicion for hydatid cyst or desmoid tumor. Despite exploratory laparotomy and initial biopsy, the diagnosis remained elusive due to equivocal immunohistochemistry. A multidisciplinary tumor board and a second pathological review from an international expert center ultimately confirmed the diagnosis of UESL. The patient received neoadjuvant chemotherapy, underwent a second extended right hepatectomy, and has currently completed 6 cycles of adjuvant chemotherapy with good progress. UESL, although rare, necessitates a high index of clinical suspicion, a thorough diagnostic workup, and collaborative multidisciplinary management to achieve favorable outcomes, particularly given its aggressive nature and potential for recurrence.