A Rare Case of Neonatal Kaposiform Hemangioendothelioma With Kasabach-Merritt Phenomenon Presenting as an Abdominal Mass Without Cutaneous Manifestations.

Kaposiform hemangioendothelioma (KHE) is a rare vascular neoplasm that typically presents in infancy or early childhood, classified as a locally aggressive/borderline vascular tumor. It most commonly involves superficial and deep soft tissues, often demonstrating infiltrative growth into adjacent muscle and bone, whereas retroperitoneal or intraabdominal presentations are less frequent. KHE is frequently complicated by Kasabach-Merritt phenomenon (KMP), a severe consumptive coagulopathy characterized by profound thrombocytopenia, microangiopathic hemolytic anemia, and hypofibrinogenemia with life-threatening sequelae. We report a case of a male neonate who developed KMP secondary to an abdominal KHE without overlying cutaneous involvement. Diagnosis was established through integration of clinical features, imaging findings, hematological evaluation, and confirmatory biopsy. This patient was managed with a multimodal regimen of sirolimus, corticosteroids, and vincristine, resulting in significant clinical improvement. This case underscores both the diagnostic complexity and therapeutic challenges of KHE complicated by KMP, particularly when lesions occur in deep anatomical sites. Given the rarity of this condition, current management strategies rely largely on expert consensus and case-based experience, though recent randomized trial and consensus have established sirolimus-based regimens as highly effective first-line therapy.