Kaposiform Hemangioendothelioma with Kasabach-Merritt Phenomenon in a Neonate: A Case Report.

Kaposiform hemangioendothelioma (KHE) is a rare, aggressive vascular tumor frequently complicated by Kasabach-Merritt phenomenon (KMP), a life-threatening consumptive coagulopathy. Neonatal KHE-KMP management requires urgent intervention but is complicated by immunosuppression risks, especially in Bacillus Calmette-Guérin (BCG)-vaccinated infants. A full-term male neonate with prenatal right upper limb thickening presented postnatally with a violaceous, firm mass. Laboratory findings confirmed KMP. Due to recent BCG vaccination, sirolimus was initially withheld. First-line therapies failed, prompting sirolimus initiation on day 3, supplemented by fibrinogen transfusions. Platelets normalized by day 13 (283 × 10 9 /L) with marked tumor regression. Transient fever/diarrhea resolved with supportive care. At discharge (day 27), platelets stabilized (183 × 10 9 /L). Three-month follow-up showed sustained platelet recovery (268-532 × 10 9 /L), near-complete tumor resolution, and age-appropriate development. Prophylactic trimethoprim-sulfamethoxazole prevented infections. Sirolimus is a critical salvage therapy for refractory neonatal KHE-KMP, even in BCG-vaccinated infants. Timely initiation reverses life-threatening coagulopathy and achieves favorable outcomes, necessitating multidisciplinary monitoring to balance immunosuppression risks.