Clinically diagnosed kaposiform hemangioendothelioma with Kasabach–Merritt phenomenon presenting as a neonatal transcalvarial osteolytic skull lesion: a case report with long-term radiological calvarial remodeling

Background Kaposiform hemangioendothelioma (KHE) complicated by Kasabach–Merritt phenomenon (KMP) is a rare but life-threatening vascular tumor of infancy. Cranial vault involvement with transcalvarial extension and extensive osteolytic destruction is exceptionally uncommon and may radiologically mimic malignant skull tumors, such as metastatic neuroblastoma or sarcoma. Evidence regarding the long-term skeletal evolution of such lesions after conservative treatment remains limited. Case presentation We report the case of a 2-month-old full-term male infant with a rapidly enlarging right occipital mass and severe consumptive coagulopathy. Cranial magnetic resonance imaging and computed tomography demonstrated a giant transcalvarial vascular lesion with intracranial and extracranial components, extensive destruction of the right occipital and parietal bones, and compression of adjacent brain structures. The vascular tumor phenotype, severe KMP-compatible coagulopathy, radiological characteristics, multidisciplinary assessment, and an available oncological workup that did not support neuroblastoma or another malignant process led to a clinical/probable diagnosis of KHE complicated by KMP. Because severe coagulopathy and the highly vascular, extensive transcalvarial lesion made biopsy unsafe, histopathological confirmation was not obtained and the diagnosis remained tissue unconfirmed. The patient received coagulation support and high-dose intravenous methylprednisolone, with major hematological recovery by March 28, 2018, before propranolol was initiated at discharge as empiric historical maintenance therapy. Serial MRI showed marked soft-tissue regression and findings compatible with progressive radiological calvarial remodeling without surgical reconstruction. Conclusions This case highlights that neonatal KHE/KMP involving the cranial vault can closely mimic malignant osteolytic skull tumors and requires integrated assessment of imaging findings, coagulation abnormalities, and evaluation for malignant mimics. In selected critically ill infants in whom surgery or biopsy is unsafe, conservative medical stabilization may be followed by sustained lesion regression and progressive radiological calvarial remodeling. However, the therapeutic contribution of propranolol cannot be inferred from a single case, and further studies are required to clarify the mechanisms and predictors of spontaneous calvarial remodeling in KHE-related osteolytic lesions.