Kaposiform Lymphangiomatosis in a Male Adolescent: A Clinical Challenge and the Role of Genetics.

Kaposiform lymphangiomatosis (KLA) is a rare and aggressive generalized lymphatic anomaly (GLA), with distinctive clinical, radiology, morphologic, and genetic features. It does not have a current standard treatment and presents poor overall prognosis. Somatic mutations in the RAS pathway were reported as the likely driver for the majority of patients. We report a case of a 17-year-old male adolescent who was referred to the emergency department due to a severe anemia. Laboratory workup confirmed the anemia and revealed coagulation factor consumption and fibrinolysis. Chest-abdomen-pelvis computed tomography revealed an extensive cervical, mediastinal, abdominal and retroperitoneal "hematoma." During admission, progressive pancytopenia, and disseminated intravascular coagulation were observed, and the hypothesis of a tumor/neoplastic etiology was considered. A thoracoscopy revealed a moderate hemorrhagic pleural effusion and a mediastinal mass resembling a "hemolymphangiomatosis" malformation, which was biopsied. Histology displayed a lymphatic-venous malformation. The patient was presented at the multidisciplinary Vascular Anomalies Center and, due to the complex vascular anomaly diagnosis, oral sirolimus monotherapy was initiated. Four years later, the patient remains clinically stable, with stability of the lesion's dimensions and characteristics. A p.Q61R variant in the