Locally Invasive Papillary Intralymphatic Angioendothelioma Arising Within a Lymphatic/Venous Malformation.

BACKGROUND Papillary intralymphatic angioendothelioma (PILA) is a rare vascular tumor affecting children and young adults, with less than 50 cases reported in the literature. This tumor typically presents in the extremities, exhibits borderline behavior, and has a prominent lymphatic phenotype. Originally thought to be malignant, PILA was later recognized for its borderline behavior and lymphatic features, leading to its current classification as a "rarely metastasizing lymphatic vascular neoplasm". CASE REPORT We present the case of a 10-year-old girl with a 6-year history of a right facial venous malformation, which was ultimately diagnosed as PILA in the background of lymphatic/venous malformation (LVM). After undergoing surgical excision of a right facial soft-tissue tumor, histopathological examination revealed scattered lymphatics and thin-walled vascular channels with blood in skeletal muscle and fibroadipose tissue. Intraluminal papillary proliferation of vascular spaces lined by cytologically bland spindle cells was observed, along with Kaposiform morphology and small-vessel proliferation. Immunohistochemical staining confirmed endothelial cell markers (D2-40, ERG, CD34, and CD31) and numerous CD3(+) lymphocytes in the lumen, surrounded by CD3(+) T lymphocytes and CD20(+) B lymphocytes in the surrounding stroma. The tumor lacked pleomorphism, significant mitotic activity, and necrosis. CONCLUSIONS PILA presents a diagnostic challenge and should be considered in the differential diagnosis of cutaneous vascular neoplasms. Long-term follow-up is crucial due to its borderline behavior and potential for local invasiveness and metastasis. Accurate diagnosis, aided by characteristic histological and immunohistochemical features, is essential for appropriate management of this rare vascular tumor.