[Low-low synovial vascular malformation of the knee (hemangiolymphangioma) - Case report].

Introduction: Low-flow vascular malformation, which usually develops during the first stage of infancy, is a rare cause of recurrent effusion of the knee. History, laboratory and X-rays are usually non-specific.

Objective: To describe a rare disease in pediatrics, emphasizing the correct classification and suspicion.

Case Report: A case is presented of a two-year-old patient with a history of effusion of the right knee who required multiple hospitalizations and antibiotic treatments. Laboratory work-up was normal. Plain X-rays of the knee revealed no bone changes. MR imaging reported low-flow vascular malformation. Surgical resection was performed, evidencing vascular lesion among the muscle fibers of the vastus lateralis of quadriceps until the capsule of the knee, as well as dissection of the fibers until the vastus lateralis of the right leg. Histology was consistent with low-flow vascular malformation. Due to the benign outcome and favorable evolution, an outpatient management was possible.

Conclusions: Although low-flow synovial vascular malformation is a rare disease among the pediatric population, it should be considered in the differential diagnosis of patients with repeated hemarthrosis and no history of either coagulopathy or hemophilia.