Intravascular Papillary Endothelial Hyperplasia (Masson’s Tumor) Involving the Knee Synovium

INTRODUCTION: Intravascular papillary endothelial hyperplasia or Masson’s tumor is a rare benign lesion of vascular origin characterized by abnormal proliferation of endothelial cells. CASE REPORT: We present a case of this lesion involving the knee joint of a Caucasian woman who was referred to our institution for the evaluation of recurrent right knee pain. Her symptoms have started insidiously 5 years earlier following minor trauma. Recurrent symptomatic knee effusion was the cardinal symptom. Following the surgical excision of the lesion, recurrence occurred 2 years later. The tumor was successfully treated with embolization of its vascular supply. CONCLUSION: Masson’s tumor involving the synovium is an uncommon condition. The intermittent symptomatology and normal appearance of biopsies taken arthroscopically during asymptomatic periods can make the diagnosis challenging. Although resection is proposed to prevent recurrence, embolization of the vascular supply of the tumor can be a viable alternative.