Intravascular organizing thrombus in the forearm: a unique imaging presentation.

Organizing thrombus is a well described histologic finding involving the reorganizing and recanalization of a healing thrombus. However, it is rarely large enough to be described on imaging. When the thrombus becomes sufficiently large, intravascular papillary endothelial hyperplasia (IPEH) must be considered. IPEH or Masson's tumor is a benign, exuberant form of organizing thrombus that typically occurs in the soft tissues of the head, neck, and distal extremities. It can occur within a vessel, hematoma, or vascular mass and can mimic benign processes or malignant lesions such as angiosarcoma. Histopathological characteristics are needed for final diagnosis. The treatment is typically complete surgical resection with excellent prognosis. We report the case of a patient presenting with swelling in his left forearm in the same site as a previously treated left basilic vein thrombus. Ultrasound demonstrated a noncompressible, heterogeneous intravascular mass with internal vascularity. Subsequent MRI showed an enhancing mass centered in the left basilic vein with a flow void with the differential diagnosis of IPEH versus intravascular neoplasm. Percutaneous biopsy was performed with histology consistent with reactive vascular proliferation and organizing thrombus. The papillary architecture diagnostic of IPEH was absent. Regardless of final specific terminology, this case presents exuberant organizing thrombus as a benign cause of an enhancing intravascular mass. This patient was treated conservatively with no further intervention.