Presentation
13 year old male with right calf pain and swelling.
Patient Data
MRI Rt lower extremity without & C+
Extensive abnormal serpiginous T2 hyperintensity and enhancement is centered within the posterior deep and superficial muscle compartments (involving the entire calf), with a smaller component involving the upper anterior muscle compartment and deep posterolateral subcutaneous space. The lateral muscle compartment is spared. Several areas of intrinsic T1 hyperintensity likely represent thrombus; no phleboliths are seen (multiple areas of central venous hypointensity are attributed to flow void artifact). The lateral head of gastrocnemius has fatty replacement. There are no fluid collections.
Mild abnormal wispy T2 hyperintensity and enhancement is present in the deep subcutaneous fat just superficial to the anteromedial tibial surface, extending from mid to distal shaft.
The posterior tibial vein is mildly enlarged and tortuous. The popliteal vein is normal in size. A prominent upper interosseous vein drains from the involved area of anterior muscular compartment to the popliteal vein.
There is diffuse fatty replacement of tibial and fibular marrow as well as the marrow of the visualized ankle bones. However, this is not appreciated in the distal femur.
Case Discussion
The clinial presentation, imaging features and location in the calf are consistent with fibroadipose vascular anomaly, also known as FAVA. The lesions are characterized by deep muscle replacement with fibrofatty overgrowth and phlebectasia (dilation of the veins). Extrafascial components consist of fatty overgrowth, phlebectasia, and an occasional lymphatic malformation. The posterior compartment of the calf is by far the most common location, followed by the wrist and thigh.
The histopathologic features of FAVA are dense fibrous tissue, fat, and lymphoplasmacytic aggregates within atrophied skeletal muscle. Histology also demonstrates large, irregular, and sometimes excessively muscularized venous channels and smaller, clustered channels. Other findings seen include organizing thrombi, a lymphatic component, and dense fibrous tissue-encircled nerves.
Surgical resection is the mainstay of treatment.