Fibroadipose vascular anomaly (FAVA)

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Fibroadipose vascular anomaly (FAVA) is a recently-described intramuscular vascular anomaly consisting of phlebectasia (dilatation of veins) and fibrofatty replacement of muscle. It is in the "provisionally unclassified" category of the ISSVA classification of vascular anomalies.

Terminology

Though the term fibroadipose vascular anomaly has only recently been proposed, patients with similar clinical and radiopathological entities have been described for several decades with inappropriate terms such as "intramuscular hemangiomas" . As with all vascular anomalies, the relative rarity of such lesions makes accurate diagnosis difficult, even for experienced physicians.

Epidemiology

FAVA has been described from birth to early adulthood. The largest case series published so far  showed a greater than 4:1 predilection for females.

Clinical presentation

Patients typically have constant severe pain, and often present with contracture of the affected muscular segments. This is in contrast to the more common venous malformations of the soft tissues, which typically have mild, episodic pain. Most patients with calf involvement have limited ankle dorsiflexion (equinus deformity).

Anatomically, the lesion has been described most commonly in the calf musculature. It can also present in the forearm and thigh.

Pathology

Macroscopically, the lesion can involve one of multiple limb muscles with extensive fibrotic changes and frequent involvement of fascial planes, nerves, subcutaneous tissues and extramuscular extension. The phlebectasia can be within the muscular component or in the adjacent subcutaneous tissue.

Histologically, there is often dense fibrous tissue, fatty replacement, muscular atrophy, dysplastic veins and lymphoplasmacytic aggregates in the skeletal muscle. Small lymphatic malformations can be also associated, as can thrombi and phleboliths.

Radiographic features

Radiography

Plain radiography is usually normal, but can demonstrate reactive bone changes adjacent to fibroadipose vascular anomaly.

Ultrasound

Ultrasound typically demonstrates a heterogenous hyperechoic intramuscular mass lesion with loss of the normal fibrillary skeletal muscle pattern. Dilated veins are easily depicted. When present, ultrasound readily shows phleboliths. FAVA lesions do not demonstrate enhanced arterial flow on Doppler.

MRI

Typically, a soft tissue mass is seen centered in skeletal muscle. There is usually fatty replacement of muscle seen as heterogenous moderately high signal on T1 and T2 weighted images. The lesion usually shows enhancement after gadolinium administration. There can be isolated muscle involvement or transfascial extension with or without subcutaneous involvement. Dilated tortuous veins are often seen within or adjacent the mass with either normal or dilated drainage veins. Reactive bone change can be seen.

Angiography

Venography can be either normal or show dilated tortuous veins draining into normal or dilated orthotopic veins. There should not be associated increased arterial flow or arteriovenous shunting.

Treatment and prognosis

Sclerotherapy has been successful in treating the abnormal veins in fibroadipose vascular anomaly, but does not resolve the prominent fibrofatty component. Therefore, the remaining contractures often require operative therapy and physiotherapy. Cryoablation has also been recently attempted with promising results .

Differential diagnosis