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Fibroadipose vascular anomaly (FAVA) is a recently characterized, complex, intramuscular vascular anomaly that is painful and infiltrative, composed of fibrous, adipose, and venous components.

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It is classified under provisionally unclassified vascular anomalies by the International Society for the Study of Vascular Anomalies (ISSVA, 2018 update) — distinct from typical venous malformations (VMs).

Etiopathogenesis

Somatic activating mutations in the PIK3CA gene (same pathway as in PROS — PIK3CA-Related Overgrowth Spectrum).
Dysregulated PI3K–AKT–mTOR signaling → proliferation of fibrofatty tissue and malformed veins within muscle.
Represents a mosaic overgrowth vascular lesion, not a true neoplasm.

Clinical Features

Feature	Description
Pain	Severe, chronic, disproportionate to lesion size; often main presenting complaint.
Swelling	Firm, noncompressible mass; may appear as pseudo-hypertrophy of muscle.
Contracture	Progressive muscle fibrosis → flexion deformity or limited motion of adjacent joint (e.g., equinus deformity in calf involvement).
Warmth / discoloration	Occasionally due to superficial venous component.
Phleboliths	Rare compared to classic venous malformations.
Neuropathic pain	May occur if lesion infiltrates along neurovascular bundle.

Clinical pattern: Usually single muscle involvement, unilateral

Common sites	Lower extremity muscles: Gastrocnemius, soleus, quadriceps, hamstrings
Less common sites	Upper limb (biceps, triceps, forearm flexors)
Age of onset	Childhood or adolescence (mean 8–15 years)
Sex	Slight female predominance

![Surgical resection of a FAVA in calf. a-c, A girl was presented with Achilles contracture and a local mass in calf. Venography demonstrated anomalous-dilated veins, and normal orthotopic veins in the affected area. d and e, The soleus was infiltrated by diffuse heterogeneous high signal on MRI. The gastrocnemius atrophy was noted. f, The deep fascia over gastrocnemius was not obviously involved. g. The soleus underlying gastrocnemius was infiltrated by dense fibroadipose tissue and tufted venous component. h. Achilles lengthening was performed following radical resection of lesion because of significant contracture. i. Surgical specimen showed an intramuscular mass with unusually rounded venous nodules intermingled with dense fibrotic tissue and yellow fat

Wang, H., Xie, C., Lin, W. et al. Fibro-adipose vascular anomaly (FAVA) - diagnosis, staging and management. Orphanet J Rare Dis 18, 347 (2023). https://doi.org/10.1186/s13023-023-02961-6](attachment:41975928-141d-442f-98ed-f59948e2be39:13023_2023_2961_Fig1_HTML.webp)

Surgical resection of a FAVA in calf. a-c, A girl was presented with Achilles contracture and a local mass in calf. Venography demonstrated anomalous-dilated veins, and normal orthotopic veins in the affected area. d and e, The soleus was infiltrated by diffuse heterogeneous high signal on MRI. The gastrocnemius atrophy was noted. f, The deep fascia over gastrocnemius was not obviously involved. g. The soleus underlying gastrocnemius was infiltrated by dense fibroadipose tissue and tufted venous component. h. Achilles lengthening was performed following radical resection of lesion because of significant contracture. i. Surgical specimen showed an intramuscular mass with unusually rounded venous nodules intermingled with dense fibrotic tissue and yellow fat

Wang, H., Xie, C., Lin, W. et al. Fibro-adipose vascular anomaly (FAVA) - diagnosis, staging and management. Orphanet J Rare Dis 18, 347 (2023). https://doi.org/10.1186/s13023-023-02961-6

Complications

Chronic pain and functional impairment (most common).
Joint contractures due to fibrosis.
Cosmetic deformity (limb asymmetry or pseudohypertrophy).
Neuropathic pain due to nerve encasement.

Etiopathogenesis

Clinical Features

Complications

Radiology