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Arteriovenous Malformation (AVM)
Arteriovenous malformation (AVM) is a defect in the formation of blood vessels where the blood flows directly from the arteries to the veins skipping the division into capillaries. It is a fast-flow malformation involving abnormal, dysmorphic arterial to venous communication usually via a nidus lacking connecting capillary bed. It is mainly sporadic, but can be seen in genetic syndromic patients.
This lesion typically appears in the head and neck region particularly in the cheek and ears, but also in other areas such as the arm, forearm, thigh, gluteal region, ankle and foot.
Symptoms and History
Most AVM lesions are present at birth and grow in proportion to the body. They are typically warm to touch, with a pink-red cutaneous stain and a palpable thrill or bruit, although some cases maybe asymptomatic.
The symptoms usually depend on the location of the AVM. For example:
- Brain AVM: headaches, seizures, developmental disabilities
- Skin AVM: non-healing wound, pain
- AVM inside the nose or mouth: bleeding from the nose or mouth
- AVM on an extremity: difficulty walking, pain, functional problems
Clinical Exam. The patient may be asymptomatic or present with a warm, pinkish-red lesion with a palpable thrill, audible bruit. In an advanced stage, there may be ulceration, ischemia (causing pain), necrosis (difficult to treat wounds) and cardiac failure.
Imaging. Ultrasound with color Doppler is the first line study demonstrating a poorly defined hypervascular lesion. MRI (Magnetic Resonance Imaging) of the affected area may be performed to help delineate the extent of the lesion.
Pathology. Usually biopsy is not needed as clinical examination and imaging studies are enough for diagnosis.
Genetics. Arteriovenous malformations can sometimes be associated with sporadic (also called somatic) genetic changes like KRAS, MAPK1, NRAS, etc.
Certain inherited (hereditary) genetic syndromes have been identified as well such as Capillary-Malformation Arteriovenous Malformation (CM-AVM) syndrome caused by genetic alterations in Rasa1 or EPHB4, Hereditary Hemorrhagic Telangiectasia (HHT) caused by mutations or deletions in ENG, ACVRL1, GDF2 or SMAD4, and PTEN-Hamartoma Tumor syndrome (PHTS/Cowden) – PTEN mutations or deletions. Genetic counseling and testing may be discussed and recommended. Having a genetic diagnosis may help guide medical management and provide information for at-risk relatives.
AVM treatment is indicated when there is pain, enlargement, deformity, recurrent bleeding, functional impairment, tissue ischemia and/or venous hypertension. It can include embolization, surgical resection or medical management with targeted therapy like MEK inhibitors.
Some AVMs may be linked to a group of problems called a syndrome. Some of the syndromes linked to AVMs are: