Arteriovenous Malformations (AVMs)

Arteriovenous malformations (AVMs) are simply characterized by abnormal connections between arteries and veins, where the arterial blood is shunted to veins. Although arteriovenous malformations are present in neonates at birth, they often suddenly become obvious when the patient is older because of various stimuli such as trauma, pregnancy, or puberty. Progression may also occur following biopsy or surgical intervention (e.g., ligation, partial surgical excision)

 
           
Photos 1,2 & 3:Lower Extremity AVMs with various presentations. Photo 4:Small Facial arteriovenous malformation in the periorbital area. This AVM (arteriovenous malformation) can be easily recognized by physical examination and imaging (typically Conventional arteriogram (DSA) or non-invasive angiography such as MRA or CTA)  is needed to see the extent of the malformation and treatment planning. This lesion can be treated surgically or embolization which is a minimally invasive procedure (performed by an Interventional Radiologist). Photo 5: Arteriovenous malformation (AVM) lesion involving the external ear and surrounding soft tissues. The ear is significantly warmer than the other ear and blood flow can be easily noticed during physical examination. 
    First photo is a young male patient with a relatively small arteriovenous lesion (high-flow birthmark) in the right hand. The skin appears normal. There is thrill over the lesion due to its high-flow nature. 2nd photo shows an extensive high-flow birthmark (AVM) involving the right ear and resulting in significant soft tissue deformity. 
 
       
Figure 1: AVM Nidus (vascular network between arteries and veins) .  Figure 2 & 3: These are contrast-enhanced magnetic resonance angiography images, early and late phases after contrast enhancement showing the AVM nidus, relatively large draining veins. Figure 4: Arteriogram/angiogram shows an extensive AVM around the knee.

 
Symptoms:Common symptoms include pain, overgrowth of the involved body part, changes related to decreased blood flow (ischemia), bleeding, and heart failure. Bleeding is usually minor, but it may be very serious; it typically occurs with dental work in patients with arteriovenous malformation of the dental arcade. Schobinger's staging (stages 1-4) is commonly used to describe the degree of progression. A stage I lesion has a pink-bluish stain and warmth. Doppler ultrasonography reveals arteriovenous shunting at this stage. In stage II, the lesion has pulsations, thrill and bruit. In stage III, the patient has dystrophic skin changes, ulceration, bleeding and pain. Finally, in stage IV, the patient has cardiac failure.

Various Presentation based on Location: Extremity arteriovenous malformations (AVMs) are relatively common. AVM may be a single focal lesion or may involve several sites in the extremity, or they may be diffuse and involve the entire extremity and adjacent trunk. Head and neck arteriovenous malformations differ somewhat because of their serious potential complications, which include bleeding from dental manipulation (common in dental arcade AVMs) and the potential risk of stroke when they are embolized. Lung AVMs (or AVFs) usually cause cyanosis, clubbing, and polycythemia, as well as strokes and brain abscesses (due to loss of the normal filtering function of the lungs). AVMs involving the lungs and/or gastrointestinal system are common in Rendu-Osler-Weber syndrome (hereditary hemorrhagic telangiectasia [HHT]). More information on HHT, visit HHT.org website.

Diagnosis: Although the overlying skin may be normal, these malformations can be easily recognized at clinical examination by the presence of a pulsatile mass, thrills, increased warmth, and redness. Focal or diffuse enlargement of the involved extremity is also a common finding. The high-flow nature of the malformation can be easily confirmed with Doppler examination, which reveals high-flow low-resistance arteries and an arterialized waveform in the draining veins.

On MRIs, the anomaly is characterized by enlarged vascular channels associated with dilated feeding and draining vessels. A discrete soft-tissue mass is typically absent. However, masslike perilesional soft-tissue signal-intensity changes and contrast enhancement may occur. This masslike appearance is usually observed when an arteriovenous malformation (AVM) is confined to a muscle sheath; this may make differentiation between an AVM and vascular tumor difficult. Abnormal arteriovenous connections are easily recognizable on MRIs as linear or punctuate signal voids (spin-echo imaging) or as hyperintensities (gradient-echo images). Please see the dedicated MRI protocol

In some patients, bones are also involved, which may cause bone deformities or fractures. Bony involvement can be diagnosed using x-rays or more dedicated CT or MR scan. 

 

     
Figure 1: AVM lesion in the calf (MR Angiography) and another AVM lesion on Doppler US examination. Today, most AVMs are studied with MR Angiography before embolization or surgery and Doppler US (Figure 2) is used in selected cases for further studying the flow dynamics. Doppler US allows flow measurements in the arteries and veins, as well as within the nidus.  Figure 3: Extensive pelvis AVM on arteriogram/angiogram.

  
     
1st image is the arterial phase (arteriography) showing an arteriovenous malformation nidus over the proximal femur region near the hip. 2nd image is a venous phase of the same arteriographic study showing an aneurysmal lesion within the region of the arteriovenous malformation nidus and large draining veins. 3rd image is a radiograph shows a cyst like bone change due to venous aneurysm and also irregular changes in the neck of the femur.

 

Recent Literature

  • Studying the effectiveness of superabsorbent polymer microsphere (SAP-MS) particles in 25 patients with AVMs concluded that SAP-MS particles can be used safely in transcatheter treatment of AVM. Transcatheter  treatment with use of SAP-MS particles was suitable for certain symptomatic AVMs, but diffuse AVMs remain a challenge and a combination of alternative methods will be necessary for further strategy >>> more
  • Retrospective review of 5 patients with high-flow lingual vascular anomalies concluded that the imaging findings in lingual AVMs can be atypical or inconclusive and can mimic hemangiomas, especially in the young patient, which may require biopsy for lesions with inconclusive imaging findings >>> abstract
  • In this report, a positional candidate gene, RASA1, encoding p120-RasGAP, was screened for mutations in 17 families. Heterozygous inactivating RASA1 mutations were detected in six families manifesting atypical CMs that were multiple, small, round to oval in shape, and pinkish red in color. This newly identified association caused by RASA1 mutations was named CM-AVM (capillary malformation arteriovenous malformation)  >>> more
  • Review of 797 patients with congenital vascular malformations concluded that diagnosis and management of AVMs by a multidisciplinary approach that integrates surgical therapy with embolism and sclerotherapy appears to improve the results and management with limited morbidity and no recurrence during early follow-up >>> abstract
  • Embolization and direct injection therapy is effective in AVMs of the mandible >>> more
  • Case report concluded that deep hypothermic circulatory arrest can be effectively used during surgical resection of AVMs >>> abstract

Skin thickening and increased fat may be seen in association with AVMs. On MRIs, osseous involvement can be seen as lytic bone expansion, lacy osseous changes, and /or cortical thinning. The feeding and draining veins in the involved body part are usually prominent. MRA and magnetic resonance venography (MRV) may be useful noninvasive imaging modalities to confirm the high-flow nature of the lesion and to map out the feeding and draining vasculature. Arteriography is usually required to evaluate of the abnormality in more detail during embolotherapy.

Treatment:

        

AVM, pre- and post-embolization. On post-embolization image, there are no feeding arteries seen. The nidus opacified on the pre-embolization image is no longer seen after the embolization. 

 
 

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