Arteriovenous Malformations

1. Essentials of Diagnosis

• Commonly noted at birth and confused with a hemangioma or a capillary malformation Eventually local warmth and pulsation lead to diagnosis Not easily compressible
• Overlying skin changes usually precede heart failure (figure 3)

2. General Considerations
AVMs are uncommon but are most often found in the head and neck (excluding intracranial lesions from this discussion). Massive bleeding after dental extraction is sometimes a presenting symptom. AVMs are sometimes referred to as "fast flow lesions." Trauma or the onset of puberty may precipitate a growth spurt. Terms such as arteriovenous fistula in general imply a more localized shunt from large artery to nearby veins. The term AVM implies a larger diffuse lesion with a myriad of microscopic and macroscopic components. Both are manifestations of the broad "AVM" class of malformations.

3. Clinical Findings
Clinical suspicion is easy to confirm with ultrasound or color Doppler. MRI/MRA is the best modality to visualize the extent of the lesion. Arteriography is typically reserved for the eventual treatment phase, combining this modality with embolization. Lesions are staged in four categories, which were originally proposed by Schobinger.

4. Differential Diagnosis
Initially AVMs are commonly noted at birth but are confused with a hemangioma or a capillary malformation. Ultrasound can differentiate these lesions if questionable.

5. Complications
Congestive heart failure may necessitate urgent embolization. Echocardiography should be done on stage three patients and at least yearly thereafter to screen for progression to stage IV.

6. Treatment
Never is it recommended to ligate a large feeding vessel. This shifts the flow to collateral vessels and serves only to accelerate growth. Complete surgical excision is the only way to ensure a successful treatment. Rarely, with early diagnosis, surgical excision of a stage I AVM is possible. Early lesions obviously have a greater chance for surgical excision. However, because of late diagnosis or surgical risk in large lesions, patients are followed until symptoms dictate intervention. Super-selective arterial embolization using permanent material can be used palliatively to relieve pain or other symptoms, or as part of a combined treatment plan with intent to completely eliminate the lesion.3 These combined treatments usually consist of either embolization followed by surgical resection or embolization followed by sclerotherapy. The former treatment combination is more typically used. If the overlying skin is normal it can be saved; however, this is often not the case. Long term follow-up is essential as these lesions have a tendency for recurrence even in experienced hands. Arteriovenous malformations are difficult to manage since the risks of recurrence are extremely high. Before treatment, it's important to determine the location of the core and its extent. Three tests can provide this information:

• A conventional MRI A MRA (magnetic resonance angiogram)
  or
• A special angiogram (digital subtraction angiogram)