The Operation for Arteriovenous Malformations in Children

Patient Positioning

• Position according to location of AVM: Positioning is dependent on the location of the AVM and will vary widely.  General principles include elevating the head to maximize venous drainage, avoiding kinking of vessels in the neck, and maximizing access to the lesion by both the primary surgeon and the assistant.
• Head fixation: Rigid head fixation is preferable, although in the very young child (under 2 years of age), it may be necessary to employ a padded headrest.

Surgical Approach

• Varies with location of AVM: Given the wide variety of AVM sizes and locations, it is impossible to identify any single approach for AVM surgery.  Specific approaches should be selected to maximize access to the lesion, avoid eloquent neurologic cortex (if possible), and afford the surgeon visualization of feeding and draining vessels to permit proximal control of blood flow.
• Opening: The approach for any AVM will vary greatly from case to case, but general principles should include a generous opening to allow access and visualization of relevant anatomy and careful dural opening to avoid injuring AVM vessels (especially draining veins).

Intraoprative image of cortical AVM: Shown is a dilated and arterialized draining vein

Intraoperative image of partially dissected cortical AVM: Shown is the method of circumferential dissection of AVM with preservation of the draining vein. Note the reduction in caliber of the draining vein and change in its appearance after interruption of the arterial supply

Intervention

• Cauterize feeding arteries first: A primary surgical principle for AVM resection is the obliteration of feeding arteries before occlusion of draining veins, as premature closure of outflow can lead to unexpected AVM rupture with uncontrolled bleeding.
• Work in circumferential pattern, maintaining even depth: AVMs are often wedge- or cone-shaped, and resection can be performed in a circumferential pattern, staying close to, but not entering, the nidus.  It is helpful to try to maintain an even depth of resection around the lesion to avoid getting in a “hole,” and caution must be taken to minimize retraction on draining vessels during dissection.
• Watch surrounding brain: Repeated inspection of the surrounding brain for swelling or bleeding can aid the surgeon in preventing complications by early identification of poorly placed retractors or clips.
• Clip vs. coagulation of feeding vessels: AVM vessels may coagulate poorly, and consideration should be given to clip application or gentle tamponade (if the bleeding is of small volume) if bipolar electrocautery is not working.  Every attempt should be made to avoid operating within the nidus itself.

Closure

• Inspect resection bed: Inspection of the operative cavity for residual nidus is important, and perioperative angiography can be a useful adjunct to ensure complete resection.
• Check for brain swelling: Evidence of brain swelling at closure may indicate occult bleeding, untreated hydrocephalus, or poorly compensated redistribution of blood flow, which can result in perfusion breakthrough hemorrhage.  Causes for swelling should be thoroughly investigated and treated, if possible, prior to leaving the operating room. 
• Routine closure technique