Indications
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Surgery is indicated for patients with arteriovenous malformations (AVMs) that have ruptured or are causing intractable seizures, progressive neurologic deficits, or intractable debilitating headaches. Often, failure of alternative therapies—embolization and stereotactic radiosurgery in symptomatic patients—is an indication for microsurgical intervention.
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It is mandatory to consider embolization and stereotactic radiosurgery for subcortical AVMs because of their location in eloquent structures. Multimodality approaches are usual, and staged resection of large AVMs is sometimes necessary.
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We favor resection of the AVM when the patient is stable and over the immediate acute period; this often means 3 to 4 weeks after the hemorrhage when the patient has had some recovery and the blood is liquefied. We also favor emergent evacuation of a hematoma that is producing significant mass effect and resecting the AVM at a later stage if possible.
Contraindications
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Surgery is contraindicated in patients who are in a poor clinical condition; patients with medical conditions that preclude surgery; very elderly patients; and patients with AVMs that are located within eloquent areas without safe surgical corridors for approach, such as the intact motor, language, or visual cortices.
Planning and positioning
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Close study of a four-vessel cerebral angiogram is necessary to evaluate the arterial, capillary, and venous phases of the vessels; presence of aneurysms; size and configuration of the nidus; and the relationship of the nidus to feeding arteries and venous drainages. Magnetic resonance imaging (MRI) details the relationship of the AVM with the surrounding neuroanatomic structures, which helps in selecting the most appropriate surgical approach. Operative or endovascular treatment of ruptured proximal aneurysms should proceed before resection of the AVM.
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Brain relaxation techniques, such as the use of mannitol and lumbar cerebrospinal fluid drainage, should be considered, especially if the ventricles are not being entered. For patients with seizures, anticonvulsants and cortical mapping to locate the epileptic foci are indicated. Localization of language dominance with amobarbital (Amytal) studies or functional MRI may be helpful.
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We routinely administer prophylactic antibiotics, employ mild hypothermia, use electrophysiologic monitoring, insert a femoral catheter sheath for intraoperative angiography, and induce hypotension during the resection. Routine equipment includes a radiolucent three-point head fixation device, neuronavigation system, microscope, microsurgical instruments, self-retaining retractor system, nonadhering bipolar forceps, aneurysm microclips, and AVM miniclips.
Figure 29-1:
Positioning of patients with callosal AVMs depends on the rostral-caudal location of the AVM. For frontal and parietal callosal AVMs, we prefer to have the patient supine, with the thorax raised 15 degrees and the head neutral and slightly flexed. The U-shaped skin flap is optimally centered over the nidus as guided by the neuronavigation system, based laterally and crossing the midline. A large enough scalp flap is fashioned to avoid compromise to the bridging veins from the medial cortex to the sagittal sinus.
Figure 29-2:
For occipital (splenial) callosal AVMs, we prefer to have the patient in a lateral position with the lesion side down and the thorax slightly elevated. A U-shaped incision centered over the AVM and large enough to incorporate the draining veins is marked, based over the superior nuchal line with the medial edge crossing the midline. This posterior interhemispheric approach is also suitable for intraventricular AVMs in the medial trigonal area.
Figure 29-3:
A transcallosal approach is favored for medial caudothalamic AVMs with the head turned so that the lesion side is down. The flap is similarly fashioned as in Figure 29-1 , guided by the neuronavigation system. For more lateral and dorsally placed pulvinar AVMs, a transcortical approach is used, with the head turned, the lesion uppermost, and an inferiorly based parietooccipital skin flap fashioned.Related posts:
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