AVMs of the Sylvian Fissure

Role of surgery

Resection of sylvian AVMs has been described for nearly four decades, with numerous case series demonstrating a high degree of efficacy and reasonable morbidity ( Table 34.2 ). Initially, resection of these lesions was reserved for patients with prior hemorrhage and significant neurologic deficits, but more recently, advances in microsurgery have allowed for a more aggressive approach in select patients. As previously discussed, the precise location of the AVM (pure sylvian or perisylvian) will significantly impact perioperative morbidity. Conventional angiography and MRI prior to potential resection are crucial for treatment decision and surgical planning. MRI can assist in the identification of the precise location of the lesion and potentially involved eloquent parenchyma. Further, while sylvian AVMs receive the large majority of their vascular supply from the MCA, additional arterial input from the anterior choroidal, posterior choroidal, and lenticulostriate arteries may be observed, rendering careful angiographic assessment essential prior to any potential treatment.

Once the decision to move forward with surgery is made, the precise location of resection will vary based on the nidal location, but all sylvian AVMs are approached with a wide sylvian fissure opening, typically utilizing a pterional craniotomy. Full fissure opening into the distal aspect of the sylvian fissure is necessary to completely skeletonize the MCA. This allows identification of the AVM arterial input, venous drainage, and nidus, but it also aids in clearly delineating the MCA and its branches as it courses through the fissure. Full anatomic exploration and identification of the native MCA and AVM vasculature are paramount prior to ligation of arterial input to the nidus in order to preserve all vessels providing blood supply to normal parenchyma.

Preservation of the parent MCA, en passage arteries, and perforating arteries limits neurologic morbidity from the procedure, although it is often difficult to parse out these different vessel types without full exposure. If there is any doubt about whether a vessel is feeding into the AVM or passing by, it should not be sacrificed until the nidus is fully exposed and a definitive assessment can be made. When AVM feeding arteries are relatively short or when the nidus is directly fed off the parent MCA, the use of suture or AVM clips is recommended to avoid coagulation damage to the native MCA. Particularly with medial sylvian AVMs, frequent use of clips, rather than cautery, is recommended, as partially cauterized vessels may retract into eloquent tissue, leading to a need for surgical manipulation of potentially eloquent areas that otherwise would be undisturbed.

The draining vein often lies within the sylvian fissure on top of the nidus, and care must be taken to preserve this structure until the nidus is ready to be removed. Venous drainage patterns tend to vary with sylvian AVM location. Pure sylvian AVMs typically drain superficially through the middle cerebral veins, whereas medial perisylvian AVMs and lateral perisylvian AVMs tend to drain through the veins of Trolard and Labbé, respectively. Deep sylvian AVMs typically exhibit deep venous drainage into the thalamostriate and internal cerebral veins. As with all AVMs, preservation of the draining vein until all arterial input has been ligated is of utmost importance.

In addition to preserving the native vasculature, minimizing manipulation of adjacent parenchyma is crucial in resection of perisylvian AVMs. Pure sylvian AVMs have no associated eloquent cortex, but medial sylvian AVMs border Broca’s area and the inferior aspect of the motor strip, lateral sylvian AVMs border Wernicke’s area and Heschl’s gyrus, and deep sylvian AVMs border the basal ganglia, internal capsule, and arcuate fasciculus. While perisylvian AVMs in the adjacent parenchyma may receive additional arterial supply from other vascular territories, such as anterior or posterior choroidal and lenticulostriate arteries, the vast majority of the arterial input arises from the MCA. In approaching perisylvian AVMs, it is recommended to prune all MCA arterial supply within the sylvian fissure prior to working around the parenchymal planes of the nidus. This allows resection to be maintained much tighter to the AVM nidus, thus reducing surgical morbidity from manipulation of eloquent cortex.

Numerous studies ( Table 34.2 ) have evaluated outcomes following resection of sylvian AVMs. Lawton et al. evaluated their series of sylvian AVMs, assessing 28 patients who underwent resection, 54% of whom presented with hemorrhage. Among this population, they observed transient neurologic deficits in 14% of the patients, but the rate of permanent neurologic morbidity was only 3.6%. No surgical mortality was observed, and 89% of the patients achieved good functional outcomes at a mean follow-up of 20 months. Similarly, Zimmerman et al. reported transient neurologic deficits in 50% of their patients, with all recovering within 3 months of surgery and no surgical mortality.

While resection of sylvian AVMs can at times be a safe and feasible option, it should be approached cautiously, appropriately weighing the risks and benefits of treatment. Factors such as age, history of rupture, eloquent cortex, insular locations, and involvement of lenticulostriate or anterior choroidal arteries need to be carefully considered prior to surgical intervention. Given these factors, a less aggressive approach with stereotactic radiosurgery (SRS) or even conservative observation may be in the patient’s best interest.