Paramedian Craniotomy and Unilateral Anterior Interhemispheric Approach for Clipping of Distal Anterior Cerebral Artery Aneurysm

Indications

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Clipping of distal anterior cerebral artery (DACA) aneurysms has a long-lasting effect; rerupture of previously clipped aneurysm is very rare.
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DACA aneurysms are usually small, with a relatively broad base; are distally located; and have one or more branches originating from their base. These factors, together with the relatively small diameter of the parent artery, favor clipping over coiling.
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When DACA aneurysms rupture, about 50% manifest with frontal intracranial hemorrhage (ICH), which needs to be (at least partially) removed during clipping.
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DACA aneurysms rupture at a smaller size (mean 6 mm) than aneurysms in many other locations, so treatment of small (<7 mm), unruptured DACA aneurysms is reasonable in young, healthy patients.
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Multiple aneurysms are found in about 50% of patients with DACA aneurysms, and multiple DACA aneurysms are found in 10%. All DACA aneurysms can usually be accessed via the same interhemispheric approach and clipped during one operation.
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Even patients with poor Hunt and Hess grade with ruptured DACA aneurysm should be treated because mortality for this aneurysm location is lower than for other aneurysms.

Contraindications

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In acute subarachnoid hemorrhage, only aneurysms that can be easily accessed through the same approach should be clipped. Extensive dissection and manipulation of cingulate gyri should be avoided to prevent neuropsychologic deficits.
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Patient with poor Hunt and Hess grade and subarachnoid hemorrhage with fixed dilated pupils and no proper reaction to pain would not benefit from active treatment.
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Old age, poor condition, and additional comorbidities are relative contraindications.

Planning and positioning

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Preoperative planning is based on computed tomography angiography or digital subtraction angiography images. Special attention is paid to (1) the vascular configuration of the anterior communicating artery region, (2) the number and course of the pericallosal arteries, (3) the actual originating artery, (4) aneurysm location with respect to the genu of corpus callosum, (5) dome projection, (6) possible ICH, (7) number and orientation of branches at the aneurysm base, (8) presence of vascular anomalies, and (9) additional aneurysms.
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Of DACA aneurysms, 85% originate from the A3 segment of the anterior cerebral artery (ACA), at the genu of corpus callosum.
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DACA aneurysms are generally approached via an anterior interhemispheric approach, the only exception being aneurysms located on the proximal A2 segment of the ACA and aneurysms located distally on the frontobasal branches of the ACA, the limit being 15 mm or less of vertical distance from the floor of the anterior fossa. These aneurysms are operated via a lateral supraorbital approach, a frontal modification of the pterional approach.
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For right-handed surgeons, the right-sided approach is more convenient because both pericallosal arteries can be reached under the lower margin of the falx for most of their course. Only very distal DACA aneurysms (A5 segment or distal callosomarginal artery) require an approach from the same side as the aneurysm. Left-sided ICH may require a left-sided approach.
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The location of the DACA aneurysm with respect to the genu of corpus callosum determines the exact location of the bone flap and the angle of approach. The more proximal the aneurysm, the more frontal the craniotomy to prevent the genu of the corpus callosum from obstructing the view toward the aneurysm base. Partial resection of the genu of corpus callosum is not recommended because it leads to cognitive impairment.
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Neuronavigation may be helpful in planning and executing the approach to the aneurysm.

Figure 25-1:

Positioning of the bone flap during interhemispheric approach for DACA aneurysms at different locations along the DACA.

Figure 25-2:

After minimal shaving, the skin is sterilized and infiltrated with a local anesthetic combined with epinephrine. An oblique skin incision is made just behind the hairline, with the base frontally and over the midline and extended more to the side of the planned bone flap.
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The patient is placed in the supine position with the head elevated about 20 cm above the heart level. The head should be in a neutral position with the nose pointing exactly upward. Tilting the head to either side risks the chance of placing the bone flap too lateral from the midline, making entry into the interhemispheric space difficult.
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The neck of the patient is slightly flexed or extended according to how proximal or distal the DACA aneurysm lies. In optimal position, the surgical trajectory is almost vertical.
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Anesthesia is maintained with propofol infusion, and mannitol is given.