Distal Anterior Cerebral Artery Aneurysms: Anterior Interhemispheric Approach

Clinical Presentation and Diagnostic Workup

In the same manner as with aneurysms in other locations, distal anterior cerebral artery (DACA) aneurysms may present symptomatically with subarachnoid hemorrhage (SAH) or may be found incidentally. ¹^‑ ⁵ When presenting with SAH, blood on computed tomography (CT) is most often prominent within the interhemispheric fissure with layering above the corpus callosum ( ▶ Fig. 10.1). This hemorrhage pattern may also be observed with superiorly directed anterior communicating artery (ACOM) aneurysms, potentially creating some diagnostic ambiguity. Depending on the dome orientation, DACA aneurysms may rupture into the ipsilateral or contralateral frontal lobe and/or into the ventricles. ⁶^, ⁷^, ⁸ Less commonly, patients may present with seizures due to irritation of the underlying cortex or thromboembolism in the anterior cerebral artery (ACA) territory.

Fig. 10.1 This patient presented with a complaint of “worst headache of life” and progressed to obtundation. Head CT demonstrated subarachnoid hemorrhage within the anterior interhemispheric fissure as well as intracerebral hemorrhage within the right medial frontal lobe (a). Catheter angiography revealed the bleed source to be a 5-mm pericallosal artery aneurysm (arrow) arising just distal to the branching of the callosomarginal artery (b).

Cerebral vascular imaging with CT and/or catheter angiography is necessary for aneurysm characterization prior to operative intervention. Although catheter angiography remains the goal standard imaging modality, axial imaging may have additional utility for mapping bridging veins and craniotomy planning. Since the aneurysm dome is not uncommonly buried within one of the medial cerebral hemispheres, magnetic resonance imaging may enhance appreciation of the aneurysm–brain interface. Although not mandatory, consideration may be given to obtaining volumetric imaging so that frameless stereotaxy can be utilized. ⁹

10.2 Treatment Options

Historically, DACA aneurysms have been most effectively treated with microsurgical clipping as opposed to endovascular coiling due to their peripheral location, small size, and unfavorable neck-to-dome and neck-to-parent artery ratios. ¹ These aneurysms, when ruptured, may also result in a “blowout” at the bifurcation from which they arise, thus making endovascular repair more difficult or impossible without adjuncts such as balloon remodeling or stents. ⁴

Given that patients with DACA aneurysms frequently harbor multiple aneurysms, consideration may be given to treating more than one aneurysm at the same time. It is our opinion that such an approach is most reasonable when multiple aneurysms can be accessed from the same surgical approach. We generally avoid treating additional unruptured aneurysms if a completely separate approach is needed so as to avoid increased operative times and additional brain manipulation. Both our experience and the literature suggest that the rupture risk of unsecured, unruptured aneurysms is not increased in the setting of hemodynamic or endovascular therapy for angiographic vasospasm and delayed cerebral ischemia. ¹⁰

10.3 Anterior Interhemispheric Approach

10.3.1 Position

Although all aneurysms at and distal to the ACOM can be approached interhemispherically, those greater than 2 cm distal to the communicating artery must invariably be attacked in this manner. The patient is positioned supine with the head pinned neutral in a three-point skull clamp ( ▶ Fig. 10.2). When the aneurysm lies below or proximal to the genu of the corpus callosum, modest head extension may facilitate the approach. Intraoperative neuronavigation can be valuable for planning the trajectory to the aneurysm as well as finding it during surgery. Slight head flexion may be beneficial for approaching aneurysms arising from the A4 or A5 segments of the pericallosal artery. Although not favored by our group, the lateral position is also reasonable.

Fig. 10.2 For the anterior interhemispheric approach, the patient is positioned supine with the head pinned in a neutral position (a). Note that the pins are placed sufficiently posterior so that they do not interfere with the planned bicoronal incision. The artist depiction illustrates an optimal neutral head position for approaching this A3 aneurysm (inset) in the region of the corpus callosum genu (b). Such aneurysms often arise just distal to the origin of the callosomarginal artery.

10.3.2 Skin Incision and Craniotomy

A bicoronal scalp incision, behind the hairline, extending from the ipsilateral zygoma across the midline to the contralateral superior temporal line is used. The temporalis fascia and muscle should be left down and intact ( ▶ Fig. 10.3). Care is taken to avoid pressure on the eyes while the scalp is flapped anteriorly. The exact rostrocaudal location of the proposed craniotomy is determined by the location of the aneurysm and of bridging veins to the superior sagittal sinus. We favor a nondominant, right-sided approach in most cases since DACA aneurysms from either ACA can generally be accessed below the falx from either side. Left-handedness, a left-sided frontal hematoma, or aberrant ACA anatomy may favor left-sided approaches. ⁸

Fig. 10.3 This bicoronal scalp flap is retracted anteriorly over the orbital rim and held in place with hooks. Care is taken to ensure that no pressure is placed on the globe during scalp retraction. Note that the temporalis muscle is left down.

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