An anterior interhemispheric approach is mandatory for most pericallosal artery aneurysms1,2,5,7–9,12,15,17). Using retraction on the medial surface of the frontal lobe, the dissection is carried down into the interhemispheric fissure. The parent artery distal to the aneurysm is generally reached first and followed by careful dissection past the aneurysm to the proximal parent artery. Thus, cases of a ruptured pericallosal artery aneurysm are an exception to the classical vascular principle of early achievement of proximal vascular control.

If uncontrolled intraoperative bleeding occurs from a ruptured pericallosal artery aneurysm, a tamponade and suction technique is the only available option, since proximal vascular control can be hampered due to adhesion of the cingulate gyri, peri-aneurysmal adhesion, or blocked operative access to the proximal parent artery by the bleeding rupture point7,18). This situation can lead to damage of the aneurysmal neck and parent artery.

Thus, a safer way to achieve proximal vascular control is needed for cases of a ruptured pericallosal artery aneurysm with a high risk of intraoperative premature rupture and technical difficulties for proximal vascular control. Accordingly, a pterional or subfrontal approach was combined to expose the bilateral A1 segments or the origin of the ipsilateral A2 segment of the ACA, allowing early and safe establishment of proximal vascular control far from the rupture point. While somewhat laborious, this combined approach is effective in avoiding catastrophic premature bleeding for high-risk patients.

A combined pterional-interhemispheric approach has already been reported in literature, yet has been limited to cases of multiple aneurysms requiring both surgical approaches3,6). In contrast, the proposed combined approach is intended to establish safe and early proximal vascular control for ruptured pericallosal artery aneurysms located in the interhemispheric fissure. The technical details and indications for the proposed combined approach are described using 3 surgical cases.

The patient is positioned supine and the head placed in a neutral position. For aneurysms that lie inferior to the genu of the corpus callosum, the neck is then extended approximately 15 degrees, whereas the neck is not extended for aneurysms lying close to the genu of the corpus callosum.

A combined pterional-paramedian craniotomy is created for the pterional approach to achieve proximal vascular control (Fig. 1A), while a frontal craniotomy bordered by the lateral orbital roof and a superior sagittal sinus is created for the combined subfrontal-interhemispheric approach (Fig. 1B).

For the combined subfrontal-interhemispheric approach, a bicoronal scalp incision is made and reflected anteriorly using an interfascial dissection of the temporalis muscle, as originally described by Yasargil et al.20). Meantime, for the combined pterional-interhemispheric approach, the temporalis muscle is separated and elevated with the scalp ipsilaterally, while an interfascial dissection of the temporalis muscle is performed contralaterally.

To create a cranial bone flap combining a pterional craniotomy and frontal paramedian craniotomy, 5 burrholes are made as follows: 1) the first hole is a keyhole just superior to the frontozygomatic suture, 2) the second hole is placed inferiorly on the temporal squamous bone, 3) the third hole is placed at the posterior aspect of the exposure just inferior to the superior temporal line, and 4) the fourth and fifth holes are placed on each side of the midline at the posterior extent of the paramedian craniotomy part. To avoid dimples in the forehead, no burrholes are made either side of the midline at the anterior extent of the craniotomy. The anteromedial border of the craniotomy is performed diagonally to avoid the frontal sinus. To create a free bone flap, the anterior and posterior extent of the craniotomy covering the superior sagittal sinus are cut using a narrow drill bit without a foot plate, while the other burrholes are connected using a narrow drill bit with a protective foot plate. Drilling the sphenoid ridge and frontal floor prominences completes the combined pterional-paramedian craniotomy.

The dural opening is initially performed in a C-shaped fashion, with the dural flap based anteriorly. Another dural incision is then connected to the C-shaped dural incision with the dural flap based medially along the superior sagittal sinus. In cases of severe brain swelling, an intraoperative ventriculostomy is performed using Paine’s technique or its modification14,16).

A self-retaining retractor is first inserted inferior to the frontal cortex using a pterional or subfrontal approach. A carotid cistern, proximal sylvian fissure, and chiasmatic cistern are opened to expose the bilateral A1 segments of the ACA. Furthermore, gyrus rectus resection and entrance into the interhemispheric fissure can expose the origin of the ipsilateral A2 segment. The retractor is then moved and inserted medial to the frontal cortex (Fig. 1C). When the inferior edge of the falx and the cingulate gyri adjacent to the ruptured aneurysm are reached, the retractor is re-inserted inferior to the frontal cortex to apply temporary clips to the origin of the ipsilateral A2 segment or bilateral A1 segments. While the origin of the ipsilateral A2 segment is the most optimal and safest point far from the ruptured pericallosal artery aneurysm, bilateral A1 segments can also be used for proximal vascular control. The ipsilateral A1 segment is clipped intermittently, following continuous clipping of the contralateral A1 segment. The duration of the temporary clipping should be minimized to avoid compromising the bilateral ACA territories.

Finally, the aneurysm is dissected and a tentative clip is applied to the rupture point. The proximal vascular control is then switched to the pericallosal artery just proximal to the aneurysm, followed by complete aneurysm dissection and neck clipping.

Proximal vascular control using a pterional or subfrontal approach is recommended in cases of a high risk of premature rupture related to surgical access and dissection of a pericallosal artery aneurysm and its parent artery. Angiographic findings, such as a contained leak of the contrast, multilobulated appearance, and large-sized ruptured aneurysms, can all be considered as risk factors of intraoperative rupture during peri-aneurysmal dissection. Furthermore, the proposed surgical technique can be mandatory if proximal vascular control is predicted to be difficult. For example, low-lying pericallosal artery aneurysms, parasagittal bridging veins hindering surgical access to the parent artery, and a rupture point or contained leak in the proximal side of the aneurysm are all indicative of difficulties in accessing the proximal parent artery interhemispherically.

The proposed combined approach also requires certain technical precautions to minimize the occlusion time of the parent vessel. The proximal vascular occlusion at the distant site should be delayed until the peri-aneurysmal area is reached interhemispherically, applied intermittently based on frequent shifting between the pterional/subfrontal and interhemispheric approaches, and only used until tentative clipping of the rupture point, thereby allowing intermittent proximal vascular control in proximity to the aneurysm interhemispherically. In addition, effective methods of cerebral protection, including induced hypertension and burst suppression on electroencephalography using propofol or pentobarbital, also need to be used.

The endovascular option is temporary balloon occlusion of a proximal vessel, although previous related reports have mostly been limited to aneurysms arising from large vessels, such as the paraclinoid internal carotid artery and basilar artery4,10,11,13,19). The critical problem with using an endovascular procedure as an adjunct to microsurgical clipping is the risk of a thromboembolism. Plus, intravenous heparinization to prevent a distal embolism can produce a bleeding tendency, making the arachnoid dissection more difficult and even generating an intracranial hemorrhage.

The proposed combined approach has certain limitations. First, it requires a larger craniotomy than a simple interhemispheric approach. Second, frequent shifting between the pterional and interhemispheric approach to alternate the proximal vascular control and aneurysmal dissection is a cumbersome process for less experienced surgeons. Third, if one or two parasagittal bridging veins are sacrificed in the anterior interhemispheric approach, the circulatory load of the venous system is collateralized via adjacent venous drainage, such as the frontal ascending draining veins and superficial sylvian vein. Thus, additional compromise of the superficial sylvian vein with the pterional approach can lead to venous infarction. Fortunately, the dissection of the proximal sylvian fissure for access to the A1 or proximal A2 segment is only minimal.

When using an anterior interhemispheric approach for a ruptured pericallosal artery aneurysm, if the risk of intraoperative rupture is high and proximal vascular control is technically difficult, a combined pterional or subfrontal approach to expose the bilateral A1 segments or the origin of the ipsilateral A2 segment of the ACA can be useful for proximal vascular control.