Basal Interhemispheric Approach for Medially Oriented Internal Carotid Artery Aneurysm

Surgical approaches for medially oriented internal carotid artery aneurysms include the ipsilateral pterional approach, the contralateral pterional approach, the interhemispheric approach, and the interhemispheric-subfrontal approach. In the ipsilateral pterional approach, the internal carotid artery obstructs direct visualization of the aneurysmal neck. In the contralateral pterional approach, the aneurysmal dome is exposed before dissection of the aneurysmal neck. In the interhe-mispheric and interhemispheric-subfrontal approaches, the aneurysmal neck can be seen without mobilization of the internal carotid artery or aneurysmal dome. The interhemispheric-subfrontal approach requires too much exposure of the brain to deal with this type of aneurysm microsurgically. There are two kinds of interhemispheric approaches, i.e., the anterior interhemispheric approach (AIH) and the basal interhemispheric approach (BIH). The basal interhemispheric approach was initially developed as an approach for high-positioned anterior communicating artery aneurysms. Compared with the AIH, the BIH can provide a wider view without additional brain retraction. We applied the BIH to 3 cases of medially oriented internal carotid artery aneurysms. Two cases of carotid-ophthalmic aneurysms and one case of an aneurysm arising from the origin of the duplicated middle cerebral artery were operated on. All aneurysms were successfully clipped. Postoperative complications included cerebrospinal fluid rhinorrhea (1 case), transient oculomotor palsy (1 case), ipsilateral visual disturbance (1 case) and anosmia (2 cases). The patients were discharged in the state of ADLs 1, 2 and 3. The advantage of the BIH for medially oriented internal carotid artery aneurysms is direct visualization of the aneurysmal neck, with better anatomical orientation for surrounding structures. With decompression of the optic canal, mobilization of the optic nerve and removal of the sphenoid sinus wall, medially oriented aneurysms arising between the carotid bifurcation and the carotid cave can be clipped completely. Disadvantages of the BIH are opening of the frontal sinus, injury to the olfactory nerve, and a narrow and deep operative field. In our cases, no serious complications such as meningitis were encountered. he basal interhemispheric approach is a useful approach for medially oriented internal carotid artery aneurysms, especially those with a small neck.