This study, approved by the relevant institutional review board and exempted from requiring informed consent due to its retrospective design, was a retrospective analysis of 25 patients with unruptured dorsal ICA aneurysms that were 4 mm or less in diameter. These patients were selected from a group of 42 consecutive patients with superior paraclinoid aneurysms who underwent microsurgery between 2017 and 2022. The mean patient age was 54.4 years (range, 34 to 76 years), with a gender distribution of 9 men and 16 women. There were 17 cases involving the left ICA and 8 cases involving the right ICA. The mean aneurysm size was 3.3 mm (range, 2.5 to 4 mm). Before surgery, all patients underwent computed tomography angiography (CTA) to assess the relationship between the aneurysm, ophthalmic artery, and ACP. Three-dimensional (3D) CTA with bone images proved highly valuable in devising surgical strategies, as it provided a clear depiction of the anatomical relationships between the aneurysm, ICA, and ACP. Digital subtraction angiography (DSA) was performed on 11 patients, and 3D DSA images aided in allowing for more accurate determination of the projection type of aneurysm by confirming its proximity to the ophthalmic artery.

Preoperatively and postoperatively, all patients were subjected to neurological examinations to monitor changes in consciousness and potential optic nerve damage. To confirm the success of the clipping, postoperative CTA was performed for all patients.

A pterional approach on the ipsilateral side was employed for all patients. To ensure proximal control without the need for additional ACP removal, the cervical ICA was meticulously exposed and secured from the ipsilateral neck. Following dural opening, the Sylvian fissure was left intact, and the carotid and optic cisterns were directly opened to expose the optic nerve and ICA. If immediate exposure of the aneurysm allowed possible neck clipping, direct neck clipping was performed without removing the falciform ligament or ACP after a temporary clip was placed on the cervical ICA (Fig. 1A, B). If the aneurysm was partially obscured by the falciform ligament, the ligament was incised using a sickle knife to expose the aneurysm. If this exposure was adequate for direct clipping without further ACP removal, a temporary clip was placed on the cervical ICA, and direct clipping was performed (Fig. 1C, D, E). If full exposure of the aneurysm remained insufficient even after cutting the falciform ligament, partial ACP drilling was conducted, followed by the same clipping method (Fig. 1F, G, H, I). Care was taken during aneurysm clipping to avoid optic nerve damage. Given the tendency of dorsal ICA aneurysms to occur at branch-free locations, the clips were positioned as parallel as possible to the ICA to prevent clip slippage and ICA twisting after the aneurysm was covered with a thin slice of cotton.

Among the 25 dorsal ICA aneurysms treated with microsurgical clipping, 8 (32%) were immediately exposed upon opening the carotid and optic cistern, allowing for clipping without the need to remove the falciform ligament or ACP. Clipping was possible after solely cutting the falciform ligament in 5 cases (20%), while in the remaining 12 cases (48%), partial ACP removal was performed after cutting the falciform ligament due to incomplete aneurysm exposure (Fig. 2). ACP removal was deemed unnecessary if the aneurysm was located distal to the ACP in all patients’ 3D CTA with bone images. Clipping was successfully performed for all patients, and postoperative CTA confirmed the complete clipping of the aneurysms without remnants. Postoperative assessments revealed modified Rankin Scale scores of 0 for all patients, with no significant postoperative complications, such as cerebral infarction, postoperative hemorrhage, or visual symptoms.

For each patient, the following data are summarized in Table 1: age, sex, aneurysm location, size, ACP removal status, falciform ligament cutting status, complications, postoperative modified Rankin Scale score, and visual symptoms.

The patient, a 38-year-old woman, had a 2.5-mm aneurysm on the right ICA, detected by brain magnetic resonance angiography (MRA) during a routine health checkup. Preoperative DSA revealed a dorsal ICA aneurysm distal to the ophthalmic artery (Fig. 3A). As per 3D CTA with bone image this aneurysm was located distal to the ACP, suggesting that ACP removal would not be necessary during surgery (Fig. 3B). We used the right pterional approach. The aneurysm was immediately exposed after opening the carotid and optic cisterns (Fig. 3C). We first wrapped the aneurysm in a thin slice of sheet to prevent clip slippage, then clipped it completely without cutting the falciform ligament or removing the ACP (Fig. 3D). The patient had an uneventful postoperative course and was discharged without any neurological deficits.

A 54-year-old woman presented with a 3-mm unruptured dorsal ICA aneurysm identified on CTA. This aneurysm was located distal to the ACP on 3D CTA with bone image, suggesting that ACP removal would not be necessary (Fig. 4A). In the operative field, the aneurysm was not fully exposed due to its proximity to the falciform ligament (Fig. 4B). After the falciform ligament was cut, the aneurysm was fully exposed without ACP removal and successfully clipped (Fig. 4C, D). The patient recovered well and was discharged without any neurological deficits.

A 34-year-old woman presented with a 4-mm unruptured dorsal ICA aneurysm detected on brain MRA. Preoperative DSA revealed the aneurysm with a bleb located distal to the ophthalmic artery (Fig. 5A). 3D CTA with bone image revealed that the aneurysm was medial, not distal, to the ACP, suggesting that partial removal of the ACP would be required (Fig. 5B). As anticipated, the aneurysm was observed intraoperatively to be partially obscured by the falciform ligament and ACP (Fig. 5C). Initially, the falciform ligament was cut with a sickle knife. As the aneurysm was still not fully exposed, the ACP was partially removed using a highspeed drill, which sufficiently exposed the aneurysm (Fig. 5D). Finally, the aneurysm was completely clipped without any difficulty (Fig. 5E). The patient had an uneventful postoperative course and was discharged without any neurological deficits.