Background/Objectives: Current bone-based landmark approaches have shown variable accuracy and poor reproducibility. We validated a two-point “tuberculum sellae–anterior clinoid process” (TS–ACP) line traced on routine 3D-computed tomography angiography (CTA) for predicting distal dural ring (DDR) position and quantified the interobserver agreement. Methods: We retrospectively reviewed data from 85 patients (87 aneurysms) who were treated via clipping between June 2012 and December 2024. Two blinded neurosurgeons classified each aneurysm as extradural, intradural, or straddling the TS–ACP line. The intraoperative DDR inspection served as the reference standard. Diagnostic accuracy, χ² statistics, and Cohen’s κ were calculated. Results: The TS–ACP line landmarks were identifiable in all cases. The TS–ACP line classification correlated strongly with operative findings (χ² = 138.3, p = 6.4 × 10⁻²⁹). The overall accuracy was 89.7% (78/87), and sensitivity and specificity for identifying intradural aneurysms were 94% and 82%, respectively. The interobserver agreement was substantial (κ = 0.78). Nine aneurysms were misclassified, including four cavernous-sinus lesions that partially crossed the DDR. Retrospective fusion using constructive interference in steady-state magnetic resonance imaging corrected these errors. Conclusions: The TS–ACP line represents a rapid, reproducible tool that reliably localizes the DDR on standard 3D-CTA, showing higher accuracy than previously reported single-landmark techniques. Its high accuracy and substantial inter-observer concordance support incorporation into routine preoperative assessments. Because the method depends on only two easily detectable bony points, it is well-suited for automated implementation, offering a practical pathway toward artificial intelligence-assisted stratification of paraclinoid aneurysms.

Background: Adult moyamoya disease (MMD) is a progressive steno-occlusive cerebrovascular disorder for which surgical revascularization is the primary treatment. The standard direct superficial temporal artery–middle cerebral artery (STA-MCA) bypass uses the frontal and/or parietal branch of the STA as the donor. However, in some patients, conventional STA-MCA bypass may be suboptimal because of a large mismatch in caliber between the STA branch and the recipient artery, increasing the risk of cerebral hyperperfusion. This study aimed to investigate the impact of a modified STA-MCA bypass on MMD treatment. Methods: We retrospectively reviewed adult cases of MMD at our institution (2012–2025) for patients who underwent modified direct STA-MCA bypass using a small side branch of the STA as the donor artery. Surgical techniques and clinical outcomes of these cases were analyzed descriptively. Results: Five cases (five hemispheres in four patients) underwent side-branch STA-MCA bypass. All procedures were completed successfully, with 100% graft patency confirmed by intraoperative indocyanine green angiography, and a mild increase in cerebral blood flow confirmed by postoperative single-photon emission computed tomography. No patients developed postoperative cerebral hyperperfusion syndrome or wound healing complications. Clinically, all patients experienced a stable or improved neurological status, with no reported new ischemic or hemorrhagic events during follow-up. Conclusions: In this small feasibility series, the side-branch STA–MCA bypass was technically feasible and safe, with no cerebral hyperperfusion syndrome observed. Any risk-mitigating effect on hyperperfusion remains theoretical and requires confirmation in comparative studies.