Anatomical triangles defining routes to anterior communicating artery aneurysms: the junctional and precommunicating triangles and the role of dome projection

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  • 1 Department of Neurological Surgery, University of Miami, Florida;
  • 2 Department of Neurological Surgery, University of California, San Francisco, California; and
  • 3 Department of Neurological Surgery, Barrow Neurological Institute, Phoenix, Arizona


Anterior communicating artery (ACoA) aneurysms are common intracranial aneurysms. Despite advances in endovascular therapy, microsurgical clipping remains an important treatment for aneurysms with broad necks, large size, intraluminal thrombus, complex branches, or previous coiling. Anatomical triangles identify safe corridors for aneurysm access. The authors introduce the A1-A2 junctional triangle and the A1-A1 precommunicating triangle and examine relationships between dome projection, triangular corridors of access, and surgical outcomes.


Preoperative catheter and CT angiograms were evaluated to characterize aneurysm dome projection. Aneurysm projection was categorized into quadrants and octants. Preoperative, intraoperative, and postoperative factors were correlated to aneurysm dome projection and patient outcomes using univariate and multivariate analyses.


A total of 513 patients with microsurgically treated ACoA aneurysms were identified over a 13-year period, and 400 had adequate imaging and follow-up data for inclusion. Surgical clipping was performed on 271 ruptured and 129 unruptured aneurysms. Good outcomes were observed in 91% of patients with unruptured aneurysms and 86% of those with ruptured aneurysms, with a mortality rate < 1% among patients with unruptured aneurysms. Increasing age (p < 0.01), larger aneurysm size (p = 0.03), and worse preoperative modified Rankin Scale score (p < 0.01) affected outcomes adversely. Aneurysms projecting superiorly and posteriorly required dissection in the junctional triangle, and multivariate analysis demonstrated worse clinical outcomes in these patients (p < 0.01).


Anteriorly and inferiorly projecting aneurysms involve only the precommunicating triangle, are simpler to treat microsurgically, and have more favorable outcomes. Superior and posterior dome projections make ACoA aneurysms more difficult to visualize and require opening the junctional triangle. Added visualization through the junctional triangle is recommended for these aneurysms in order to facilitate dissection of efferent branch arteries, careful clip application, and perforator preservation. Dome projection can be determined preoperatively from images and can help anticipate dissection routes through the junctional triangle.

ABBREVIATIONS ACA = anterior cerebral artery; ACoA = anterior communicating artery; FpA = frontopolar artery; ICG = indocyanine green; mRS = modified Rankin Scale; OfA = orbitofrontal artery; RAH = recurrent artery of Heubner; SAH = subarachnoid hemorrhage.

Supplementary Materials

    • Tables S1–S3 (PDF 460 KB)

Contributor Notes

Correspondence Michael T. Lawton: Barrow Neurological Institute, Phoenix, AZ.

INCLUDE WHEN CITING Published online April 5, 2019; DOI: 10.3171/2018.12.JNS183264.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.


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