Incidence, classification, and treatment of angiographically occult intracranial aneurysms found during microsurgical aneurysm clipping of known aneurysms

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OBJECTIVE

During the microsurgical clipping of known aneurysms, angiographically occult (AO) aneurysms are sometimes found and treated simultaneously to prevent their growth and protect the patient from future rupture or reoperation. The authors analyzed the incidence, treatment, and outcomes associated with AO aneurysms to determine whether limited surgical exploration around the known aneurysm was safe and justified given the known limitations of diagnostic angiography.

METHODS

An AO aneurysm was defined as a saccular aneurysm detected using the operative microscope during dissection of a known aneurysm, and not detected on preoperative catheter angiography. A prospective database was retrospectively reviewed to identify patients with AO aneurysms treated microsurgically over a 20-year period.

RESULTS

One hundred fifteen AO aneurysms (4.0%) were identified during 2867 distinct craniotomies for aneurysm clipping. The most common locations for AO aneurysms were the middle cerebral artery (60 aneurysms, 54.1%) and the anterior cerebral artery (20 aneurysms, 18.0%). Fifty-six AO aneurysms (50.5%) were located on the same artery as the known saccular aneurysm. Most AO aneurysms (95.5%) were clipped and there was no attributed morbidity. The most common causes of failed angiographic detection were superimposition of a large aneurysm (type 1, 30.6%), a small aneurysm (type 2, 18.9%), or an adjacent normal artery (type 3, 36.9%). Multivariate analysis identified multiple known aneurysms (odds ratio [OR] 3.45, 95% confidence interval [CI] 2.16–5.49, p < 0.0001) and young age (OR 0.981, 95% CI 0.965–0.997, p = 0.0226) as independent predictors of AO aneurysms.

CONCLUSIONS

Meticulous inspection of common aneurysm sites within the surgical field will identify AO aneurysms during microsurgical dissection of another known aneurysm. Simultaneous identification and treatment of these additional undiagnosed aneurysms can spare patients later rupture or reoperation, particularly in those with multiple known aneurysms and a history of subarachnoid hemorrhage. Limited microsurgical exploration around a known aneurysm can be performed safely without additional morbidity.

ABBREVIATIONS ACA = anterior cerebral artery; AChA = anterior choroidal artery; ACoA = anterior communicating artery; AO = angiographically occult; BA = basilar apex; CTA = CT angiography; DSA = digital subtraction angiography; ICA = internal carotid artery; ISUIA = International Study of Unruptured Intracranial Aneurysms; MCA = middle cerebral artery; PCA = posterior cerebral artery; PCoA = posterior communicating artery; SAH = subarachnoid hemorrhage.

Article Information

Correspondence Michael T. Lawton: Barrow Neurological Institute, Phoenix, AZ. michael.lawton@barrowbrainandspine.com.

INCLUDE WHEN CITING Published online February 22, 2019; DOI: 10.3171/2018.11.JNS182416.

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

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    AO aneurysm rate over time in years (A) and proportion of cases with and without 3D angiography in patients with and without AO aneurysms (B).

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    Case 1. A 44-year-old woman with a right PCA (P1 segment) aneurysm clipped via an orbitozygomatic transsylvian approach. During surgery an additional small BA aneurysm was found and clipped (D), which was not observed on preoperative angiography (A–C; circles indicate region of additional aneurysm found during surgery). Postoperative angiography confirmed clipping of the 2 aneurysms (E and F).

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    Case 2. A 45-year-old man with a small, ruptured ACoA aneurysm (arrow, A) that was found on catheter angiography (A–C), which was surgically clipped through a left pterional craniotomy (D and E). An additional anteriorly and inferiorly projecting unruptured ACoA aneurysm was found and clipped (F–H), which was not seen on preoperative angiography (B and C, circles indicate region of additional aneurysm found during surgery). Postoperative angiography confirmed complete occlusion of both aneurysms (I and J). iA1 = ipsilateral A1 ACA; iA2 = ipsilateral A2 ACA; HA = recurrent artery of Heubner; cA2 = contralateral A2 ACA. *known aneurysm; **occult aneurysm.

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    Case 3. A 53-year-old woman underwent clip placement for a right ICA pseudoaneurysm (asterisk, D). Preoperative catheter angiography (A–C, circles indicate region of additional aneurysm found during surgery) was not able to show an additional AO MCA aneurysm (arrow) found during surgery (E), which was clipped with temporary occlusion of the M1 segment (F and G). Postoperative CTA shows the clipped aneurysms (H). CN II = cranial nerve II.

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