Letter to the Editor. How does size ratio affect the clinical result of open surgery for cerebral aneurysms?

Toshikazu Kimura MD, PhD
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  • Japanese Red Cross Medical Center, Tokyo, Japan
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TO THE EDITOR: I read with interest the article by Matsukawa et al.1 (Matsukawa H, Kamiyama H, Kinoshita Y, et al: Morphological parameters as factors of 12-month neurological worsening in surgical treatment of patients with unruptured saccular intracranial aneurysms: importance of size ratio. J Neurosurg [epub ahead of print September 21, 2018. DOI: 10.3171/2018.4.JNS173221]). They reported on their large cohort of patients with surgically treated unruptured saccular intracranial aneurysms (USIAs). They found that the ratio between the aneurysm diameter and the parent artery diameter was a factor more related to neurological worsening at 12 months after surgery than the absolute size of the aneurysm. As the article mentioned, studies based on computed flow dynamics analysis showed that size ratio and aspect ratio are related to aneurysm bleeding or to the possibility of sufficient coil embolization. However, in most cases that involve surgical clipping, we can observe the structures around the aneurysm. The patency of the related arteries should have been confirmed after application of clips or after revascularization, using Doppler sonography and/or indocyanine green video-angiography, which they should also have used. The authors speculated that a larger size ratio resulted in a need for greater manipulation of structures around the aneurysms, which caused neurological worsening. However, as they described, the size ratio is highly correlated with the maximal size of the aneurysm, since the ratio is derived by simply dividing the diameter of the aneurysm by the diameter of the parent artery. Considering previous reports noting risk factors related to surgical clipping, Matsukawa and colleagues’ results may also indicate that large aneurysms pose a higher risk of surgical morbidity. Or, owing to their good clinical outcome, the number of cases of neurological worsening was so small that the statistical power was not sufficient enough to extract the true primary risk factor after multiple regression analyses. In addition, according to their results, the specific anatomical location of the aneurysm and the presence of a postoperative ischemic lesion significantly contributed to the neurological worsening at 12 months. Generally speaking, distal basilar aneurysms are considered to be difficult-to-treat lesions due to the risk of infarction of the thalamoperforating artery. Also, large paraclinoid-segment aneurysms may pose the surgical risk of occluding the anterior choroidal artery. I suppose that there is multicollinearity between the aneurysm’s location and postoperative ischemic lesion causing neurological worsening at 12 months.

Disclosures

The author reports no conflict of interest.

References

1

Matsukawa H, Kamiyama H, Kinoshita Y, Saito N, Hatano Y, Miyazaki T, : Morphological parameters as factors of 12-month neurological worsening in surgical treatment of patients with unruptured saccular intracranial aneurysms: importance of size ratio. J Neurosurg [epub ahead of print September 21, 2018. DOI: 10.3171/2018.4.JNS173221]

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  • Stroke Center, Teishinkai Hospital, Sapporo, Japan
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Response

We appreciate the valuable comments from Dr. Kimura regarding our article.

First, as Dr. Kimura suggested, the patency of the related arteries should have been confirmed after application of clips or after revascularization by performing Doppler sonography and/or indocyanine green video-angiography; however, each of these monitoring tools has its limitations in detecting blood flow insufficiency in the perforating arteries. A perfect method for monitoring blood flow disturbance in the perforating arteries has not been established. In fact, even with confirmation of the patency of perforating arteries with either of the aforementioned intraoperative monitoring modalities and without causing direct injury to perforating arteries, an unexpected infarction due to blood flow reduction in the parent artery and/or perforating arteries branching close to the aneurysm can still occur.1–3 We strongly agree with these facts.

Second, Dr. Kimura stated, “Considering previous reports noting risk factors related to surgical clipping, Matsukawa and colleagues’ results may also indicate that large aneurysms pose a higher risk of surgical morbidity.” In this regard, we have performed multivariate analysis for 12-month neurological worsening based on the size ratio, maximum size, dome-to-neck ratio, and aspect ratio, as well other factors as covariates. After adjustment of these aneurysm morphological characteristics, size ratio was still a 12-month negative prognostic factor (Table 3 in our article). Therefore, we consider size ratio to be a risk factor for 12-month neurological worsening in surgically treated patients with USIAs, although the size ratio should be further studied in a large, prospective, observational cohort.

Third, Dr. Kimura suggested that there is multicollinearity between the aneurysm location and the presence of a postoperative ischemic lesion causing neurological worsening at 12 months. Because this is true, as stated above, we have performed multivariate analysis using aneurysm location and postoperative ischemic lesion as covariates (Table 3 in our article).

References

  • 1

    Friedman JA, Pichelmann MA, Piepgras DG, Atkinson JL, Maher CO, Meyer FB, : Ischemic complications of surgery for anterior choroidal artery aneurysms. J Neurosurg 94:565572, 2001

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  • 2

    Sakuma J, Suzuki K, Sasaki T, Matsumoto M, Oinuma M, Kawakami M, : Monitoring and preventing blood flow insufficiency due to clip rotation after the treatment of internal carotid artery aneurysms. J Neurosurg 100:960962, 2004

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  • 3

    Yaşargil MG, Yonas H, Gasser JC: Anterior choroidal artery aneurysms: their anatomy and surgical significance. Surg Neurol 9:129138, 1978

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Contributor Notes

Correspondence Toshikazu Kimura: tkim-tky@umin.ac.jp.

INCLUDE WHEN CITING Published online November 23, 2018; DOI: 10.3171/2018.10.JNS182796.

Disclosures The author reports no conflict of interest.

  • 1

    Matsukawa H, Kamiyama H, Kinoshita Y, Saito N, Hatano Y, Miyazaki T, : Morphological parameters as factors of 12-month neurological worsening in surgical treatment of patients with unruptured saccular intracranial aneurysms: importance of size ratio. J Neurosurg [epub ahead of print September 21, 2018. DOI: 10.3171/2018.4.JNS173221]

    • Search Google Scholar
    • Export Citation
  • 1

    Friedman JA, Pichelmann MA, Piepgras DG, Atkinson JL, Maher CO, Meyer FB, : Ischemic complications of surgery for anterior choroidal artery aneurysms. J Neurosurg 94:565572, 2001

    • Search Google Scholar
    • Export Citation
  • 2

    Sakuma J, Suzuki K, Sasaki T, Matsumoto M, Oinuma M, Kawakami M, : Monitoring and preventing blood flow insufficiency due to clip rotation after the treatment of internal carotid artery aneurysms. J Neurosurg 100:960962, 2004

    • Search Google Scholar
    • Export Citation
  • 3

    Yaşargil MG, Yonas H, Gasser JC: Anterior choroidal artery aneurysms: their anatomy and surgical significance. Surg Neurol 9:129138, 1978

    • Search Google Scholar
    • Export Citation

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