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Original Research
An angiographic atlas of intracranial arterial diameters associated with cerebral aneurysms
  1. J Mocco1,
  2. John Huston2,
  3. Kyle M Fargen3,
  4. James Torner4,
  5. Robert D Brown Jr5
  6. for the International Study of Unruptured Aneurysms Investigators
  1. 1Department of Neurosurgery, Vanderbilt University, Nashville, Tennessee, USA
  2. 2Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
  3. 3Department of Neurosurgery, University of Florida, Gainesville, Florida, USA
  4. 4Department of Epidemiology, University of Iowa, Iowa City, Iowa, USA
  5. 5Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA
  1. Correspondence to Dr Kyle M Fargen, Department of Neurosurgery, University of Florida, Box 100265, Gainesville, FL 32610, USA; Kyle.fargen{at}neurosurgery.ufl.edu

Abstract

Introduction The successful treatment of intracranial aneurysms is dependent on a full understanding of the anatomic relationship of a given aneurysm to its parent artery(s) and nearby branches. Furthermore, new endovascular technologies are often limited by size constraints. Currently, there is no complete atlas describing diameters for each major intracranial arterial segment. We sought to obtain these data by performing a systematic analysis of selected cerebral angiography images from the International Study of Unruptured Intracranial Aneurysms (ISUIA).

Methods Four hundred and forty-five patients with unruptured intracranial aneurysms from the ISUIA database were reviewed. Using previously described techniques, artery diameters were measured for all arteries involved in the aneurysm neck for each patient.

Results Measurements were obtained from 695 different aneurysm-associated arterial segments among 445 patient angiograms (mean 1.6 measurements per aneurysm). Artery diameters, mean, median, SEM and IQRs based upon the different arterial segments are presented.

Conclusions This angiographic almanac of aneurysm-associated intracranial arterial diameters may be of benefit in establishing standard norms through which devices, protocols and research aims may be developed.

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Introduction

The successful treatment of intracranial aneurysms is dependent on a full understanding of the anatomic relationship of a given aneurysm to its parent artery(s) and nearby branches. Although detailed imaging morphometrics have been provided for some important arterial segments,1–4 there is no complete atlas describing diameters for each major intracranial arterial segment. Additionally, there is no comprehensive database of intracranial vasculature segment diameters developed from angiography rather than post mortem cadaveric dissection. Given that the endovascular management of aneurysms is closely dependent upon local aneurysm and parent artery characteristics and that new technologies are often limited by size constraints, a detailed almanac of intracranial parent artery diameters would be of value to the literature. We sought to obtain these data by performing a systematic analysis of selected cerebral angiography images from the International Study of Unruptured Intracranial Aneurysms (ISUIA).5

Methods

ISUIA is an international multicenter study of treated and untreated patients with unruptured intracranial aneurysms that required central review of cerebral angiograms.5 Four hundred and forty-five patients with unruptured intracranial aneurysms from the ISUIA database were selected; 150 were selected randomly and 395 had been previously identified and prepared as part of an unrelated case–control study, with a 3:1 ratio of aneurysms that did not and did rupture during follow-up. All patients had an unruptured intracranial aneurysm confirmed by angiography and met prior inclusion and exclusion criteria for ISUIA. Fusiform aneurysms were excluded from the initial ISUIA study and were therefore excluded from this analysis. All measurements were made from catheter angiograms which were required for all cases entered into ISUIA. The origination of this analysis was to focus upon the diameter of arteries specifically associated with a given aneurysm, so a complete survey of each individual patient's vasculature was not performed. Rather, only measurements of those arteries directly in contact with an aneurysm were performed for each angiogram. Using previously described techniques,6 artery diameters were measured for all arteries involved in the aneurysm neck to the nearest 0.5 mm. Measurements were performed from a site at the proximal neck of the aneurysm to the opposite arterial wall in a perpendicular plane (figure 1). If additional branches were involved in the neck of the aneurysm (eg, a terminal or bifurcation aneurysm), then each artery associated with the aneurysm neck was measured at the point nearest to the aneurysm neck where a circumferential artery could be identified and a perpendicular drawn. A limited number of aneurysms had dilated or dolichoectatic parent vessels; these were measured at the nearest point to the neck of the aneurysm to be consistent with the overall study methodology. It was felt that these targeted measurements were of specific value, as the primary information of relevance in aneurysm treatment technology development and aneurysm pathogenesis evaluation is the anatomy of those arteries involved in the aneurysmal origin. While it is unknown whether there is a significant difference in the ‘typical’ diameter of normal arteries compared with those harboring aneurysms, it was our hope to determine arterial diameters with particular relevance to arteries associated with aneurysms.

Figure 1

Diagram depicting parent vessel artery measuring protocol.

Results

A total of 445 cases were reviewed. Measurements were obtained from 695 different aneurysm-associated arterial segments (mean 1.6 measurements per aneurysm). Artery diameters (mean and SEM) based on the different arterial segments are displayed in table 1.

Table 1

Mean parent and associated artery diameters for all aneurysms at all locations

Discussion

Arterial diameter is of particular importance when choosing endovascular technologies for the treatment of cerebral aneurysms as the diameter may dictate which devices may be employed. This has become increasingly relevant with the development of intracranial stents, balloons and flow diverters as these devices have dimensions that must comply with the given parent arterial diameter for safe and effective use. While it is evident that, for any individual patient, the particular aneurysm and associated arterial diameters should be measured prior to treatment decisions being made (thereby ensuring selection of the optimal technologies for treatment), a listing of angiographic parent artery diameters provides significant value in establishing standard values through which devices, protocols and research aims may be developed. Detailed anatomic reports based on imaging have been provided for certain arterial segments in patients without aneurysms.1–4 However, no complete listing of arterial diameters for the majority of segments affected by aneurysms currently exists in the literature. The goal of this project was therefore to provide the average arterial diameter for patients with cerebral aneurysms affecting each particular segment based upon angiographic imaging, so that clinicians, researchers and device engineers might have norms to facilitate further research and technologic innovation. We did consider measuring all arteries from a given patient, but it was decided only to measure those segments of an angiogram that were directly involved in an aneurysm. This methodology was specifically chosen in order to avoid any potential inaccuracy should there be an as yet unrecognized difference in those arteries harboring aneurysmal pathology versus those that do not. As it is our intention to provide data relevant to morphology analyses and technology development associated with intracranial aneurysms, we felt limiting each individual analysis to those arteries affected by the aneurysm would provide the most accurate arterial measurements.

ISUIA is a multicenter international prospective and retrospective study aimed at describing the natural history of unruptured intracranial aneurysms. The initial results, including nearly 2000 aneurysms in nearly 1500 patients, were published in 1998.5 Further analyses, including a more detailed account of prospectively assessed aneurysm rupture risks based upon size and location, were published in 2003.7 The data provided by the ISUIA investigators represent the largest study of unruptured aneurysms. This database represents an appropriate sample population for obtaining average arterial diameters, especially given that measurements made from this population form the foundation of widely-used rupture risk estimates.

An interesting observation from the data is the number of arterial segments with mean diameters of <2 mm, most notably the anterior communicating artery, A2 segment, posterior communicating artery and M2 segment. These are common locations for stent deployment for the purposes of stent-assisted aneurysm coiling; however, there are currently no stents on the market indicated for use in arteries that are <2 mm in size. These data suggest that stent-assisted treatment of aneurysms involving these arteries may occasionally not be in accordance with the prescribed instructions for use (IFU) of devices. Several studies suggest that self-expanding stents for aneurysm embolization may still be used safely in arteries smaller than dictated in the IFU.8–10 Development and refinement of endovascular technologies based upon accurate cerebral arterial size, using a delineation of such diameters as presented here, may be an important step in expanding the versatility of devices while optimizing safety and efficacy through improved conformability to actual human arterial diameters.

It is important to note the several limitations in this study. Most notable is the low number of measurements for certain arterial segments. This limitation was present despite analyzing almost 450 separate patient studies and, while further analysis would always be better, the logistical and overall labor burden limited our analysis to this total number of cases at this time. Furthermore, there is inherent error in obtaining artery measurements, a limitation discussed in detail in the previous ISUIA methodology paper.6

Conclusions

We provide aneurysm-associated parent artery diameters for 445 patients with cerebral aneurysms. This angiographic almanac of aneurysm-associated intracranial arterial diameters may be of benefit in establishing standard norms through which devices, protocols and research aims may be developed.

References

View Abstract

Footnotes

  • Contributors All authors made substantial contributions to the conception and design, acquisition of data or analysis and interpretation of data; drafted or critically revised the article; and gave final approval of the version to be published.

  • Funding This work is supported by grants NS068092 ‘Predictors of Long-Term Outcome of Unruptured Intracranial Aneurysms’ and NS028492 ‘Unruptured Intracranial Aneurysms: Neurologic Outcome’ from the National Institute of Neurological Disorders and Stroke.

  • Competing interests None.

  • Ethics approval Ethical approval was obtained from the Institutional Review Board at the Mayo Clinic.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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