Aneurysm Measurements

Management of unruptured intracranial aneurysm is traditionally based on the size of the aneurysm.

Calculations to classify aneurysms according to treatment difficulty:

  1. aspect ratio – aneurysm height-to-neck width
  2. neck width
  3. dome-neck ratio – maximum aneurysm dome width-to-neck diameter


Old criteria to define a “wide-neck” aneurysm:

  1. dome to neck ratio <2.0 [original definition by Debrun, et al]
  2. neck size >4.0  [original definition by Zubillaga, et al]

A retrospective study (2009) propose a new criteria for defining wide-neck aneurysms: (based on need to use adjunctive measures)

  1. wide neck – dome-to-neck ratio <1.6, aspect ratio <1.6
  2. very wide-neck for dome-to-neck <1.2, aspect ratio <1.2

The study found that coiling of aneurysms without adjunctive techniques (stent placement and balloon remodelling) is favored for aneurysms with aspect ratio >/=1.6, dome-to-neck ratio >/=1.6, and neck size <4mm.  Coiling with adjunctive techniques is favored for aneurysms with dome-to-neck ratios <1.2 and aspect ratios <1.2.  For aneurysms with dome-to-neck ratios or aspect ratios between 1.2 and 1.6, coiling can be done with or without adjunctive techniques.

Morphological parameters that may be associated with ruptured basilar tip aneurysms

  1. aneurysm volume
  2. aspect ratio – divide perpendicular height by the neck diameter
  3. size ratio – divide maximum eight by average composite diameter of all vessels (BAv, RPCAv, LPCAv, RSCAv, LSCAv) involved with the aneusrysm [composite diameter – average of the initial diameter of the vessel (BA1, RPCA1, LPCA1, RSCA1, LSCA1) at vessel branching point by aneurysm neck with diameter of the vessel away from the initial diameter (BA2, RPCA2, LPCA2, RSCA2, LSCA2)]
  4. aneurysm angle – angle between vectors formed by maximum height of the aneurysm and neck of the aneurysm
  5. basilar vessel angle – angle between the vector of flow and the neck of the aneurysm
  6. basilar flow angle – angle between vector of flow and vector formed by the maximum height of the aneurysm
  7. vessel to vessel angles – a study found that a larger angle between PCA (P1-P1 angle) was most strongly associated with aneurysm rupture

3D model of BTA aneurysm depicting morphological variables previously studied in the literature.

3 vessel to vessel angles -measured

  1. Parent-Daughter angle – average of two angles formed between BA and each PCA
  2. P1-P1 angle – angle formed between the two PCAs
  3. SCA-SCA angle – angle formed between the two SCAs

3D model of BTA aneurysm depicting angular variables of the surrounding vasculature.



Brinjikji, W., H.J Cloft, and D.F. Kallmes. ‘Difficult Aneurysms For Endovascular Treatment: Overwide Or Undertall?’. American Journal of Neuroradiology 30.8 (2009): 1513-1517. Web. 3 Oct. 2015.

Ho, Allen L., Amr Mouminah, and Rose Du. ‘Posterior Cerebral Artery Angle And The Rupture Of Basilar Tip Aneurysms’. PLoS ONE 9.10 (2014): e110946. Web. 2 Oct. 2015.

Sekhar, Laligam N. et al. ‘Basilar Tip Aneurysms’. Neurosurgery 72.2 (2013): 284-299. Web. 2 Oct. 2015.


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