Accuracy of CT angiography in the assessment of the circle of Willis: comparison of volume-rendered images and digital subtraction angiography

Acta Radiol. 2011 Oct 1;52(8):889-93. doi: 10.1258/ar.2011.110223. Epub 2011 Jul 29.


Background: Computed tomography angiography (CTA) is increasingly used for non-invasive imaging of the cerebrovascular diseases.

Purpose: To evaluate the accuracy of CTA in the assessment of the variation of the segment calibers of the circle of Willis.

Material and methods: One hundred and 17 patients with acute SAH (51 men and 66 women, mean age 50.9 years) who underwent CTA using a 16 detector-row CT scanner and DSA were evaluated retrospectively. The CTA and DSA studies were performed within 24 h after the onset of symptoms and within 24 h of each other. A total of 819 arterial segments (A-comA, right and left A1 segment, right and left P-com A, and right and left P1 segment) of the circle of Willis were determined to be aplastic (grade 1), hypoplastic (grade 2), or normal-sized (grade 3) by blinded observers evaluating CTA volume-rendered images. The CTA results were then compared with findings on the corresponding DSA images (reference standard).

Results: The overall agreement between CTA and DSA was 92.4%. We had 62 (7.6%) cases of disagreement (58 cases of under-estimation and four cases of over-estimation by CTA) between tow modalities. The sensitivity and specificity of CTA in the detection of aplastic and normal-sized segments were more than 90%. In contrast, subgroup analysis of the hypoplastic segments showed a sensitivity of 52.6% and a specificity of 98.2%.

Conclusion: CTA is highly accurate in the assessment of anatomical variations of the circle of Willis; however, its sensitivity is limited in depicting hypoplastic segments.

Publication types

  • Comparative Study

MeSH terms

  • Angiography, Digital Subtraction / methods*
  • Cerebral Angiography / methods*
  • Circle of Willis / diagnostic imaging*
  • Contrast Media
  • Female
  • Humans
  • Iohexol
  • Male
  • Middle Aged
  • Radiographic Image Interpretation, Computer-Assisted
  • Retrospective Studies
  • Sensitivity and Specificity
  • Subarachnoid Hemorrhage / diagnostic imaging*
  • Tomography, X-Ray Computed / methods*


  • Contrast Media
  • Iohexol