OBJECTIVE: To investigate the hemodynamic mechanism of pseudoaneurysm in the anterior communicating artery (AcoA) area in magnetic resonance (MR) angiography. METHODS: For the clinical study, a total of 62 patients who undertook digital subtraction angiography (DSA) because of the rupture of an aneurysm originating from a location other than the AcoA area were examined with MR angiography. The relation between signal defect at the AcoA in MR angiography and anatomic variation of the anterior cerebral artery (ACA) was evaluated. For the experimental study, MR angiography and DSA were performed on elastic silicon vascular phantoms with 2 different bifurcation angles (70 degrees and 140 degrees). Hemodynamic factors producing signal defects were evaluated, and the results were compared by computational fluid dynamics (CFD). RESULTS: In a clinical study, 21 of 62 patients had a hypogenetic A1 segment on either side of the ACA. Their MR angiography showed signal defects in the axilla area of the bifurcated AcoA complex in 14 patients, 7 of which could make the residual normal vessel seem to be an aneurysm. All the cases with an intact AcoA complex showed no signal defect. In an experimental study, MR angiography of vascular phantoms with broad-angle bifurcation (140 degrees) showed signal defects at the axilla areas of bifurcation, and these were shown as turbulent flow in DSA and CFD. Phantoms with narrow-angle bifurcation (70 degrees) did not show a significant signal defect, however. CONCLUSIONS: A hypoplastic A1 segment accompanying a broad bifurcation angle of the contralateral A1 segment may cause a pseudoaneurysm in MR angiography because of signal defect in the AcoA area.
OBJECTIVE: To investigate the hemodynamic mechanism of pseudoaneurysm in the anterior communicating artery (AcoA) area in magnetic resonance (MR) angiography. METHODS: For the clinical study, a total of 62 patients who undertook digital subtraction angiography (DSA) because of the rupture of an aneurysm originating from a location other than the AcoA area were examined with MR angiography. The relation between signal defect at the AcoA in MR angiography and anatomic variation of the anterior cerebral artery (ACA) was evaluated. For the experimental study, MR angiography and DSA were performed on elastic silicon vascular phantoms with 2 different bifurcation angles (70 degrees and 140 degrees). Hemodynamic factors producing signal defects were evaluated, and the results were compared by computational fluid dynamics (CFD). RESULTS: In a clinical study, 21 of 62 patients had a hypogenetic A1 segment on either side of the ACA. Their MR angiography showed signal defects in the axilla area of the bifurcated AcoA complex in 14 patients, 7 of which could make the residual normal vessel seem to be an aneurysm. All the cases with an intact AcoA complex showed no signal defect. In an experimental study, MR angiography of vascular phantoms with broad-angle bifurcation (140 degrees) showed signal defects at the axilla areas of bifurcation, and these were shown as turbulent flow in DSA and CFD. Phantoms with narrow-angle bifurcation (70 degrees) did not show a significant signal defect, however. CONCLUSIONS: A hypoplastic A1 segment accompanying a broad bifurcation angle of the contralateral A1 segment may cause a pseudoaneurysm in MR angiography because of signal defect in the AcoA area.