Morphological Change of Unruptured Vertebral Artery Dissection on Serial MR Examinations. Evaluation of the Arterial Outer Contour by Basi-parallel Anatomical Scanning (BPAS)-MRI.

Basi-parallel anatomical scanning (BPAS)- MRI is a simple MRI technique to reveal the surface contour of the intracranial vertebrobasilar artery. The purpose of this study was to investigate the usefulness of BPAS-MRI for observing the temporal course of unruptured vertebral artery (VA) dissection in patients by means of serial MR examinations. Since April 2003, we performed serial MR examinations in four patients with unruptured acute vertebral artery dissection. The frequency of the MR examinations during the follow-up period in each patient varied from twice within seven months to five times within 19 months. Both MRA and BPAS-MRI were obtained in each MR examination. We investigated the course of morphological changes within the dissected artery on BPASMRI (outer contour) and on MRA (inner lumen). Although the initial MRA showed fusiform dilatation, irregular stenosis or normal caliber at the dissected lesion, the initial BPAS-MRI disclosed fusiform dilatation in all of the four patients. In two patients, MRA finding of the VA lesion had changed, though the fusiform appearance had been stationary on BPAS-MRI. Then both dissolution of the fusiform dilatation on BPAS-MRI and normalization of the inner luminal caliber on MRA were confirmed within nine months. In one patient, fusiform dilatation on both BPAS-MRI and MRA resolved simultaneously on the MR examination at eight months after the initial symptom. In another patient, fusiform dilatation of the outer contour was still enlarging on BPAS-MRI ten months after the onset, though the fusiform dilatation on MRA had been stationary since the eighth week. We performed endovascular coil embolization in this patient eleven months after the initial symptom. Resolution of the fusiform dilatation on BPAS-MRI should be a healing sign of VA dissection. Persisting the fusiform dilatation or progressively enlarging outer contour on BPASMRI may be an unstable sign. BPAS-MRI provides more information about the instability of the dissected lesion. We should obtain not only MRA but also BPAS-MRI for the course observation of unruptured VA dissection.