Background/purpose Various aneurysm animal models have been utilized to study the histological reaction post coil embolization. Our aim was to evaluate the imaging findings at day 14 of a rat external carotid artery side wall aneurysm treated with coil embolization using a gradient echo sequence on 7 T MRI and to correlate this with the histological findings.

Materials and methods Male Sprague Drawley rats were utilized to create a sidewall external carotid artery blind pouch aneurysm. A 5 mm segment of hydrocoil or bare platinum coil was inserted into the created aneurysm. Five sham operated rats were used as controls. The arterial construct was harvested on day 14. The block of tissue was evaluated with histopathology and immunohistochemistry. Prior to sacrifice, the animal underwent 7 T MRI. Statistical analysis was then performed to assess the correlation of signal abnormality with intra-aneurysmal thrombus formation on histology.

Results 10 rats were used for the experiment. Five rats had implantation of hydrocoils and five of bare platinum coils. There was a statistically significant linear correlation between the intra-aneurysmal thrombus on histology and gradient echo 7 T MRI sequences. There was no correlation demonstrated in the hydrocoil implanted group. No thrombus or abnormal signal was seen in the sham group.

Conclusions In our experiment, thrombus formation in aneurysms treated with bare platinum coils is well correlated with the presence of abnormal signal on 7 T MRI at 14 days. No correlation was appreciated in the hydrocoil implanted group due to the presence of intra-aneurysmal reactive tissue instead of thrombus.