Observations on experimental saccular aneurysms in the rat after 2 and 3 months.

After 2 and 3 months we re-exposed 20 experimental saccular aneurysms. Under the operating microscope, we measured their sizes and compared them with the sizes immediately after induction. All aneurysms had grown significantly and none was thrombosed. Pathological examinations showed that the sac of the aneurysm was similar to that of the human saccular aneurysms. Based on the operating microscopy and pathological findings we postulate that abnormal histological structure and haemodynamic stress are the major causes of aneurysm enlargement. We also noted that there were some regenerative processes in these experimental aneurysm walls. The results prove that this model is reliable, because these aneurysms have the main characteristics of human saccular aneurysms, not only grossly but also microscopically.