The basement membrane thickened, while the internal elastic lamina thinned and disrupted in the >24 months old group, and the internal elastic laniina branched into media and the lipid deposited in the internal elastic lamina.

• （3）24月龄以上组基增厚，内弹性膜变薄，不均质，边缘伸出分支到中膜，内皮细胞和平滑肌细胞向内弹性膜穿过，内弹性膜内出现脂质，并有分层、断裂现象，胶原纤维增多。