title: Nontraumatic and noninfectious pseudoaneurysms on the circle of Willis: 2 case reports and review of the literature.
abstract: BACKGROUND
  Nontraumatic and noninfectious pseudoaneurysms with similar shape of true saccular aneurysm on the circle of Willis are rare.
  
  
  METHODS
  Two patients with such pseudoaneurysms are reported, one is a 37-year-old man, the other is a 50-year-old woman. They presented with sudden headache; CT scan showed subarachnoid hemorrhage in both. Thorough medical history had been reviewed; physical and laboratory examination had been made but demonstrated no evidence of craniocerebral injury and intracranial or systematic infection. On the cerebroangiogram, they represented the same imageologic changes of true saccular aneurysm, but subsequent operation and pathologic examination revealed that they were pseudoaneurysms consisting of blood clot enclosed with a layer of connective tissue; degenerative changes may have contributed to their formation.
  
  
  CONCLUSIONS
  Careful attention should be given in classifying these saccular pseudoaneurysm from true saccular aneurysms because of their friable nature, tendency of rupture, and different pathologic findings.
authors.affiliation: Department of Neurosurgery, West China Hospital of Sichuan University, Chengdu, Sichuan 610041, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Ding
authors.forename: Chao
authors.initials: C
authors.lastname: You
authors.forename: Hao
authors.initials: H
authors.lastname: Yin
mesh_terms: D000328:Adult; D017541:Aneurysm, False / Q000175:diagnosis* / Q000209:etiology / Q000601:surgery*; D002941:Circle of Willis; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000175:diagnosis* / Q000209:etiology / Q000601:surgery*; D008297:Male; D008875:Middle Aged