title: The paraclinoid aneurysms and the distal dural ring: a new classification.
abstract: OBJECTIVE
  The aneurysms of the paraclinoid region are a heterogeneous group of lesions, whose terminology and classification are contradictory because of the complex anatomy and the lack of key anatomical references. A surgical anatomical study to identify an anatomical reference is presented, a new classification of these aneurysms is proposed, and radiological guidelines are given to distinguish an intra from extradural lesion on the x-rays.
  
  
  METHODS
  A surgical anatomical study of the paraclinoid region has been performed on 10 human cadaveric heads, formalin-fixed and injected with colored silicone rubber, and on skulls, with particular emphasis on the distal dural ring (DDR), anterior clinoid process (ACP) and their relationships with the cavernous, clinoid and ophthalmic segments of the internal carotid artery. On the basis of anatomical considerations a new classification of the aneurysms of the paraclinoid region centered on the DDR has been presented. Furthermore, 50 skulls and 5 injected cadaveric heads underwent radiological evaluation in order to develop x-ray criteria to identify the DDR.
  
  
  RESULTS
  The key anatomical element is the DDR. This allows the differentiation of aneurysms of the paraclinoid region into 4 groups (supra-DDR, para-DDR, infra-DDR, transitional). The radiological identification of the planum sphenoidale, tuberculum sellae and optic canal allows to distinguish intra versus extradural lesions.
  
  
  CONCLUSIONS
  A new classification of the aneurysms of the paraclinoid region which uses the DDR as key anatomical element is proposed. Radiological guidelines able to identify the DDR and, thus, to distinguish intra versus extradural aneurysms are provided.
authors.affiliation: Department of Neurosurgery, Neuroscience Institute and the University of Cincinnati College of Medicine, Ohio 45267, USA. berettafederica@yahoo.com
authors.forename: F
authors.initials: F
authors.lastname: Beretta
mesh_terms: D002343:Carotid Artery, Internal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000473:pathology; D020215:Carotid Artery, Internal, Dissection / Q000145:classification* / Q000000981:diagnostic imaging / Q000473:pathology; D002426:Cavernous Sinus / Q000033:anatomy & histology; D002533:Cerebral Angiography; D035262:Cranial Fossa, Anterior / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D035301:Cranial Fossa, Middle / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D004388:Dura Mater / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006801:Humans; D002532:Intracranial Aneurysm / Q000145:classification* / Q000000981:diagnostic imaging / Q000473:pathology; D009802:Oculomotor Nerve / Q000033:anatomy & histology; D009880:Ophthalmic Artery / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D009900:Optic Nerve / Q000033:anatomy & histology; D012658:Sella Turcica / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D013100:Sphenoid Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging