[On the anatomical measurements of the posterior fossa using dry skulls--from neurosurgical standpoint].

For the purpose of studying anatomy of the posterior fossa from neurosurgical standpoint, detailed observation and measurements were performed on dry skulls. In addition, literatures were reviewed concerning size and shape of the tentorial incisura, as well as anatomical locations of dural penetration of the cranial nerves, three to twelve, and numbers of their rootlets. As a cardinal landmark for posterior fossa craniotomy, junction of the transverse and the sigmoid sinuses was chosen. This corresponds to the crossing point of the following two lines: A) parieto-mastoid suture B) a line drawn from the mastoid tip perpendicular to a line connecting the mastoid tip and the inferior orbital ridge. The point also corresponds to the lateral extremity of the ridge of the petrous pyramid. Average length of the ridge of the petrous pyramid: 49.5 +/- 2.9 mm. Average distance from the lateral extremity of the ridge of the pyramis and the posterior margin of the internal acoustic meatus: 27.5 +/- 2.6 mm. Average distance from the lateral extremity of the ridge of the pyramis and that of the posterior clinoid process: 52.4 +/- 3.1 mm. Average distance from the anterior margin of the internal acoustic meatus to the lateral edge of the posterior clinoid process: 24.6 +/- 2.0 mm. Average distance from the posterior margin of the internal acoustic meatus to the posterior end of the semicircular canal: 13.1 +/- 1.9 mm. Average distance from the internal acoustic meatus to the facial canal (through which, tympanic segment of the facial nerve runs): 11.5 +/- 1.5 mm.(ABSTRACT TRUNCATED AT 250 WORDS)