[Topography and morphometry of the porus trigeminus].
The trigeminal nerve passes from the posterior to the middle cranial fossa above the superior edge of the petrous part and below attachment of the tentorium cerebelli. Behind this place it is surrounded by the dural trigeminal cave which opens posteriorly as the porus trigeminus. The aim of this study was to describe the porus trigeminus along with its relation to the trigeminal nerve and selected structures around. The study was performed on the material of 20 human, formalin fixed specimens of the cranial base. Measurements were taken with a surgical microscope with an ocular ruler, with precision of 0.2 mm. Mean width of the porus was 7.3 (+/-1.0) mm and height 2.2 (+/-0.4) mm. Dimensions of the trigeminal nerve within the porus were 5.8 (+/-0.8) mm and 2.1 (+/-0.4) mm, respectively. The porus is surrounded by shallow ellipsoid hollow measuring 12.1 (+/-1.8) over 5.1 (+/-1.1) mm. Relation of the porus to the petrous vein was described, as well as to other veins emptying to the dural sinuses in its vicinity. Distances between the porus and venous dural openings were very variable. The following distances were measured from the porus trigeminus to: the internal acustic porus [6.6 (+/-1.7) mm], jugular foramen [16.2 (+/-1.8) mm], jugular tubercle [18.9 (+/-1.8) mm], abducent nerve [5.9 (+/-1.2) mm], trochlear nerve [4.6 (+/-1.4) mm], oculomotor nerve [8.4 (+/-1.9) mm], posterior clinoid process [14.7 (+/-1.8) mm] and median plane [left 13.7 (+/-1.0), and right 13.5 (+/-1.9) mm]. Obtained results may be helpful during planning surgical approaches to the Meckel's cave and petroclival region.