Microsurgical anatomy of the sphenoid ostia.

We aimed to determine the position, number and variability of the sphenoid sinus ostia. A total of 32 dry skulls were examined under x6 magnification. The septum and nasal turbinates were removed to expose the anterior wall of the sphenoid sinus. A caliper was used for measurements. We found 2 ostia per skull, except for one (3%), in which the left ostium was absent. The inferior edges of both ostia were found at the same height in only four skulls (12.5%), and the superior edges of both ostia were found at the same height in only one skull (3%). Thus, in 27 skulls (84%) the lower and upper margins of both ostia were at different levels. The distance from the internal edge of the right ostium to the midline was 2.04mm on average (range: 0.3-5.3mm). The distance from the internal edge of the left ostium to the midline was 2.18mm on average (range: 0.2 to 5.1mm). In most skulls, the sphenoid ostia are located at different heights on each side; also a great variability in the distance from the internal border of the ostia to the midline was found. We found this anatomical knowledge useful when performing a transsphenoidal approach to the sella turcica.