The endoscopic endonasal approach (EEA) has emerged as an effective surgical intervention for various cranial pathologies including meningiomas and pituitary adenomas. During expanded EEA to skull base lesions, reliable and consistent landmarks for the medially positioned CN VI become critical to prevent its iatrogenic injury. 

Thirty-five adult cadaveric heads were dissected bilaterally, yielding 70 PPsb specimens for analysis. Digital calipers were used to measure PPsb width, dorsum sellae width, sellar floor width, the distance from the tuberculum sella to the dorsum sellae, and the distance from the PPsb to the foramen lacerum, as well as their relationship to the intracranial course of CN VI. Statistical analyses were performed to assess the consistency of these anatomic relationships.  

Cisternal, interdural, and cavernous segments of CN VI were identified from a transcranial approach. The PPsb formed the osseous floor of the inferomedial compartment of the cavernous sinus, demarcating the transition between the cavernous and interdural segments of CN VI. The PPsb was a bilaterally symmetrical structure, measuring 3.68 mm (SD=0.35, SEM=0.06) on the right and 3.55 mm (SD=0.35, SEM=0.06) on the left, respectively, with no significant differences between sides. It was present bilaterally in all but one specimen (n=34, 97.1%), in which hyperostosis of the inner table of the petrous apex distorted its structure unilaterally and thereby its relationship to the right abducens nerve. 

The PPsb was an accurate, reproducible landmark for CN VI from its interdural to cavernous segments. Intraoperative use of the PPsb may inform early CN VI identification and safer expanded EEA to skull base tumors, although variations from osseous pathology warrant further study.