The variations of osseous structure of the ınternal acoustic canal: an anatomical study

•Facial canal crest and double parallel transverse crests are unprecedented findings.•IAM anatomy variations may explain disease course differences.•Awareness of anatomical variations in the IAM may help improve surgical outcomes. The internal acoustic meatus is an osseous canal that connects the inner ear to the posterior cranial fossa. It is located in the petrous portion of the temporal bone. A thin cribriform osseous plate known as the fundus is situated at the lateral end of the canal. This study assesses the structural and numerical variations of the fundus formations. Fifty-four temporal bones of unknown gender and age were examined with the surgical microscope. The temporal bones analyzed were 46.2% right-sided and 53.7% left-sided. Only one temporal bone had two parallel transverse crests, while three had a single anterior crest that split into two branches posteriorly. The number of foramina at the transverse crest varied, with 29.6% having none, 48.1% having a single foramen, and 22.2% having several foramina. An anterior crest structure was seen in 53.7% of the temporal bones, with 5% having a slightly constricted entry to the facial canal. In cases with a single nerve foramen, 48.1% had one, while 51.8% had more than one, including examples with three or four foramina. A crest was found between the foramina of the single nerve in 7% of patients. Furthermore, a crest between the saccular nerve foramen and the high fiber foramina was seen in 25.9% of cases, and 5% had two saccular nerve foramina. We think that revealing the anatomical, structural and numerical variations in the fundus will be useful in explaining the disease-symptom relationship. Level 4.