Development of an experimental model for the study of the ossification of the petro‐occipital fissure and its ties to age‐related hearing loss

Age changes in the human posterior cranial base – particularly the petro‐occipital fissure (POF) – is poorly understood. Aging in this region has recently been shown to be tightly regulated and correlate with onset of age‐related hearing loss (AHL), although functional associations are not established. The cochlear aqueduct (CA) communicates the inner ear with the sub‐arachnoid space through its opening into the posterior POF, thus raising questions of related aging changes among POF, CA, and AHL. Although most studies on hearing/AHL are on rats or mice, their POF region has not been documented. Our objective is to develop a protocol for micro‐dissection approaches that allows for consistent/replicable visualization of POF and landmark structures (e.g., fissure dimension, CA opening) in rats. Dry skull dissections using diamond drill bits were done to define the POF and identify the location of the CA cannaliculus. Three approaches were tested on fresh specimens: midsagittal, permitting simultaneous endocranial/exocranial visualization; ventral neck, for an exocranial view; and dorsal, removing the cranial vault for an endocranial view. While each has value, only the ventral approach did not disfigure the bony anatomy and preserved all the landmarks in their original positions. Establishment of this protocol will set the stage for an experimental model to evaluate our hypothesis.