Anatomy and Histology of the Petrous Carotid Membrane: Application to Skull Base Surgery

BACKGROUND: Published reports regarding the tissue types that surround the internal carotid artery (ICA) as it travels through the carotid canal vary. Reports have var-iably defined this membrane as periosteum, loose areolar tissue, or dura mater. With such discrepancies and real-izing that knowledge of this tissue might be important for skull base surgeons who expose or mobilize the ICA at this location, the present anatomical/histological study was performed.METHODS: In 8 adult cadavers (16 sides), the contents of the carotid canal were evaluated; specifically, the mem-brane surrounding the petrous part of the ICA was studied, and its relationship to the deeper lying artery was observed. These specimens were stored in formalin and submitted for histological evaluation.RESULTS: Grossly, the membrane within the carotid canal traversed the entire carotid canal and was loosely adherent to the underlying petrous part of the ICA. Histologically, all membranes surrounding the petrous part of the ICA were consistent with dura mater. The dura mater of the carotid canal had an outer endosteal layer and an inner meningeal layer as well as a clear dural border cell layer in most specimens that approximated and was loosely applied to the adventitial layer of the petrous part of the ICA.CONCLUSIONS: The membrane that surrounds the petrous part of the ICA is dura mater. To our knowledge, this is the first histological investigation of this structure and thus serves to establish the true identity of this membrane and correct previous reports in the literature that have errone-ously concluded that it is periosteum or loose areolar tissue.