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Petrous part of temporal bone Pars petrosa ossis temporalis

As its name suggests, the Pars Petrosa (Hard, Petrified) Ossis (Bone) Temporalis (Temporal Cranium) is one of three parts that make up the Temporal bone of the skull. It sits laterally adjacent to the inferior aspect of the occipital bone and forms part of the base of skull.

This thin but dense bone houses the structures of the inner ear (the Vestibulocochlear network which is predominantly responsible for hearing and balance) as well as a network of blood vessels including the second part of the carotid artery.

Blood vessel supply to and from the Vestibulocochlear network runs through the Pars Petrosa Ossis Temporalis structure, as well as innervation channels for the tympanic branch of the glossopharyngeal nerve and the auricular branch of the vagus nerve. Also passing through the Pars Petrosa Ossis Temporalis is the aquæductus cochlea which connects the perilymphatic space with the subarachnoid space and provides an anchoring point for the Dura Mater.

Blunt head trauma to the Pars Petrosa Ossis Temporalis can result in significant life-threatening injury. The shearing forces from a blow to the side of the head can fracture the bone and sever/damage the vital structures that run through it. Fractures involving the Pars Petrosa Ossis Temporalis frequently result in ‘battle sign’, or haematoma formation behind the ear, and ‘otorrhea’ as blood and cerebrospinal fluid drain from the ear through a ruptured tympanic membrane. The presence of cerebrospinal fluid in blood indicates a basal skull fracture and would prompt further investigation by Computerised Tomography (CT Scan).

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