Fig. 12.1 Fractures through the petrous pyramid may result from either posterior or lateral blows to the head. The skull base fractures more easily when struck from the side, on the thin temporal squamosa, than posteriorly on the thick occipital bone. Fractures resulting from temporal blows tend to propagate medially along a course parallel to the long axis of the petrous pyramid and thus are termed “longitudinal.” Strong occipital blows characteristically produce a fracture which disrupts the foramen magnum ring and then propagates anteriorly across the petrous pyramid at right angles to its long axis. These are termed “transverse fractures.” Longitudinal fractures tend to be associated with conductive hearing loss due to hemotympanum and ossicular disruption. Transverse fractures tend to break the otic capsule and result in permanent sensory hearing loss and acute vertigo. Either can produce facial nerve injury or cerebrospinal fluid leakage.

Fig. 12.2 In longitudinal temporal bone fractures, the break originates through cortical areas of weakness such as through the external auditory canal anteriorly, or through the mastoid air cells posteriorly. Fractures originating through the external canal will usually present with bloody otorrhea, a torn tympanic membrane, and a bony canal step-off. Those originating more posterior will have an intact tympanic membrane, hemotympanum, and a Battle’s sign due to blood seeping from the mastoid emissary vein. Regardless of their origin, the fractures generally pass through the middle ear space to be deflected anteriorly by the otic capsule to the foramen lacerum. The inner ear and fallopian canal are usually spared.

Fig. 12.3 Possible courses of longitudinal temporal bone fractures: the majority of fractures will terminate in the floor of the middle fossa, or in the sphenoid bone (top left). Approximately one-third will extend across the midline to be continuous with a contralateral temporal bone fracture (top right). A minority of fractures will extend anteriorly to exit the cranium through the anterior fossa floor laterally (bottom left), or at the midline through the cribriform plate (bottom right).

Fig. 12.4 In transverse temporal bone fractures, the cortical origin of the fracture is generally in the occipital bone, where it extends to the foramen magnum. The fracture then traverses the petrous pyramid perpendicular to its long axis, passing from the foramen magnum to the floor of the middle fossa. The otic capsule is usually fractured, resulting in complete loss of inner ear function and often facial nerve injury.

Fig. 12.5 Possible courses of transverse temporal bone fractures: In its course from the foramen magnum to the floor of the middle fossa, the transverse fracture may pass either lateral to, through or medial to, the otic capsule. The most common path is directly through the otic capsule, thereby disrupting the inner ear (center). In the rare case where the fracture spares the otic capsule by passing medial to it (left), the facial and vestibulocochlear nerves are at risk as the fracture traverses the internal auditory canal. Also rare, the fracture may spare the otic capsule by passing lateral to it through the middle ear (right).

Fig. 12.6 Encephaloceles of the temporal bone most commonly occur through the floor of the middle cranial fossa. These may penetrate the roof of the mastoid, middle ear, or petrous apex. Most frequently, they are traumatic in origin arising either due to cranial base fracture or following iatrogenic injury sustained during mastoid surgery. Spontaneous meningoceles and encephaloceles also occur, presumably due to prominent arachnoid granulations which penetrate the eggshell thin tegmen mastoideum or tympani. Chronically increased intracranial pressure may play a role in such cases.

Fig. 12.7 Encephaloceles of the temporal bone with a small brain hernia impinging upon the ossicular chain resulting in conductive hearing loss. This may occur with either intact dura or a dural defect in which case brain may be visible behind the tympanic membrane. Dashed lines show bone cuts for middle fossa extradural repair of the dehiscent tegmen.

Fig. 12.8 Operative view of a meningoencephalocele herniating into the mastoid via the tegmen. A small middle fossa craniotomy has been performed to gain access to the temporal floor from above.

Fig. 12.9 Extradural retraction of the temporal lobe brings into view the base of the hernia.

Fig. 12.10 When the brain is not necrotic, an attempt should be made to reduce the hernia back into the temporal fossa.

Fig. 12.11 When the brain hernia is necrotic or cannot be reduced, it should be amputated at the level of the cranial base.

Fig. 12.12 Narrow deficiencies in the temporal floor can be repaired with a soft-tissue graft alone, but a supplemental osseous layer is desirable. Wider defects should be bridged by a bone graft, as depicted here, in addition to a connective tissue sheet.

Fig. 12.13 When the dural defect is large, placing a supplemental fascia graft intradurally is desirable. The advantage of an intradural graft is that the weight of the brain helps to coapt the graft with the surrounding dura.