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Lyme Disease and
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Facial Paralysis after Head TraumaFacial paralysis occurring after head trauma can be due to several causes. Most commonly, the temporal bone (through which the facial nerve travels) can fracture, leading to either temporary or permanent damage to the nerve. Less commonly, direct brainstem injury or stroke related to the trauma can lead to brain malfunction, so that the facial musculature does not work properly, even if the nerve itself is intact. Temporal bone fractures are classified into either longitudinal or transverse fractures, depending on their course through the bone. The schematic to the right illustrates the difference in direction between the two types. Longitudinal fractures are more common, and account for 80% of all temporal bone fractures. They occur from a blow to the side of the head; the fracture line tends to run along the floor of the ear canal, can rupture the ear drum, and can result in bleeding from the ear. In only about 20% of these cases, the facial nerve is injured in its course through the temporal bone. While nerve crush or transection can occur, more commonly the etiology of the facial paralysis is swelling within the tight bony canal through which the nerve runs. Since there is no room for swelling to occur, the nerve gets "squeezed" within the facial canal, leading to nerve malfunction. In this clinical situation, usually the facial muscles are working normally right after the injury, but become weak in the ensuing several hours to days, as the swelling sets in. The best prognostic factor for ultimate facial nerve function is whether the facial paralysis is immediate or delayed. Often this is unknown, based upon the fact that health care providers are occupied managing the life threatening injuries in the first hours after any serious accident, and observations of facial nerve function are of secondary importance. Measures to decrease swelling, such as administration of steroid medications, can sometimes hasten recovery. Another approach to relieve the squeezing phenomenon on the nerve is to perform a facial nerve decompression, though some feel this is a large operation for a problem likely to resolve on its own. It is important to emphasize that in cases of delayed palsy, standard management is eye protection and patience. Regeneration falls along a spectrum, and ultimately facial nerve recovery can take over a year. Transverse temporal bone fractures occur only 20% of the time, and usually result from a blow to the front or the back of the head. They tend to be more severe injuries, because the force required to fracture the temporal bone in its transverse dimension is greater than that required for longitudinal fracture. The pathway for these fractures may be directly through the inner ear hearing and balance organs, so hearing loss and vertigo are more common. The facial canal is also more commonly disrupted with a transverse fracture, with a 50% incidence of facial paralysis. Immediate onset facial paralysis with a transverse temporal bone fracture suggests disruption of the nerve, and should be repaired when the patient is medically stable. The complicating factor in head trauma is that commonly, other life threatening issues are occurring, and require substantial attention before the temporal bone fracture is addressed. Moreover, a good assessment of facial function requires a cooperative patient, and many patients are comatose following head trauma, making thorough examination of nerve function impossible.
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