Nevertheless, fractures cannot be dismissed without further comment for several reasons. Overall, brain injury is estimated to be 5 to 10 times more frequent with skull fractures than without them and perhaps 20 times more frequent with severe and multiple fractures. Fractures assume further importance in providing an explanation for cranial-nerve palsies, and in creating potential pathways for the ingress of bacteria and air or the egress of cerebrospinal fluid (CSF leak). In these respects, fractures through the base of the skull are of special significance, and are considered below.
Figure 34-2 illustrates the major sites and directions of basilar skull fractures. One can readily perceive the possibilities of injury to cranial nerves. Fractures of the base are difficult to detect in plain skull films and may be missed by other imaging techniques, but their presence should be suspected in the presence of any one of a number of characteristic clinical signs. Fracture of the petrous pyramid often deforms the external auditory canal or tears the tympanic membrane, with resultant leakage of CSF (otorrhea); or, blood may collect behind an intact tympanic membrane and discolor it. If the fracture extends more posteriorly, damaging the sigmoid sinus, the tissue behind the ear and over the mastoid process becomes boggy and discolored (Battle sign). Basal fracture of the anterior skull may also cause blood to leak into the periorbital tissues, imparting a characteristic “raccoon” or “panda bear” appearance. The presence of any of these signs calls for CT scanning of the skull base using bone window settings to detect a fracture.
The existence of a basal fracture is also indicated by signs of cranial nerve damage. The olfactory, facial, and auditory nerves are the ones most liable to injury, but any one, including the 12th, may be damaged. Anosmia and an apparent loss of taste (actually a loss of perception of aromatic flavors, as the elementary modalities of taste are unimpaired) are frequent sequelae of head injury, especially with falls on the back of the head. In the majority of cases the anosmia is permanent. If unilateral, it will not be noticed by the patient. However, mechanism of these disturbances is thought to be a displacement of the brain and tearing of the olfactory nerve filaments in or near the cribriform plate, through which they course, rather than being attributable to a fracture. A fracture in or near the sella may tear the stalk of the pituitary gland with resulting diabetes insipidus. Rarely, such a fracture may cause bleeding from a preexisting pituitary adenoma and produce the syndrome of pituitary apoplexy (see Chap. 30). A fracture of the sphenoid bone may lacerate the optic nerve, with blindness from the beginning. The pupil is unreactive to a direct light stimulus but still reacts to a light stimulus to the opposite eye (consensual reflex). The optic disc becomes pale, that is, atrophic, after an interval of several weeks. Partial injuries of the optic nerve result in scotomas and a troublesome blurring of vision.