In most penetrating injuries from high-velocity missiles, the object (such as a bullet) causes a high-temperature coagulative lesion that is sterile and does not require surgery if the projectile exits the skull. In these instances, the main considerations are the development of infection or CSF leaks or, in the long term, epilepsy or aneurysms in distal blood vessels. The latter are considered to be the result of disruption of the vessel wall by the local high-energy shock wave.
If the brain is penetrated at the lower levels of the brainstem, death is instantaneous because of respiratory and cardiac arrest. Even through-and-through wounds at higher levels, as a result of energy dissipated in the brain tissue, may damage vital centers sufficiently to cause death immediately or within a few minutes.
Once the initial complications are dealt with, the surgical problems, as outlined by Meirowsky, are reduced to three: prevention of infection by debridement accompanied by the administration of broad-spectrum antibiotics; control of increased ICP and shift of mid-line structures by removal of clots of blood and the administration of mannitol or other dehydrating agents, and the prevention of life-threatening systemic complications.
When first seen, the majority of patients with penetrating cerebral lesions are comatose. A small metal fragment may have penetrated the skull without causing concussion, but this is usually not true of high-velocity missiles. In a series of 132 patients analyzed by Frazier and Ingham, consciousness was lost initially in 120. The depth and duration of coma seemed to depend on the degree of cerebral necrosis, edema, and hemorrhage. In the series of the Traumatic Coma Data Bank, the mortality rate in 163 patients who were initially comatose from a cranial gunshot wound is 88 percent—more than twice the rate from severe blunt head injury. On emerging from coma, the patient passes through states of stupor, confusion, and amnesia, not unlike those following severe closed head injuries. Focal or focal and generalized seizures occur in the early phase of the injury in some 15 to 20 percent of cases.
Recovery may take months. Frazier and Ingham commented on the “loss of memory, slow cerebration, indifference, mild depression, inability to concentrate, sense of fatigue, irritability, vasomotor, and cardiac instability, frequent seizures, headaches, and giddiness, all reminiscent of the residual symptoms from severe closed head injury with contusions.” Every possible combination of focal cerebral symptoms may be caused by such lesions. The excellent older articles by Feiring and Davidoff, by Russell, and by Teuber are still very useful references on this subject.
Epilepsy is the most troublesome long-term sequela and is described further on. Ascroft and also Caviness, in reviewing World War II cases, found that approximately half of all patients with bullet or shrapnel wounds that had penetrated the dura eventually developed seizures, most focal in nature; the figures reported by Caveness for Korean War veterans are about the same.
CSF rhinorrhea, discussed earlier and in Chap. 29, may occur as an acute manifestation of a penetrating injury that produces a fracture through the frontal, ethmoid, or sphenoid bones. Cairns listed these acute cases as a separate group in his classification of CSF rhinorrheas, the others being (1) a delayed form after craniocerebral injury, (2) a form that follows sinus and cranial surgery, and (3) a spontaneous variety. Pneumoencephalocele (aerocele)—that is, air entering the cerebral subarachnoid space or ventricles spontaneously or as a result of sneezing or blowing the nose—is evidence of an opening from the paranasal sinus through the dura, as mentioned earlier in relation to skull fracture (see Fig. 34-3).