Contemporary Problems in Trauma Surgery
Penetrating Craniocerebral Trauma
Robert H. Rosenwasser, MD, FACS, * David W. Andrews, MD,t and D. Fernando Jimenez, MD:j:
In the United States, trauma is the primary cause of death in people aged 1 to 45 years. 48 In men aged 45 to 64 years, trauma exceeds even stroke and cancer as a cause of death. In more than 50% of trauma-related deaths, head injury contributes significantly to the morbidity and directly to the outcome. In patients with multiple injuries, the head is the most commonly involved part. In nearly 75% of the victims of fatal road accidents, injury to the central nervous system (CNS) is found at autopsy. In 1974, the first survey was performed on head and spinal cord injury.28 The report, written by the National Institute of Neurological and Communicative Disorders and Stroke, estimated 422,000 cases of head injury during 1974, or 200 cases per 100,000 population. lO As hospital admission was a criterion for inclusion in the study, one can surmise that the true incidence is much higher. In 1976, the National Safety Council reported approximately 100,000 deaths from accidental injury in a population of 211,000,000. 35 There have been few studies regarding the epidemiologic nature of head injury in the United States. Difficulties with the studies have often been methodological, therefore confusing the conclusions that can be drawn. However, the data do indicate an incidence of head injury of approximately 200 to 300 per 100,000 persons. Applied to the population in this country, this means that approximately 500,000 new cases of head injury occur yearly, of which 30% to 40% are moderate to severe, with mortality and serious morbidity rates of perhaps 10% each. One can deduce that as many as 50,000 US citizens are killed, and another 50,000 disabled, by head injuries each year. 4. 5.15.27 One can see from the above statistics that the combined medical and *Associate Professor, Neurosurgery and Physiology, and Director, Neurosurgical Intensive Care Unit, Temple University Hospital, Philadelphia, Pennsylvania tAssistant Professor, Neurosurgery, Temple University School of Medicine, Philadelphia, Pennsylvania tChief Resident, Neurosurgery, Temple University Hospital and St. Christopher's Hospital for Children, Philadelphia, Pennsylvania
Surgical Clinics of North America-Vol. 71, No.2, April 1991
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social costs for caring for a head injury are extensive. On the basis of 1977 figures, such costs have been approximately $6 billion a year and lost income from head injury deaths approximately $22 billion. PATHOPHYSIOLOGY AND SECONDARY CENTRAL NERVOUS SYSTEM INJURY Primary brain injury is defined as that event at the time the missile or other instrument penetrates the skull, causing the injury. It also occurs at the time the head goes through the windshield or experiences severe acceleration-deceleration. The rate of primary injury will be reduced only through public awareness and education, as well as through improvement of the safety of our vehicles. Secondary injury, which occurs as a direct consequence of loss of autoregulation, hypoxia, or infection, is a significant contributor to morbidity after CNS injury. As alluded to previously, serious head injury is often associated with severe systemic abnormalities of hypotension and hypoxia. Without a doubt, these are the most commonly associated causes of secondary brain injury with CNS injuries. Numerous studies have confirmed that de saturation of arterial blood gases, as well as hypotension, markedly increase the probability of a poor outcome. These patients often have abnormal vascular autoregulation, elevated intracranial pressure, and abnormal metabolic response from the primary injury, which may exacerbate the secondary phenomenon. PERFORATING AND PENETRATING WOUNDS Wounds that result from a stab to the cranium may lacerate eloquent areas of the brain and result in a deficit or provoke massive intracranial hemorrhage, leading to neurologic deterioration or death. 17 However, most patients with this type of injury are conscious when first seen and may have a marked deficit or no deficit at all. Thus, the absence of a deficit should not give a false sense of security to the initial examiner. If unnoted, these injuries may result in severe infection such as meningitis or brain abscess, which increase the morbidity of head injury markedly. Small punctate wounds of the face and skull should be looked for, as is routinely performed on the ventral and surface aspect of all extremities and the trunk of trauma victims. Particularly silent are wounds of the anterior cranial fossa and middle fossa, as anterior temporal regions as well as anterior frontal regions are not neurologically eloquent. 9 • 18 Vascular lesions are often associated with perforating wounds and may present as a carotid-cavernous or arteriovenous fistula, arterial occlusion, arterial transection, or traumatic aneurysm. 2 Most of the injury that occurs after a penetrating missile wound is imparted by the velocity of the missile, because the kinetic energy varies with the square of velocity. There have been reports from the military literature that indicate a 23% mortality rate in high-velocity injuries, as
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opposed to a 7.5% mortality rate in injuries by lower-velocity fragments. 25 With low-velocity missiles, however, the skull may be fractured on the inner table, and a portion of this bone may enter the cerebral parenchyma as a missile in its own right without actual penetration of the cranial cavity. According to Hopkinson and Marshall,26 injury to the CNS parenchyma results from three mechanisms, dependent on missile velocity. At less than 320 mIs, injury results from direct disruption and laceration of tissue. At greater than 320 mIs, shock waves and tissue cavitation resulting from passage of the missile become increasing important. Shock waves at 15 to 20 milliseconds, traveling at the speed of sound, emanate from the missile, and, with high-velocity injuries, wounds can attain amplitudes of 80 kg! cm 2. Summation of the reflected shock waves may produce significant pressure gradients, although this is less common with low-velocity injuries. It is the pressure gradients that disrupt neural structure and function remote from the path of the missile. Lastly, a missile imparts a centrifugaJ movement to the parenchyma, resulting in cavitation. The temporary cavity may have a diameter of more than 30 times that of the missile, generating significant strains in surrounding tissue and causing severe axonal tear and vascular disruption. The cavity collapses within 10 to 20 milliseconds but may reverberate, with five or six cycles of expansion and relaxation. In experimental studies, it has been demonstrated that the intracranial pressure may rise to 100 mm Hg, with a concomitant fall in cerebrovascular resistance and blood volume. 30 Initial Evaluation The emergency room management of patients with perforating and penetrating head injuries is identical to that of the polytrauma patient with other systemic injuries. Restitution and maintenance of respiratory and cardiovascular functions is paramount. Performance and documentation of appropriate clinical neurologic and general physical examinations are essential. Finally, it is important to plan and execute all appropriate diagnostic procedures in a timely fashion. Neurologic assessment is often made by the trauma surgeon prior to the arrival of the neurologic surgeon but should include basics such as pupillary function, spontaneous breathing, the presence or absence of decerebrate or decorticate posturing, and the presence or absence of gross focal neurologic deficits such as hemiparesis or paraparesis. Radiologic Evaluation Computed tomography (CT) has virtually eliminated the need for standard skull radiographs, although if they can be obtained in a timely fashion in the emergency area, they may be helpful in assessing the presence of the injury. As in all polytrauma patients, cervical spine films should be obtained prior to manipulation of the head and neck. Computed tomography of the frontobasal region also assesses the extent and severity of injuries to the osseous extracranial soft tissue and intracranial components. The scan outlines the trajectory of the missile, associated parenchymal hematomas, and the amount of foreign debris along the missile tract. The presence or absence of basal cisterns correlates directly with outcome.
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Severe cerebral swelling with loss of cisterns indicates an 80% to 90% mortality rate secondary to intractable high intracranial pressure. 8 When perforating or penetrating injuries involve portions of the sphenoid bone, temporal bone, and posterior fossa, vascular structures such as the carotid and vertebral arteries may be involved. Prior to craniotomy, cerebral arteriography should be performed to rule out a vascular occlusion, traumatic dissection, or false aneurysm. Follow-up CT scans should be performed 12, 24, and 36 hours after the initial surgical procedure to rule out delayed hematoma formation in areas of damaged parenchymal tissue, which occurs in as many as 30% of cases. 46 Operative Management of Penetrating and Perforating Wounds Penetrating and perforating wounds of the skull and brain are compound: the dura has been torn, and in most cases, the underlying brain has been lacerated and penetrated. Perforating wounds created by sharp objects are often treated in an exact fashion as an open depressed fracture. The scalp flap should be outlined according to general neurosurgical principles of vascular supply of the scalp. In general terms, burr holes usually are created in normal bone, and craniectomy is performed around the protruding fragment or knife blade. No attempt to remove the wounding instrument in the emergency room or the operating theater should be made until the cranial opening is completed and the surgeon is ready to open the dura widely to manage underlying hemorrhage once the object is removed. This should always be done under direct vision. As indicated earlier, if a vascular injury is confirmed by arteriography, obViously, proximal and distal control of vessels within the intracranial compartment, as well as extracranially, should be gained before removing the instrument of penetration. Operative Management of Missile Injuries As with perforating wounds, missile injuries are considered compound and dirty and require surgical debridement and closure. One would be reluctant to take a patient to the operating room for debridement if pupillary reflexes are absent, oculocephalic responses are absent, and there are virtually no somatic reflexes of any kind, because this patient is clinically brain dead, and the mortality rate will be virtually 100%. Even if the patient does survive, he or she will be vegetative. All other patients should be prepared for surgery for debridement of the missile tract, to remove fragments, and to prevent delayed infection. Antibiotics should be administered in meningitic doses prior to the surgical incision. During the Vietnam conflict, penicillin and chloramphenicol were the most commonly used antibiotics for this type of injury.24 In recent times, third-generation cephalosporins, in conjunction with either nafcillin or vancomycin in meningitic doses, have been efficacious in preventing delayed meningitis and brain abscess. Antibiotics are usually continued for 10 days to 2 weeks after the injury.l, 3 Also, epilepsy occurs in 30% or more of patients with penetrating brain wounds, and therefore, anticonvulsant therapy is strongly recommended. 45, 49 Phenytoin, carbam-
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azepine, and phenobarbital are all acceptable, and blood levels should be monitored. The therapeutic levels of those drugs are 10 to 20 mg/dl, 4 to 12 mg/dl, and 20 to 40 mg/dl, respectively. The scalp incision may be performed in one of several manners. An Sshaped or curvilinear incision may be used to expand the missile tract to gain adequate exposure for craniectomy. In the case of a frontal and temporal wound, a large question-mark incision may be useful in debriding the tract, as well as in performing temporal lobectomy and frontal lobectomy to aid in the management of elevated intracranial pressure. Grossly contaminated bone fragments should not be replaced; cranioplasty may be performed later if the patient survives the initial insult and the cosmetic deformity is severe. As a general rule, two to four burr holes are placed 2 to 3 cm from the entry site, and the craniectomy is made in a circumferential fashion around the missile tract. The dura is then opened in a cruciate fashion, gaining adequate exposure to the entry site. All devitalized br