Neuroscience Clerkship

PROGNOSTIC FACTORS IN GUNSHOT WOUNDS OF THE BRAIN

Gunshot wounds (GSW) of the brain are among the most lethal injuries, reflecting 35% of deaths from all brain injuries. GSW result in injury to the soft tissues, bone and brain parenchyma. The overwhelming majority of patients who have sustained a penetrating brain injury have an unfavorable outcome. More precisely, approximately 63% of all penetrating brain injuries result in death, approximately 2% result in a vegetative state, 5% result in severe disability, and 13% result in moderate disability as determined by the Glasgow Outcome Scale. Thus, only about 17% of patients with a penetrating brain injury are expected to have a good recovery. GSW are usually fatal if the bullet crosses the mid-line, traverses both hemispheres, or lodges in a ventricle.

Among the fatalities, 80% are pronounced dead at the scene or immediately upon arrival at the emergency department. For the 20% who are still alive upon arrival at the emergency department, numerous indicators have been studied and found to have prognostic value.

The prognostic factors have been divided into class I, class II, and class III based on the number, the quality, and the validity of published studies.

Class I prognostic indicators

Glasgow Coma Scale (GCS) score is the most studied prognostic indicator and shows the strongest correlation with patient outcome. In many studies, mortality among patients who presented to the emergency department in deep coma was extremely high. Three case series demonstrated a 100% mortality rate associated with patients who present in deep coma. Only 5 of 490 patients with a GCS score of 3-5 had a favorable outcome. On the other hand, patients who were alert at hospital admission had a mortality rate of less than 10%. Patients admitted with a GCS score of 13-15 had a 0% mortality rate. The GCS score is a widely-accepted, objective, and reliable measure of level of consciousness and is by far the best prognostic indicator in patients with penetrating brain injuries. However, one must keep in mind that drug or alcohol use prior to a gunshot injury (not uncommon in suicides and homicides) can decrease the reliability of the GCS score as a prognostic indicator.

The presence of intraventricular hemorrhage (IVH) or subarachnoid hemorrhage (SAH) confirmed by CT scan has been strongly associated with increased mortality. The mortality odds ratio for someone presenting with intraventricular hemorrhage following a gunshot injury to the brain was 2.83 according to one study. Another study compared the outcomes of patients with and without subarachnoid hemorrhage and found an odds ratio of 10.6

Class II prognostic indicators

Mortality from gunshot wounds to the brain is significantly higher in suicide attempts than in accidental shootings or homicidal action. Seven out of nine studies show higher mortality and poorer outcome for patients attempting suicide.

Bi-hemispheric injuries, defined as injuries in which the bullet trajectory crosses the midsagittal plane on CT scan, has been linked with higher mortality. Patients with bi-hemispheric involvement have an odds ratio of mortality varying between 1.18 and 20.05. However, one study has shown bifrontal lesions to be an exception to this rule.

High intracranial pressure (ICP) measured by intracranial pressure monitors or ventriculostomy, in the first 72 hours following a gunshot wound to the brain, has been shown in one study to predict higher mortality. The study found that the average ICP during the first 72 hours among patients who died was 62 mmHg, compared to 31 mmHg in patients who survived.

Class III prognostic indicators

Increasing age has been suggested as a prognostic indicator of poor outcome after a gunshot wound to the brain. While multiple studies have demonstrated such a trend, only one study has shown a significant relationship between age and outcome.

Perforating brain injuries (gunshot wounds to the head characterized by both an entry and exit wound) are associated with a poorer outcome than penetrating brain injuries (gunshot wounds to the head with only an entry wound and retention of the bullet within the skull) and tangential brain injuries (gunshot wounds that glance off the skull and may cause bone fragmentation but without actual bullet penetration into the brain parenchyma). While such a conclusion may seem logical, the only studies that have demonstrated this with clinical significance have been in a military setting; no civilian studies have arrived at such a conclusion thus far.

Some evidence in the literature suggests that ventricular penetration and poor outcome are correlated.

The presence of a coagulopathy in a penetrating brain injury patient portends a poorer prognosis, especially at lower GCS scores. One study showed that among non-survivors, 94% had at least one abnormal coagulation test (PT, aPTT, TT, fibrinogen level, fibrin split products, and/or platelet counts) while only 71% of survivors had at least one abnormal coagulation test. Another study demonstrated an mortality odds ratio of 50 in patients with coagulopathy but the validity of the study is in question because most patients in the study with a coagulopathy tended to have a low GCS score as well.