Firearm Injuries Involving the Skull

The likelihood of a perforating injury of the skull increases with the caliber and velocity of the bullet, and with the proximity of the weapon to the head at the time of discharge (142,190).

The shapes of entry and exit wounds in the skull are variable, but most entries generally are round or oval (191,192). Exits tend to be irregular and larger because of projectile tumbling and deformation (191,192). Bone fragments do create multiple internal wound tracks in the brain (16,177).

19.1. Beveling

A cratered defect appearing on the inner ("beveled-in") or outer ("beveled-out") bony tables is seen in gunshot entry and exit wounds, respectively (16,193). Typically, beveling is observed in the skull but can be seen in other bones (Fig. 46). No association has been found between the size of the entry and the extent of beveling (194). Asymmetric inner beveling does not assist in determining the trajectory of the track (194).

Beveling assists in the determination of the direction of fire—i.e., entry vs exit— particularly if the cutaneous entry has an unusual shape or is not assessable because of fragmentation, decomposition, or surgical intervention (193,194). Beveling can be absent if there is involvement of thin bone (e.g., orbital plates, maxilla) or dense bone (petrous temporal bone [16,191,193]). A beveled-in entry can show outer beveling (16).

Fig. 38. Homicide. Three rifle wounds of torso. (A) Entry, left lower abdomen. Semicircular abrasion suggested muzzle imprint and implied the accused "finished off" the deceased at close range after firing two shots at a distance. (B) Examination of deceased's pants showed that a bullet had struck and deformed a circular metal button near the beltline.

Fig. 38. Homicide. Three rifle wounds of torso. (A) Entry, left lower abdomen. Semicircular abrasion suggested muzzle imprint and implied the accused "finished off" the deceased at close range after firing two shots at a distance. (B) Examination of deceased's pants showed that a bullet had struck and deformed a circular metal button near the beltline.

Examples include a keyhole defect resulting from tangential shooting, perpendicular contact gunshot wounds, and distant wounds (Fig. 47; refs. 193-196). Bullets can, on rare occasions, exit through an entry, which then shows outer beveling (153). Various mechanisms to explain outer beveling in an entry site have been proposed. They include temporary cavity formation by high-velocity projectiles and blowback of gases in contact-range wounds. The latter is supported by the observation of bone fragments outside the skull (152,191,196). Twisting of the bullet has been dismissed.

An exit associated with a contact range wound of the head can show inner beveling (191,197). An exit can also show a keyhole defect unrelated to a tangential shot (197,198).

19.2. Fracture Patterns Associated With Entry Site

If kinetic energy is totally absorbed at the entry site, then fractures are not present (191). Circumferential stresses around the entry and exit lead to radial fractures (Fig. 5; refs. 191 and 199). The radial fractures are not as long at the exit because less energy is available by the time the projectile reaches this site. Intracranial overpressure leads to concentric fractures around entry and exit holes (176,200). These fractures connect with already formed radial fractures, which indicates that they occur after radial fractures have formed (176). The concentric fractures adjacent to exits are less conspicuous than

Fig. 39. High velocity hunting rifle used to commit a homicide. (A) Radiograph: "snowstorm" pattern owing to fragmentation of the bullet. (B) Considerable destruction of heart in wound path, a reflection of the large temporary cavity created during passage of the projectile. (Courtesy of the office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 39. High velocity hunting rifle used to commit a homicide. (A) Radiograph: "snowstorm" pattern owing to fragmentation of the bullet. (B) Considerable destruction of heart in wound path, a reflection of the large temporary cavity created during passage of the projectile. (Courtesy of the office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 40. Contact head wound. Partial-jacketed bullet. (A) Jacket (arrow): core separation, seen in radiograph. (B) Removed projectile. The jacket shows visible linear striations (arrows), a general characteristic of the barrel rifling.

those around entries (200). Concentric fractures are not observed without radial fractures (200). Because bone strength is less in tension than in compression, concentric fractures can appear beveled-out (200). Radial fractures are seldom extensively beveled (200). Fracture lines from an exit are arrested by preexistent entry fractures, implying that fractures propagate faster than a bullet travels (191,197,200,201). If multiple entries are present (e.g., multishot suicide), then interrupted fractures can assist in determining

Fig. 41. Surgical alteration of a contact gunshot wound of the head.

the sequence of shots (22,201). If cutaneous entry and exit wounds are altered (e.g., decomposition), beveling and intersection of fracture lines are helpful in distinguishing them (201).

19.3. Fractures of Skull Base and Entire Skull

The base of the skull is predisposed to fracture because of its variable thickness and perforation by nerves and vessels (65). If there is an entry directly involving the base, then a majority of cases show fractures of the middle cranial fossa (65). Temporary cavity formation results in fractures remote from the entry site. Low- and high-energy firearms cause "indirect" fractures of the anterior cranial fossa (e.g., thin orbital and

Fig. 42. Self-inflicted gunshot wound. Coronal slice of formalin-fixed brain. Circumscribed wound track caused by low-caliber gun.

ethmoid plates; see Fig. 48 and refs. 65, 176, 177, and 182). Fractures of the middle and posterior cranial fossae tend to be associated with higher velocity weapons (65). "Hinge" fractures, extending across the middle cranial fossa, are associated with high intracranial pressure resulting from shotgun or hunting rifle injuries (65). Gas "blowout" of the anterior head area has been described in contact shotgun wounds of the temple (202). Bullet wounds of the head can cause basal skull fractures and fatal brain contusions without actual penetration of the brain (see Subheading 19.5. and ref. 16).

Massive skull destruction is seen typically, but not invariably, in certain contact-range wounds. This depends on the kinetic energy of the projectile and volume of gas generated (Fig. 29; refs 16, 124, 138, 176, and 177). Examples of weapons causing severe destruction include magnum revolvers, hunting/military rifles, and shotguns (59,69,119,120,137,138,203). Contact shotgun entries in the temple, forehead, and scalp generally leave the face intact. Wounds of the mouth and submental area can destroy the face.

Massive brain destruction with ejection of tissue is possible (16,124,176,203,204). Tremendous destruction of the brain does not preclude a neuropathological examination for underlying disease that could have precipitated the fatal incident (205,206).

19.4. Intracranial Ricochet

Bullets, associated with penetrating injuries, usually come to rest without reaching the contralateral inner skull surface (142). Intracranial ricochets typically involve a small-caliber weapon (16). From the skull entry site, the path of the bullet in the brain parenchyma is straight (Fig. 49; ref. 177). The bullet, after passing through the brain,

Fig. 43. Cerebral contusion (arrows) opposite (contrecoup) to the gunshot entry site (right temple). Formalin-fixed brain.

strikes the inner table and usually re-enters the brain, creating a superficial "gutter" on the surface (Fig. 50). The ricochet path can be extensive. A projectile, on its original path before it ricochets, can cause an impression or an outwardly displaced fracture at the site of impact on the inner skull table (Fig. 50; ref. 16). In most cases in which a ricochet from the contralateral skull surface occurs, the initial track of the bullet is the most prominent one but, in some cases in which fragmentation of the projectile has occurred, it may be difficult to determine the initial direction of the bullet.

19.5. Tangential Gunshot Wounds

Tangential gunshot wounds to the head occur when a bullet or bullet fragments do not penetrate the inner table of the skull. These injuries are sometimes fatal, but they are

Fig. 44. Intraoral self-inflicted shotgun wound. Injuries remote from the wound track. Cerebellar tonsillar contusions (arrows). Brainstem hemorrhages (arrowheads). Formalin-fixed brain.

usually seen when the victim dies because of other injuries. In one series, on clinical examination, 25% of subjects with tangential gunshot wounds showed CT abnormalities, which included skull fractures, isolated cortical contusions, and isolated subarachnoid, subdural, or intracerebral hemorrhages (Fig. 51; ref. 207). In addition, intracranial hemorrhages at more than one site—including, on rare occasions, epidural hemorrhages—are found in 43% of cases with CT abnormalities. Bleeding in the cranium is also more likely if the victim lost consciousness at the time of impact or showed a Glasgow coma scale score of less than 15 when examined in the hospital. A temporal or parietal region impact site, skull fractures, and retained bullet fragments in the scalp or skull are also associated with a greater risk of intracranial hemorrhage.

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