Patterns of Tissue Injury

Classification

One of the commonest determinations of the forensic pathologist is the range of fire. Gunshot wounds are typically classified as:

1. Contact
2. Intermediate range
3. Distant range

Example images demonstrating gross and microscopic appearances of gunshot wounds:

1. Sooting of hand, gross
2. Contact range gunshot wound, gross
3. Contact range gunshot wound, gross
4. Contact range gunshot wound, gross
5. Contact range gunshot wound, gross
6. Blood spatter on hand, gross
7. Gunshot entrance wound with GSR, microsopic
8. Intermediate range gunshot wound, gross
9. Intermediate range gunshot wound, gross
10. Entrance-exit wound in close proximity from low angle of bullet entrance, gross
11. Exit gunshot wound, gross

Entrance wounds

Contact wounds characteristically have soot on the outside of the skin, and muzzle imprint, or laceration of the skin from effects of gases. Contact wounds of airguns usually lack these features (Cohle et al, 1987). Intermediate, or close-range, wounds may show a wide zone of powder stippling, but lack a muzzle imprint and laceration. The area of powder stippling will depend upon the distance from the muzzle. (Denton et al, 2006)

Distant range wounds are lacking powder stippling and usually exhibit a hole roughly the caliber of the projectile fired.

The most difficult problem is distinguishing a distant from a contact wound. The factors that can affect the amount and distribution of gunshot residue (GSR) on skin and clothing include: (1) firing distance, (2) length and diameter of the firearm barrel, (3) characteristics of the gunpowder, (4) angle between the firearm barrel and target, (5) characteristics of the cartridge, (6) the environment (moisture, wind, heat), (7) type of clothing, (8) intermediate targets, and (9) characteristics of the target (tissue type, putrefaction, blood marks) (Tugcu et al, 2006).

Examination for GSR may aid in distinguishing entrance from exit wounds, for the entrance wound will have more than the exit, or the exit will have none. Residue is lacking in entrance wounds with airguns (Denton et al, 2006) (Cohle et al, 1987). The alizarin red S stain can be utilized in microscopic tissue sections to determine the presence of barium as part of GSR (Tschirhart, Noguchi, Klatt, 1991).

Scanning electron microscopy of entrance wounds shows gunshot residue within collagen fibrils. The entrance wound appears abraded, with loss of the papillary pattern and laceration of basement membrane (Torre et al, 1986). Computer assisted image analysis may aid detection of GSR (Tugcu et al, 2006).

Entrance wounds into skull bone typically produces bevelling, or coning, of the bone at the surface away from the weapon on the inner table. In thin areas such as the temple, this may not be observed. Sternum, iliac crest, scapula, or rib may show similar features. These observations may permit determination of the direction of fire. A small, dense projectile may "punch out" a rounded portion of cranium, while a larger projectile may produce circumferential fractures that radiate outward from the point of entrance. (Jandial et al, 2008)

Example images demonstrating gunshot wounds to skull:

1. Skull, contact range gunshot wound, gross
2. Bullet track through skull, diagram

Tangential entrance wounds into bone may produce "keyhole" defects with entrance and exit side-by-side, so that the arrangement of bevelling can be used to determine the direction of fire. (Dixon, 1982) (Denton et al, 2006)

Dixon (1984a) has described how the direction of fire of a graze gunshot wound of the skin surface can be determined by careful examination of the so-called skin tags located along the lateral margins of the graze wound trough, by use of a dissecting microscope or hand lens. Characteristically, the side of the tag demonstrating a laceration is the side of the projection toward the weapon.

"Shoring" of entrance wounds can occur when firm material is pressed against the skin, such as when a victim is shot through a wooden, glass, or metal door while pressing against it to prevent entry of an assailant. A study by Dixon (1980) showed that such wounds have a greater wound diameter and demonstrate greater marginal abrasion than control wounds produced by the same weapons. The features were directly proportional to the KE of the projectile and the rigidity of the shoring material. Stellate radiating lacerations of some shored wounds could lead to misinterpretation of distant range of fire as a contact wound. (Denton et al, 2006)

Use of silencers (or "muzzle brakes" to deflect gas and recoil) may produce atypical entrance wounds. A silencer is a device, often homemade, fitting over the muzzle that attempts to reduce noise by baffling the rapid escape of gases. Their possession is illegal. Entrance wounds produced when silencers are present lead to muzzle imprints that are erythematous rather than abraded and disproportionately large for the size of the wound. Entrance wounds may appear atypical at close range. (Menzies et al, 1981)

Firearm missile emboli ("wandering bullets") are rare, with only 87 reported through 1984, but may occur in victims that survive for some time and may require surgical intervention. (Chapman and McClain, 1984)

Entrance wounds associated with black powder handguns are associated with extensive sooting, a long range of travel of the sooting into the wound, and skin burns. Large pocket-like underminings may be seen even in deeper tissue layers with contact range wounds. (Karger and Teige, 1998)

The skin defect at the entrance site occurs from multiple mechanisms. Most of the defect results from skin fragmentation with fragements carried into the bullet track. The negative pressure of temporary cavitation pulls skin particles into the wound. There is also backspatter of skin particles away from the direction of bullet travel upon entrance. (Perdekamp et al, 2005)

Infection may result from gunshot wounds. Bullets are not sterile objects, either before or after firing. Bacteria are ubiquitous on skin surfaces and clothing. The bullet carries bacteria into the wound track. Skin particles serve as a transport vehicle for the bacteria. (Perdekamp et al, 2006)

Burn injury at the entrance site with close contact range is typically a minor component of the tissue injury, but some coagulative necrosis does occur. (Tschirhart et al, 1991). Toy cap guns with no projectile, may produce injury via burn alone. (Maze and Holland, 2007).

Bullet Tracks

Exit wounds

Most bullets are designed to hit the target without exiting, for this imparts all the bullet's KE to the target and does the most damage. However, in many situations an exit wound will be present. This may be due to the use of a projectile more powerful than necessary, or the projectile may strike an area (such as an extremity) with minimal tissue.

Exit wounds are generally larger than entrance wounds, due to the fact that the bullet has expanded or tumbled on its axis. Exit wounds either do not exhibit gunshot residues or far less residues than associated entrance wounds. In bone, typical "bevelling" may be present that is oriented away from the entrance wound. (Denton et al, 2006)

Scanning electron microscopy of exit wounds shows irregular lacerations with protruding collagen fibers, but relatively undamaged papillae. (Torre, 1986)

Fragmentation of the bullet may produce secondary missiles, one or more of which may have exit wounds. The bullet path may be altered by striking bone or other firm tissues, such that the bullet track may not be linear, and exit wounds may not appear directly opposite entrance wounds.

It is important to remember that the orientation of the bullet track may be positional. The victim may have been shot while standing or sitting, but when the body is typically examined at autopsy, it is lying down, so that soft tissues may shift position. This must be remembered when rendering opinions as to the angle, or direction, of fire.

If the exit wound is "shored" or abutted by a firm support such as clothing, furniture, or building materials, then the exit wound may take on appearances of an entrance wound, such as a circular defect with an abraded margin. This can occur with contact, close range, or distant shots. 92% of shored exit wounds in one study had a round or ovoid defect, and all had some degree of abrasion. The degree of shoring abrasion increased directly with the KE of the projectile and the rigidity of the shoring material. (Dixon, 1981)

A keyhole lesion, typically identified with entrance wounds, has been described with an exit wound. (Dixon, 1984b)

Sequence of fire

In some situations, pathologic findings may help to establish in what sequence the bullets were fired that caused the injuries. For example, multiple gunshot wounds to the head may produce fracture lines, and a subsequent fracture line will not cross a pre-existing fracture line (Spitz and Fisher, 1973).

Subjective reasoning would suggest that the first shot may be horizontal (victim upright) but subsequent shots would be oriented down or to the back of the victim as he fell or fled. Without witnesses and scene investigation, such opinions would be conjectural.

Sexton and Hennigar (1979) have reported cases in which examination of projectile collisions have aided in determining the sequence of fire.

The management of gunshot wounds may require accounting for all bullets and bullet fragments to determine the need for surgery. A simple rule of accounting for bullets is as follows: the number of entrance wounds must equal the number of exit wounds plus bullets retained. An unequal number may result from bullet fragmentation or from embolization, migration, or ricochet to unsuspected tissue sites.

Radiologic Imaging

Radiographic imaging may be needed to account for retained bullets and fragments and to help determine the bullet track. This has been accomplished for decades with plain film radiography, utilizing multiple projections. Bullets and fragments, including primer and jacket, are radiopague, improving ease of detection. (Folio, McHugh, and Hoffman, 2007).

Computed tomographic (CT) imaging has been applied to forensic investigations. CT provides multiple views with higher resolution than plain film radiography. In addition, radiography post-mortem is not limited by potential hazards of cumulative radiation exposure as would be the case in a living person. Thus, higher amounts of radiation energy, and unlimited dosages, can be utilized. With CT, cross sections can be computationally arranged into three dimensional images. (Jeffery et al, 2008)

MDCT imaging can be superior to conventional radiology for detection of soft tissue injuries. A three dimensional display improves localization of bullets and bullet fragments as well as determining details of fractures present. (Harcke HT et al, 2008).

Manner (Mode) of Death

The manner of death from firearms injuries can be classified as homicide, suicide, accident, or undetermined. There is no single characteristic appearance of a gunshot wound that defines the manner of death. Such a determination requires analysis of multiple pieces of evidence, including the scene investigation, the examination of the body, ballistics evidence, analysis for gunshot residue, and interviews of persons involved with the decedent and the scene of death.

In many cases, the distinction between death from homicide and suicide must be determined. The presence of multiple entrance wounds may not exclude suicide. Kohlmeier et al (2001) have analyzed a large series of 1704 suicidal firearms deaths and determined characteristics of those injuries. The type of weapon used was a revolver in 49.8%, an automatic pistol in 19.5%, a rifle in 30.0%, and some other firearm in 0.7%. The site of the entrance wound involved the head in 83.7% of cases, the chest in 14.0%, the abdomen in 1.9%, and a combination of sites in 0.4%. The table below identifies the site of the entrance wound by type of weapon used in suicidal firearms deaths:

In the above series, contact wounds were found in 97.9%, intermediate in 2.0%, and a combination of these or an unknown range in the remainder.

Proceed to Criminalistics Laboratory Methods.

Return to the Firearms Tutorial menu.