Contusions (Bruises)

A contusion (also called a bruise) can be defined as injury or discoloration due to hemorrhage into tissue from a ruptured blood vessel(s) beneath the skin surface without disruption of the skin itself

Figure 7.4 Documentation of a contusion on the tongue of a deceased cat.

(Dorland’s Illustrated Medical Dictionary, 1988). A contusion has also been defined as a visible lesion from extravasation of red blood cells into subcutaneous and surrounding tissues due to trauma from a blunt instrument (Barington & Jensen, 2013). Contusions can also occur within the internal organs and the brain.

Contusions occur when BFT, while leaving the skin intact, ruptures blood vessels resulting in hemorrhage of the tissue underneath (Figure 7.4). The hemorrhage, under the influence of gravity, will travel along the tissue planes following the path of least resistance. Because of this, the pattern of the contusion may not accurately reflect the size and shape of the object causing the trauma. The size, shape, and development of the bruise can be affected by the thickness of the skin, location, size and type of blood vessel damaged (artery, vein, capillary), the depth and extent of the injury, the dispensability of the tissue, the type of tissue damaged, the activity of the animal, and the blood pressure of the animal at the time of the trauma. Contusions may be difficult to observe on an animal, depending on its hair coat and skin pigmentation.

Depending on the object causing the trauma and the factors described above, a contusion may retain the pattern of the object. Although patterned bruises are relatively rare in animals, in part due to the dissipation of the force from the hair coat, the patterned bruise called a “tramline” caused by impacts from narrow objects onto thinly-haired skin have been seen in animals (Munro & Munro, 2008). Tramlines are parallel lines of bruising separated by skin that appears normal. This occurs when the object compresses but does not rupture the underlying blood vessels, while shearing forces tear the peripheral vessels resulting in hemorrhage. In pigs, due to the light pigmentation and thin hair coat, the pattern of the object causing the trauma may be distinctive, especially after the removal of the epidermis (Barington, & Jensen, 2013).

Contusions go through color changes as well. Initially, the red blood cells appear bright to dull red depending on their oxygenation saturation. As the oxygen levels fall, the bruise turns from red to blue-purple. The red blood cells deteriorate and leak hemoglobin. As the hemoglobin is metabolized to different byproducts, the color changes to green (biliverdin), yellow (hematoidin), and brown (hemosiderin) (DiMaio & DiMaio, 2001; Gerdin, 2014; McCausland & Dougherty, 1978; Munro & Munro, 2008).

Hemorrhage can occur as a result of BFT or natural causes. A bruise is typically considered to be a hemorrhage of 1 cm or larger in diameter (Gerdin, 2014). Hemorrhage measuring <3 mm is called petechiae and may be caused by thrombocytopenia (low platelet counts) or diseases causing platelet dysfunction. Purpura is hemorrhage measuring 3 mm-1 cm and is often a result of a diseasecausing vasculitis (Gerdin, 2014). Ecchymosis, hemorrhage of >1 cm, can be caused by a disease such as von Willebrand disease (Côté 2007) or ingestion of a toxic substance such as rodenticides

(Miller & Zawistowski, 2013). Ecchymosis and bruising may be difficult to distinguish clinically. Large amounts of hemorrhage containing blood clots are often called hematomas (Gerdin, 2014).

Clinically, bruising must be differentiated from disease conditions and/or toxin ingestion. If the opportunity exists, the clinician should take an exhaustive history from the owner, officer, or reporting party. Since the size, pattern of distribution, and location of the lesions may be the deciding factors, the veterinarian should conduct a thorough physical examination with mapping and detailed description of each lesion. Depending on the situation, the clinician should consider clipping or shaving the animal to locate all of the lesions (Munro & Munro, 2008). BFT to the skin may cause concurrent abrasions and/or lacerations. These lesions would not be associated with disease or toxin ingestion (Gerdin, 2014). On live animals, the lesions should be photographed as soon as possible and again during the subsequent evaluations of the animal to chart the progress, development, and resolution of the contusion(s). On deceased animals, the skin should be reflected from the body to document all of the contusions. Forensic necropsy techniques and documentation of blunt force trauma are further explained in Chapter 10.

Lacerations

A medical dictionary defines a laceration as “a torn, mangled wound” {Dorland’s Illustrated Medical Dictionary, 2008). In the author’s experience in veterinary medicine practice, the word "laceration” is typically used to mean any cut or tear in the animal’s skin or underlying tissue regardless of cause. In the veterinary forensic field, a laceration is an injury caused by BFT in which the tissue is torn, split, sheared, stretched, or crushed (Gerdin, 2014; Tong, 2014) (Figure 7.5). Like contusions, lacerations can be found in internal organs without visible wounds to the overlying tissues. Lacerations may or may not reflect the shape of the object which caused the injury. DiMaio suggests that long thin objects tend to produce linear lacerations, while objects with flatter surfaces tend to produce irregular or Y-shaped lesions (DiMaio & DiMaio, 2001).

The margins of lacerations may also show abrasions and/or contusions. In addition, there is often bridging present within the laceration. This bridging is made up of tissue strands that were not completely torn at the time of the trauma. Bridging is typically not found in sharp force wounds (Gerdin, 2014; Gerdin & McDonough, 2013). Sharp force wounds are generally called incised, chop, or stab wounds. Keep in mind that a gray area may exist between BFT and SFT: a dull knife may cause abrasions on the skin margins, and a large, heavy object with a sharp edge may produce a lesion mimicking an incised wound. In these cases, terms such as "penetrating blunt trauma” or “puncture wound” maybe appropriate (DiMaio & DiMaio, 2001; Recknagel & Stefan et al., 2011).

Figure 7.5 Documentation of an eyelid laceration with swelling (edema).

Figure 7.6 (a) Example of a clegloving injury to mandible of a dog. (b) Additional view of the same degloving injury.

Exploration of the depths of a laceration may show debris or trace evidence from the impacting object (DiMaio & DiMaio, 2001). In addition, if the BFT occurs tangentially to the skin, the side from which the blow came may be beveled and abraded while the skin on the receiving side may be undermined (DiMaio & DiMaio, 2001).

A special class of laceration is an avulsion. Avulsions are seen when the shearing force impacts the body at an angle such that the tissues are twisted. These avulsions may cause the creation of pockets between and within tissue in which hemorrhage may occur. If severe enough, an avulsion may result in the "twisting off” of the skin from the underlying tissue or of the organ from the pedicle attaching it to the body (avulsion of a kidney). A typical avulsion injury is the degloving of an extremity (Figure 7.6a,b). An injury resulting in the skin being peeled away from the paw/leg is often from a vehicular accident or may be secondary to a ligature (Merck, 2013). In the author’s experience, some cases in which the skin has been peeled back from the rib cage were the result of coyote attacks on small dogs and cats.