The carotid artery ganglion, also called the carotid body, is a cluster of cells located at the bifurcation of the carotid artery. An important neurologic sensor, the carotid body is primarily stimulated by oxygen and is highly sensitive to carbon dioxide. The carotid body’s main function is to trigger nerve impulses, relaying important information to the central nervous system. Although it requires a specific area of compression with strangulation, sustained stimulation of the carotid body for 3 to 4 minutes could activate the carotid sinus reflex, resulting in bradycardia and hypotension. However, death does not occur from carotid sinus stimulation.21,22
HYOID BONE
The hyoid bone is a horseshoe-shaped bone located at the base of the mandible and above the larynx (Figure 3). It is free-floating (ie, not connected to any other bone in the body). The hyoid bone’s main function is to support a wide range of tongue, pharyngeal, and laryngeal movements, including swallowing. A fracture of the hyoid bone may lead to difficulty swallowing (ie, dysphagia), painful swallowing (ie, odynophagia), and pain on neck rotation. Effective swallowing is important to maintain uncompromised air flow during respiration. Therefore, the impact of a hyoid bone fracture on swallowing, as well as the potential for associated bleeding and/or swelling, may compromise airway patency. Hyoid bone fracture is reported with a frequency of 17% to 71% in fatal strangulation27 and occurs during manual strangulation, ligature strangulation, and in hangings. Hyoid bone fracture is infrequently recognized in nonfatal strangulation.28
Figure 3. The hyoid bone. The greater horns (cornu) are the most common location for fractures.
JUGULAR VEINS
The jugular veins are vessels located on the left and right side of the anterior neck and are more external and lateral to the carotid arteries. The jugular veins return the majority of CO2 gases in deoxygenated blood from the brain and head back to the heart and lungs where the CO2 gases are exhaled as waste.
It takes approximately 4.4 pounds of pressure to occlude the jugular veins. This occlusion causes venous outflow obstruction, resulting in deoxygenated blood backing up into vessels of the head and brain. This build-up of deoxygenated blood is known as stagnant hypoxia. If venous outflow is obstructed without carotid artery occlusion, the veins above the level of constriction begin to dilate in order to accommodate the incoming blood that cannot exit the neck. This obstructive process causes the veins to engorge, resulting in increased internal venous pressure. When pressure is sustained for approximately 20 to 30 seconds without complete arterial (carotid and vertebral) occlusion, the dilated vessels rupture, causing pinpoint hemorrhages known as petechiae. Petechiae may occur anywhere above the level of constriction, including the brain, scalp, skin, conjunctiva of the eyes, soft palate of the mouth, and the external ear canal.
LARYNX
The larynx (ie, voice box) is a tubular structure of cartilage between the superior hyoid bone and inferior trachea. The larynx serves 2 important functions: first, it is part of the respiratory tract, allowing inhaled air to pass while simultaneously keeping food and liquid from obstructing the airway; second, the larynx is the area with vocal cords and subsequently functions to produce sound and vocalizations. The larynx contains the following structures, which are important to swallowing and vocalization.
—Cricoid cartilage: A ring-shaped structure providing the transition from larynx to trachea. Provides an attachment point for the cartilage, ligaments, and muscles involved in sound production and the opening and shutting of the airway.
—Epiglottis: An elastic, spoon-shaped flap extending from the posterior tongue to the anterior border of the thyroid cartilage. During swallowing, the epiglottis folds over to cover the opening of the larynx (ie, glottis) to block any food or fluid from entering the airway.
—Thyrohyoid membrane: A fibrous, elastic membrane connecting thyroid cartilage to the hyoid bone by a mucosa bursa that aids the upward movement of the larynx in swallowing.
—Thyroid cartilage: A semicircular structure positioned on the anterior larynx. Consists of a fusion of 2 cartilage plates. The external point of fusion is the laryngeal prominence (ie, Adam’s apple) and is more pronounced in men. The thyroid cartilage supports and protects the upper larynx and anchors the anterior portion of the vocal cords.
—Vocal cords: Situated in the mucous membrane on each side of the larynx opening. As exhaled air moves through the larynx, the vocal cords vibrate and produce sound.
The compressive forces of strangulation may lead to occlusion, fractures, and hemorrhages of the larynx’s cartilaginous framework. It takes approximately 22 pounds of force for airway occlusion at the level of the thyrohyoid membrane, 31.5 pounds of force to fracture the thyroid cartilage, and 41 pounds of force to fracture the cricoid. Laryngeal fractures often allow air to escape into the soft tissues of the neck, producing subcutaneous emphysema (ie, subcutaneous crepitation), which can result in potential airway compromise that can develop into acute asphyxia, and eventually, death. Subsequent hemorrhages and swelling may also play a role in airway compromise as a result of these injuries. If these fractures or hemorrhages go untreated or unrecognized, the victim may survive initially, but over hours, or even days, the victim may develop life-threatening airway complications, leading to a delayed death. Vocal cord injury that leads to swelling or hematoma formation may result in temporary or long-term vocal dysfunction that includes a hoarse voice (ie, dysphonia) or the inability to produce a voice (ie, aphonia).
TRACHEA
The trachea is a hollow tube located along the body’s midline that connects the larynx to the 2 main bronchi of the lungs. Incomplete, highly elastic, C-shaped cartilage rings are located anteriorly along the tracheal wall. The trachea’s primary function is to allow air flow to and from the lungs. It takes approximately 33 pounds of pressure to completely occlude the trachea. Tracheal occlusion inhibits the inhalation of oxygen and the exhalation of carbon dioxide, resulting in multisystem hypoxia and acidosis. The force of the strangulation pressure may also fracture the trachea, causing subcutaneous emphysema and subsequent airway compromise.
ANATOMY OF THE EAR
When documenting injuries on a patient after strangulation, it is important to inspect and photograph both sides of the ears (Figure 4). Initial injury, unless it involves dermal capillary injury, may not be visible but over time may surface, allowing for reassessment and documentation.
—Triangular fossa: A shallow depression in the anterior part of the top of the ear’s auricle between the 2 crura into which the antihelix divides.
—Scaphoid fossa: A shallow oval depression that is situated above the pterygoid fossa on the pterygoid process of the sphenoid bone and that provides attachment for the origin of the tensor veli palatini muscle.
—Helix: The outer rim of the ear that extends from the superior insertion of the ear on the scalp (root) to the termination of the cartilage at the earlobe. The helix can be divided into 3 approximate parts: the ascending helix, which extends vertically from the root; the superior helix, which begins at the top of the ascending portion, extends horizontally, and curves posteriorly to the site of Darwin tubercle; and the descending helix (sometimes called posterior), which begins inferior to Darwin tubercle and extends to the superior border of the earlobe. The lower portion of the posterior part is often noncartilaginous. The border of the helix usually forms a rolled rim, but the helix is highly variable in shape.
Figure