When considering swelling of the neck, it helps to roughly divide the neck into thirds, and to know the very basic anatomy of the regions. The upper region, under the mane, is mostly composed of ligament tissue. The middle third is the flat, muscular region commonly used for intramuscular injection, and the lower region contains the spinal column and jugular groove. There are important structures that run through the lower region, including the jugular vein, carotid artery and major nerves. Injury to these structures can be serious and so swelling here must be taken seriously. See the Quick reference image of head and neck.

Swelling of the upper region is rare and is most common after a misplaced, high IM injection. The middle region swells most commonly as a result of injection reaction. The lower region swells with spinal column injury, and any misplaced IV injection. Damage to the jugular vein can result in swelling here as can heart failure with blood backup into the jugular vein. Fractures and injury of the spine can be associated with swelling here too. Damage to the trachea allows air to escape and become trapped under the skin. This causes a specific type of crackly, soft swelling. Traumatic injury is possible in any region.