A septal hematoma is a bruise or bleeding within the nasal septum. The septum of the nose separates the two nostrils.
A broken nose or any soft tissue injury to the area may cause a septal hematoma. This can occur more often in children because their septums are thicker and have a more flexible lining covering the area. An injury disrupts the blood vessels in the area, allowing fluid and blood to collect under the lining.
Bluestone CD, Stool SE, Alper CM, et al. Pediatric Otolaryngology. 4th ed. Philadelphia, Pa: WB Saunders; 2002.