Patterns of injury Injuries to the auditory system are a recognized complication of exposure to blast overpressure. The injuries include:
- rupture of the tympanic membrane (eardrum)
- disruption of the ossicular chain (the bones of the middle ear)
- damage to the sensory structures of the basilar membrane
1. Confined space vs open space
Compared with an explosion in an open space, an explosion in a confined space results in a higher incidence of primary blast injury a greater mortality and a greater injury severity (measured as the Injury Severity Score, ISS).
In a study of 297 victims of 4 terrorist bombings in Israel (Leibovici et al 1996) 204 casualties from open air bombings were compared with 93 casualties from bus bombings. The following differences were noted:
Difference in blast types resulting in injuries
|Bus bomb||Open air bomb||Significance|
|Primary blast injury||77.5%||34.2%||p=0.00003|
2. Predictor of pulmonary injury
Traditional teaching has emphasized that the presence of a perforated tympanic membrane is an indicator for the potential development of pulmonary blast injury.
However, analysis of pooled data from 11 terrorist bombings in Israel does not support this theory: this analysis suggests isolated tympanic membrane perforation in survivors does not appear to be a marker of concealed pulmonary blast injury nor of a poor prognosis.
In a study of 647 survivors examined at hospital following 11 terrorist bombings in Israel between 1994 and 1996 (Leibovici et al 1999), 193 (29.8%) had primary blast injuries including 142 with isolated tympanic membrane rupture and 51 with other blast injuries (18 isolated pulmonary blast; 31 combined pulmonary and otic blast; and 2 intestinal blast). All patients who had a perforated tympanic membrane had a chest radiograph and at least 24 hours of observation. No patient presenting with isolated tympanic membrane perforation later developed signs of pulmonary or intestinal blast injury. In a mass casualty situation, persons with isolated tympanic membrane perforation can be safely discharged after a chest radiograph and a brief observation period.
The same analysis confirms that the absence of a perforated tympanic membrane does not exclude pulmonary blast injury.
3. Healing and treatment
Repeated observational studies identify a high rate of spontaneous healing of ruptured eardrums following blast injury, except for large defects. Surgical intervention will be considered for a drum that remains perforated at 3 months post-injury or in the emergency setting for disruption of the ossicular chain and damage to the oval window.
Kronenberg et al (1993) evaluated healing in 147 patients with 210 perforated eardrums following blast. Spontaneous healing occurred in 155 ears (74%) at one year although 131 of these healed within the first 3 months. Large and central kidney-shaped perforations had the least tendency to heal and usually required surgical intervention. Tympanoplasty was performed on 33 ears, ossiculoplasty on 5 and mastoidectomy on 10.
Sprem et al (2001) set out to establish whether hearing loss after eardrum blast injury could be recovered by tympanoplasty performed immediately after injury, and what material is most suitable for eardrum closure. 119 patients (with 181 injuries) underwent tympanoplasty between 1991 and 2000. The authors concluded that small ruptures should be left to heal spontaneously, but patients with rupture that did not heal spontaneously within 3 months should undergo tympanoplasty.
There was no significant difference in technical success to achieve eardrum perforation closure using temporal fascia, perichondrium from the tragus or heterograft.
Pahor (1981) in describing ENT problems following the Birmingham bombings in 1974 identified that defects involving over 80% of the surface area of the drum persisted, whereas those involving
The attached algorithm provides a simple approach to referral for specialist opinion on the management of blast-induced eardrum perforation. A damaged eardrum that has not perforated may undergo secondary rupture if exposed to significant changes in barometric pressure, for example diving or commercial airline flight.
A baseline audiogram and tympanogram are desirable for all patients exposed to a significant blast load and should follow ENT assessment.
Conductive hearing loss will occur following blast-induced perforated eardrum. Sensorineural hearing loss, tinnitus and disorders of balance can also occur. Scrupulous attention to keeping the ear dry is an important factor in minimizing secondary infection.
Roth et al (1989) retrospectively studied Israeli soldiers with perforated eardrums following blast between 1967 and 1986. “Most” had impaired hearing, of whom 74% had sensorineural or mixed hearing loss and 60% complained of tinnitus and/or vertigo. In 13% there was an associated purulent discharge and in 8% a cholesteatoma had developed 1 to 4 days after injury.
Lucic (1995) studied 49 wounded with explosive injury of the middle ear: 79% had a ruptured ear drum, 16% had a fractured ossicular chain and 5% had paralysis of the facial nerve. Secondary infection developed in 18% and chronic otitis developed in 10%.
Colonel T J Hodgetts QHP OStJ MMEd FRCP FRCSEd FFAEM FIMC FRGS
Defence Consultant Adviser in Emergency Medicine Honorary Professor of Emergency Medicine and Trauma
Academic Department of Military Emergency Medicine at the Royal Centre for Defence Medicine and the University of Birmingham
Kronenberg J, Ben-Shosan J, Wolf M. Perforated tympanic membrane rupture after blast injury. Am J Otol 1993; 14(1): 92-4.
Leibovici D, Gofrit ON, Stein M et al. Blast injuries: bus versus open-air bombings - a comparative study of injuries in survivors of open-air versus confined space explosions. J Trauma 1996; 41(6): 1030-5.
Leibovici D, Gofrit ON, Shapira SC. Eardrum perforation in explosion survivors: is it a marker of pulmonary blast injury? Ann Emerg Med 1999; 34(2): 168-72.
Lucic M. Therapy of middle ear injuries caused by explosive devices. Vojnosanit Pregl 1995; 52(3): 221-4.
Roth Y, Kronenberg J, Lotem S et a_l. Blast injury of the ear. _Harefuah 1989; 117(10): 297-301.
Sprem N, Srecko B, Dawidowsky K. Croatian Medical Journal 2001; 42(6): 642-5.