The incidence of diaphragm laceration caused by blunt trauma is about 2% (203,338,339). The most common cause is motor vehicle trauma; and occupants in nearside impacts are at greater risk than individuals in a frontal collision (339-344). A review of National Automotive Sampling System data from 1995 to 1999 showed a greater likelihood of diaphragm injury, if frontal or near-side occupant compartment intrusion was more than 30 cm (12 in.) or the velocity change (8 V) during impact was greater than 40 km/h (25 mph) (345). Injury mechanisms include shear stress on a stretched diaphragm, avulsion of diaphragm attachments, and sudden transmission of force by abdominal viscera (203,344).

Various series of diaphragm injury show a left-sided predominance (203,339, 343,346-348). The right hemidiaphragm is protected by the liver (203,338). Bilateral tears are uncommon (203,339,346,347,349,350). Intrathoracic herniation and strangulation of abdominal organs (e.g., stomach, intestine, omentum, spleen, liver) can occur (Fig. 38; refs. 346 and 351). The pressure gradient between the abdomen and thorax is increased by abdominal pressure and maximal respiratory effort; this promotes hernia-tion into the chest cavity (203,338). One series showed that herniation occurred through defects 10 cm (4 in.) or more (339). Rupture of a hemidiaphragm results in diminished ventilation, compounded by a herniated organ compressing a lung (203). Mediastinal displacement leads to impaired venous return to the heart (203). Immediate death is uncommon (338).

Diaphragmatic tears are rarely isolated and are usually associated with other severe injuries (203,338,339,341-343,347,348,350,352). A significant number of

Fig. 38. Traumatic rupture of diaphragm. Motor vehicle collisions (two cases). (A) Chest radiograph. Herniation of large bowel. Bowel gas seen (arrow). (B) Another case shows herniation of stomach (arrow) through the torn left hemidiaphragm.

uncomplicated diaphragm tears are not diagnosed (203,339). In a literature review, a preoperative diagnosis was made in about 44% of cases and at autopsy or thoracotomy in 41%. The diagnosis was delayed in about 15%. Diaphragmatic tears rarely heal without surgical repair (338,339,341). Strangulation of herniated intra-abdominal viscera can be a delayed complication (338,347).

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