A man dies in a crowd crush with his chest trapped against a barrier. Petechial haemorrhages cover his face, scalp, conjunctivae and the skin above the clavicles, but the legs show none. The reason for this distribution is:

• A Disseminated intravascular coagulation triggered by crush injury of muscle
• B Direct mechanical crushing of the facial capillaries by the compressing mass
• C Retrograde transmission of the abruptly raised intrathoracic pressure through the valveless veins draining the head, neck and upper limbs ✓
• D Gravity-dependent settling of blood in the upper body during the agonal period

Explanation

In traumatic asphyxia the compressed thorax cannot expand and the glottis is closed, so intrathoracic pressure rises abruptly. Because the veins of the head, neck and upper extremities lack valves and drain into the superior vena cava, this pressure is transmitted backwards, distending and rupturing small venules and capillaries of everything drained by the SVC, producing petechiae confined to territory above the clavicles or nipple line. Direct crushing explains nothing outside the contact area, and DIC or gravity do not respect this anatomical boundary.

Reference: Knight's Forensic Pathology, 4th ed.

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Written and medically reviewed by the StethoPrep medical team.