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Fig. 1. Petechiae of thymus in a case of sudden infant death syndrome. In areas, multiple petechiae have become confluent.

The presence of petechiae has been causally linked with asphyxia. Capillary rupture was thought to be caused by increased intravascular pressure and hypoxia (12-18). Their distribution in the head and neck arouses suspicion of neck compression; however, petechiae are noted in nonhypoxic individuals and in survivors of strangulation who were not rendered unconscious (19). Cephalic petechiae are observed in volunteers suspended upside down, resulting in increased intraocular pressure (20).

Increased cephalic venous pressure alone is the factor responsible for the development of postmortem petechiae in areas of lividity, particularly cephalic petechiae in the head-down position (see Chapter 2, Subheading 3.3. and ref. 21). Subgaleal petechiae are considered an artifact of scalp reflection during autopsy; however, in the context of a case, they can indicate increased cephalic venous pressure, either antemortem or postmortem (i.e., face down; see Fig. 2 and refs. 1, 15, 22, and 23). In certain types of mechanical asphyxia, cephalic petechiae reflect increased venous pressure with variable arterial blood flow (10,14,24,25). Cephalic petechiae imply incomplete or intermittent neck compression. Their absence, in the context of neck compression, means complete reduction of arterial and venous blood flow to the head (e.g., "complete" hanging; see Subheading 2.1.6.). In rare cases, carotid sinus stimulation by neck compression leads to sudden death from vagal-induced cardiac arrest (3,5). In this scenario, cephalic petechiae

Fig. 2. Reflected anterior scalp exposing calvarium. Scattered petechiae on scalp under-surface (arrow) and temporalis muscle (arrowhead.) Deceased found facedown.

are absent (5,26). Certain types of mechanical asphyxia (e.g., smothering), which do not involve vascular compression, rarely show petechiae, and if observed, they are few.

Conjunctival petechiae do occur in the absence of facial cutaneous petechiae. Although some sources have stated that facial petechiae are not present without ocular petechiae, cases of isolated facial petechiae have been described (e.g., 1-yr-old suspended from crib, overlaying death in child [24,27,28]). Observers have noted that petechiae tend to be less frequent in pediatric asphyxial deaths (17,29).

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