The term SIDS was initially coined in 1969 to define any unexpected death of an infant or young child that remained unexplained after a thorough investigation, including autopsy. It is essentially a diagnosis of exclusion. Currently, to determine that a death is due to SIDS, one has to adhere to a strict guideline, which includes a child between the age of 1 month and 1 year, without any pre-existing conditions including prematurity, and being found supine on an appropriate sleep surface without anything that could compromise the child’s ability to breathe. The diagnosis cannot be made until a complete autopsy has been performed, including toxicology, histology, metabolic analysis, review of medical records, and a thorough scene investigation. If no other potential or actual etiologically specific pathology is found, the cause of death can be deemed SIDS. The rate of SIDS has decreased dramatically over the years. The reason for the decreased incidence is twofold: (a) the back to sleep campaign, and (b) the change in the definition of SIDS. In 1994, the National Institute of Child Health and Development initiated the Back to Sleep campaign. Over the following 10 years, the rate of SIDS deaths decreased by greater than 50%, decreasing from 1.34 per 1000 live births to 0.64 per 1000 births (22). A number of risk factors for SIDS have been identified such as male sex, black race, and winter months. Most cases of SIDS occur before 6 months of age, usually between 2 and 4 months of age. A meta-analysis of 35 case control studies revealed that both prenatal and postnatal maternal smoking was associated with an increased risk of SIDS (23). This was dose dependent and suggested that maternal cessation of smoking may be protective against SIDS. Another meta-analysis, this time on 18 studies, showed that breastfeeding of any extent and duration was protective against SIDS, possibly as a result of its immunologic benefits (24,25). There is a divide between medical examiners as to the manner of death in SIDS cases, whether it be natural or undetermined. Many believe that all external factors have been ruled out and thus it is a natural death, whereas others believe that we still do not know why the child died and thus it deserves an undetermined manner. The autopsy in these cases is essentially negative, thus ruling out any obvious natural disease or traumatic injury. A common finding at autopsy is the presence of petechiae on the serosal surfaces of the thymus, lungs, and heart. These are nonspecific findings, which can be seen in other causes, such as asphyxia. Microscopically, these petechiae may be seen, as well as pulmonary edema, congestion, and slight hemorrhage. Recent research has focused on morphologic differences in the brainstems of children who have died of SIDS suggesting that these cases may be due to immature development of the centers responsible for arousal, cardiovascular, and respiratory functions. When these children are faced with an environmental stressor, they are vulnerable to sudden death. This has led to the triple risk model: underlying vulnerability, critical stage of development (peak between 2 and 4 months of postnatal life), and an exogenous stressor (26,27). Intrinsic and extrinsic risk factors have been identified. The intrinsic risk factors include African American race, male gender, prematurity, and prenatal maternal smoking or alcohol use, whereas extrinsic risk factors include any physical stressor present around the time of death such as prone or side sleep, bed sharing, over bundling, soft bedding, or the child’s face being covered (26). Ninety-nine percent of SIDS infants had at least 1 intrinsic or extrinsic risk factor, and 75% had at least 1 of each (26). As will be described below, a diagnostic shift has taken a number of these extrinsic factors and changed the terminology from SIDS to SUID (sudden unexplained infant death) (27). There is an adage that the first unexpected death of a child in a family may be SIDS, a subsequent death may be deemed undetermined, and a third death is a homicide until proven otherwise.

Recent studies have highlighted the prevalence of cardiac channelopathies in sudden infant deaths. Some of the more well-known disorders that are identified in sudden death in young individuals are long QT syndrome, Brugada syndrome, short QT syndrome, and catecholaminergic polymorphic
ventricular tachycardia. Long QT syndrome has a prevalence of 1 in 2500 and is currently known to involve over 700 mutations in 12 genes (28). Mutations in repolarizing cardiac potassium channels KCNQ1/Kv7.1 (LQT1) and hERG1/Kv11.1 (LQT2) are the most common and predispose the individual to ventricular arrhythmias, syncope, and sudden cardiac death (29). Schwartz et al. identified that 50% of a cohort of SIDS deaths had a prolongation of the corrected QT interval and that if there was the presence of a prolonged corrected QT interval in the first week of life, it imparted a 41.6 times increased risk of SIDS (30). The other disorders mentioned have varying mutations and lethality but usually present with the same symptoms. The above-mentioned known channelopathies are seen in SIDS cases but research on children who have died of SIDS shows that the majority of the channelopathies in these deaths are related to mutations in the sodium channels (29). The importance of identifying a channelopathy as the cause of death is not only to help the family come to an understanding of why their child died but to alert the family to the possibility of a sibling having the same mutation and to refer him or her for evaluation. Other genetic abnormalities have been found in infants who die suddenly and unexpectedly, such as medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which is the most common inherited disorder of fatty acid metabolism, which presents in early childhood with a potentially fatal episode of hypoketotic hypoglycemic crisis (28).

An apparent life-threatening event (ALTE), which used to be termed “near miss SIDS,” is defined as “an episode that is frightening to the observer, since it is characterized by some combination of apnea (centrally or occasionally obstructive), color change (usually cyanotic or pallid, but occasionally erythematosus or plethoric), and marked change in muscle tone (usually marked limpness), choking or gagging” (31). In approximately half of these cases, an underlying etiology such as episodic gastroesophageal reflux, respiratory infection, and seizure disorder is found. The other half are termed idiopathic (32). Current research has focused on polymorphisms in genes that regulate brainstem neurotransmitters. The medullary serotonin or 5-hydroxytryptamine (5-HT) system with the serotonin transporter gene (5-HTT) regulates multiple autonomic homeostatic functions such as ventilation, thermoregulation, and arousal (28). Abnormalities in the genes that regulate these functions can have serious consequences and thus are thought to possibly play a role in sudden infant deaths. Serotonin seems to play a role in these deaths and may be a valuable tracer for the risk of SIDS in a child with idiopathic ALTE (32). There have been varying reports as to the number of infants who have experienced an ALTE prior to a lethal episode.

SUID utilizes the findings in SIDS but adds in one or a number of the above-mentioned risk factors. The most common investigative findings that result in a death being deemed an SUID instead of an SIDS is bed sharing with an adult in an adult-sized bed (Figure 7-5). Bed sharing is a controversial subject with many believing it is an unsafe sleep environment and others believing it to be safe and promote bonding between the caregiver and child. A nationwide telephone survey revealed that 19.4% of mothers shared a bed with their infant more than 50% of the time, 27.6% bed shared sometimes, and 52.7% never bed shared (33). Another study in Oregon, which represented a greater diversity in its study population, revealed that 35.2% of mothers frequently bed shared, 41.4% sometimes bed shared, and 23.4% never did (34). This, or any of the other risk factors of an unsafe sleep environment, raises the possibility of an asphyxial death, but there is no way to prove it without a confession from the caregiver that the caregiver, or another individual in the bed, was lying on top of the child when he/she was found (see following section for asphyxial deaths) or that the face was
covered in some manner. The weakness of the infant neck muscles makes the infant more prone to asphyxia as a result of rebreathing carbon dioxide and decreased oxygen intake. The autopsies in these cases are most often also essentially negative, but the history or scene investigation shows an unsafe environment.

The autopsy of a child who died of asphyxia is also quite often completely negative. For this reason, the investigation may hold the key to determining the cause of death to be asphyxia. This may be elucidated by a doll re-enactment with photographs, documentation of the postmortem changes at the scene, and witness accounts. The autopsy in these cases may show pallor over the nose and mouth, indicating pressure over these areas, or a line of demarcation in lividity suggestive of compression (Figure 7-6). Asphyxial deaths can result from wedging (the child wedged between two surfaces such as a mattress and wall), overlaying (an individual found lying on top of the child), or obstruction of the face (such as by a blanket or pillow). Overlaying is most often seen in children less than 5 months of age but has been found in children up until 2 years of age (35). As the number of bed sharers increases so does the risk of overlaying. The bed sharers do not need to be adults. There have been documented cases of other children, often siblings, found lying on top of one another where the child located beneath the other child was dead. Parental intoxication increases the risk of overlaying, and some states have even considered criminal charges against these parents. The child may not be able to cry out as the mouth and nose may be covered and the thorax compressed. If the history conveyed by the caregiver suggests the possibility of overlaying but external examination reveals multiple cutaneous or oral injuries, inflicted trauma should be strongly considered. Homicidal asphyxia, such as smothering, can be very difficult to diagnose at autopsy as these examinations may be completely unremarkable as well. In these cases, the pathologist should pay specific attention to the oral region. One may see abrasions of the lips or nose and lacerations of the mucosal surface of the lips or frenula (Figure 7-7). There has been the suggestion by some that severe pulmonary hemorrhage and/or a marked number of intra-alveolar siderophages is consistent with an asphyxial death. Krous et al. looked at 444 cases of infant deaths that were determined to die of SIDS, accidental suffocation, or inflicted suffocation (36). They reviewed the files and microscopic slides to evaluate for intrathoracic petechiae, pulmonary hemorrhage, and siderophages. They
determined that any of these findings in isolation cannot confidently be used to distinguish between a diagnosis of SIDS or suffocation, but if there is significant pulmonary hemorrhage, a thorough inspection of the body for signs of trauma should be considered. In addition, when the number of intra-alveolar siderophages is prominent, the diagnosis of idiopathic pulmonary hemosiderosis should be considered (37). This is a rare disease with a possible hereditary component and a clinical history of cough and hemoptysis. In the acute setting, acute pulmonary hemorrhage is its usual presentation.

Special subtypes of asphyxia include drowning and smoke inhalation. In drowning deaths, a full autopsy examination should be performed in an attempt to identify any natural disease or traumatic event that may have led to the drowning. In infants, drowning often occurs in the bathtub, especially if they are not attended to appropriately, whereas toddlers drown in pools more often as they may wander and enter the pool without the ability to swim. Once adolescence is reached, the risks change to include open bodies of water. Toxicologic analysis should be performed in these cases as often there is the combination of alcohol and swimming that contribute to the death of these adolescents. Young children are considered a high-risk group for deaths due to smoke inhalation, the most common scenario occurring as a result of a house fire. Autopsy examination of these children should be performed not only to test for a carboxyhemoglobin level but also to rule out other injuries. Carboxyhemoglobin saturation is one test used to identify if the child may have been alive prior to the start of the fire, which will be displayed by a carboxyhemoglobin level of 10% or more. Indicators that suggest carbon monoxide exposure include cherry-red lividity and cherry-red discoloration of the viscera. Black soot may be found focally or throughout the tracheobronchial tree (Figure 7-8).

Accidental strangulation is another form of asphyxia that used to be seen more often but has decreased in incidence due to the acts of the Consumer Product Safety Commission, public awareness, and manufacturing changes. Common household items that have led to accidental strangulation include pull strings on window blinds and pacifier strings. Ligature hanging can be seen in the teenage years as a result of suicidal intent or accidentally due to autoerotic asphyxia or “pass out games.” Just the weight of the head is needed to cause death via hanging; thus, it is not uncommon to find the individual sitting, kneeling, or with the feet touching the ground (Figure 7-9A). These cases deserve the attention of the medical examiner due to the sensitive nature of these deaths. Determining the cause and manner of death in these cases may elicit strong emotional responses from families. External examination of the neck in any form of hanging may reveal a ligature furrow around the neck. This is usually composed of an area of depression with abrasion or dried yellow skin. The furrow usually has a horizontal orientation on the anterior neck and angles upward and backward behind both ears in suicidal hangings but may have a different configuration
in other types of hangings, depending on the position of the body (Figure 7-9B). The furrow findings will be present if the individual was hanging for at least a number of minutes to hours. Internal examination of the neck should reveal the lack of intramuscular hemorrhage in the strap muscles, and there should not be any fracture of the hyoid bone or thyroid cartilage. The same is true in the case of autoerotic asphyxia, except that the ligature furrow may have varying configurations depending on the apparatus that was used. Autoerotic asphyxia describes an act performed by an individual seeking to heighten orgasm by restricting oxygen to the brain. This is usually done by placing a ligature around the neck, which is attached to an escape mechanism that allows the person to release the tension on the neck prior to passing out. Essentially, these deaths are due to the failure to utilize the escape mechanism in a timely manner, most likely due to the individual losing consciousness. Once again, scene investigation may be the most important aspect of the investigation. Suicidal hangings may have a “note of intent” at the scene, or messages may be found on the individual’s phone or social media account that sheds light on his or her mental state. In autoerotic asphyxia cases, the scene has often been altered prior to law enforcement or emergency medical services arrival due to the social stigma that may accompany this type of death. At the scene of an autoerotic asphyxial death, look for any sort of pornography, clothing of the opposite sex, and any information on the deceased’s computer that may indicate the possibility of experimentation. The manner of death in autoerotic asphyxia cases is accident. The mechanism of death in any of these cases is usually one of vascular occlusion and not as a result of airway occlusion. Depending on the width of the ligature used, pressure will be placed on the jugular veins first and carotid arteries next. Petechiae can be seen on the conjunctivae, oral mucosa, and face when the drainage of blood from the brain is halted due to occlusion of the veins with continuation of blood supply to the brain through the carotid arteries. Asphyxial games (a.k.a. the choking game, Space Monkey, Funky Chicken, etc.) are becoming more prevalent in the teenage population. Autopsy findings include florid facial petechiae, but often, there is absence of conjunctival petechiae. These games are often performed in isolation, as opposed to historically being done in groups. The mechanism of death is similar to those of autoerotic asphyxia, but there is no elaborate setup and no sexual connection. If the right questions are asked, the investigator may be able to elicit a history of playing this game with a continuous attempt to prolong the length of time of asphyxia (38). Cervical spine fracture, “hangman’s fracture,” is not seen in any of the above described cases as they occur in judicial hangings or the rare instance where an individual jumps from a height with a noose around the neck. There needs to be a drop from a height with rapid deceleration to cause this type of fracture.

Injuries to a child may be accidental or nonaccidental. Children who present with injuries should be examined by a physician who specializes in the evaluation of these types of injuries. This is of vital importance in order to avoid a false accusation of child abuse and possible criminal conviction of an individual who is innocent and vice versa. It is important to note that the lack of external trauma does not rule out inflicted injury as significant internal injuries can be found without any external evidence. Conversely, external trauma does not necessarily correlate with internal injuries and is not definitively diagnostic of child abuse. When documenting injuries, the distribution, pattern, and severity of the injuries need to be considered. Does the overall injury profile correlate with the history given? Epidemiologic studies have shown that the most common perpetrator of child abuse is the biologic father followed by the mother’s boyfriend. Often, there is the given history of a minor fall at home, which does not correlate with the injuries found to the child, or that the child was found unresponsive with no traumatic history. The true incidence of inflicted head injury is not known as the child may present with nonspecific signs that resolve, and a false diagnosis, such as a viral syndrome, may be given. The most common form of abusive injury is that of head trauma with abdominal trauma being the second most common form of inflicted trauma. Hospitalization rates for abused children aged 0 to 3 years have remained relatively stable at 2.36 per 10,000 over the last 14 years, the most prevalent group being those under 1 year old. If there is a previous report from child protective services concerning a specific child, there is a 3 times higher risk of that child suffering a sudden unexplained death (39).

The most common form of injury found in child death investigation is that of blunt force. The cutaneous manifestations are usually in the form of contusions, abrasions, or lacerations. A contusion (bruise) is the result of a blunt impact that tears the subcutaneous vessels leading to bleeding beneath the skin (Figure 7-10). Of note, a contusion should not be aged on gross examination; thus, punch biopsies of identified contusions should be processed for microscopic examination. Many variables may affect the color and size of a contusion, including the individual’s skin color, coagulation disorders,
inflammatory disorders, hormonal abnormalities, depth of the bleeding, location on the body, amount of blood, and the light in which the injury is evaluated. Studies of bruising in adults showed development of a bruise within 30 minutes of a traumatic insult. The size of the contusion varied but generally decreased over time (40). The one color change that may be utilized is that yellow discoloration indicates at least 18 hours since the onset of the injury due to the presence of hemosiderin. Histology may be helpful in the determination of aging a contusion but is still an estimation and not specific. In general, perivascular polymorphonuclear leukocytes may be visible around 4 hours after injury, with a peripheral infiltration by around 12 hours. Macrophages peak around 16 to 24 hours and may contain hemosiderin by 72 hours. Fibroblasts may appear at 2 to 4 days (41). An abrasion (scrape) is the result of shearing off of the superficial layers of the epidermis (Figure 7-11). A laceration is a splitting of the skin due to a blunt impact. Examining the depths of a laceration may reveal strands of vessels and nerves “bridging” one side of the wound to the other (Figure 7-12). This helps in distinguishing a laceration from a stab wound, which will cut across all of the deep tissues, including the vessels and nerves.