Unexpected Perinatal Death and Sudden Infant Death Syndrome (SIDS): Anatomopathologic and Legal Aspects

Sudden Infant Death Syndrome - Role of Trigeminocardiac Reflex: A Review

Sudden infant death syndrome (SIDS) is an unexplained death in infants, which usually occurs during sleep. The cause of SIDS remains unknown and multifactorial. In this regard, the diving reflex (DR), a peripheral subtype of trigeminocardiac reflex (TCR), is also hypothesized as one of the possible mechanisms for this condition. The TCR is a well-established neurogenic reflex that manifests as bradycardia, hypotension, apnea, and gastric hypermotility. The TCR shares many similarities with the DR, which is a significant physiological adaptation to withstand hypoxia during apnea in many animal species including humans in clinical manifestation and mechanism of action. The DR is characterized by breath holding (apnea), bradycardia, and vasoconstriction, leading to increase in blood pressure. Several studies have described congenital anomalies of autonomic nervous system in the pathogenesis of SIDS such as hypoplasia, delayed neuronal maturation, or decreased neuronal density of arcuate nucleus, hypoplasia, and neuronal immaturity of the hypoglossal nucleus. The abnormalities of autonomic nervous system in SIDS may explain the role of TCR in this syndrome involving sympathetic and parasympathetic nervous system. We reviewed the available literature to identify the role of TCR in the etiopathogenesis of SIDS and the pathways and cellular mechanism involved in it. This synthesis will help to update our knowledge and improve our understanding about this mysterious, yet common condition and will open the door for further research in this field.

Anatomopathological changes of the cardiac conduction system in sudden cardiac death, particularly in infants: advances over the last 25 years

Sudden cardiac death (SCD) is defined as the unexpected death without an obvious noncardiac cause that occurs within 1 h of witnessed symptom onset (established SCD) or within 24 h of unwitnessed symptom onset (probable SCD). In the United States, its incidence is 69/100,000 per year. Dysfunctions of the cardiac conduction and autonomic nervous systems are known to contribute to SCD pathogenesis, even if most clinicians and cardiovascular pathologists lack experience with detailed examination of the cardiac conduction system and fail to recognize lesions that are crucial to explain the SCD itself. In this review, we sought to describe the advances over the last 25 years in the study of the anatomopathological changes of the conducting tissue, in SCD, in mature hearts and particularly in sudden infant death syndrome (SIDS) and sudden intrauterine unexpected death syndrome (SIUDS), through the articles published in our journal Cardiovascular Pathology (CVP). We carried out an extensive Medline search to retrieve and review all articles published in CVP in which the sudden unexpected death of one or more subjects believed healthy was reported, especially if associated with lesions of the conducting tissue in settings that revealed no other explained causes of death, particularly in infants and fetuses. The cardiac conduction findings of resorptive degeneration, His bundle dispersion, Mahaim fibers, cartilaginous meta-hyperplasia, persistent fetal dispersion, left-sided His bundle, septation of the bifurcation, atrioventricular node dispersion, sinus node hypoplasia, Zahn node, His bundle hypoplasia, atrioventricular node, and His bundle dualism were similarly detected in SIDS and SIUDS victims.

The nucleus pararaphales in the human, chimpanzee, and macaque monkey

The human cerebral cortex and cerebellum are greatly expanded compared to those of other mammals, including the great apes. This expansion is reflected in differences in the size and organization of precerebellar brainstem structures, such as the inferior olive. In addition, there are cell groups unique to the human brainstem. One such group may be the nucleus pararaphales (PRa); however, there is disagreement among authors about the size and location of this nucleus in the human brainstem. The name "pararaphales" has also been used for neurons in the medulla shown to project to the flocculus in the macaque monkey. We have re-examined the existence and status of the PRa in eight humans, three chimpanzees, and four macaque monkeys using Nissl-stained sections as well as immunohistochemistry. In the human we found a cell group along the midline of the medulla in all cases; it had the form of interrupted cell columns and was variable among cases in rostrocaudal and dorsoventral extent. Cells and processes were highly immunoreactive for non-phosphorylated neurofilament protein (NPNFP); somata were immunoreactive to the synthetic enzyme for nitric oxide, nitric oxide synthase, and for calretinin. In macaque monkey, there was a much smaller oval cell group with NPNFP immunoreactivity. In the chimpanzee, we found a region of NPNFP-immunoreactive cells and fibers similar to what was observed in macaques. These results suggest that the "PRa" in the human may not be the same structure as the flocculus-projecting cell group described in the macaque. The PRa, like the arcuate nucleus, therefore may be unique to humans.

Sudden unexpected death related to medullary brain lesions

The sudden unexpected death of a person believed healthy has occasionally been followed by a detailed postmortem examination that revealed no cause of death except for the unexpected presence of a medullary brain lesion. Our review of all available cases of sudden unexpected death related to medullary brain lesions (SUD-MBL) revealed the absence of any specific constellation of ante-mortem disease characteristics, together with the finding that major motor and sensory pathways were grossly preserved in most cases. The wide variety in ages of the victims, and in specific types of tissue pathology affecting the medulla, makes this illness extremely difficult to anticipate when the medullary lesions are not otherwise known to exist during life. SUD-MBL may be a specific clinico-neuropathologic disease entity, having significant importance for forensic investigators trying to establish the cause of sudden unexpected death in a victim of any age. Because victims often harbor their medullary lesions for days or weeks before SUD-MBL, clinical physicians as well need to consider the possibility of medullary brain involvement by any disease process, neurologic or systemic, while managing their patients.

Perinatal perimortem and postmortem examination: obligations and considerations for perinatal, neonatal, and pediatric clinicians

Clinicians are called upon to participate in a variety of clinical scenarios in which babies will die. A number of factors have caused the most appropriate method of evaluating cause(s) of death, namely autopsy, to fall to record low numbers during the past decade. Because of obligations unique to the stillborn fetus, dead or dying infant or child, and family and siblings, it is important for clinicians to understand the importance and utility of postmortem examination. Postmortem examination is of multidisciplinary importance to determine the cause of death and contributing and related diagnoses. This article summarizes some of what is known about postmortem examination and provides a list of guidelines available on the Internet and in the medical literature for the systematic assessment of perinatal death and the provision of appropriate testing. Clinicians are encouraged to use their leadership roles to improve rates of postmortem examination and to participate in research and education to improve its occurrence.

Histological and biological developmental characterization of the human cerebellar cortex

The aim of this study was to investigate the histological and biological features of the human cerebellar cortex development and differentiation. We analyzed 52 brains of fetal and infant death victims, aged from 17 gestational weeks to 12th postnatal month. In particular, in the cerebellar cortex at different ages we evaluated, besides the structural aspects, the expression of several biomarkers implicated in proliferative processes (c-fos, PCNA and apoptosis). We observed morphological patterns progressively evolving every month, from the indefinite structure of the second gestational trimester to the four-layered structure (external granular layer, molecular layer, Purkinje cell layer, internal granular layer) of the late fetal cortex and subsequently to the three-layered postnatal definitive morphology, due to involution of the external granular layer. The evaluation of the biological features of the cerebellar cortex showed high proliferative activity mainly confined to the transient external granular layer in prenatal life, and high apoptotic index after birth. Thus, the histological examination, better with the support of biomarker investigations, allows with accuracy to describe the dynamic sequence of steps that occur in human cerebellar cortex development and to establish in each case the age, namely the pre- or postnatal month of life. Consequently, we can diagnose delayed or altered processes of differentiation during the development of the human cerebellar cortex.

Sudden infant death syndrome (SIDS) shortly after hexavalent vaccination: another pathology in suspected SIDS?

Experts from panels of the European Agency for the Evaluation of Medical Products have investigated whether there might be a link between hexavalent vaccines and some cases of deaths that occurred. Participants included pathologists with experience in the field of vaccines and sudden infant death syndrome who conducted autopsies. However, to the best of our knowledge, little, if any, attention was paid to examination of the brainstem and the cardiac conduction systems on serial sections, nor was the possibility of a triggering role of the vaccine in these deaths considered. Herein we report the case of a 3-month-old female infant dying suddenly and unexpectedly shortly after being given a hexavalent vaccination. Examination of the brainstem on serial sections revealed bilateral hypoplasia of the arcuate nucleus. The cardiac conduction system presented persistent fetal dispersion and resorptive degeneration. This case offers a unique insight into the possible role of hexavalent vaccine in triggering a lethal outcome in a vulnerable baby. Any case of sudden unexpected death occurring perinatally and in infancy, especially soon after a vaccination, should always undergo a full necropsy study according to our guidelines.