Bulbo-spinal pathology in neurocardiac sudden death of adults: a pragmatic approach to a neglected problem

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.

Medullary mediation of the laryngeal adductor reflex: A possible role in sudden infant death syndrome

The laryngeal adductor reflex (LAR) is a laryngeal protective reflex. Vagal afferent polymodal sensory fibres that have cell bodies in the nodose ganglion, originate in the sub-glottal area of the larynx and upper trachea. These polymodal sensory fibres respond to mechanical or chemical stimuli. The central axons of these sensory vagal neurons terminate in the dorsolateral subnuclei of the tractus solitarius in the medulla oblongata. The LAR is a critical, reflex in the pathways that play a protective role in the process of ventilation, and the sychronisation of ventilation with other activities that are undertaken by the oropharyngeal systems including: eating, speaking and singing. Failure of the LAR to operate properly at any time after birth can lead to SIDS, pneumonia or death. Despite the critical nature of this reflex, very little is known about the central pathways and neurotransmitters involved in the management of the LAR and any disorders associated with its failure to act properly. Here, we review current knowledge concerning the medullary nuclei and neurochemicals involved in the LAR and propose a potential neural pathway that may facilitate future SIDS research.

Cytoarchitectural and functional abnormalities of the inferior colliculus in sudden unexplained perinatal death

The inferior colliculus is a mesencephalic structure endowed with serotonergic fibers that plays an important role in the processing of acoustic information. The implication of the neuromodulator serotonin also in the aetiology of sudden unexplained fetal and infant death syndromes and the demonstration in these pathologies of developmental alterations of the superior olivary complex (SOC), a group of pontine nuclei likewise involved in hearing, prompted us to investigate whether the inferior colliculus may somehow contribute to the pathogenetic mechanism of unexplained perinatal death. Therefore, we performed in a wide set of fetuses and infants, aged from 33 gestational weeks to 7 postnatal months and died of both known and unknown cause, an in-depth anatomopathological analysis of the brainstem, particularly of the midbrain. Peculiar neuroanatomical and functional abnormalities of the inferior colliculus, such as hypoplasia/structural disarrangement and immunonegativity or poor positivity of serotonin, were exclusively found in sudden death victims, and not in controls. In addition, these alterations were frequently related to dysgenesis of connected structures, precisely the raphé nuclei and the superior olivary complex, and to nicotine absorption in pregnancy. We propose, on the basis of these results, the involvement of the inferior colliculus in more important functions than those related to hearing, as breathing and, more extensively, all the vital activities, and then in pathological conditions underlying a sudden death in vulnerable periods of the autonomic nervous system development, particularly associated to harmful risk factors as cigarette smoking.

Sudden adult death

In the investigation of sudden death in adults, channelopathies, such as long QT syndrome, have risen to the fore in the minds of forensic pathologists in recent years. Examples of these disorders are touched upon in this review as an absence of abnormal findings at postmortem examination is characteristic and the importance of considering the diagnosis lies in the heritable nature of these conditions. Typically, a diagnosis of a possible channelopathy is evoked as an explanation for a 'negative autopsy' in a case of apparent sudden natural death. However, the one potential adverse effect of this approach is that subtle causes of sudden death may be overlooked. The intention of this article is to review and discuss potential causes of sudden adult death (mostly natural) that should be considered before resorting to a diagnosis of possible channelopathy. Nonetheless, it becomes apparent that many of the potential causes of sudden death can have a genetic basis. Thus, it becomes an important consideration that there may be a genetic basis to sudden death that extends beyond the negative autopsy.

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.

Oxygen-conserving reflexes of the brain: the current molecular knowledge

The trigemino-cardiac reflex (TCR) may be classified as a sub-phenomenon in the group of the so-called 'oxygen-conserving reflexes'. Within seconds after the initiation of such a reflex, there is neither a powerful and differentiated activation of the sympathetic system with subsequent elevation in regional cerebral blood flow (CBF) with no changes in the cerebral metabolic rate of oxygen (CMRO(2)) or in the cerebral metabolic rate of glucose (CMRglc). Such an increase in regional CBF without a change of CMRO(2) or CMRglc provides the brain with oxygen rapidly and efficiently and gives substantial evidence that the TCR is an oxygen-conserving reflex. This system, which mediates reflex protection projects via currently undefined pathways from the rostral ventrolateral medulla oblongata to the upper brainstem and/or thalamus which finally engage a small population of neurons in the cortex. This cortical centre appears to be dedicated to reflexively transduce a neuronal signal into cerebral vasodilatation and synchronization of electrocortical activity. Sympathetic excitation is mediated by cortical-spinal projection to spinal pre-ganglionic sympathetic neurons whereas bradycardia is mediated via projections to cardiovagal motor medullary neurons. The integrated reflex response serves to redistribute blood from viscera to brain in response to a challenge to cerebral metabolism, but seems also to initiate a preconditioning mechanism. Better and more detailed knowledge of the cascades, transmitters and molecules engaged in such endogenous (neuro) protection may provide new insights into novel therapeutic options for a range of disorders characterized by neuronal death and into cortical organization of the brain.

Carotid barochemoreceptor pathological findings regarding carotid plaque status and aging

BACKGROUND

Carotid barochemoreceptor pathological lesions have been studied in animals, but few human necropsies have been performed. Therefore, data rely on case patients following surgery, radiotherapy and carotid endarterectomy. Almost no data are available regarding whether the effect of aging prevails over pathological conditions, despite the classic description that glomic fibrosis increases with age.

OBJECTIVE

To morphometrically characterize the alterations of the carotid barochemoreceptors and their supplying arteries.

METHODS

Patients (n=23) who had suffered and died from stroke, with and without complicated internal carotid atheromatosis, were divided by age (group 1: older than 80 years; group 2: 65 to 80 years; and group 3: younger than 65 years). Carotid segments were obtained at autopsy. The specimens were stained for light microscopy and immunohistochemistry.

RESULTS

Carotid glomus presented from moderate-to-severe atrophy and fibrosis. A focal decrease in vascularization (CD34-positive) of the glomus (greater than 50%) was observed in areas of atrophy and fibrosis. Damaged nerve endings (S100 protein-positive) were observed at the media of the carotid sinus. Morphometric data showed no differences between groups for glomus area, number of type 1 and 2 cells, and the wall to lumen arteriole ratio. No statistical differences were demonstrated in the pathological findings of the carotid glomus when comparing complicated with noncomplicated plaques or age groups.

CONCLUSION

Severe carotid chemoreceptor damage exists in patients who have died from stroke and suffered from carotid atheromatosis. These findings were independent from aging and plaque type. However, damage was correlated with a marked narrowing of the supplying arterioles as a consequence of hemodynamic and/or metabolic alterations (dyslipidemia, diabetes).

Leptomeningeal neurons are a common finding in infants and are increased in sudden infant death syndrome

Developmental abnormalities of the brain, in particular, the brainstem potentially affecting centers for breathing, circulation and sleep regulation, are thought to be involved in the etiology of sudden infant death syndrome (SIDS). In order to investigate whether leptomeningeal neurons could serve as morphological indicators for a developmental failure or retardation in cerebral maturation, we evaluated the density of isolated leptomeningeal neurons (without associated glia) in 15 brain regions of 24 SIDS and 8 control cases, representing part of the German Study on sudden infant death. Leptomeningeal neurons were encountered in 79% of SIDS and 68% of control cases. More leptomeningeal neurons in SIDS versus control cases were found in lower pons (p = 0.002), upper pons (p = 0.016), cerebellar hemispheres (p = 0.012), lower medulla oblongata (p = 0.039), and temporal lobe (p = 0.041). Summarizing the data according to gross anatomical region of origin (i.e., brainstem, cerebellum or cerebrum), higher numbers of leptomeningeal neurons in SIDS cases were only found in the brainstem (p = 0.006 vs. 0.13 and 0.19, respectively). Our data show that single leptomeningeal neurons are present in most normal infantile brains. The age-dependent increase of leptomeningeal neurons among SIDS cases may either (a) represent a delayed maturation or retardation, i.e., a later or slower reduction of neurons or a delayed peak in occurrence (shift toward an older age), or (b) may be interpreted as a generally increased occurrence of leptomeningeal neurons among SIDS cases as a result of a diffuse developmental abnormality during central nervous system maturation.

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.

Sudden infant death triggered by dive reflex

The dive reflex is the reflex mechanism most frequently considered in the aetiopathogenesis of sudden infant death syndrome (SIDS). This seems to persist in human beings as an inheritance from diver birds and amphibians. It has been reported that washing the face with cold water or plunging into cold water can provoke cardiac deceleration through the intervention of the ambiguus and the vagal dorsal nuclei. This report describes a case of SIDS that offers a unique insight into the role of the dive reflex in determining a lethal outcome. Examination of the brainstem on serial sections revealed severe bilateral hypoplasia of the arcuate nucleus and gliosis of the other cardiorespiratory medullary nuclei. The coronary and cardiac conduction arteries presented early atherosclerotic lesions. The possible role of parental cigarette smoking in the pathogenesis of arcuate nucleus hypoplasia and early coronary atherosclerotic lesions is also discussed.

Severe carotid barochemoreceptor involvement in stroke

BACKGROUND

Physiopathology of barochemoreception is hindered by the scarce information on its morphology in disease. The baroreflex is of major importance for the maintenance of arterial pressure during orthostatic stress. The purpose of this paper was to characterize the morphological alterations of carotid glomus in old patients who died from stroke and suffering obstructive carotid atheromatosis.

METHODS

Bilateral carotid segments were obtained at autopsy from 17 patients (51-89 years old). Specimens were stained with hematoxylin and eosin; Azan trichrome, Grimelius silver stain for catecholamine detection, and were immunophenotyped for CD34 and S-100. Similar segments of both carotid arteries of six patients (62-77 years old) who died by accidents were used as controls.

RESULTS

The carotid glomus of patients who died from stroke presented atrophy and fibrosis (2.59+/-0.5 vs. 1.17+/-0.39 in the control group; p<0.0001). There was a loss of chief cells and of the argyrophilic staining granules. A focal diminution of glomus vascularization was observed in the areas of atrophy and fibrosis (2.73+/-0.45 vs. 1.5+/-0.52 in the control group; p<0.0001). The arterioles to glomus showed severe fibrointimal proliferation, disruption of internal elastic lamina and luminal narrowing, and luminal thrombi.

CONCLUSION

A severe carotid glomic damage does exist in old patients who died from stroke and suffering from carotid atheromatosis, independent from aging, of note, a "culprit" marked narrowing of the corresponding arterioles was observed.

Pathological changes of the heart in sudden infant death

There are more than 120 different theories on the possible causes of sudden infant death (SID). In particular, dysfunctions of the central nervous system, cardiorespiratory insufficiency due to infections including atypical immune reactions, and cardiac dysregulation have been discussed during the previous decade. Reports on disturbances of the cardiac rhythmogenic function due to LQTS were among the most speculative. Based on gross histological, immunohistochemical and molecular genetic investigations of SID cases, the most important and most frequent findings of the heart are shown. The significance of different types of myocarditis, hypoxia-related changes, disturbances of the rhythmogenic function, cardiomyopathy, and other changes is discussed with regard to the cause of death. In conclusion, most of the changes reported in the literature are not sufficient to explain the cause of death. Problems in the diagnosis are shown which influence the classification of these disturbances as well as the classification of SID.

Sudden death in a 35-year-old man with occult malformation of the brain and aseptic meningitis

A 35-year-old man was found dead by his wife. He was reported to have had symptoms of a common cold the week preceding his death. The medicolegal autopsy yielded signs of central dysregulation (ectasia of the urinary bladder and rectum, dystelectasis of the lungs) together with marked brain edema and fresh bite marks on the tongue. The cause of death was presumed to be lethal epileptic seizure. Neuropathologic examination revealed neuronal nodular heterotopia as well as discrete lymphocytic meningitis (aseptic meningitis). The death was most probably caused by the combination of the meningitis with the occult malformation, leading to a lowered seizure threshold and subsequent lethal seizure. The morphologic findings of this case are presented, and the probable mechanisms of death are discussed.

Prolonged QT interval and sudden infant death--report of two cases

In the two cases where infants died suddenly and unexpectedly the electrocardiogram (ECG) of a younger sibling (case 1) and of a living twin (case 2) led to the suspicion that the two infants could have died from long QT syndrome (LQTS). In case 1, a His bundle (HB) dispersion and a pronounced hypoplasia of the right external nucleus arcuatus were detected. In case 2, a severe interstitial pneumonia and an accompanying mild myocarditis were found by histology. Molecular genetic investigations of the coding regions of the genes, HERG, KVLQT1 and SCN5A gave no indication for the mutations, thus, affecting related myocardial ion channels as possible sources of inhomogeneity of repolarisation. Since a molecular genetic deviation could not yet be elaborated the possible role of related disturbance remains unknown.