Abstract:Complete examination of the brainstem involves transverse serial 5-m sections made throughout the entire brainstem. The number of serial sections varies from 360 in sudden intrauterine unexplained death (SIUD) to 600 in term fetuses to over 1400 sections in sudden infant death syndrome (SIDS) victims. The procedure is not applicable in all histopathological laboratories, owing to the need for additional technical personnel. The simplified procedure allows a remarkable reduction of the number of sections. The brainstem is divided into 3 blocks. The first, cranial block, extends from the border between the medulla oblongata and pons up to the upper pole of the olivary nucleus. The second, intermediate block, corresponding to the submedian area of the inferior olivary nucleus, has as reference point the obex and extends 2 to 3 mm above and below the obex itself. The third, caudal block, includes the lower pole of the inferior olivary nucleus and the lower adjacent area of the medulla oblongata. Examinations of the brainstems from 106 SIDS victims, 30 controls, and 51 stillborns underlined a remarkable variability, particularly of the arcuate nucleus. The simplified examination of the brainstem makes it possible to evaluate the structures, examining 3 specific levels, defined by morphologic reference points.

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ABSTRACT. Objectives. To evaluate the frequency, morphology, and pathogenesis (primary or secondary) of the abnormally developed medullary arcuate nucleus (ARCn) in stillbirths.Methods. We examined 26 stillbirths (24 antepartum, 2 intrapartum) that had a gestational age between 25 and 40 weeks and a normal karyotype. All of the stillborns were described as well-developed, with body length and weight proportional to their gestational age. Each case was submitted to complete autopsy examination, which included a systematic gross and microscopic evaluation of the body, the placental disk, and the umbilical cord and membranes. The brainstem was the particular focus of the histologic examination. The study of the various nuclei (nucleus hypoglossus, dorsal vagus motor nucleus, tractus solitarii nucleus, nucleus ambiguus, trigeminal tractus and nucleus, arcuate nucleus, and ventrolateral reticular formation and its neurons and parabrachial/ Kö lliker-Fuse complex) was performed on transversal serial sections through the entire pons and medulla oblongata. The histologic analysis was supplemented by volumetric reconstruction and immunohistochemical detection of both apoptosis and proliferating cell nuclear antigen.Results. Histologic examination showed abnormalities of the medulla oblongata ARCn in 9 fetuses (35%). In 8, a marked hypoplasia was evident, characterized by a volume reduction of the nucleus accompanied by neuronal depletion, whereas in 1 fetus the nucleus was completely absent (agenesis). The absence of gliosis, the negativity of the proliferating cell nuclear antigen analysis, and the similarities in apoptotic indices between the hypoplastic and well-developed arcuate are in keeping with a primary developmental defect. This anomaly is frequently associated with hypoplasia of the reticular formation and chronic hypoxia. ABBREVIATIONS. SIDS, sudden infant death syndrome; ARCn, arcuate nucleus; VMS, ventral medullary surface; PCNA, proliferating cell nuclear antigen; PBS, phosphate-buffered saline; TdT, terminal deoxynucleotidyl transferase; dUTP, digoxigenin-conjugated deoxyuridine; GFAP, glial fibrillary acidic protein.S tillbirth is defined as late fetal death before the complete expulsion or retraction of the fetus from the mother. 1 Advances in maternal and fetal care have produced a significant reduction in perinatal mortality but have not changed the prevalence of stillbirth. With a prevalence of 5 to 12 per 1000 births, 2,3 stillbirths represent approximately half of the cases of perinatal mortality. The risk of unexplained, near-term, intrauterine death is present in any pregnancy, and the cause remains obscure in most instances. 4 Unexpected and unexplained fetal death is far more common than sudden infant death syndrome (SIDS), but the pathologic investigations that have been conducted in it unfortunately are sporadic and incomplete. [5][6][7][8] Investigations of the pathology of the autonomic nervous system in fetuses are sadly lacking, despite that abnormalities of these structures are often the...

The human arcuate nucleus (ARCn) is postulated to be homologous to ventral medullary cells involved in chemoreception, and respiratory and blood pressure responses. Abnormalities in central respiratory control may result from dysfunction of this anatomic ventral area. We evaluated the changes of the neuronal population of the medullary ARCn in infants victims of the sudden infant death syndrome (SIDS). In this study we tested the hypothesis that anatomical deficiency of the ARCn is associated with SIDS. The volume and neuronal density of the ARCn were morphometrically quantified with an image analyzer in 36 cases of SIDS and 12 age-matched controls. We found a marked hypoplasia in the SIDS ARCn compared to controls and, particularly, in 11 SIDS cases (30%) in which the ARCn exhibited a severe hypoplasia, being almost totally absent. Three-dimensional reconstructions and morphometric measurements of ARCn confirmed this marked hypoplasia in all the serial sections examined (P = 0.0001) and the reduced neuronal density (P = 0.0025) in relation to control cases. In conclusion these abnormalities observed in the ARCn are consistent with the idea that ARCn dysfunction plays an important role among the causative factors of sudden infant death. The hypoplasia of the ARCn represents the most frequent congenital abnormality in our experience, and can be a plausible morphological substrate for a subset of SIDS.

The authors are the first to identify in man the preBötzinger complex, a structure of the brainstem critical for respiratory rhythmogenesis, previously investigated only in rats. The evaluation of the neurokinin 1 receptors and somatostatin immunoreactivity in a total of 63 brains from 25 fetuses, nine newborns and 29 infants, allowed to delineate the anatomic structure and the boundaries of this human neural center in a restricted area of the ventrolateral medulla at the obex level, ventral to the semicompact ambiguus nucleus. The neurons of the pre-Bötzinger complex were roundish in fetuses before 30 gestational weeks and lengthened after birth, embedded in a dendritic system belonging to the reticular formation. Besides, structural and/or functional alterations of the pre-Bötzinger complex were present in a high percentage of sudden deaths (47%), prevalent in late fetal deaths. In particular, different developmental defects (hypoplasia with a decreased neuronal number and/or dendritic hypodevelopment of the reticular formation, abnormal neuronal morphology, immunonegativity of neurotransmitters, and agenesis) were found. The authors suggest that the preBötzinger complex contains a variety of neurons not only involved in respiratory rhythm generation, but more extensively, essential to the control of all vital functions. Sudden death and in particular sudden unexpected fetal death could therefore be ascribed to a selective process when developmental alterations of the pre-Bötzinger complex arise.

The parabrachial/Kölliker-Fuse complex has been defined, in different animal species, to lie in the dorsolateral part of the pontine tegmentum and to be subdivided into three well-defined regions: the medial parabrachial nucleus, the lateral parabrachial nucleus, and the Kölliker-Fuse nucleus. Experimental studies have shown that the parabrachial/Kölliker-Fuse complex is involved in a variety of functional activities and above all plays an important role in respiratory modulation. In human brainstem, the cytoarchitecture and physiology of this complex have not yet been fully characterized. The aim of the present study was to examine fetal and infant human brainstems in order to define the precise morphology of the three nuclei of the parabrachial/Kölliker-Fuse complex, and to determine whether this nervous center shows morphologic alterations in sudden infant death syndrome (SIDS) and in sudden intrauterine unexplained death (SIUD). In serial sections of 31 brainstems of subjects aged from 32 gestational wk to 10 months of life, we studied, by morphologic and morphometric analyses, the cytoarchitecture and the extension of the three nuclei of the parabrachial/Kölliker-Fuse complex. All the morphometric parameters were very similar in SIUD and SIDS cases to those of the respective control group, as shown by the absence of significant statistical differences between the two fetus and infant groups. We observed that the features of both the lateral and the medial parabrachial nuclei are largely consistent with those reported in experimental studies. In contrast, the Kölliker-Fuse nucleus appears to be more developed in human beings than in other animal species, showing a greater extension and a more complex structure, as well as subdivision into two subnuclei (compactus and dissipatus).

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