Anatomo-pathological techniques for the study of brainstem in sudden infant death syndrome (SIDS) and unexpected late fetal stillbirth

Recent observations have identified, both in SIDS victims and stillborn fetuses, frequent developmental abnormalities in the brainstem, particularly in the arcuate nucleus (ARCn), an important cardio-respiratory center of the ventral medullary surface. ARCn hypoplasia, sometimes associated with alterations in other brainstem structures, has been detected in 30-35% of SIDS and stillbirth cases. Aim of the present work is to define our anatomo-pathological techniques for the study of the brainstem. The procedure for the complete examination of the brainstem involves trasversal serial 5-mm sections made throughout the entire brainstem. The number of serial sections varies in relation to the age of the analyzed victim, from 360 in the stillborn to 600 in the term fetus to over 1,400 sections in the SIDS victims. Such procedure, although having the merit of the completeness and accuracy, it is not rountinary applicable in all histopathological laboratories, for the obvious necessities of additional technical personnel. The procedure for the simplified examination of the brainstem allows a remarkable reduction of the sections number. It requires a careful and precise sampling. The brainstem is divided in three blocks: the first cranial one is extended by the border between medulla oblongata and pons up to the upper pole of the olivary nucleus; the second, intermediary one, correspondent to the sub-median area of the inferior olivary nucleus, has as point of repere the obex and it is extended 2-3 mms above and under the obex itself; the third, caudal one, includes the lower pole of the inferior olivary nucleus and the lower adjacent area of the medulla oblongata. The examination of brainstem in 106 SIDS victims, in 30 control infants died within the first year of life, and of 51 stillborn after the 25th week of gestation, has underlined a remarkable variability, particularly of the ARCn, both in dimension and the neuronal density. Therefore, the complete evaluation the brainstem’s structures and their possible abnormalities and/or alterations, requires its full examination on serial sections or, in the simplified procedure, the individualization of defined and constant section levels, identifiable through anatomical repere points. In the first cranial block, the ARCn is well recognizable, either medially and in the initial lateral portions, the hypoglossus nucleus, the dorsal nucleus of the vagus, the tractus solitarius nucleus and the ambiguous nucleus are just recognizable, while the reticular formation and the inferior olivary nucleus are well evident. In the second block, the ARCn appears clearly in the lateral portions, while is reduced in the medial portion; the hypoglossus, dorsal of the vagus , ambiguous, inferior olivary nuclea and the reticular formation are clearly detectable. In the third block the ARCn is detectable, particularly in the fetuses, in the lateral portions, while medially it is absent; all the other nuclei are well recognizable. From the comparative examination of our observations on the ARCn with those reported in the main anatomical textbooks and precisely the texts by Testut, by Martin, and the Olszewski and Baxter atlas, agreements and discordances have emerged. On the basis of these considerations, we conclude that the autopsy protocol for the SIDS and stillborn victims, must include the examination of the autonomous nervous system according to the herein described guidelines”.