Relief of Intractable Vomiting from Surgical Lesions in the Area Postrema

I N THE human brain there are at least three small widely separated areas that have certain features in common but differ histologically from surrounding tissues. On the basis of their topographic location they are referred to as the supra-optic crest, the intercolumnar tubercle and the area postrema. 4,1~ Histologically these structures are characterized by the presence of many small glialoid cells resembling astroblasts, larger cells which, in man at least, appear to be neurons and numerous sinuslike capillaries. 5 These anatomical entities differ from most other tissues in the central nervous system in that they are readily permeable to many particulate substances such as t rypan blue which do not penetrate tlle central nervous system except very slowly and in small amounts. TM The area postrema, which is the subject of this study, was first described in 1896 by Retzius s and further elucidated in an excellent monograph by Cammermeyer in 1945. 6 Since the investigations of Wislocki and Putnam u,~2 in 1920 and 19~4, some secretory or excretory function of area postrema has been suspected. Its importance in the process of vomiting of certain animals has been demonstrated the last 10 years. Although it has long been known that the basic central mechanism that controls vomiting is situated in the medulla oblongata, 7 a functional distinction between a specialized medullary-chemoreceptor apparatus and the neural-coordinating center for emesis has been made only recently2 ,9 The morphological separation of the superficial trigger zone (CT-zone) of the medullary emetic chemoreceptor from the ventrally situated vomiting center has been accomplished in the cat and dog by means of direct central electrical stimulation 2 and ablative procedures. 3 The discrete connections and receptor functions of the CT-zone remain to be delineated exactly, but it is evident that in some animals an important role in the activation of emesis must be assigned to the area postrema, which is considered to be the morphological substrate of the site of the central emetic receptor. 1 On the basis of the experience with chronic CT-zone ablations in certain animals, a similar procedure was deemed justifiable on human beings in an a t tempt to control intractable vomiting in strictly selected patients. While therapeutic surgical lesions had previously, to the best of our knowledge, not been applied to the area of the 4th ventricle, it was reassuring that in most cases of medullary-tract sections, modus SjSqvist, the complications had been minor or temporary. One of us (P. A. L.) therefore selected 5 patients with severe vomiting, and on them performed a superficial ablation of the area postrema for therapeutic purposes. The studies of these 5 patients are reported herein and discussed.