The Posterior Median Aperture of the Fourth Ventricle

Home , Fourth ventricle, Median aperture, Obex

Loyola University Chicago Loyola eCommons

Master's Theses Theses and Dissertations

1931

Ethel Althea Chapman Loyola University Chicago

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THE POSTERIOR MEDIAN APERTURE OF THE FOURTH VENTRICLE A .-. THESIS SUBMITTED TO '!HE FACULTY OF • LOYOLA UNIVERSITY GRADUATE SCHOOL IN CANDIDACY FOR THE DEGREE OF MASTERS OF SCIENCE

BY ETHEL ALTHEA CHAPMAN

DEPARTMENT OF ANATOMY

CHICAGO, ILLINOIS 1931 -1-

Introduction The posterior median aperture of the fourth ven.tricle, most commonly known as the foramen of Magendie, has been

8 subject of controversy since the ~~rly part of the nine teenth century. At that time Francois !lagendie described its location as being at the extreme caudal end of the roof o! the fourth ventricle in the !idline. The chor1~14 plexus of the roof has the form of a T with the stem of the T directed caudally towards the anterior boundary of' the foramen of Magendie. The obex, which is the most posterior attachment of the root to the medulla, is caudal to the a.perture.

Some workers believe that the ~perture is mer an artifact produced frequently in gross dissection be use of the delicateness of the root. Dr. Strong for some time haa'been interested in this controversy and suggested that a microscopic study o the foramen be made. Therefore, as many human fetuses and adult monk s as were available were obtained and fixed thoroughly as soon as possible after death. The problem consisted of removing the brains without injury to the meninges o the medulla and cerebellum, and making serial secti through the caudal end of the fourth ventricle. -2-

~ese secti~ns were examined for an aperture and to d~er •ine whether any Qperture that might be found is a true to ramen. I am very greatly indebted to Dr. George w. Bartelmez of the University of Chicago for supplying me with the brains of monkeys. To Dr. Bertha Van Hoosen I wish to express my appreciation for herr kindl).ess in notifying me ot available fetuses as well as to the Women's and Cbild ren•·s Hospital, Holy Cross Hospital, Oak Park Hospital, west Suburban Hospital, Dr. Pritikin, and Dr. Guerra for tet.al material. Yost of the technical work in connection with the problem was done under the QUidance of Ur. Warren. At all times he was ready with invaluable advice and assistance. Lastly I want to thank Dr. Essenberg, Dr. Job, and • Dr. Chandler for their interest in the success of the problem and for all thoughtful suggestions and Dr. Strong to whom entire credit goes for its undertaking. All points of interest in the sections were discussed thoroughly with Dr. Strong before any conclusions were reached. , All microphotographs were made by our artist, Miss Bakehouse. - -3- Literature • The history of the study of the foramen of Magendie has been reviewed quite thoroughly by Blake (1900), Dandy and Blackfan (1914), Weed (1917), and Levinson (1918). Levinson (9) writes that Heroph'ilus in 300 BC had learn ed of the existence of the ventricles and of the chorioid plexus but none of the early anatomists up to the time of Varoli (1575) ever mentioned a fluid in the ventricles. Domenico Contugno and Albertus von Haller (1708-1777) noticed that the fluid descended through the bottom of the ventricles. However, it was Francois Magendie (1825) who first demonstrated an opening in the roof at the caudal end of the fourth ventricle in experimental animals. After this, the existence of the aperture was denied •· by such reliable scientists as Monroe, Krause, Virchow, Todd and Reichert, according to Dandy and Blackfan (3). Then Luschka (1854) demonstrated the presence of the opening to his own satisfaction and named it in honor of Magendie. He found it absent in some animals but thought that accompanied large lateral apertures. Key and Retzuis confirmed Luschka's findings. Retzius (1896) examined one hundred human brains and found the foramen of Magendie absent in only two. Likewise, Hess examined the brains of thirty human adults, ten new born children, and seven human embryos - -4- making a total of forty-seven, and found the metapore• absent in only one. He also found openings in the cat embryo. Wilder in 1884 was doubtful of ..the existence of a true aperture but wrote that one seemed to be present • .After examining Hess's paper in which the above de.ta were given he reached several additional ionclusions (1886). First he determined that in the cat there is no foramen. However, in man he believed that there is a posterior median foramen approximately rhomboidal in outline, about five millimeters wide and eight to ten millimeters long. The margins of the foramen he found irregular and ragged even when most car-efully exposed. In 1893 Wilder wrote that there are at least two kinds of metapores, one in which the metaplexuses barely ... project at the margins, the other in which they extend for some distance upon the cerebellum. He quotes Minots theory of two possibilities in the develop-ment of the metapore: either it is a break in the epithelium or it is the orifice of an evagination. New negative evidence was brought out by Cannieu in 1898 who investigated by both gross and microscopic methods. By gross dissection he found the metapore pres ent in the dog, cat, rabbit, guinea-pig, horse, ox, ass, and man. But he made sections of the brains ~ ~~------~ -5- • of the dog and the cat, and found it absent. He concluded that its apparent presence in the gross specimen was dae to a poor state of preservation of the brains. Scbmorl, after making a study of the cerebro-spinal ...fluid and foramen of Magendie agreed with Cannieu. In the twentieth century workers seem to have favored the true existence of the foramen. Blake's work in 1900 was largely responsible for this stand. He made histolog ical sections of the brains of both man and lower animals. When practicable, the whole head was sectioned after decal

c~fication. Otherwise the brain was removed after fixation with the cerebellum and tentorium intact. He used Van Gieson•s stain by which he felt he could differentiate clearly between membranes and the ependymal 8pithelium. He found the metapore present in two specimens at the age of • four months and not present in embryos of twenty-two to forty-two millimeters. Blakets hypothesis has been quite extensively quoted lately. He found a caudal bulging of the tela choriodea which became more and more extensive in older embryos. In man he believed this pouch became sheared off leaving the foramen of Magendie. In some adults he found the chorioid plexus projecting out through the foramen. Mall (1904), in his study of the development of the vessels of the brain, found that India ink passed through ~------, -6- • the foramen of Kagendie from the subarachnoid space. Heuser (7) studied the development of the cerebral veins

and examineu the roof of the fourth ventricle. He s~ated tbat caudad to the cho,rioid plexus the... roof is slightly dis- tended or putred up, thus forming a caudal protrusion such as Blake mentioned in his paper. But in the pig embryo the protrusion is dome-shaped rather than finger-like. Frazier and Peet (1914) saw the aper.ture by incision posterior to the occipital protuberance and careful removal of the dura. Dandy and Blackfan (3) studied the existence of the foramen in connection with a study of hydrocephalus, as did Levinson. Both men consider it as being normally present. Jlore recent and extensive work has. been done by Weed (1917) and the same kind of work by Keegan who worked inde- • pendently. Weed made a study of tbe roof of the fourth ven tricle in a.bryos of several species and different ages. The existing cerebro-spinal fluid in a living embryo was replace-d by a true solution of ferric ammonium citrate and potassium ferrocyanide and the exit of the solution from the ventricle was studied. He found a round area of flattened cells at the caudal end of the roof of the ventricle, where the fluid passed freely in to the subarachnoid space. In order to dis cover at what time the area first appeared it was traced 'tbrough t;he yo:m!JBI" embryos. It is found first at the fifteen ~~------~ -7- • m1ll1meterl stage in the human being and according to Weed bas been an unmistakable differentiation or the ependyma

already tormed. In o~her words, the columnar~pendymal cells

have become pavement cells in this ov~l area. The area increases rapidly in extent, and when the cerebello-medulllary cystern is formed it is the sole separation of the ventricle from the future subarachnoid space. Even the oldest fetuses studied by Weed showed no break- ing down or shearing ott or a projection to form an aper ture. Whether this area becomes perforated to form the posterior median aperture or persists as an intact membrane, Weed could not determine, but it is certain that foramina play no part in the circulation of the cerebral fluid up to the time of at least twenty-six millimeters. ,.. ------~-a Material and Methods. • The material used included human fetuses of ages above five months and adult monkeys. In both types of material the same method of fixation was adopted. Fetuses were obtained as.-. soon as possible after death. Due to delay in notification, the fetuses were at least twenty-four hours dead but had been kept cold immediately after death so that the tissues were.. in good condition for

sectioning. The great difficu~ty was found with masceration and in several specimens the cerebellum was so distorted that sections were not made. Whenever the specimens appeared feasible for sectioning, a ten percent solution of formalin was injected into the aorta, with as little pressure as necessary, and allowed to pass out through the jugular vein. Then, either the calvarium was removed or a hole was made in it and a slit in the cranial dura to facilitate penetration when the whole head was immersed in formalin. After four days of immersion, the brain was removed from the head. This was done by sawing in a parasagittal plane on both sides of the cerebellum after the calvarium had been removed. The bones dorsal to the medulla and cerebellum were removed by careful trephining_ so that the dura mater was left intact on the cerebellum. Then a cut was made transversely through the nervous tissue rostal to the cerebellum. The dura was cut on both sides lateral to -9- the cerebellum and the brain stem and cerebellum lifted out with the dura intact on the dorsal side only. In spite of great care in trephining the bones in the region of the foramen of Magendie it was impossible not to have some strain on the membranes so that there was great danger of tearing the thin roof of the fourth ventricle. The brains of the monkeys were fixed immediately after death at the University of Chicago. Intraarterial inJection of formalin was done by means of the carotids, the skull cap was removed and the brain immersed in five percent formalin. After several weeks of fixation removal was undertaken as in the fetuses. Fixation was continued until the tissues seemed firm. Then they were dehydrated through a series of alcohols and celloidin preparations were made and sectioned. Ordinary hematoxin and eosin staining was used for all preparations. -10- • Discussion In the monkey both a transverse and a sagittal series were examined, and in the human fetuses a sagittal series was studied carefully with special regard to the ependymal lin- . ' .., ing, the pia of the cerebellum, and the tela chorioidea and chorioid plexus. All three series reveal a similarity in several points which will bear careful consideration. Firstly, the tela chorioidea in the medial region dorsal to the central canal does not appear to be attached to the medulla in any of the sections. In other words, the most caudal part of the roof of the fourth ventricle, usually called the obex, appears to contain an aperture. Secondly, the tela chorioidea and chorioid plexus in both transverse sections and sagittal sections can be traced caudally along the ventral surface of the vermis until it definitely ends in a connection with the pia of the cerebellum. This connection occurs near the caudal end of the ventral surface of the cerebellum. See Series A. Thirdly, in both series of sagittal sections, the ependymal lining of the floor of the ventricle comes to an abrupt ending at a point caudal to the entrance of the central canal into the fourth ventricle, Diagrams A-3 and C-5.

The tela chorioidea extends much further caudally th~n this point of termination of the· lining of the floor. Further more, the pia of the medulla extends cranially almosu. to -ll- the ependymal cells so that for some distance the tela •chorioidea and chorioid plexus are separated from the medulla by the pia mater of the medulla. Diagram A-4 and B-Jr. Since the delicate membranes in this region are so easily torn, it was highly iaportant to scrutinize the area near the obex to discover any apparant te.ars. Each series will be taken up separately from this Jtandpoint. The sagittal sections of the monkey•s brain, Series A., had the arachnoid membrane wholly intact between the cere bellum and the medulla so that the cysterna cerebello-med ullaris appeared in the sections. Also the pia of the cere bellum was unharmed and the tela chor1oidea showed no break throughout its extent. Examination of sections to the right and left of the med ial section showed small elevations on the surface of the medulla just caudal to the point of termination of the epen dymal cells of the floor of the ventricle. Diagram A-~~

~ These elevations are mentioned in the discussion because the tela chorioidea came in contact with the.. Whether there was an actual attachment could not be determined. However, on either side of the elevations there was no contact between the roof and the floor of the ventricle and no indication of the tela chorioidea having been torn away from the medulla. Further laterally, the tela came in centact with the point whera -- -12- the epen~a of the floor ended. Diagram A-~. • In the transverse series of the monkey brain, Series B, in a region through the central canal, the tela joined the medulla on each side and the ependymal cells could be seen continuously on the ventrul surface Bf the roof and over the floor of the ventricle. Diagram B-l. About ten sec tions caudal to this section, Diagram B-2X, the roof on one • side was separa~ed from the medulla. It was impossible to decide by use of the microscope that this separation is not a tear. At any rate, all sections rostrally show a continuous connection, whereas all sections caudally show the separation. The roof on the other side does not separ ate from the medulla for a number of sections caudally, B-J. The ependyma of the floor in these sections could not be traced caudally because it was very indefinite, even in the closed part of the ventricle in sections caudal to the entrance of the central canal. However, the epen dyma of the roof was traced back through every slide until it blended with the pia of the cerebellum. Diagram B-,,, In the most caudal sections the ependymal root is separ

ated from the medulla by pia mater, Diagram B-~ to B-~. Tracing this portion of the pia cranially, I noticed that it disappears medially and becomes attached to the lateral side of the medulla until at the point where the roof joins the floor it becomes continuous with the pia r ~------, -13- of the tela chorioidea. In none of the sections is there any indication of the roof joining the medulla at a poster ior point. Also the relation of the tela to the cerebellum seems to indicate that the former extends out into the subarachnoid space in a natural way. In a sagittal section of a human fetus, Series c, the chorioid plexus projects caudally as \n the monkey. It can not be traced to a connection with the pia of the cerebellum because the latter is some what torn. However, as in the monkey, the ependyma of the floor seems to end at a definite point caudal to the entrance of the central canal. Tracing from the extreme lateral side of the fourth ventricle, Diagram C-1 to C-4, the sections show the ventricle at first to end blindly, then as the plane becomes more medial, the roof is found to separate from the • medulla. Again it could not be determined that the separ ation was not a tear. However, at this point the blind end of the roof was very thick, and so not likely to be easily torn. Upon reading sections medially from the separation, it was found that the thickened membrane grad ually becomes thinner. In the medial region the tela chorioidea projects caudally for quite a distance. -15- Li\erature Cited l. Blake, Root and Lateral Recesse~ of the Fourth Ventricle Considered Morphologically a~ Embryologically. Jour. Comp. Neurol., X, 79-108, 7: pl., 1900. 2. Cushing, H, · Some Experimental and Clinical Observations Concern ing States of Increased Intracranial Tension. Am. Jour. Med. Sci., cxxiv, 325-400, 1902. Studie•c· of Cerebro-spinal Fluid. Jour. Ued, Res., xxxi, No. 1,, 1-19, 1914. 3. Dandy, w. E. and B1acktan, K. D., An Experimental and Clinical Study of Internal HYdrocephalus. Jour. Am. Med. Assoc., LXI, p 2216,, 1913. ,,r' • Internal Hydrocephalus. Am. Jour. Dis. Child/~,# VIII, 406-482, 1914, 23pl. .~· 4. Dixon, w. E. and Halliburton w. D. Cerebro-spinal Fluid. The Secretion of the Fluid. Jour. Phys., LXVll, 341, 1913. 5. Frazier, c. H. The Cerebro-spinal Fluid in Health and Disease. Jour. Am. Jled. Assoc., LXIV, 1119-1124, : >.. 1915. 6. Frazier and Peat, Factors of Influence in the &rigin and Circulation ot Cerebro-spinal Fluid. Am. Jour. Phys., XXXV, No. 1, 268-282, 1914. 7. Hawser, C. H. Developement of the Cerebral Ventricles in the Pi~. Am. Jour. Anat., XV, p. 215-220, 1913-14. a. Keegan - RDot ot the Fourth ventricle in the Embryo.Anat. Rec., XI, 379-380. 9. Levinson, A., - History of Cerebro-spinal Fluid. Am. Jour. Syph., tl~ 267-275' 1918. 10. Magendie, Francois - Richerches Sur le Liquid~ Cephalo-rachidien. Paris, 1825. -16- • 11. Mall, F. P., Ofi the Deve1opement of the Blood Vessels of the Brain in the Human Embryo. Am. Jour. Anat., Iv, No. l, 1904. 12. Matt, F. W., Oliver Sharpy Lectures of Cerebro-spinal Fluid. Lancet, London, XI, l~79l~910

13. Weed, L. H. ~ An Anatomical Consideration of the Cerebro spinal Fluid. Anat. Rec., XII, 461-496, 1917 • The deve1opementaof the Cerebro Spinal Fluid. Cont. to Embr., V, No. 14. 14. Wilder, B. G. Notes on the Foramen of Magendie in Man and the Cat. Jour. Nerv. and Ment. Dis., XIII, 206, 1886. The Foramen of Magendie-N. Y. Med. Jour., XXXIX, p. 458, 1884. The Metapore in Man and Orang. Med News, LXIII, 439, 1893. 15. O'Carroll, Two cases of Hydr~halus Associ~ted with Complete Absence of Openings. Dublin Jour. of Med. Sc. Act: l, 1894, 273-276. ... 17 SERI ES A SAGI TAL SECTIONS OF MONKEY BRAIN 1 SECTI ON THROUGH CENTRJili CANAL

2 SECTION THROUGH PAJ?ILIJ1. 18 p ERI ES .A S.AGITAL SE C TIONS OF l.{Olnlli"'Y BRAIN

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2 SEPARATIO N OF TELA FROM :MEDULLA 20 SERIES B CROSS SECTIONS OF MONKF~Y BRAIN

3 SEPARATION OF TEL.A FROM l~'lEDULLA

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6 DISAPPEARANCE OF TELA CHORIOIDEA 22 SERIES C SAGITTAL SECTIONS OF HUMAN BRAIN

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5 COMPLETE SE:PAR TION OF OBEX FRO: MEDULL.

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