Paper - Anterior and posterior rhachischisis (1941)
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|skull and axial skeleton development.
Also by this author: Dodds GS. The area of the chorionic villi in the full-term placenta. (1922) Anat. Rec. 24(5): -294.
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Anterior and Posterior Rhachischisis
G. S. Dopps, Ph.D.
From the Histological Laboratory, School of Medicine, West Virginia University, Morgantown, W. Va.
- Received for publication February 20, 1941.
Two fetuses exemplifying anterior and posterior rhachischisis have appeared in the embryological collection of the School of Medicine of West Virginia University. Both show clearly the anomaly of the vertebral column, together with the characteristic complex of visceral anomalies associated with it. The condition must be rather rare; I have found reference to only thirty cases in the literature. Yet, it cannot be dismissed casually as a developmental curiosity because it involves an extensive complex of anomalous characteristics, which, in all recorded cases, run true to type. For this reason, it seems worth while to describe the two cases, together with notes on earlier records and comments upon the probable mode of development.
Reports of Cases
Male fetus (No. 121) had a menstrual age of 8 months and weighed 2.3 Kg. The head measured 42.5 cm. in circumference. The neck was very short and thick (Figs. 1 and 2). It had club feet (talipes varus), and there were in each jaw four completely erupted incisor teeth. It was secured through Dr. W. B. Scherr, of Morgantown, W. Va.
The Skull. The foramen magnum was unusually large, measuring 27 by 24 mm. (Figs. 2 and 3). Otherwise the skull showed no conspicuous anomalies, except a separation of the bones of the skull cap, characteristic of hydrocephalic infants.
The Vertebral Column. The outstanding anomaly was the complete division into right and left halves of all the cervical and the first seven thoracic vertebrae (Figs. 3 and 5). The two halves of the divided vertebral column were widely separated in their mid-portion, due to strong lateral curvature, so that they bounded a somewhat circular opening about 2 cm. across, lying just below the foramen magnum (Fig. 3). Both halves of the vertebral column also showed strong lordosis (Figs. 4 and 6). The divided vertebrae were decidedly shorter than the corresponding vertebrae in a normal fetus. These three factors were responsible for the great shortening of the neck. Each half vertebra had a well developed half arch and half body, between which, on the medial surface, was a notch representing a half intravertebral foramen.
The Central Nervous System. The brain was typical for hydrocephalic infants, with very large lateral ventricles enclosed by greatly distended, thin walls (Fig. 2). The spinal cord was not divided in the region of the divided vertebral column, but was expanded laterally to form a discoid enlargement occupying the circular opening between the two halves of the vertebral column. The spinal nerves radiated from this expansion to their respective vertebral foramina.
The Thoracic and Abdominal Viscera. The viscera showed conspicuous anomalies characterized by extensive ectopia of abdominal organs into the thorax (Fig. 2). On the right side, the diaphragm was complete except for a slit about 1 cm. long. The left side was practically without diaphragm. The pericardium had, on the left side, a hole about 1 cm. across. Thus, pleural, pericardial and peritoneal cavities were in communication with each other.
The heart and lungs were at their usual level above the diaphragm, but lay wholly to the right of the mid-plane of the body and in the ventral half of the thorax. The mediastinum lay obliquely, with its ventral and caudal margins well to the right of the mid-plane. The stomach and the greater part of the small intestine lay in the right pleural cavity, occupying the dorsal half of the right side of the thorax. The stomach was partly in the mediastinum and partly attached to its right side. The esophagus was short. At a little distance above the level of the diaphragm. the small intestine crossed from the right to the left side of the body, and thence coursed to the lower abdominal region. The large intestine was poorly developed.
The left pleural space was occupied largely by about one-third of the liver which entered through the opening in the diaphragm. The spleen lay in the extreme cephalic end of the left pleural space, attached to the left side of the mediastinum. A narrow spatulate lobe of the liver entered the right pleural cavity through the small slit in the diaphragm.
The great omentum was present as a serous sac lying between ANTERIOR AND POSTERIOR RHACHISCHISIS 863
the stomach and the right lung. Its attachments were to the right side of the mediastinum and to the greater curvature of the stomach. Otherwise, the serous relations of the abdominal viscera were so distorted that they cannot be designated in conventional terminology.
Full-term female fetus (No. 53) weighed 4.3 Kg. It was secured through Dr. A. D. Hunger, of Point Marion, Pa. In all essential features of the complex of anomalies, it was similar to case 1, differing only in details and in external appearance. The head was of normal size. The neck was very short and thick. From the lower occipital region and the short neck there arose a large, pendulous, skin-covered meningeal sac about 12 cm. long and 10 cm. wide (capacity about 200 cc.), hanging to about the tenth thoracic segment (Fig. 7).
The Skull. The skull had no evident gross anomalies, except that the foramen magnum was very large, measuring 4.7 cm. in anteroposterior diameter by 3.0 cm. in width (Figs. 7 and 9). Its unusual expansion was in dorsal and lateral directions. Its ventral edge was in the usual position. Its ventral portion communicated with the spinal canal; its dorsal portion opened above the vertebral column, and through it the meningeal sac protruded (Fig. 7).
The Vertebral Column. There was complete division into right and left halves (as in case 1) of all cervical and the first thoracic vertebrae. The two halves were divergent and well separated, leaving between them a somewhat circular opening about 1 cm. in diameter (Fig. 8). There was lordosis in this region and the individual vertebrae were not of normal length.
The Central Nervous System. The brain was of about normal size and form. The cerebellum was represented by a disintegrating mass, of about the usual size for the organ, enclosed by a meningeal covering. It protruded by about half its diameter through the upper part of the foramen magnum into the meningeal sac (Fig. 7). The cervical spinal cord was conspicuously malformed in that it simulated somewhat the cross-sectional form of the medulla oblongata, with a thick floor of nervous tissue and a thin, broad roof of non-nervous tissue. In fact, the medulla oblongata and the cervical portion of the cord together appeared like an extended medulla. The fourth ventricle was directly continuous, without decrease in size, with the greatly expanded central canal of the cervical cord, forming a continuous cavity about 1.5 cm. wide by 2.5 cm. long. The actual boundary between medulla and cord was at about the usual level with reference to the foramen magnum, as indicated by spinal and cranial nerves and as shown by microscopic sections.
It was from the thin roof of this part of the cord, at about the level of the fourth cervical nerves, that the meningeal sac arose, by a passage measuring about 1.5 cm. in lateral extent by 0.5 cm. in height (Fig. 7). The sac was covered externally by skin, inside which were the spinal meninges. Though microscopic sections were studied from different regions of the sac as well as from the cervical spinal cord, it was not determined with certainty whether the layer lining the sac was an extension of the roof plate of the spinal cord or was derived from the meninges.
There was an anomalous filament of nervous tissue, about 5 mm. long by 0.5 mm. thick, extending ventrad from the floor of the cervical cord at about the level of the fourth cervical nerves.
It occupied the center of the circular opening between the two halves of the vertebra. Its basal portion was of gray matter, continuous with the gray matter of the cord; from its more distal portion arose several groups of medullated axons which could not be traced far. The possible significance of this structure will be discussed later.
The Thoracic and Abdominal Viscera. The anomalies of these organs (Fig. 7) were of the same general nature as in case 1. The diaphragm was almost wanting on the left side, but was complete on the right. The pericardium was incomplete on the left side, having a hole about 1.5 cm. in diameter. The right pleural sac was normally closed, but the left pleural sac, the pericardial cavity and the abdominal cavity were in free communication.
The heart and lungs were at the usual level above the diaphragm, but were displaced, together with the mediastinum, into the right side of the thorax. The spleen was high in the left side of the thorax. About one-third of the liver extended into the left thorax through the large opening in the diaphragm. The stomach was just above the level of the diaphragm; the esophagus reached the stomach through the posterior mediastinum, but entered it on its caudal side; the small intestine (165 cm. long), except for the pyloric end of the duodenum, lay in the abdominal region. The large intestine was well developed (about 20 cm. long) and abnormally placed, in that from its origin in the lower left abdominal region it coursed almost directly cephalad to the upper end of the thorax and thence directly caudad to the anus. The ectopic abdominal organs occupied not only the left side of the thorax, but had encroached to a considerable extent upon the right side, leaving much less than half the thoracic space for the usual thoracic organs.
The great omentum was recognizable as a small serous sac above the diaphragm with connections to stomach, spleen and large intestine. The mesentery of the small intestine was of about normal form, but the other serous connections of the alimentary organs were greatly distorted.
Discussion the Occurrence of the Anomaly
Though rhachischisis and spina bifida in their ordinary forms are very common anomalies of the vertebral column and spinal cord, the complete division of a series of vertebral segments into widely separated right and left halves is relatively rare.
In A Reference Handbook of the Medical Sciences* is pictured a vertebral column which shows this anomaly. The illustration is from specimen No. 831 in the Warren Anatomical Museum of the Harvard Medical School. In a personal communication from the curator of the Museum, I have received a brief description of this fetus by Dr. Isaac F. Galloup, 1858. This clearly portrays the anomalies of the vertebrae and viscera which characterize this condition. I have found no other case described in American literature.
Gruber (1926) gives abstracts of 17 cases described by various authors, the earliest in 1824. To these he adds 2 cases from his own observations. Feller and Sternberg (1929 and 1934) add 6 more from the literature and describe 3 others. In all but one of these cases, the cervical and upper thoracic vertebrae were involved, the exception, listed by Gruber (from Reinke, 1877), having the division in the lumbar region. Adelmann (1920) describes a similar lumbar anomaly in a calf.
The General Nature of the Anomaly
It appears, from consideration of the several recorded cases, that the two described herein are typical and that the anomaly is not simple, but includes the following complex of anomalous features:
- The affected vertebrae (usually the cervical and upper thoracic) are completely divided (both arches and bodies) into right and left halves which are widely divergent from each other (Figs. 3, 5 and 8). This condition is fundamentally different from thachischisis of the ordinary sort in which only the arches are divided.
- The neck is very short (Figs. 1, 2 and 7). This condition must not be confused with the shortened neck of the ordinary anencephalic or craniorhachischitic fetus, which is due to a quite different defect.
- In probably all of the recorded cases, there is extensive dis_ placement of abdominal viscera into the thorax (Figs. 2 and 7). The displacement of abdominal viscera into thoracic levels is, in some cases, associated with incompleteness of the diaphragm and the pericardium, while in other cases the diaphragm is complete and the displacement is by way of the posterior mediastinum.
- Very frequently some division of the alimentary canal is in intimate relation with the spinal cord in the region of the divided vertebrae. Almost any segment of the gut may be involved. Sometimes a loop of the gut passes through the cleft vertebrae and a segment (frequently the stomach) lies dorsad to the vertebral column. There have been observed various forms of patent connections between gut and neural groove, non-patent diverticula and fibrous connections; while some cases show no demonstrable connection of any kind.
- In the majority of recorded cases, the neural tube is unclosed as in ordinary rhachischisis, giving rise to myeloschisis with its characteristic area medullovasculosa. Various forms of anencephalia and acrania are also of frequent occurrence. But nonclosure of the neural tube is not a necessary part of the anomaly, for less frequently there has been recorded complete closure, with the skin completely covering the mid-dorsal region of head and body. The head may be of normal form and size; or it may be hydrocephalic; or there may be meningocele.
- The spinal cord, or the open neural groove in the affected region, may be either single or divided into right and left halves; or it may be variously deformed.
Ordinary rhachischisis does not involve any accompanying complex of visceral anomalies; anterior and posterior rhachischisis seemingly always involves ectopia of abdominal organs into the thorax, frequently with incompleteness of the diaphragm. This anomaly of the diaphragm should not be confused with simple congenital hernia of the diaphragm, a much more common condition. This latter condition is well illustrated by Liebow and Miller (1940) who also give a good bibliography. In simple congenital diaphragmatic hernia, the distortion of the digestive organs and serous membranes (mesenteries and omenta) is much less radical than in anterior and posterior rhachischisis; and the ectopic abdominal organs frequently may be restored to their abdominal position by operation. The two types, while having much in common, are in reality fundamentally different in their nature and mode of genesis.
Both of the cases here reported exhibit fully the essential features of the anomaly. Both belong to the type with fully formed head and enclosed spinal cord. In neither is the spinal cord divided. In neither is any connection observed between alimentary canal and neural tube, though in case 2 the nervous projection from the ventral side of the cervical spinal cord may be a remnant of a former connection. Both cases belong to the type in which the displacement of abdominal viscera is associated with incomplete diaphragm; the misplaced viscera lie directly within the pleural cavities, not in the posterior mediastinum.
Inasmuch as this anomaly involves an extensive and definite complex of congenital structural defects, it should have a distinctive name. It has frequently been called “spina bifida.” But that is hardly a suitable name because, in its strict application, as defined in dictionaries and encyclopedias and as commonly used in textbooks, it designates those conditions in which there is a meningeal protrusion through a rather minor defect in the vertebrae. On the other hand, the application of the term has been so loose and so varied that its use in this case would not be at all definitive. Nor is “rhachischisis” in its ordinary meaning applicable. It has sometimes been designated as “Wirbelk6rperspalte,” which is a fairly descriptive term, but hardly one which might come into general use. ‘“Vertebra bipartita” has apparently not been used with exactly this application, though it seems suitable.
Probably the best terms (though somewhat cumbersome) are “anterior and posterior spina bifida” and “anterior and posterior rhachischisis.”” Both of these have been used, and I believe that neither has been applied to any other form of cleavage of the spine. Of the two terms, I have chosen the latter as the more suitable, because “rhachischisis” has not been used with so many different applications as has “spina bifida.” In this paper the phrase “anterior and posterior rhachischisis” carries with it not only its primary significance (division of vertebral arches and bodies), but also implies the entire complex of visceral anomalies which seem to be universally associated with it.
The Probable Course of Development of the Anomaly
The common types of spina bifida and rhachischisis result from varying failure of the neural tube to close. On the other hand, anterior and posterior rhachischisis involves failure of the paired sclerotomes to unite, the failure occurring either with or without proper closure of the neural tube. Consequently, this anomaly can in no sense be considered an extreme manifestation of either spina bifida or rhachischisis, but rather an anomaly of a different type. It would seem, further, that non-fusion of sclerotomes is determined by forking (doubling) of the notochord, inasmuch as notochordal rests have been observed in each half of such vertebral bodies (Feller and Sternberg, 1929). Several writers have contended that the forking of the notochord results from anomalous behavior of the primitive node, and that the anomalous connection, sometimes patent, between gut and neural tube is a persistent neurenteric canal. Adelmann (1920) and other writers support this view by reference to Hertwig (1892) and other experimenters who have produced, in amphibian embryos, duplications of axial structures and non-closure of neural tube (all loosely called “spina bifida”). These results were brought about by experimental procedures which were timed to prevent normal development in the region of the blastopore. ANTERIOR AND POSTERIOR RHACHISCHISIS 869
. Study of these earlier papers shows that the experimental defects produced in amphibian embryos are by no means identical with the human anomalies under consideration. Confusion on this point has arisen because both sets of conditions have been loosely designated as “spina bifida.” Moreover, recent experimental work has presented strong evidence that the avian and mammalian primitive streak and neurenteric canal are not derived from the amphibian blastopore. Nevertheless, there are suggestive similarities between the two sets of structures, and recent experimental work gives unexpected support to the view that anterior and posterior rhachischisis may indeed result from anomalous behavior of the primitive node and the neurenteric canal.
According to this recent conception (Jacobson, 1938; Weiss, 1939; and others) the primitive node is a restricted area through which there invaginate two lateral areas of presumptive notochordal material which unite just cephalad to the node to form the definitive notochord. In a somewhat similar manner, the neural plate is formed by the confluence of two lateral areas of presumptive neural material. By this concept, the neurenteric canal, a temporary opening through the node, lies between the two converging streams of notochordal material which normally unite just cephalad to it. So much seems clearly established by experimental procedures.
On this basis, it seems safe to assume that, in rare cases, as an anomaly, an unusually large neurenteric canal, or one which persists too long, might produce doubling of the notochord by preventing the union of the two notochordal streams. Two notochords, separated by a considerable interval, might well prevent the normal union of the paired sclerotome masses, thus producing a series of vertebral bodies about each notochord. The interval of separation would also prevent the union of right and left halves of the neural arches, even though the neural tube might have undergone normal closure. In like manner, the two neural streams might also fail of fusion, thus producing two spinal cords or one malformed cord.
The fact that it is usually in the cervical and upper thoracic regions that such division of vertebrae occurs, correlates well with the probable location of the neurenteric canal during its normally short existence. There is increasing agreement that the primitive node, at the time of its first appearance, is located in what corresponds to the posterior cephalic region, whence it recedes in a caudal direction as the notochord is spun through it. The human neurenteric canal makes its appearance in the primitive node shortly after the formation of the first pair of somites, and it normally closes after about six pairs have been formed (Bartelmez, 1926, and others). Inasmuch as the somites take definite form at some little distance cephalad to the primitive node, the neurenteric canal, during its period of normal patency, must lie in the cervical or upper thoracic regions, the very levels at which divided vertebrae are common observed. A persistent neurenteric canal is strongly indicated in those cases of anterior and posterior rhachischisis in which there is a patent connection between gut and open spinal cord; a partial persistence is suggested by the diverticula and fibrous connections found in others, or by the nervous appendage observed in case 2.
Since the division of the vertebrae is usually limited to cervical and upper thoracic levels, such anomalous neurenteric canal is clearly left behind in that region instead of receding caudad along with the primitive node. The retention of this union in the cervical region is probably due to attachment to structures which do not normally recede as does the primitive node or the abdominal and thoracic viscera. In the several described cases of anterior and posterior rhachischisis, the peculiar ectopic positions of the abdominal organs are clearly indicative of retention rather than of herniation into the thorax after a normal descent. The anomalous connection between gut and cervical neural tube would prevent the normal recession of other parts of the entodermal tube and its associated mesodermal structures. Faulty development of diaphragm, pericardium and other serous membranes would also result.
On the other hand, it is commonly believed that in simple congenital hernia of the diaphragm, the ectopic abdominal organs have entered the thorax by actual herniation from the abdomen, probably not earlier than the eighth week (Liebow and Miller, 1940). Herein lies a significant distinction between the two types of visceral ectopia.
In general, it would seem that the entire complex of anomalies finds its most reasonable explanation in anomalous behavior of the neurenteric canal, an explanation which serves to tie together the striking anomalies of skeleton, nervous system and body viscera.
The two fetuses described in this paper had the following anomalies which are characteristic of the general complex designated here as “anterior and posterior rhachischisis”:
- The neck was very short and thick.
- The shortness of the neck was due to the complete division into right and left halves of all of the cervical vertebrae and some of the thoracic vertebrae.
- The diaphragm was practically wanting on the left side. There was a good-sized opening in the left side of the pericardium between the pericardial cavity and the left pleural cavity.
- A large portion of the liver, the spleen and portions of the abdominal alimentary tract were in the thorax, crowding the heart and lungs wholly to the right side of the median plane.
Each fetus had other external and internal anomalies which are not considered as part of the general complex comprising anterior and posterior rhachischisis.
There is included a discussion of about thirty previously described cases, together with comments upon opinions of earlier writers as to the mode of origin of the anomaly, interpreted in the light of certain recent experimental embryological work. Anterior and posterior rhachischisis is compared with the ordinary forms of spina bifida and rhachischisis, and with the common congenital diaphragmatic hernia.
Adelmann, H. B. An extreme case of spina bifida with dorsal hernia in a calf. Anat. Rec., 1920, 19, 29-34.
Bartelmez, G. W., and Evans, H. M. Development of the human embryo during the period of somite formation, including embryos with 2 to 16 pairs of somites. Contributions to Embryology, Carnegie Institute of Washington, 1926, 17, No. 85, 1-67.
Feller, A., and Sternberg, H. Zur Kenntnis der Fehlbildungen der Wirbelsdule. I. Die Wirbelkérperspalte und ihre formale Genese. Virchows Arch. f. Path. Anat., 1929, 272, 613-640. 872 DODDS
Feller, A., and Sternberg, H. Zur Kenntnis der Fehlbildungen der Wirbelsaule. V. Uber Fehlbildungen der Wirbelkérper bei Spaltbildungen des Zentralnervensystems und ihre formale Genese. Ztschr. f. Anat. u. Entwicklungsgesch., 1934, 103, 609-633.
Gruber, G. B. Zur Frage der neurenterischen Offnung bei Friichten mit vollkommener Wirbelspaltung. Ztschr. f. Anat. u. Entwicklungsgesch., 1926, 80, 433-453 Hertwig, Oscar. Urmund und Spina bifida. Eine vergleichend morphologische, teratologische Studie an missgebildeten Froscheiern. Arch. f. mikr. Anat., 1892, 39, 353-503.
Jacobson, W. The early development of the avian embryo. II. Mesoderm formation and the distribution of presumptive embryonic material. J. Morpkhol., 1938, 62, 445-501.
Liebow, A. A., and Miller, H. C. Congenital defects in the diaphragm. Am. J. Patk., 1940, 16, 707-738.
Weiss, Paul. Principles of Development. Henry Holt & Co., New York, 1939.
Description of Plates
Fig. 1. Case 1. External form. Photograph after preservation in solution of formaldehyde.
Fig. 2. Case 1. Photograph after sectioning in the sagittal plane, showing the absence of neck, the expanded skull and the distended cerebral hemispheres characteristic of hydrocephaly, the somewhat enlarged foramen magnum, the spinal canal (spinal cord removed) connecting with the foramen magnum, the undivided lower thoracic vertebrae, the divided upper thoracic and cervical vertebrae (the divided vertebrae are not seen in the plane of this section on account of their strong lateral curvature as shown in Fig. 5), the large liver partly in the thorax, the incomplete diaphragm partly subdividing the liver, and the stomach lying between the thoracic liver and the vertebral column.
Fig. 3. Case 1. Dissection to show division of vertebral column in an oblique view. The two halves of the divided vertebrae bound a roughly circular opening through which are seen the base of the skull and the foramen magnum. The expanded portion of the spinal cord occupied this opening, giving off nerves radially through foramina in the encircling half vertebrae.
Fig. 4. Case 1. Lateral view after dissection. The strong lordosis of the divided part of the vertebral column and the pronounced lateral curvature (see Fig. 3) bring the base of the skull close to the upper thoracic vertebrae. Shortening of the segments in the divided region is also shown. AMERICAN JOURNAL OF PatHoLocy. VoL. XVII PLATE 138
Fig. 5. Case 1. Anteroposterior roentgenogram. showing forking of vertebral column in mid-thoracic region. The effective length of the vertebral column is reduced by strong lateral curvature of the two halves.
Fig. 6. Case 1. Roentgenogram of lateral half of fetus. showing the extent of cervical and thoracic vertebrae. The strong lordosis has brought the spinous processes of the divided thoracic vertebrae close to the base of the skull.
Fig. 7. Case 2. Photograph after sectioning in the sagittal plane. There are many features similar to those of case 1 (Fig. 2): absence of neck; very large foramen magnum; divided cervical vertebrae; displacement of abdominal viscera (liver. large intestine and stomach) into the thorax through a large opening in left side of diaphragm. There is a very large meningocele covered with skin. arising by a narrow passage from the thin roof of the cervical spinal cord immediately opposite the divided vertebrae.
Fig. 8. Case 2. Anteroposterior roentgenogram showing division of cervical vertebrae. The irregular longitudinal cleft in the photograph is an artefact. The photograph was taken after the fetus had been bisected and the two halves laid together again.
Fig. 9. Case 2. Lateral roentgenogram of base of skull and upper vertebrae. showing lordosis of the divided vertebral column. There is a very large foramen magnum.
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