View source for Paper - Abnormal ribs and vertebrae in a human foetus (1919)

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=Abnormal Ribs and Vertebrae in a Human Foetus =

By C. L. Pasricha, B.A., 

Gonville and Caius College, Cambridge (Communicated by W. L. H. Duckworts)


==Introduction==

A human foetus dissected in the Cambridge Anatomy School during the Long Vacation, 1918, presented an unusual deformation of the ribs and vertebral column as described in the following paragraphs.


The specimen (Fig. 1) was a female measuring 200 mm. in length from the vertex to the coccyx. It seemed to have been born at some time during the sevénth month of intra-uterine life, but no data were available as to its history. The most striking superficial features were a large ventral hernia (Fig. 2), and a large depressed scar-like area in the mid-dorsal line of the thorax and abdomen. The latter feature was clearly indicative of spina bifida, though no tumour existed. Dissection was commenced with a view to ascertaining the nature of the herniated mass, but in the course of the work the-skeletal abnormalities associated with the hernia and spina bifida proved to be exaggerated in degree and very rare in kind. Consequently the ribs and the vertebrae will be described first.

Fig. 1. Human foetus (Mus. Anat. Cant. specimen VH) with abnormal vertebrae and ribs.

Fig. 2. Human foetus (Mus. Anat. Cant. specimen VH) with abnormal vertebrae From vertex to coccyx the length was 202 mm. and ribs. The limbs of the left side have been removed to exhibit the ventral hernia.


Ribs and Vertebrae (Fig. 3, A and B). The thoracic skeleton looked as though strong lateral compression had been exerted on its surface and on the right side the ribs were actually pressed inwards. Moreover the ribs were abnormal in number, only nine being identified on each side. In the vertebral column the neural arches were complete as far as the fifth cervical vertebra (inclusive) but beyond this tailwards the vertebral canal was open. Angular curvature of the column is pronounced at the disc between the first and second thoracic vertebral and a violent dislocation seems to have occurred here. For the first thoracic centrum (carrying the cervical vertebrae and the skull with it) appears to have slipped forwards (i.e. ventrally) abandoning the centrum of the second thoracic vertebra (Fig. 3, B). The first thoracic centrum has formed a new lower articulation as described in the sequel.



Fig. 3. Human foetus (Mus. Anat. Cant. specimen VH), with abnormal vertebrae and ribs. A, frontal view; B, side view of the vertebral column and ribs.

 


The two halves of the second thoracic neural arch have not merely failed to unite, but so far from moving dorsally as is usual, their pedicles have actually moved in the ventral direction (Fig. 4). So far have they swung thus, that they bound a ventral neural cleft. This narrow cleft is closed ventrally by a mass of bone representing the heads and necks of the two ribs (right and left) which at this level have coalesced in the median plane. The portion common to the two ribs is prolonged towards the cleft between the two pedicles of the neural arch. But a more surprising observation is that the same portion (common to the two ribs) actually supports the first thoracic vertebra, and consequently the vertebrae above this (cf. Figs. 8, B and 4).



Fig. 4. (x 2 approx.) Human foetus (Mus. Anat. Cant. specimen VH) with abnormal vertebrae and ribs. Upper surface of second thoracic vertebra with associated ribs. 1. Centrum of second thoracic vertebra. 2, 3. Pedicles ” ” ” 4, 5. Laminae with narrow elliptical intervertebral articular areas on their ventral margins. 6. Area of articulation with lower aspect of first thoracic centrum. This area is situated on the conjoined heads of the third right and left ribs. 7. Fourth rib of left side.

The laminae of the second thoracic vertebra project laterally and that on the left side (but not its pedicle) has coalesced with the following lamina (third thoracic vertebra).

The extraordinary conformation of the second thoracic vertebra is -repeated in essentials by those that follow it as far as to the sixth. Thereafter the normal relation of centrum to centrum is re-established.

In addition to this dislocation, lateral curvature was detected, and the crowding together of the ribs may be assigned in part to the latter factor. Indeed a partial fusion of the ribs of the same side was observed in several instances. The last rib on each side ran towards the iliac crest to which a strong fibrous band tethered it. Intercostal branches of the thoracic aorta seem to have been suppressed, and the sympathetic cord in the thorax descended as in Reptiles, i.e. in a position dorsal to the necks of the ribs. | One instance of coalescence of two successive neural processes has been mentioned above. In addition to this, the imperfect separation (or partial coalescence) of the fifth and sixth neural processes on the right side reproduces the same phenomenon, which recurs again on the left side, the seventh and eighth thoracic segments being involved here. The various distortions may be described as “‘ pressure-effects”’ of some cause unknown. That the amnion is responsible cannot be alleged with confidence, though the probability is great. The process of events in the upper thoracic neural “‘arches”’ presents a certain analogy with that whereby the somato-pleural walls of the amniomedullary cavity are displaced ventrally in consequence of the progressive increase in the contents of that cavity. Such speculation does not imply rejection of what may be termed “ chemical” causes, such as those on which the late Professor Mall laid so much stress (Keibel and Mall; Manual of Human Embryology, Vol. I, p. 281). The peculiarities of the ribs and vertebrae here described could doubtless be matched in otherexamples of Spina bifida. Specimens described by Dr J. P. Good (Studies in Anatomy from the Anatomical Department of the University of Birmingham, 1910) evidently owned similar deformities, but the latter are not figured in the publication mentioned.

The hernia. The hernial sac contained a large part of the liver together with most of the small intestine, the caecum with its appendix, and part of the colon. The caecum occupied a part of the sac corresponding to the proximal portion of the umbilical cord. The latter was much distended here. But though the caecum had not receded into the abdominal cavity, torsion of the alimentary canal had occurred, for the caecum is on the right side of the sac.

Abdominal contents. Apart from the general distortion of its form, the liver presented no anomaly of lobation. The ascending colon (traced backwards from the sac to the abdominal cavity) seemed to plunge into the mesentery above the small intestine, and then turned leftwards in the abdominal cavity towards the spleen. A further flexure brought the colon across to the right iliac fossa which was filled by a loop evidently representative of a pelvic colic loop. At first the condition seemed analogous to the abnormality of torsion described by Mrs Flemming in the Proceedings of the Anatomical Society, March 1897, but careful re-investigation showed that this is not the case. Apart from the peculiar relation mentioned above (whereby the “ascending”’ and “transverse” parts of the colon appeared to share the mesentery with the small intestine) the usual torsion of the alimentary canal was simply incomplete.

The peritoneum formed a distinct genito-mesentric fold (Reid) extending to the right iliac fossa where the fimbriated portion of the oviduct was bound down to the peritoneal floor of the fossa by a distinct fold with a curved margin. Beneath the duodenum a large “inferior duodenal”’ fossa was seen. In regard to other organs, the partial contact of the two kidneys was noticed, the left kidney having passed to the right, insinuating its upper pole behind the aorta. The adrenal bodies were likewise ‘in contact but had not coalesced.

Thoracic contents. The absence of aortic intercostal arteries and the anomalous course of the sympathetic cord have been mentioned already. Here it may be added that a transverse communication between the right and left sympathetic cords was found on the centrum of the 7th cervical vertebra, the commissure in question being thickened and apparently ganglionic. The heart had a bifid apex and the right and left ventricular walls were approximately equal in thickness. The right lung had but two lobes and the costal aspects of both lungs were deeply channelled by grooves corresponding to the depressed ribs. The latter were found to run towards a sternum in which no anomaly was detected.

Central nervous system. The spinal cord ended as a distinct “cord” at the level of the 5th cervical vertebra. Thereafter the cord was replaced by a “cauda equina,” probably different in nature from the normal sheaf of nerve roots so designated. No anomalies of the limb plexuses were detected, although the exposure of the central nervous system below the 5th vertebra had been accompanied by much disintegration of the cord itself. No anomalous conditions appeared in the brain, but the falx cerebri was largely defective in its hinder portion, and the two hemispheres were in contact with each other in that region. Yet a superior longitudinal sinus was present, and the right superior petrosal sinus was represented by two offshoots from the cavernous sinus which were widely separated in the floor of the middle cranial fossa before they united to form a single vessel entering the transverse sinus.

In terminating this description, I have to thank Dr Duckworth for his aid in arranging the notes and in preparing the illustrations.

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