Paper - A case of atresia ani in a human embryo of 26 mm
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A case of Atresia Ani in a Human Embryo of 26 mm
Franklin Paradise Johnson
The Anatomical Laboratory of the University of Missouri
Among the most common anomalies of the rectum are those of atresia ani, atresia recti, and atresia ani et recti. The ﬁrst of these is described as being present when an anal opening is lacking. An anal invagi.nation may or may not be present, or the site of the anus may be marked by a surface elevation. In atresia recti simplex the anal opening is present and normally developed, but the upper part of the rectum, failing to unite with the anal portion, ends blindly in the pelvis. In atresia ani et recti, both anal opening and a portion of the ampulla recti are missing. These simple atresiae may be complicated by the additional anomalous conditions of ﬁstulae into the urethra, bladder, vagina, vulva, or through the scrotum and perineum.
Such anomalies of the rectum, which are usually detected at the time of birth or shortly afterward, have aroused considerable interest, and various theories have arisen as to their probable origin. Among those who have studied the causes of rectal anomalies should be mentioned the names of Rotter ('03) and Jones (’04).
However correct any of the theories regarding the formation of these atresiae may be, before they can be deﬁnitely accepted, they demand not only a correct knowledge of the normal development of of these parts, but direct evidence concerning the time and manner of deviation from the normal. It is because of this that the present atresia, found at a comparatively early stage of the embryo, is described. Although the author knows of no other case of this kind found in an embryo, the observation which Keibel made on an embryo of 11.5 mm. should be mentioned. He found that the lumen of the rectum in its lower part had become occluded at two small places. The observation, however, offers no evidence, direct or indirect, that this would develop into a case of atresia. It seems probable that the lumen might have again opened up, for in corresponding stages of pig and rabbit embryos (Lewis ’03) and of chick embryos (Minot ’00), where there is normally an epithelial occlusion of the rectum, such reopening occurs. It should also be recalled that epithelial occlusion occurs normally in the developing duodenum (Tandler ’O(), Johnson ’10).
Fig. 1 Graphic reconstruction of the pelvis of a human embryo of 26 mm. (H 99). all., allantois; amp.7“ec., ampulla recti; bul.a., blindly ending bulbus analis; d, lﬂiillerian and Wolfﬁan ducts; (7.1. and ('.IV, first and fourth coccygeal vertebrae; SJ, ﬁrst sacral vertebra.
The case of atresia under consideration (see accompanying ﬁgure) was found in Embryo H 99 of Prof. C. M. Jackson’s collection, the crown—rump length of which is 26 mm. The sections were cut transversely to the long axis of the embryo, hence the plane of sectioning through the lower part of the rectum is longitudinal. The upper part of the rectum is apparently normal. Its epithelial tube has a transverse diameter of 0.23 mm. and is composed of two to three layers of cells. More caudally the rectal tube expands, forming what has been termed in a former paper (Johnson ’14) the bulbus analis. This has a transverse diameter of 0.29 mm. at its widest place and its epithelium is of about the same thickness. A single deep infolding extends itself along the ventral Wall of the tube. The epithelium of the upper part of the bulbus analis is regular, its nuclei are closely packed and distinct, but cell boundaries are not distinguishable. At about the middle of the bulbus analis the epithelium becomes broken up, and from this point caudally becomes more and more irregular. In this region the nuclei are more scattered and in places less sharply outlined than above. The lumen becomes gradually ﬁlled up with broken-off pieces of the epithelium, and lower down becomes lost in a mass of epithelial debris. The lower portion of the bulbus analis is smaller in size, and ﬁnally disappears from View altogether. The last remnants are seen as a few nuclei scattered about in the mesenchyma. The epidermis of the anal region is found about 0.55 mm. caudad to these last remnants. An anal invagination is present but it is Very shallow.
Surrounding the epithelial tube throughout its whole length is mese-nchyma. In the upper part of the bulbus analis this lies close to the epithelium, but in the lower part, where the epithelium is broken down, the mesenchyma is separated from it by a distinct shrinkage space. At the termination of the epithelium the shrinkage space again disappears. Between the lower end of the rectum and the anal invagination, the mesenchyma shows no special features. It is possible that some of the nuclei seen in the rnesenchyma of this region belong to the epithelium, but this point is not determinable.
The inner circular and the outer longitudinal layers of the muscularis are distinct. They terminate a short distance above the last remnants of the epithelium. As has been formerly shown (Johnson ’14) the circular muscle coat terminates normally at the constriction between the bulbus analis and the bulbus terminalis. This affords a means of determining that the last portions of the epithelium represent a part of the bulbus terminalis.
In front or ventral to the rectum is seen the urogenital sinus, which at this stage is quite widely separated from the rectal tube. Opening into it are seen the united Mullerian ducts and on either side, the two Wolflian ducts, although their epithelia are somewhat broken up and irregular. The ureters do not join the urogenital sinus but end blindly, their epithelium being broken down in a similar manner to that of the rectum.
The results of my work on the development of the normal rectum have shown that the bulbus analis and the bulbus terminalis go into the formation of the zona columnaris and zona intermedia of the pars analis recti respectively. Since in this anomalous embryo the epithelium of the rectum terminates in the region of the bulbus terminalis, it is evident that the missing portion of the rectal tube represents what would have normally been the zona intermedia. The anomaly should, therefore, be classiﬁed as a case of atresia ani simplex. However, owing to the peculiar disposition of the ureters, it is doubtful Whether it would have retained its simple relations, had the embryo lived longer.
Regarding the cause of this anomaly little can be deﬁnitely said. It is doubtful whether the anal membrane is in any way concerned. In an examination of 19 embryos of 15.5 mm. and over, Keibel and Elze (’08) show that in stages of 15.5, 16, 17, 18, 18, 18.5, 19.5, 20, 20, 20, 20, 20.5, 22, 22.5, 24, 24, 26 and 26 mm. the anal membrane was present and the anal passage closed to the outside, while in only one case (22.5 mm.) was the passage open. Broman (’11) states that an anal opening is not effected until the embryo is about 33 mm. in length. The results of my own work show that the anal membrane is present in embryos of 17, 19 and 22.8 mm. and has disappeared in those of 16, 29, 30, 30 and 31 mm. and above. From these observations it will be seen that usually at 26 mm. the anal membrane occludes the anal passage, so that the above anomaly cannot be explained by a failure of the anal membrane to break down normally. Constriction and a subsequent breaking apart of the epithelial cord at this place must have occurred.
BROMAN, I. 1911 Normale und abnorme Entwicklung des Menschen. Wiesbaden.
JONES, F. W. 1904 The nature of the malformations of the rectum and urogenital passages. Brit. Med. Jour., vol. 2, pp. 1630-1634.
KEIBEL, FR., and ELZE, C. 1908 Normentafel zur Entwicklelungsgeschichte des Menschen. Jena.
Minot CS. On the solid stage of the large intestine in the chick. (1900) Jour. Boston Soc. Med. Sci. 4: 153-164.
ROTTER, J. 1903 Die Krankheiten des Mastdarms und des Afters; in the Handbuch der pracktischen Chirurgie by Bergmann et al.
TANDLER, J. 1900 Zur Entwickelungsgeschichte des Menschlichen Duodenum in friihen Embryonalstadien. Morph. Jahrb., Bd. 29, pp. 187-216.
Cite this page: Hill, M.A. (2020, January 29) Embryology Paper - A case of atresia ani in a human embryo of 26 mm. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_A_case_of_atresia_ani_in_a_human_embryo_of_26_mm
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