The urachus: an investigation of its development, anatomy and histology; its relation to urinary umbilical fistula, with a complete analysis of the literature; also a study of the history of its central epithelium and its connection with adenomatous tumours of the urinary tract and the umbilicus

Abstract

This Thesis, as originally planned, was to have, been confined to the subject of Urinary Fistula and Patent Urachus. An examination of the literature on these topics soon convinced me, however, of the necessity of a personal study of the normal anatomy and histology of the structures concerned, a theme about which the ordinary text-books of anatomy are singularly reticent. I was enabled to carry out, by gross dissection, microscopical dissection and microscopy, a complete examination of twenty -eight specimens of urachus, derived from a consecutive series of post -mortem cases, from dissecting -room bodies and from still -born foetuses. In the course of this examination, much new information was obtained, throwing light on pathological changes in vestigial epithelium, which had hitherto been un- :explained. This, to my mind, the most valuable part of the Thesis is embodied in Chapter III. The conclusion was inevitably reached, that the normal conception of the Urachus, as a solid fibro- muscular cord, reaching to the umbilicus is incorrect. It is not a solid fibro- muscular cord, nor does it reach to the umbilicus. Such a radical change in anatomical knowledge compelled one to elaborate a new pathology to explain the various types of umbilical fistulae usually ascribed to the presence of a patent urachus. Incidentally, much evidence was found in support of the view that the allantois has nothing to do with the formation of the urachus, which developes, in company with the bladder, from the ventral cloaca.CHAPTER I. (1) The current anatomy of the Urachus, as given by standard authorities, requires revision. The structure does not reach the umbilicus, but only one third of the way. It averages 5 c.m. in length; and is attached to the posterior aspect of the navel by fibrous cords derived from the obliterated hypogastric arteries.(2) Its epithelial canal is never obliterated by fibrous tissue, but remains patent, although impervious in parts owing to epithelial debris derived from its own cells. The lumen of this canal is in direct continuity with the bladder cavity in about 35% of all subjects.(3) The orifice where the canal opens into the bladder is guarded by a valve of mucous membrane in only about 5% of cases. This is the first time this question has been investigated since Wutz, in 1883, asserted that such a valve existed in all cases.(.) The lowest centimetre or two of the urachal canal is frequently sacculated in cases where it communicates with the bladder. This sacculus was observed in 30% of museum specimens where the bladder had been dilated from chronic distension.(5) This sacculus sometimes ruptures from pressure of urine, and the fluid passes up between the transversalis fascia and the peritoneum. It is circumscribed laterally by the attach - :ments of the hypogastric arteries to both peritoneum and fascia, and vents at the weak point formed by the umbilical pit.(6) The normal histology of the urachus is studied and the relation of its component parts to those of the bladder. A suggestion is mad that it has an active function in the adult.(7) The various methods by which the urachus terminates is considered and it is proved that, in all cases, it has an intramural course through the muscular wall of the bladder, reaching the submucosa. Even where no communication exists with the bladder, the urachal canal remains patent to this point.(8) The development of the Urachus: It is reasoned that erroneous early views on this subject gave rise to the present false conception of the pathology of congenital urinary umbilical fistulae and urachal cysts. Evidence is given from the clinical and pathological side to support the modern embryological view that the Allantois takes no share in the formation of the Urachus. It is derived from the upper part of the ventral cloaca, the bladder being formed from the lower part. Sometimes no urachus forms, the bladder then reaching to the umbilicus at birth. Normally, the apex of the urachus reaches the umbilicus at birth, but it is carried down with the descent of the bladder. The lack of closure of the upper end of the bladder, where this occurs, interferes with that organ's descent. In many cases where a urinary fistula existed at the umbilicus the bladder was found to reach that structure. In others, this condition was found at laporotomy for some other reason. Such cases usually appear in the literature described as patent urachus. Further evidence in favour of the cloacal origin of the urachus is given in the fact that epithelial rests and glands were found in it similar in nature to those found in the bladder wall.CHAPTER II. UMBILICAL URINARY FISTULA. (1) Confusion exists in the literature between true congenital fistulae in which urine is discharged from the umbilicus, and acquired fistula of the same nature. Also between true urinary fistulae and cases where a supposed urachal cyst has ruptured through. The pathology of all three conditions is different.(2) Congenital fistulae are of two varieties: (a) Where the urine flows freely or perhaps exclusively from the umbilicus. These cases are due to complete non- development of the urachus - the cavity of the bladder reaching the umbilicus. They are easily closed but tend to reopen if there is backward pressure in later life. (b) Where the urine escapes drop by drop. These are due to retarded closure of the ventral cloaca to form the urachus. When once cured, the bladder tends to descend naturally and the urachus forms; so that when once they are cured, there is no tendency for the fistula to reopen.(3) A urachus which has once descended and assumed normal proportions can never convey urine from the bladder to the umbilicus.(4) It follows that acquired fistulae are of two types: (a) Where, through mal-development, there is no urachus, and the bladder apex is at the umbilicus. This condition is shown by reported cases to have been frequently present. (b) Urine escapes through the dilated terminal centimetre of the urachal canal, or through the weak point at the junction of the urachus with the bladder. It creeps up in the confined limits of the space in which it finds itself. The peritoneum and transversalis fascia fuse near or at the umbilicus, preventing its further progress and it bursts through the weak point formed by the depression in the lowermost quadrant of the umbilicus. All the cases existing in the literature are analysed to prove these points.CHAPTER III. (1) This deals with cysts and tumours of the umbilicus and a new explanation is given of their pathology. Urachal cysts are of two kinds as they exist in the reports: (a) A large variet which are merely collect :ions of fluid outside the peritoneum and may have or not have a connexion with the lower dilated centimetre of the urachal canal. (b) A small variety of cyst which is present, in embryonic form at least, in over 50% of all normal subjects past middle age. These occasionally attain sufficient size to attract attention during laporotomy or post-mortem.(2) A study of a series of sections shows that these (class (b) ) are of the nature of cystic glandular structures and not merely dilatations of the central canal. The lumina of their loculi are formed by a degeneration of the central cells of the original column, which is derived from the proliferation of the epithelial cells of the central canal. This proliferation is caused by the impetus of the fibrous tissue to close the canal, a goal which it never attains.(3) The separated masses of epithelium by proliferation form various columns and masses of cells, so that a solid adenomatous type of growth may be formed instead of a cystic type. Bases of such growths in an advanced state are referred to and they are proved to be identical in structure with the early stage found in my specimens. These growths and the small type of cyst, therefore, own an identical etiology.(4) Although the urachus does not ascend more than a third of the way between the bladder and the umbilicus, yet some of its cells may be shed in its descent. By this means typical glandular tumours and cystic structures may be found in this region. An illustration of such a condition is found in one of my slides and illustrated.(5) The process of formation of these pathological structures is shown in a series of drawings from actual sections, and no doubt they also illustrate the method by which the puzzling glandular tumours in the bladder wall arise.(6) The investigation, therefore, elucidates what is considered a very obscure section of the pathology of the urinary tract.Finally, a complete Bibliography of all known literature on the Urachus is appended. This includes practically all the cases that have ever been reported.