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Role of the Gubernaculum and Intraabdominal Pressure in the Process of Testicular Descent
0022-5347 /84/1313-0574$02.00/0 Vol. 131, March
THE JOURNAL OF UROLOGY
Printed in U.S.A.
Copyright© 1984 by The Williams & Wilkins Co.
ROLE OF THE GUBERNACULUM AND INTRAABDOMINAL PRESSURE IN THE PROCESS OF TESTICULAR DESCENT HOWARD L. FREY AND JACOB RAJFER* From the Division of Urology, Department of Surgery, UCLA School of Medicine, Harbor/UCLA Medical Center, Torrance, California
ABSTRACT
In an attempt to more accurately define the role of the gubernaculum in the descent of the testis, a series of microsurgical procedures was performed in the newborn rat and the incidence of testicular descent was noted 4 weeks later. When the proximal attachment of the gubernaculum to the testis/ epididymis was severed, descent occurred in 17 of 17 (100 per cent) of the testes. When the distal attachment of the gubernaculum to the scrotum was severed, 0 of 10 (O per cent) of the testes descended. When the entire gubernaculum was removed, 0 of 18 (O per cent) of the testes descended. When the gubernaculum on 1 side and the testis on the contralateral side were both excised, the solitary testis descended into the contralateral hemiscrotum in 34 of 45 (76 per cent) animals. When 1 testis was excised and only the attachment between the contralateral testis and its gubernaculum was severed, the solitary testis was capable of descending into either hemiscrotum. When 1 gubernaculum was completely excised leaving both testes and a solitary gubernaculum present, either 1 or both testes were capable of descending into the hemiscrotum containing the intact gubernaculum. In addition, if a testis was excised prior to normal testicular descent and a silicone prosthesis was placed intraabdominally, the prosthesis was capable of migrating into the scrotum 55 per cent (11 of 20) of the time. These data suggest that in the rat, 1) the gubernaculum with an intact distal attachment is a necessary prerequisite for testicular descent, 2) contraction of the gubernaculum is most likely not the mechanism by which testicular descent occurs and 3) intraabdominal pressure appears to play a major role in testicular descent. Experimental observations in laboratory animals1• 2 and clinical correlations in humans 3 - 6 suggest that an intact hypothalamic-pituitary-testicular axis is a necessary prerequisite for testicular descent. The exact target tissue that effects testicular migration is still unknown. The gubernaculum, the tissue that connects the testis and epididymis to the scrotal wall, is in a preeminent position to guide the testis from the abdomen into the scrotum, and this observation has led a number of investigators over the past 2 centuries to suggest that the gubernaculum is the target tissue responsible for testicular migration. However, all attempts by our laboratory to implicate the gubernaculum as the androgen target tissue responsible for testicular descent have failed. This failure to implicate the gubernaculum has stimulated us to reinvestigate the data reported in the literature regarding the exact role of the gubernaculum in testicular descent. To accomplish this, we devised a series of microsurgical experiments using the laboratory rat as our animal model. MATERIALS AND METHODS
Sprague-Dawley male rats 1 to 2 days old with nursing mothers were obtained. The mothers were fed rat chow and water ad libitum. Various operative procedures utilizing a diploscope were performed on the male offspring either in the newborn period (day 1 of age) or at 2 weeks (14 days) of age. Anesthesia was induced by ether inhalation. The abdominal cavity was opened transversely midway between the umbilicus and the external genitalia, and abdominal closure was accomplished with nylon sutures. In the rat, testicular descent normally occurs on or about the 21st day of age. 2 As a result, the following operative procedures were performed in the newborn period and the incidence of testicular descent was observed at 28 days of age. In Group A, Accepted for publication October 13, 1983. *Requests for reprints: Box 5, Harbor/UCLA Medical Center, 1000 W. Carson St., Torrance, CA 90509. 574
the control group, the animals were sham operated at day 1 of age. Each testis, epididymis and gubernaculum was identified and lifted onto the abdominal wall and then placed into the abdominal cavity (fig. lA). In Group B, the testis, epididymis and gubernaculum were removed on 1 side while on the contralateral side only the proximal attachment of the gubernaculum to the testis/epididymis was severed (fig. 2A). This experiment was performed to determine if the proximal attachment of the gubernaculum to the testis/epididymis was necessary for testicular descent to occur. In Group C, the testis, epididymis and gubernaculum were excised on 1 side while on the contralateral side only the distal attachment of the gubernaculum to the scrotum was severed (fig. 3A). This experiment was performed in order to determine whether the distal attachment of the gubernaculum to the scrotal wall was essential for testicular descent to occur. In Group D, the testis, epididymis and gubernaculurn were excised on 1 side, while on the contralateral side the gubernaculum was completely excised leaving only a solitary testis and epididymis present (fig. 4A). This experiment was performed to determine whether testicular descent could proceed without the presence of the gubernaculum. In Group E the testis and epididymis were removed from 1 side leaving the gubernaculum attached only by its distal scrotal attachment, while on the contralateral side, only the proximal gubernacular attachment to the testis/epididymis was severed (fig. 5A). This experiment was performed to determine the movement of a solitary free testis in the presence of both gubernacula. In Group F, the testis and epididymis were removed on 1 side again leaving the ipsilateral gubernaculum intact, while on the contralateral side the entire gubernaculum was excised leaving the testis and epididymis intact (fig. 6A ). This experiment was performed to see if the descent of a solitary testis could somehow be influenced by a solitary contralateral gubernaculum. In Group C, the entire gubernaculum was excised on 1 side leaving the testis/epididymis intact, while on the contralateral side only the proximal attachment of the gubernaculum to the testis/epididymis was severed (fig. 7A). This experiment was
575
GUBERNACULUM AND INTRAABDOMINAL PRESSURE IN TESTICULAR DESCENT 1- Day-Old Rat
28-Day-Old Rat
A
(
FIG. 1. Normal internal genital anatomy of male rat (Group A, no.=7). A, at 1 day of age. B, at 28 days of age at which time all testes have descended into scrotum.
FIG. 4. Neonatal surgical procedure and results at 28 days of age in Group D (no.=18) animals. A, excision of entire gubernaculum on 1 side and excision of testis/epididymis and gubernaculum on contralateral side. B, testicular descent did not occur in any of animals (0/18) at 28 days of age.
B
Bladder
Bladder
FIG. 2. Neonatal surgical procedure and results at 28 days ofage in Group B (no.=7) animals. A, proximal attachment of gubernaculum incised on 1 side with testis/epididymis and gubernaculum excised on contralateral side. B, testicular descent occurred in 17/17 animals at 28 days of age.
FIG. 5. Neonatal surgical procedure and results at 28 days of age in Group E (no.=42) animals. A, incision only of proximal gubernacular attachment to the testis/epididymis on 1 side, and excision of just contralateral testis/epididymis but not gubernaculum. B, testicular descent occurred in 42/42 (100%) of animals by day 28 of age; 30 testes descended into ipsilateral hemiscrotum and 12 into contralateral hemiscrotum.
B
"' \ 0/10 (0%)
FIG. 3. Neonatal surgical procedure and results at 28 days of age in Group C (no.=10) animals. A, distal attachment of gubernaculum incised on 1 side with testis/epididymis and gubernaculum excised on contralateral side. B, testicular descent occurred in none (0/10) of animals at 28 days of age.
performed to see whether a solitary gubernaculum could in some way influence the descent of both testes_ On a separate group of animals (Group H) that were operated on at 14 days of age, the testis and epididymis were excised on 1 side leaving the ipsilateral gubernaculum intact. The contralateral side was left intact in order to provide a normal hormonal environment. A silicone prosthesis (#382 medical grade elastomer) was then placed into the abdomen on the side where the testis has been removed (fig. BA). The prosthesis was fashioned in an elliptical form similar in size to the excised testis_ The abdomen was then closed. In several of the animals in Groups A, F and G, a radioopaque #30 stainless steel wire cut to 1½ mm. length was pushed into the body of the testis so that sequential x-rays could be taken to monitor testicular migration. Prior to each x-ray the animal was anesthetized using ether and then placed on the x-ray film in a prone position. Immediately after these surgical and x-ray procedures, the
576
FREY AND RAJFER
animals were revived from their anesthesia and placed into cages with their mothers until they were 28 days of age, at which time the animals were sacrificed and the position of the testes and silicone prostheses noted. If any part of the testis was observed in the abdominal cavity, it was considered undescended. Those testes not totally free of adhesions, even if within the scrotum, were excluded. The testicular prostheses which were fixed by adhesions in the abdomen were classified as undescended.
Bladder
RESULTS
FIG. 6. Neonatal surgical procedure and results at 28 days of age in Group F (no.=45) animals. A, excision of both entire gubernaculum on 1 side and testis/epididymis on contralateral side. B, testis descended into contralateral hemiscrotum in 34/45 animals, but never into ipsilateral hemiscrotum. Bladder
Bladder
FIG. 7. Neonatal surgical procedure and results at 28 days of age in Group G (no.=19) animals. A, excision of entire gubernaculum on 1 side, but incision only of proximal gubernacular attachment to testis/ epididymis on contralateral side. B, both testes descended into same scrotal compartment (containing the gubernaculum) in 7/19 animals at 28 days of age. 14-Day-Old Rat
A
28-Day-O\d Rat
B
,, I
11/20 (55%)
FIG. 8. Surgical procedure performed at 2 weeks of age and results at 28 days of age in Group H (no.=20) animals. A, excision of testis/ epididymis on 1 side leaving ipsilateral gubernaculum attached distally and contralateral testis/epididymis and gubernaculum intact. Silicone prosthesis was placed in area of excised testis/epididymis. B, prosthesis descended into ipsilateral hemiscrotum in 11/20 animals.
In the sham operated group (Group A) of 7 animals, testicular descent was present bilaterally in all animals by day 28 of age (fig. lB). After severing the proximal attachment of the gubernaculum to the testis/epididymis (Group B), all testes descended (17 of 17) by 4 weeks of age (fig. 2B). However, after severing the distal attachment of the gubernaculum to the scrotum (Group C), none of the testes (O of 10) descended by day 28 of age (fig. 3B). When the entire gubernaculum was removed (Group D), as expected the testis did not descend (0 of 18) by 28 days of age (fig. 4B). These 3 experiments involving Groups B, C and D provide ample evidence that a gubernaculum with at least an intact distal (scrotal) attachment is necessary for testicular descent to occur. When both gubernacula were present with a solitary testis (Group E), the lone testis/epididymis descended ipsilaterally in 30 out of 42 animals; but surprisingly, in 12 animals the testis crossed over the midline into the contralateral hemiscrotal compartment (fig. 5B), again suggesting that not only was a gubernaculum with an intact distal (scrotal) attachment necessary for testicular descent to occur, but that a testis could migrate to the contralateral hemiscrotum if a gubernaculum was present there. Similarly, when a solitary testis was left in the presence of a solitary contralateral gubernaculum, the testis was found to cross over to the contralateral hemiscrotum where the gubernaculum remained (Group F) in 34 of 45 animals (fig. 6B). As expected in this group, the testis never descended on the ipsilateral side where the entire gubernaculum was excised, thereby confirming the observation in the Group D animals. When both testes were present with a solitary proximally free gubernaculum (Group G), both testes descended into the same hemiscrotum in 7 of 19 animals (fig. 7B). Of the remaining 12 animals in this group, only unilateral descent occurred in 10 animals, but in 4 of these 10 animals the testis crossed over to descend into the contralateral hemiscrotum. However, testicular descent never occurred on the side where the gubernaculum was completely excised. In the remaining 2 animals of Group G, testicular descent did not occur. In the final experiment in which a silicone prosthesis was substituted for a testis (Group H), the silicone prosthesis descended into the ipsilateral hemiscrotum in 11 of 20 (55 per cent) animals (fig. 8B). In 1 animal the prosthesis crossed over the bladder from the right side and descended with the normal left testis into the left hemiscrotum. Of the 9 undescended silicone prostheses, 6 had formed dense adhesions to the abdominal wall or small bowel mesentery. In all these animals the natural left testis descended normally into the left scrotum (table 1). Utilizing x-rays (figs. 9, 10, 11), it was determined that testicular descent had occurred between the 2nd and 4th weeks of age and that crossover of the testis had occurred on or about the 10th day of age. DISCUSSION
Ever since John Hunter first described the gubernaculum over 2 centuries ago,7 its role in testicular descent has engendered much controversy. The position of the gubernaculum between the testis and scrotum would lead one to assume that it is somehow involved in guiding the testis from the abdomen
GtTBERNACULUlVi ANT) Il\TTRAAB[H.)!v!Il'-JAL PRES.SURE rt~J TESTICULAR [PESCEl¾JT TABLE l,
Incidence of testicular descent in various groups
No. Animals
Testicular Descent (%)
A B C D E
7 17 10 18 42
7(100%) 17 (100%) 0 (0%) 0 (0%) 42 (100%)
F G
45 19
34 (76%) 7'' (63%)
H
20
llt (55%)
Groups
577
Testis Location In Scrotum 100% ipsilateral 100% ipsiiateral
71 % 29% 100% 54 % 46% 91 % 9%
ipsilateral contralateral contralateral ipsilateral contralateral ipsilateral contralateral
* 37% in this group showed bilateral descent into the same hemiscrotum.
t Descent of silicone prosthesis. Fm. 11. Sequential x-rays demonstrating testicular migration in Group G animal in which entire gubernaculum on l side was excised with incision only of attachment between testis/epididymis and gubernaculum on contralateral side. Both testes, each with steel wire inserted, descend together into same hemiscrotal compartment sometime between 2 and 4 weeks of age. A, day 1. B, day 14. C, day 28.
scrotum," After the testis reaches the scrotum, the processus vaginalis obliterates and the gubemaculum atrophies. Over the years, various theories have been formulated to explain the mechanism by which the testis migrates from the abdomen into the scrotumo Foremost are certain physical facFIG. 9. Sequential x-rays demonstrating testicular migration in con trol (Group A) animal. steel wire was inserted into each testis at day tors which include 1) traction on the testis by the gubernacu1 of age. B, testes are undescended at 14 days of age. C, testes have lum, 2) differential growth of the body wall in relation to a descended by day 28 of age. relatively immobile gubemaculum and, 3) intraabdominal pressure pushing the testis through an inguinal canal that is engorged by the swollen ne1rm,c1.uum, Seiler 15 and Curling16 1st proposed that muscular contraction of the gubernaculum pulled the testis into the scrotum. Support for this concept comes from the observation of Lewis 17 that testicular descent was prevented in rats after severance of the genitofemoral nerve that innervates the gubernaculum. Nevertheless, there are several anatomical observations and experimental studies that appear to refute this traction theory. For example, in the human fetus"· 12 · 18 and in the domestic pig9 ' 190 20 only a weak distal scrotal attachment exists between the gubernaculum and scrotum, which is probably insufficient to support any traction on the testiso fo addition, W ells 21 in the ground squirrel and Fm. 10. Sequential x-rays demonstrating testicular migmtion in Bergh 22 in the rat found that testicular descent could proceed Group F animal in which entire gubernaculum on 1 side and testis/ despite severance of the gubernaculum. The differential growth epididymis on contralateral side have been excised. Testis with steel theory adheres to the concept that as the body wall grows, the wire inserted is seen crossing over into contra!atera! nem1:scr'Otl testis is kept in proximity to the internal inguinal ring and is sometime between 2 and 4 weeks of age. A, day l. B, day 14. then pulled into the scrctum the relatively immobile gubernaculum. 23 How·ever, this has refuted Wyndham, 12 who to demonstrated that the gubemaculum increased in size Lemeh, 13 who showed that the gubernaculum occurs while descent, and cv;wJ,nH<- descent. 8 in fact faster than the as a whole. Elder et al. 2'· have the m,v,1r/4-,:i,nc,c, of the gubematheoretical supporting the concept the descent of the testis have that intraabdominal pressure, as 1st proposect by Gier and Marion 25 ' 26 in 1970, play a in testicular descent. The gubemaculum 1st <.nnc,»'Q in the human fetus during If this is true, then gubemaculum might indeed be the the 6th week of gestation, same time the germ rudder, as Hunter suggested/ that guides the testis into the cells arrive at the genital ridge. 9 At this stage development scrotum. The gubernaculum appears to be an important link in the the gubemaculum consists mainly of mesenchyma! cells and extends in a straight line from the genital ridge to the site of movement of the testis from the abdomen into the scrotum. the future scrotum. Between the 7th and 15th week of gestation, First, if the gubernaculum is not present or if its scrotal differentiation of the gonads and the internal and external attachment is severed, the testis will not descend, On the other genitalia occurs, 10 The testis assumes a stationary position near hand, severing the testicular/epididymal attachment of the the internal inguinal ring" between the 15th week and the 7th gubernaculum does not impede descent. These findings, in month of gestation, at which time the processus vaginalis, an accord with those of Bergh et al., 21 suggest that traction by the out-pouching of the peritoneum, grows along the ventral aspect gubemaculum on the testis is not an important mechanism in of the gubernaculum 12 which begins to expand until its diameter promoting testicular descent in the rat. Otherwise, severance is equal to or greater than that of the testis, 90 n, 13 The testicular of the attachment of the proximal gubemaculum to the testis/ vessels as well as the vasa deferentia elongate and the scrotum epididymis would result in testicular maldescent. More imporbegins to develop,"· 14 The testis than migrates very rapidly tantly, however, this study demonstrates that the solitary testis from the abdomen through the inguinal canal and into the is capable of crossing over the bladder to descend into the
578
FREY AND RAJFER
contralateral scrotal compartment as long as a gubernaculum is present there. Two possible explanations for this crossover phenomenon are immediately apparent. The 1st and least likely is that the gubernaculum may secrete some as yet unknown chemotactic substance that may draw the testis/epididymis to its location. The gubernaculum of the postnatal rat is believed to be composed mainly of rhabdomocytes and acid mucopolysacharides27 which are not known to be secretory in any way. The 2nd explanation, and the more tenable, involves the role of intraabdominal pressure. When the gubernaculum is either incised distally or excised in its entirety, the ipsilateral hemiscrotum does not fully develop. This may be due to the fact that the gubernaculum is known to increase in size just prior to descent and it is this swelling that may cause the scrotum to develop and obtain its characteristic shape. In the rabbit, for example, part of the gubernaculum is encompassed into the developing scrotum8 • 24 and it is not difficult to theorize that any defect in the gubernaculum may contribute to underdevelopment of the scrotum. It is possible that when this hemiscrotum is underdeveloped, the testis which is free in the abdominal cavity is pushed into the most accommodating available space. In this case the push may be due to intraabdominal pressure, whereas the most accommodating and available space may be the developed contralateral hemiscrotum. This is consistent with the observation that when both gubernacula are present and therefore each hemiscrotum well-developed and available to receive a testis, a solitary free gonad can descend into either scrotal compartment. Additionally, when both testes are free and a solitary gubernaculum is present descent will only occur on the side where the gubernaculum is present and, surprisingly, both testes can descend together into the same scrotal compartment. This latter finding exactly parallels what is observed in the rare clinical entity of crossed testicular ectopy. 2B-3o In this disorder, both testes are found in the same scrot11l compartment. Usually the blood supply, vas deferens and epididymis to 1 of the testes comes from the contralateral side. The etiology of this condition is not known, but it is interesting to speculate that a unilateral abnormality of the gubernaculum may be responsible. Based on the observation that the testis could cross over into the contralateral hemiscrotum, we felt that intraabdominal pressure could well be responsible for testicular migration in this experimental setting. Substitution of a free silicone prosthesis for a testis resulted in prosthetic descent in a high percentage of the animals. This clearly suggested that some physical force that can act on an inert substance such as silicone may be active in promoting testicular descent. The finding that a prosthesis could descend into the scrotum is novel and is not the same as that observed by Martins 32 in which he replaced the testis with paraffin within the tunica albuginea and found that it could descend into the scrotum. Martins used adult rats in which testicular descent had already occurred and, consequently, was studying testicular retraction rather than testicular descent. In studying factors responsible for scrotal dilatation, Backhouse9 refers to an experiment in the rat in which a stainless steel ball was sutured to the tunica albuginea after the testicular contents had been removed, but the epididymis with its attachment to the gubernaculum was left intact. Clearly, our experiment differs in that the silicone prosthesis lies totally free within the abdomen, not subjected to any possible effects from an attached epididymis or gubernaculum. In summary, this study suggests that in the rat the gubernaculum appears to be an absolute prerequisite for testicular descent. The crossover phenomenon and the finding that an intact distal attachment of the gubernaculum to the scrotum is necessary for scrotal development and subsequent testicular migration also suggests that the traction theory of testicular descent does not appear to be operative in this animal model. Yet, these findings are certainly consistent with the theory that
intraabdominal pressure may have a major role in facilitating the descent of the testis. The intraabdominal theory of testicular descent is further supported by the observation that a free silicone prosthesis placed intraabdominally is capable of descending into the scrotum at the appropriate time. How intraabdominal pressure works in tandem with an intact hypothalamic-pituitary-testicular axis to facilitate descent remains to be determined. REFERENCES
1. Engel, E. T.: Experimentally induced descent of the testis in the Macacus monkey by hormones from the anterior pituitary and pregnancy urine. Endocrinology, 16: 513, 1932. 2. Rajfer, J. and Walsh, P. C.: Hormonal regulation of testicular descent: experimental and clinical observations. J. Urol., 118: 995, 1977. 3. Hamilton, J.B. and Hubert, G.: Effect of synthetic male hormone substances on descent of testicles in human cryptorchidism. Proc. Soc. Exp. Biol. Med., 39: 4, 1938. 4. Hamilton, J.B.: The effect of male hormone upon the descent of the testes. Anat. Record, 70: 533, 1938. 5. Bigler, J. A., Hardy, L. M. and Scott, H. V.: Cryptorchidism treated with gonadotropic principal. Am. J. Dis. Child., 55: 273, 1938. 6. Arnheim, E. E.: The treatment of undescended testes with gonadotropic hormones. J. Mt. Sinai Hosp., 4: 1036, 1938. 7. Hunter, J. A.: A description of the situation of the testis in the fetus with its descent into the scrotum. In: Observations on Certain Parts of the Animal Oeconomy. New Orleans: John J. Haswell and Co., p. 42, 1841. 8. Rajfer, J.: Morphological study of testicular descent in the rabbit. Invest. Urol., 18: 293, 1980. 9. Backhouse, K. M.: Embryology of testicular descent and maldescent. Urol. Clin. North Am., 9: 315, 1982. 10. Jost, A.: A new look at the mechanisms controlling sex differentiation in mammals. J. Hopkins Med. J., 130: 38, 1972. 11. Wells, L. J. Descent of the testis: anatomical and hormonal considerations. Surgery, 14: 436, 1943. 12. Wyndham, H. R.: A morphological study of testicular descent. J. Anat., 77: 179, 1943. 13. Lemeh, C. N.: A study of the development and structural relationships of the testis and gubernaculum. Surg. Gyn. Obstet., 110: 164, 1960. 14. Wells, L. J.: Descensus testiculorum: androgenic stimulation of the scrotum, inguinal bursa and ductus deferens. Anat. Rec., 88: 465, 1944. 15. Seiler, B. W. (1817) as cited by Backhouse, K. M. and Butler, H.: The gubernaculum testis of the pig (sus scropha). J. Anat., 94: 107, 1960. 16. Curling, J.B.: Observations on the structure of the gubernaculum and on the descent of the testis in the fetus. Lancet, 2: 70, 1840. 17. Lewis, L. G.: Cryptorchidism. J. Urol., 60: 345, 1948. 18. Tayakkanonta, K.: The gubernaculum testis and its nerve supply. Aust. NZ J. Surg., 33: 61, 1963. 19. Backhouse, K. M. and Butler, H.: The gubernaculum testis of the pig (sus scropha). J. Anat., 94: 107, 1960. 20. Backhouse, K. M.: The gubernaculum testis Hunteri: testicular descent and maldescent. Ann. R. Coll. Surg. Engl., 35: 15, 1964. 21. Wells, L. J.: Descensus testiculorum: descent after severance of gubernaculum. Anat. Rec., 88: 465, 1944. 22. Bergh, A., Helander, H.F. and Wahlquist, L.: Studies on factors governing testicular descent in the rat-particularly the role of gubernaculum testis. Int. J. Andrology, 1: 342, 1978. 23. McMurrich, J. P.: The Development of the Human Body, A Manual of Human Embryology. Philadelphia: P. Blakiston's Son & Co., 7th edition, pp. 374-376, 1923. 24. Elder, J. S., Isaacs, J. T. and Walsh, P. C.: Androgenic sensitivity of the gubernaculum testis: evidence for hormonal/mechanical interactions in testicular descent. J. Urol., 127: 170, 1982. 25. Gier, H. T. and Marion, G. B.: Development of the mammalian testis. In: The Testis. Edited by A. D. Johnson and G. B. Marion. New York: Academic Press, vol. 1, chapt. 1, p. 1, 1970. 26. Bergin, W. C:;' Gier, H. T., Marion, G. B. and Coffman, J. R.: A developmental concept of equine cryptorchidism. Biol. Reprod., 3: 82, 1970. 27. Radhakrishnan, J., Morikawa, Y., Donahoe, P. K. and Hendren,
579 ""(¥. H.: Observations on the g-ubernaculun1 during descent of the testis. Invest, UroL, 16: 365, 1979, 28. Davis, J.E.: Transverse aberrant testicular maldescent. U.S. Armed Forces Med. J., 8: 1046, 1957, 29. Mukerjee, S. and Amesur, N. R.: Transverse testicular ectopia with unilateral blood supply. Ind. J. Surg., 27: 547, 1965. 30. Dajani, A. M.: Transverse ectopia of the testis. Brit. J. UroL, 41:
80, 1969. 3L Scorer, C. Go and Farringto:t1i G·. I-I.: l'i,a:re deformities of th2 testiEL
In: Congenital Deformities of the Testis and Epididymis. New York: Appleton-Century-Crofts, chapt. 13, p. 175, 1971. 32. Martins, T.: La testosterone peut provoquel' la descente de testicules artificiels de paraffine. Compt. Rend. Soc. de Biol., 131: 299, 1938.
THE JOURNAL OF UROLOGY
Printed in U.S.A.
Copyright© 1984 by The Williams & Wilkins Co.
ROLE OF THE GUBERNACULUM AND INTRAABDOMINAL PRESSURE IN THE PROCESS OF TESTICULAR DESCENT HOWARD L. FREY AND JACOB RAJFER* From the Division of Urology, Department of Surgery, UCLA School of Medicine, Harbor/UCLA Medical Center, Torrance, California
ABSTRACT
In an attempt to more accurately define the role of the gubernaculum in the descent of the testis, a series of microsurgical procedures was performed in the newborn rat and the incidence of testicular descent was noted 4 weeks later. When the proximal attachment of the gubernaculum to the testis/ epididymis was severed, descent occurred in 17 of 17 (100 per cent) of the testes. When the distal attachment of the gubernaculum to the scrotum was severed, 0 of 10 (O per cent) of the testes descended. When the entire gubernaculum was removed, 0 of 18 (O per cent) of the testes descended. When the gubernaculum on 1 side and the testis on the contralateral side were both excised, the solitary testis descended into the contralateral hemiscrotum in 34 of 45 (76 per cent) animals. When 1 testis was excised and only the attachment between the contralateral testis and its gubernaculum was severed, the solitary testis was capable of descending into either hemiscrotum. When 1 gubernaculum was completely excised leaving both testes and a solitary gubernaculum present, either 1 or both testes were capable of descending into the hemiscrotum containing the intact gubernaculum. In addition, if a testis was excised prior to normal testicular descent and a silicone prosthesis was placed intraabdominally, the prosthesis was capable of migrating into the scrotum 55 per cent (11 of 20) of the time. These data suggest that in the rat, 1) the gubernaculum with an intact distal attachment is a necessary prerequisite for testicular descent, 2) contraction of the gubernaculum is most likely not the mechanism by which testicular descent occurs and 3) intraabdominal pressure appears to play a major role in testicular descent. Experimental observations in laboratory animals1• 2 and clinical correlations in humans 3 - 6 suggest that an intact hypothalamic-pituitary-testicular axis is a necessary prerequisite for testicular descent. The exact target tissue that effects testicular migration is still unknown. The gubernaculum, the tissue that connects the testis and epididymis to the scrotal wall, is in a preeminent position to guide the testis from the abdomen into the scrotum, and this observation has led a number of investigators over the past 2 centuries to suggest that the gubernaculum is the target tissue responsible for testicular migration. However, all attempts by our laboratory to implicate the gubernaculum as the androgen target tissue responsible for testicular descent have failed. This failure to implicate the gubernaculum has stimulated us to reinvestigate the data reported in the literature regarding the exact role of the gubernaculum in testicular descent. To accomplish this, we devised a series of microsurgical experiments using the laboratory rat as our animal model. MATERIALS AND METHODS
Sprague-Dawley male rats 1 to 2 days old with nursing mothers were obtained. The mothers were fed rat chow and water ad libitum. Various operative procedures utilizing a diploscope were performed on the male offspring either in the newborn period (day 1 of age) or at 2 weeks (14 days) of age. Anesthesia was induced by ether inhalation. The abdominal cavity was opened transversely midway between the umbilicus and the external genitalia, and abdominal closure was accomplished with nylon sutures. In the rat, testicular descent normally occurs on or about the 21st day of age. 2 As a result, the following operative procedures were performed in the newborn period and the incidence of testicular descent was observed at 28 days of age. In Group A, Accepted for publication October 13, 1983. *Requests for reprints: Box 5, Harbor/UCLA Medical Center, 1000 W. Carson St., Torrance, CA 90509. 574
the control group, the animals were sham operated at day 1 of age. Each testis, epididymis and gubernaculum was identified and lifted onto the abdominal wall and then placed into the abdominal cavity (fig. lA). In Group B, the testis, epididymis and gubernaculum were removed on 1 side while on the contralateral side only the proximal attachment of the gubernaculum to the testis/epididymis was severed (fig. 2A). This experiment was performed to determine if the proximal attachment of the gubernaculum to the testis/epididymis was necessary for testicular descent to occur. In Group C, the testis, epididymis and gubernaculum were excised on 1 side while on the contralateral side only the distal attachment of the gubernaculum to the scrotum was severed (fig. 3A). This experiment was performed in order to determine whether the distal attachment of the gubernaculum to the scrotal wall was essential for testicular descent to occur. In Group D, the testis, epididymis and gubernaculurn were excised on 1 side, while on the contralateral side the gubernaculum was completely excised leaving only a solitary testis and epididymis present (fig. 4A). This experiment was performed to determine whether testicular descent could proceed without the presence of the gubernaculum. In Group E the testis and epididymis were removed from 1 side leaving the gubernaculum attached only by its distal scrotal attachment, while on the contralateral side, only the proximal gubernacular attachment to the testis/epididymis was severed (fig. 5A). This experiment was performed to determine the movement of a solitary free testis in the presence of both gubernacula. In Group F, the testis and epididymis were removed on 1 side again leaving the ipsilateral gubernaculum intact, while on the contralateral side the entire gubernaculum was excised leaving the testis and epididymis intact (fig. 6A ). This experiment was performed to see if the descent of a solitary testis could somehow be influenced by a solitary contralateral gubernaculum. In Group C, the entire gubernaculum was excised on 1 side leaving the testis/epididymis intact, while on the contralateral side only the proximal attachment of the gubernaculum to the testis/epididymis was severed (fig. 7A). This experiment was
575
GUBERNACULUM AND INTRAABDOMINAL PRESSURE IN TESTICULAR DESCENT 1- Day-Old Rat
28-Day-Old Rat
A
(
FIG. 1. Normal internal genital anatomy of male rat (Group A, no.=7). A, at 1 day of age. B, at 28 days of age at which time all testes have descended into scrotum.
FIG. 4. Neonatal surgical procedure and results at 28 days of age in Group D (no.=18) animals. A, excision of entire gubernaculum on 1 side and excision of testis/epididymis and gubernaculum on contralateral side. B, testicular descent did not occur in any of animals (0/18) at 28 days of age.
B
Bladder
Bladder
FIG. 2. Neonatal surgical procedure and results at 28 days ofage in Group B (no.=7) animals. A, proximal attachment of gubernaculum incised on 1 side with testis/epididymis and gubernaculum excised on contralateral side. B, testicular descent occurred in 17/17 animals at 28 days of age.
FIG. 5. Neonatal surgical procedure and results at 28 days of age in Group E (no.=42) animals. A, incision only of proximal gubernacular attachment to the testis/epididymis on 1 side, and excision of just contralateral testis/epididymis but not gubernaculum. B, testicular descent occurred in 42/42 (100%) of animals by day 28 of age; 30 testes descended into ipsilateral hemiscrotum and 12 into contralateral hemiscrotum.
B
"' \ 0/10 (0%)
FIG. 3. Neonatal surgical procedure and results at 28 days of age in Group C (no.=10) animals. A, distal attachment of gubernaculum incised on 1 side with testis/epididymis and gubernaculum excised on contralateral side. B, testicular descent occurred in none (0/10) of animals at 28 days of age.
performed to see whether a solitary gubernaculum could in some way influence the descent of both testes_ On a separate group of animals (Group H) that were operated on at 14 days of age, the testis and epididymis were excised on 1 side leaving the ipsilateral gubernaculum intact. The contralateral side was left intact in order to provide a normal hormonal environment. A silicone prosthesis (#382 medical grade elastomer) was then placed into the abdomen on the side where the testis has been removed (fig. BA). The prosthesis was fashioned in an elliptical form similar in size to the excised testis_ The abdomen was then closed. In several of the animals in Groups A, F and G, a radioopaque #30 stainless steel wire cut to 1½ mm. length was pushed into the body of the testis so that sequential x-rays could be taken to monitor testicular migration. Prior to each x-ray the animal was anesthetized using ether and then placed on the x-ray film in a prone position. Immediately after these surgical and x-ray procedures, the
576
FREY AND RAJFER
animals were revived from their anesthesia and placed into cages with their mothers until they were 28 days of age, at which time the animals were sacrificed and the position of the testes and silicone prostheses noted. If any part of the testis was observed in the abdominal cavity, it was considered undescended. Those testes not totally free of adhesions, even if within the scrotum, were excluded. The testicular prostheses which were fixed by adhesions in the abdomen were classified as undescended.
Bladder
RESULTS
FIG. 6. Neonatal surgical procedure and results at 28 days of age in Group F (no.=45) animals. A, excision of both entire gubernaculum on 1 side and testis/epididymis on contralateral side. B, testis descended into contralateral hemiscrotum in 34/45 animals, but never into ipsilateral hemiscrotum. Bladder
Bladder
FIG. 7. Neonatal surgical procedure and results at 28 days of age in Group G (no.=19) animals. A, excision of entire gubernaculum on 1 side, but incision only of proximal gubernacular attachment to testis/ epididymis on contralateral side. B, both testes descended into same scrotal compartment (containing the gubernaculum) in 7/19 animals at 28 days of age. 14-Day-Old Rat
A
28-Day-O\d Rat
B
,, I
11/20 (55%)
FIG. 8. Surgical procedure performed at 2 weeks of age and results at 28 days of age in Group H (no.=20) animals. A, excision of testis/ epididymis on 1 side leaving ipsilateral gubernaculum attached distally and contralateral testis/epididymis and gubernaculum intact. Silicone prosthesis was placed in area of excised testis/epididymis. B, prosthesis descended into ipsilateral hemiscrotum in 11/20 animals.
In the sham operated group (Group A) of 7 animals, testicular descent was present bilaterally in all animals by day 28 of age (fig. lB). After severing the proximal attachment of the gubernaculum to the testis/epididymis (Group B), all testes descended (17 of 17) by 4 weeks of age (fig. 2B). However, after severing the distal attachment of the gubernaculum to the scrotum (Group C), none of the testes (O of 10) descended by day 28 of age (fig. 3B). When the entire gubernaculum was removed (Group D), as expected the testis did not descend (0 of 18) by 28 days of age (fig. 4B). These 3 experiments involving Groups B, C and D provide ample evidence that a gubernaculum with at least an intact distal (scrotal) attachment is necessary for testicular descent to occur. When both gubernacula were present with a solitary testis (Group E), the lone testis/epididymis descended ipsilaterally in 30 out of 42 animals; but surprisingly, in 12 animals the testis crossed over the midline into the contralateral hemiscrotal compartment (fig. 5B), again suggesting that not only was a gubernaculum with an intact distal (scrotal) attachment necessary for testicular descent to occur, but that a testis could migrate to the contralateral hemiscrotum if a gubernaculum was present there. Similarly, when a solitary testis was left in the presence of a solitary contralateral gubernaculum, the testis was found to cross over to the contralateral hemiscrotum where the gubernaculum remained (Group F) in 34 of 45 animals (fig. 6B). As expected in this group, the testis never descended on the ipsilateral side where the entire gubernaculum was excised, thereby confirming the observation in the Group D animals. When both testes were present with a solitary proximally free gubernaculum (Group G), both testes descended into the same hemiscrotum in 7 of 19 animals (fig. 7B). Of the remaining 12 animals in this group, only unilateral descent occurred in 10 animals, but in 4 of these 10 animals the testis crossed over to descend into the contralateral hemiscrotum. However, testicular descent never occurred on the side where the gubernaculum was completely excised. In the remaining 2 animals of Group G, testicular descent did not occur. In the final experiment in which a silicone prosthesis was substituted for a testis (Group H), the silicone prosthesis descended into the ipsilateral hemiscrotum in 11 of 20 (55 per cent) animals (fig. 8B). In 1 animal the prosthesis crossed over the bladder from the right side and descended with the normal left testis into the left hemiscrotum. Of the 9 undescended silicone prostheses, 6 had formed dense adhesions to the abdominal wall or small bowel mesentery. In all these animals the natural left testis descended normally into the left scrotum (table 1). Utilizing x-rays (figs. 9, 10, 11), it was determined that testicular descent had occurred between the 2nd and 4th weeks of age and that crossover of the testis had occurred on or about the 10th day of age. DISCUSSION
Ever since John Hunter first described the gubernaculum over 2 centuries ago,7 its role in testicular descent has engendered much controversy. The position of the gubernaculum between the testis and scrotum would lead one to assume that it is somehow involved in guiding the testis from the abdomen
GtTBERNACULUlVi ANT) Il\TTRAAB[H.)!v!Il'-JAL PRES.SURE rt~J TESTICULAR [PESCEl¾JT TABLE l,
Incidence of testicular descent in various groups
No. Animals
Testicular Descent (%)
A B C D E
7 17 10 18 42
7(100%) 17 (100%) 0 (0%) 0 (0%) 42 (100%)
F G
45 19
34 (76%) 7'' (63%)
H
20
llt (55%)
Groups
577
Testis Location In Scrotum 100% ipsilateral 100% ipsiiateral
71 % 29% 100% 54 % 46% 91 % 9%
ipsilateral contralateral contralateral ipsilateral contralateral ipsilateral contralateral
* 37% in this group showed bilateral descent into the same hemiscrotum.
t Descent of silicone prosthesis. Fm. 11. Sequential x-rays demonstrating testicular migration in Group G animal in which entire gubernaculum on l side was excised with incision only of attachment between testis/epididymis and gubernaculum on contralateral side. Both testes, each with steel wire inserted, descend together into same hemiscrotal compartment sometime between 2 and 4 weeks of age. A, day 1. B, day 14. C, day 28.
scrotum," After the testis reaches the scrotum, the processus vaginalis obliterates and the gubemaculum atrophies. Over the years, various theories have been formulated to explain the mechanism by which the testis migrates from the abdomen into the scrotumo Foremost are certain physical facFIG. 9. Sequential x-rays demonstrating testicular migration in con trol (Group A) animal. steel wire was inserted into each testis at day tors which include 1) traction on the testis by the gubernacu1 of age. B, testes are undescended at 14 days of age. C, testes have lum, 2) differential growth of the body wall in relation to a descended by day 28 of age. relatively immobile gubemaculum and, 3) intraabdominal pressure pushing the testis through an inguinal canal that is engorged by the swollen ne1rm,c1.uum, Seiler 15 and Curling16 1st proposed that muscular contraction of the gubernaculum pulled the testis into the scrotum. Support for this concept comes from the observation of Lewis 17 that testicular descent was prevented in rats after severance of the genitofemoral nerve that innervates the gubernaculum. Nevertheless, there are several anatomical observations and experimental studies that appear to refute this traction theory. For example, in the human fetus"· 12 · 18 and in the domestic pig9 ' 190 20 only a weak distal scrotal attachment exists between the gubernaculum and scrotum, which is probably insufficient to support any traction on the testiso fo addition, W ells 21 in the ground squirrel and Fm. 10. Sequential x-rays demonstrating testicular migmtion in Bergh 22 in the rat found that testicular descent could proceed Group F animal in which entire gubernaculum on 1 side and testis/ despite severance of the gubernaculum. The differential growth epididymis on contralateral side have been excised. Testis with steel theory adheres to the concept that as the body wall grows, the wire inserted is seen crossing over into contra!atera! nem1:scr'Otl testis is kept in proximity to the internal inguinal ring and is sometime between 2 and 4 weeks of age. A, day l. B, day 14. then pulled into the scrctum the relatively immobile gubernaculum. 23 How·ever, this has refuted Wyndham, 12 who to demonstrated that the gubemaculum increased in size Lemeh, 13 who showed that the gubernaculum occurs while descent, and cv;wJ,nH<- descent. 8 in fact faster than the as a whole. Elder et al. 2'· have the m,v,1r/4-,:i,nc,c, of the gubematheoretical supporting the concept the descent of the testis have that intraabdominal pressure, as 1st proposect by Gier and Marion 25 ' 26 in 1970, play a in testicular descent. The gubemaculum 1st <.nnc,»'Q in the human fetus during If this is true, then gubemaculum might indeed be the the 6th week of gestation, same time the germ rudder, as Hunter suggested/ that guides the testis into the cells arrive at the genital ridge. 9 At this stage development scrotum. The gubernaculum appears to be an important link in the the gubemaculum consists mainly of mesenchyma! cells and extends in a straight line from the genital ridge to the site of movement of the testis from the abdomen into the scrotum. the future scrotum. Between the 7th and 15th week of gestation, First, if the gubernaculum is not present or if its scrotal differentiation of the gonads and the internal and external attachment is severed, the testis will not descend, On the other genitalia occurs, 10 The testis assumes a stationary position near hand, severing the testicular/epididymal attachment of the the internal inguinal ring" between the 15th week and the 7th gubernaculum does not impede descent. These findings, in month of gestation, at which time the processus vaginalis, an accord with those of Bergh et al., 21 suggest that traction by the out-pouching of the peritoneum, grows along the ventral aspect gubemaculum on the testis is not an important mechanism in of the gubernaculum 12 which begins to expand until its diameter promoting testicular descent in the rat. Otherwise, severance is equal to or greater than that of the testis, 90 n, 13 The testicular of the attachment of the proximal gubemaculum to the testis/ vessels as well as the vasa deferentia elongate and the scrotum epididymis would result in testicular maldescent. More imporbegins to develop,"· 14 The testis than migrates very rapidly tantly, however, this study demonstrates that the solitary testis from the abdomen through the inguinal canal and into the is capable of crossing over the bladder to descend into the
578
FREY AND RAJFER
contralateral scrotal compartment as long as a gubernaculum is present there. Two possible explanations for this crossover phenomenon are immediately apparent. The 1st and least likely is that the gubernaculum may secrete some as yet unknown chemotactic substance that may draw the testis/epididymis to its location. The gubernaculum of the postnatal rat is believed to be composed mainly of rhabdomocytes and acid mucopolysacharides27 which are not known to be secretory in any way. The 2nd explanation, and the more tenable, involves the role of intraabdominal pressure. When the gubernaculum is either incised distally or excised in its entirety, the ipsilateral hemiscrotum does not fully develop. This may be due to the fact that the gubernaculum is known to increase in size just prior to descent and it is this swelling that may cause the scrotum to develop and obtain its characteristic shape. In the rabbit, for example, part of the gubernaculum is encompassed into the developing scrotum8 • 24 and it is not difficult to theorize that any defect in the gubernaculum may contribute to underdevelopment of the scrotum. It is possible that when this hemiscrotum is underdeveloped, the testis which is free in the abdominal cavity is pushed into the most accommodating available space. In this case the push may be due to intraabdominal pressure, whereas the most accommodating and available space may be the developed contralateral hemiscrotum. This is consistent with the observation that when both gubernacula are present and therefore each hemiscrotum well-developed and available to receive a testis, a solitary free gonad can descend into either scrotal compartment. Additionally, when both testes are free and a solitary gubernaculum is present descent will only occur on the side where the gubernaculum is present and, surprisingly, both testes can descend together into the same scrotal compartment. This latter finding exactly parallels what is observed in the rare clinical entity of crossed testicular ectopy. 2B-3o In this disorder, both testes are found in the same scrot11l compartment. Usually the blood supply, vas deferens and epididymis to 1 of the testes comes from the contralateral side. The etiology of this condition is not known, but it is interesting to speculate that a unilateral abnormality of the gubernaculum may be responsible. Based on the observation that the testis could cross over into the contralateral hemiscrotum, we felt that intraabdominal pressure could well be responsible for testicular migration in this experimental setting. Substitution of a free silicone prosthesis for a testis resulted in prosthetic descent in a high percentage of the animals. This clearly suggested that some physical force that can act on an inert substance such as silicone may be active in promoting testicular descent. The finding that a prosthesis could descend into the scrotum is novel and is not the same as that observed by Martins 32 in which he replaced the testis with paraffin within the tunica albuginea and found that it could descend into the scrotum. Martins used adult rats in which testicular descent had already occurred and, consequently, was studying testicular retraction rather than testicular descent. In studying factors responsible for scrotal dilatation, Backhouse9 refers to an experiment in the rat in which a stainless steel ball was sutured to the tunica albuginea after the testicular contents had been removed, but the epididymis with its attachment to the gubernaculum was left intact. Clearly, our experiment differs in that the silicone prosthesis lies totally free within the abdomen, not subjected to any possible effects from an attached epididymis or gubernaculum. In summary, this study suggests that in the rat the gubernaculum appears to be an absolute prerequisite for testicular descent. The crossover phenomenon and the finding that an intact distal attachment of the gubernaculum to the scrotum is necessary for scrotal development and subsequent testicular migration also suggests that the traction theory of testicular descent does not appear to be operative in this animal model. Yet, these findings are certainly consistent with the theory that
intraabdominal pressure may have a major role in facilitating the descent of the testis. The intraabdominal theory of testicular descent is further supported by the observation that a free silicone prosthesis placed intraabdominally is capable of descending into the scrotum at the appropriate time. How intraabdominal pressure works in tandem with an intact hypothalamic-pituitary-testicular axis to facilitate descent remains to be determined. REFERENCES
1. Engel, E. T.: Experimentally induced descent of the testis in the Macacus monkey by hormones from the anterior pituitary and pregnancy urine. Endocrinology, 16: 513, 1932. 2. Rajfer, J. and Walsh, P. C.: Hormonal regulation of testicular descent: experimental and clinical observations. J. Urol., 118: 995, 1977. 3. Hamilton, J.B. and Hubert, G.: Effect of synthetic male hormone substances on descent of testicles in human cryptorchidism. Proc. Soc. Exp. Biol. Med., 39: 4, 1938. 4. Hamilton, J.B.: The effect of male hormone upon the descent of the testes. Anat. Record, 70: 533, 1938. 5. Bigler, J. A., Hardy, L. M. and Scott, H. V.: Cryptorchidism treated with gonadotropic principal. Am. J. Dis. Child., 55: 273, 1938. 6. Arnheim, E. E.: The treatment of undescended testes with gonadotropic hormones. J. Mt. Sinai Hosp., 4: 1036, 1938. 7. Hunter, J. A.: A description of the situation of the testis in the fetus with its descent into the scrotum. In: Observations on Certain Parts of the Animal Oeconomy. New Orleans: John J. Haswell and Co., p. 42, 1841. 8. Rajfer, J.: Morphological study of testicular descent in the rabbit. Invest. Urol., 18: 293, 1980. 9. Backhouse, K. M.: Embryology of testicular descent and maldescent. Urol. Clin. North Am., 9: 315, 1982. 10. Jost, A.: A new look at the mechanisms controlling sex differentiation in mammals. J. Hopkins Med. J., 130: 38, 1972. 11. Wells, L. J. Descent of the testis: anatomical and hormonal considerations. Surgery, 14: 436, 1943. 12. Wyndham, H. R.: A morphological study of testicular descent. J. Anat., 77: 179, 1943. 13. Lemeh, C. N.: A study of the development and structural relationships of the testis and gubernaculum. Surg. Gyn. Obstet., 110: 164, 1960. 14. Wells, L. J.: Descensus testiculorum: androgenic stimulation of the scrotum, inguinal bursa and ductus deferens. Anat. Rec., 88: 465, 1944. 15. Seiler, B. W. (1817) as cited by Backhouse, K. M. and Butler, H.: The gubernaculum testis of the pig (sus scropha). J. Anat., 94: 107, 1960. 16. Curling, J.B.: Observations on the structure of the gubernaculum and on the descent of the testis in the fetus. Lancet, 2: 70, 1840. 17. Lewis, L. G.: Cryptorchidism. J. Urol., 60: 345, 1948. 18. Tayakkanonta, K.: The gubernaculum testis and its nerve supply. Aust. NZ J. Surg., 33: 61, 1963. 19. Backhouse, K. M. and Butler, H.: The gubernaculum testis of the pig (sus scropha). J. Anat., 94: 107, 1960. 20. Backhouse, K. M.: The gubernaculum testis Hunteri: testicular descent and maldescent. Ann. R. Coll. Surg. Engl., 35: 15, 1964. 21. Wells, L. J.: Descensus testiculorum: descent after severance of gubernaculum. Anat. Rec., 88: 465, 1944. 22. Bergh, A., Helander, H.F. and Wahlquist, L.: Studies on factors governing testicular descent in the rat-particularly the role of gubernaculum testis. Int. J. Andrology, 1: 342, 1978. 23. McMurrich, J. P.: The Development of the Human Body, A Manual of Human Embryology. Philadelphia: P. Blakiston's Son & Co., 7th edition, pp. 374-376, 1923. 24. Elder, J. S., Isaacs, J. T. and Walsh, P. C.: Androgenic sensitivity of the gubernaculum testis: evidence for hormonal/mechanical interactions in testicular descent. J. Urol., 127: 170, 1982. 25. Gier, H. T. and Marion, G. B.: Development of the mammalian testis. In: The Testis. Edited by A. D. Johnson and G. B. Marion. New York: Academic Press, vol. 1, chapt. 1, p. 1, 1970. 26. Bergin, W. C:;' Gier, H. T., Marion, G. B. and Coffman, J. R.: A developmental concept of equine cryptorchidism. Biol. Reprod., 3: 82, 1970. 27. Radhakrishnan, J., Morikawa, Y., Donahoe, P. K. and Hendren,
579 ""(¥. H.: Observations on the g-ubernaculun1 during descent of the testis. Invest, UroL, 16: 365, 1979, 28. Davis, J.E.: Transverse aberrant testicular maldescent. U.S. Armed Forces Med. J., 8: 1046, 1957, 29. Mukerjee, S. and Amesur, N. R.: Transverse testicular ectopia with unilateral blood supply. Ind. J. Surg., 27: 547, 1965. 30. Dajani, A. M.: Transverse ectopia of the testis. Brit. J. UroL, 41:
80, 1969. 3L Scorer, C. Go and Farringto:t1i G·. I-I.: l'i,a:re deformities of th2 testiEL
In: Congenital Deformities of the Testis and Epididymis. New York: Appleton-Century-Crofts, chapt. 13, p. 175, 1971. 32. Martins, T.: La testosterone peut provoquel' la descente de testicules artificiels de paraffine. Compt. Rend. Soc. de Biol., 131: 299, 1938.