Continuing Education Article #4 Refereed Peer Review

in Horses. Part I. L~OCALPOINT I Anatomy, Causes, and Diagnosis

Auburn University Dwayne H. Rodgerson, DVM R. Reid Hanson, DVM

ryptorchidism, or hilure of one or both testes to descc I into d turn, is a cammon developmental d&ct in horses.'- ked Care sometimes referred to as rigs or ridgh~gs.'*~"Like lnnal st horses with a retained testis frequentlfhave un2eshble behavioral chamcd tics.'"."' Cryptorchid stallions are generally diagnosed as having a retains testis during inspection of the scrotum at the time of castration or during 4 amination before or after sale.' It is a challenge to confirm or diagnose a torchidism in a mature horse that is purported to be a gelding and that exb stallionlike behavior; an unconfirmed history of castration will complicate 4 process. I fl PREVALENCE In a retrospective study at 16 veterinary teaching hospitals in North Bo ca, one of every six 2- to 3-year-old referred colts was cryptorchid9The p lence of cryptorchidism was highest in Percherons, followed by Americaa dle horses and Quarter Horses? The overall prevalence in Thoroughbd Standardbreds was lower than that in other breeds. Although both testes may fail to descend into the scrotum, unilateral 6 tion is nine times more prevalent than bilateral retention.1° Studies b that the frequencies of left- and right-sided retention are nearly equal.xlW' testis was within the abdomen in 75% of horses with lefi-sided retend in only 42% of horses with right-sided retention.1° Inguinal retentian 4 testis was most often associated with the right testis (58%, versus 25% , left testis) .lo The incidence of inguinal retention decreases with age, whereas rhr) dence of abdominal retention increases with age.''-l3 The overall frequd bilateral retention of the testes is reportedly 9% to 14% of all cases o torchidism.1"'2 Bilaterally re- triangular space bordered tained abdominal testes were cranially by the caudal edge nearly 2.5 times more com- of the internal abdominal mon than were bilaterally re- oblique muscle, caudally by tained inguinal testes.'' the pelvis and ~ngdliga- Left-sided unilateral testic- ment, and vennomedially ular retention was present in by the rectus abdominis 42 of 77 (55%) cryptorchid muscle and prepubic ten- horses evaluated at the Vet- d~n.'~.'~ erinary Teaching Hospital at The vaginal ring is inter- Auburn University during nal to the deep inguinal the last 5 years. Twenty-five ring and is considered to be (32%) of these horses had separate from the inguinal right-sided unilateral reten- canal14 (Figure 1C). The tion. Abdominal retention Figure 1-(A) The deep inguinal ring is a triangular space vaginal ring is the opening occurred in 32 of 42 (76%) bordered cranially by the caudal edge of the Internal abdomi- of the vaginal tunic; it de- horses left-sided reten- nd oblique muscle (L40),caudally by the pehrk and inguinal marcates the division be- tion and in 6 of 25 (24%) ligament, and venmmedidy by the rectus abdorninis musde tween the peritoneal cawicy with right-sided retention. (RA) and prepubic tendon. (B) The superficial inguinal ring and the cavity of the u&d is a slit in the aponeurosis of the external abdominal oblique Inguinal retention was docu- tunic.14." The v@ tunic muscle (EAO),slightly cranial to the deep inguinal ring. in 76% (I9 of 25) of (C) A sagittal section through the demon- traverses the deep and su- the horses with right-s1ded strates the relationship between the vaginal ring and the deep perficial inguinal rings and retention and in 24% (10 of and superficial inguinal rings. The vaginal tunic traverses the surrounds the testes in the 42) of those with left-sided deep and superficial inguinal rings and surrounds the testis scrotum. retention. The incidence of in the scrotum. :r. - ---*--**--* bilateral retention was 13% """"""'-mod Testicular and (10 of 77). Epididymal Attachments I The paired equine testes ANATOMY AND are normally situated in the DEVELOPMENT 0 F 1 scronun with their long axis THE TESTES in a horizontal dirrcti~n.~'~ The testes move fiom the The head of the epididyruis abdomen into the scrotum joins the cranial aspect of by passing through the r&t the testis. The Myof the or left inguinal canal. The is sitl~atedon inguinal canal is a slitlike the dorsolateral aspect of passage formed between the the testis. The tail of the superficial and deep inguinal epididymis is loosely at- rings.14.15 Compared with taehed to the caudal pole of that of other domesticated the testis by the proper liga- species, the inguinal canal ment of the testis (Figure of a horse is relatively long 2A) and to the vaginal tunic Figure 2-Association between the testis and epididymis. (average length, 10 ~m).~.'~ the ligament of the tail (A) In the normal scrota testis, the tail of &e epididymis is by The dOSelyatached to the caudal of the testis by the proper the 'pididymis. The ring is a slit in the aponeu- ligamentof the t*s (-4. (B) the crypfOfid mes, nal tunic is attached to the rosis of the external abdomi- the proper ligamentof the testis ~s gi* the scrotum by the scrod kg- nal oblique mu~clel*~~~(Fig- ~esestis and varying d~mof association (mww). ment.2

- - - I 4--- I-----marry-*--- rr- * r - - --- r -- - - - 1). The direction of he I v-' .-+- ,' +, - ?-, -. I'I In cryptorchid stallions, superficial inguinal ring is . -.. -') .* . --,... the retained testis and the parallel to the course of the tail of the epididymis can fibers in the tendon of the external abdominal oblique have varying degrees of a~sociation.~'~'"~W~th cryp- muscle. The superficial inguinal ring is external to and torchid testes, the proper ligament of the testis, the lig- slightly cranial to the deep inguinal ring,14 which is a ament of the tail of the epididymis, and the scrotal lig- ament are often elongated changes are related to the (Figure 2B). early proliferation and sub- sequent degeneration of the The Fetal Testis fetal interstitial cells.17." The equine gonads origi- nate in the dorsolumbar re- Descent of the Testis gion of the at approx- The process of descent of imately day 27 of gestation. the testis is complex and in- Sexual differentiation of the completely under~tood.~JO gonads into testes or ova- Normal descent depends on ries does not occur until day many developmental events 40.'s22 Gonadal development occurring properly and in entails the merging of three synchrony. After the deteri- separate embryonic tissues: oration of the caudal por- the primitive germ cells, the Figure 3-The attachments of the fetal testis-(I) cranial, the tion of the mesonephric intermediate , and diaphragmatic or cephalic ligament; (2) dorsal, the mesorchi- kidney at approximately day the early embryologic meso- urn; and (3) caudal, the or posterior gonadal 65 of gestation,'"22 the tes- nephric kidney." The primi- ----ligan-a-* ...... tis is suspended from the tive germ cells line the inner dorsal body wall by cranial, surface of the mesonephric dorsal, and caudal attach- tubules in the cranial portion ments~4.~~.zz (Figure 3). of mesonephric kidney; the Intraabdominal pressure primitive germ cells of the in the fetus increases shortly male gonad evolve into the after the umbilical canal spermatogonia of the testis. closes to produce a closed The extensive network of peritoneal cavity." The pres- in this sure from the peritoneal flu- portion of the mesonephric id in the abdominal cavity kidney gives rise to the semi- causes an outward extension niferous tubules of the tes- of parietal (the tis. The of parietalis, or the associated mesonephric vaginal process) at 45 to 50 kidney evolves into the epi- days of gestation14*"s22(Fig- didymis and ductus deferens. ure 4A). The vaginal process The surrounding intermedi- extends through the deep ate mesoderm becomes the inguinal ring and eventually stroma or interstitium of the through the inguinal canal testis.21 into the scrotum to form The equine fetal testis is the vaginal tunic of the unique in that it changes testis. The vaginal process dramatically in size and extends around the lateral shape throughout gesta- and ventral borders of the tion.17,19-22 At day 150 of ges- caudal inguinal insertion of tation, the testis is cylind: the gubernaculum." weighs approximately 20 The gubernaculum, or and is 3 cm in diameter.'" posterior gonadal ligament, day 250, the fetal testis has Figure 4-Various stages of descent of the testis. (A) The is a fetal mesenchymal cord- enlarged to approximately 5 vaginal process is formed at approximately day 45 to 50 of like structure that extends cm in diameter and weighs gestation. (B) The tail of the epididymis normally reaches or caudally from the caudal 50 g. At day 300, it is ellip- enters the vaginal ring at approximately day 150. (C) The pole of the testis to the in- tic, weighs 30 g, and has testis reaches the vaginal ring at approximately day 275 to guinal region of the peri- decreased to approximately 300. (D) The testis enters the scrotum between day 315 of toneal cavity.'4.".2'J2 Ini- 2.5 cm in diameter. These ...... gestation and 10 days after birth. tially, the gubernaculum is

-- -. -- . EQUINE 'GONADS"W SIZE OF FETAL~EST~S W VAGIN~~~-'- retroperitoneal; during gesta- dally.20 The tail of the epi- tion, it becomes suspended didymis normally reaches from the dorsal body wall by the vaginal ring or is within a peritoneal fold that is con- the inguinal canal at approx- tinuous with the mesorchi- imately day 150 of gesta- of the te~tis.'~,".~~Early in tion" (Figure 4B). The testis gestation, the mesonephric b. gubernaculum proprium does not reach or enter the duct from the early embry- vaginal ring until approxi- c. pars vaginalis gubernaculi ologic mesonephric kidney mately 270 to 300 days of divides the gubernaculum gestation (Figure 4C). into two segments.22 . gubemacular ligament Pressure from the abdomi- With the further develop- nal viscera is believed to help ment of the vaginal process keep the testis positioned and deterioration of the cau- near the vaginal ri~~g.'~.~~The dal portion of the meso- Figure %After the deterioration of the caudal portion of the &ange in size and shape of nephric kidney, the pber- mesonephric kidney and the further development of the vagi- the testis and the enlarge- naculum can be divided into nal process, the gubernaculum can be divided into four parts: ment of the vaginal ring and four segmentsz2 (Figure 5). (a) the caudal gonadal ligament, (b) the gubernaculum pro- inguinal canal enable the prium, (c) the pars vaginalis gubernaculi, and (d) the pars in- The segment of the guber- testis to move through the fravaginalis gubernaculi. The latter part is continuous with a naculum that extends from separately described structure, (e) the gubernacular ligament. inguinal Expansion the caudal pole of the testis ...... of the inguinal canal is relat- to the mesonephric duct is ed to the enlargement of the the caudal gonadal ligament caudal three segments of the (referred to after birth as the proper ligament of the gubernaculum and the tail of the epi~lidymis.'~.".~~The testis). The portion of the gubernaculum that extends enlarged caudal portion of the gubernaculum is often caudally from the mesonephric duct to the blind end of palpable in the scrotum after parturition and may be the vaginal process is the gubernaculum proprium (re- confused with a scrotal testi~.~,'~,~~The testes move into ferred to after birth as the ligament of the tail of the the scrotum at day 315 of gestation to 10 days after epididymis). The gubernaculum proprium is partially birth" (Figure 4D). within the abdominal cavity and partially within the vaginal process until the tail of the epididymis passes CLASSIFICATION through the vaginal ring. Failure of testicular descent can be categorized ac- The extraabdominal part of the gubernaculum that cording to the location of the nondescended testis (in- intricately surrounds the vaginal process is the pars guinal or abd~minal).'~~'~.'~~~~Inguinal retention de- vaginalis gubernaculi. The extraabdominal segment scribes a testis that has passed through the vaginal ring that is not invaded by the vaginal process is the pars but has not reached or entered the scr~tum.'~An in- infra~a~inalisgubernaculi, which is continuous with guinal retained testis can be located external to the su- the gubernacular ligament. This ligament, which is de- perficial inguinal ring (Figure 6A) or in the inguinal scribed separately from the other four segments of the canal26 (Figure 6B). Inguinal retained testes have re- g~bernaculum,~~is believed to provide some directional portedly entered the scrotum in horses up to 2 to 3 guidance for the vaginal process" or to create a tunnel years of age.4J'J3 of low resistance into which the vaginal process ex- Abdominal retention describes a testis that has not tends.12 The gubernacular ligament and pars infravagi- passed through the vaginal ring and remains in the lalis gubernaculi are together referred to as the inguinal abdomen." Such retention has been classified as in- txtension of the gubernaculum.23~24After birth, this em- complete or partial abdominal retention (Figure 6C) or )ryologic structure becomes the scrota1 ligan~ent.~~,~~ complete abdominal retenti~n".".~~.~~(Figure 6D). With The gubernaculum guides the testis caudally toward incomplete or partial abdominal retention, the testis re- the vaginal ring and through the inguinal canal.' The mains within the abdomen but the tail and a portion of testis and epididymis shift caudally because of the ten- the body of the epididymis descend through the vaginal sion placed on the gubernaculum by the everting vaginal ring and into the inguinal Complete abdom- Process, the enlargement of the metanephric kidney, and inal retention is failure of both the testis and epididymis the elongation of the pelvic region.7*"~'0~22~25The guber- to pass through the vaginal ring. In horses with com- ~aculumdoes not actively contract to pull the testis cau- plete abdominal retention, the vaginal ring and the vagi-

~ -..- ---. ------. - - .~ - - GUBERNACULUM SEGMENTS W EVERTING VAGINAL PROCESS INGUINAL RETENTION nal process are often I 1 CAUSES poorly devel~ped.'~.*~ A genetic basis for equine cryptorchi- PATHOLOGY dism has been pro- Nondescended tes- posed.2.7,30,45The de- tes are generally smal- creasing incidence of ler and softer than A B cryptorchidism in are scrotal teste~.~.'~.~' certain lines of horses Nondescended tes- suggests that prudent tes are sterile because selection of breeding spermatogenesis is stock may have some inhibited by the ele- effect on the condi- vated environmental ti~n.~.~'Autosoma] temperature around d~minant~.~~and a"- the ;eta lined te~tis.~,~' tosomal recessive7 In unihnerd cryptor- modes of inheritance chid stallions, the de- have been proposed. . . scended testes arc: ca- Some researchers sug- pable ()f produczing Figure &(A) Inguinal retention with the testis situated external to the super- gest thatcryptorchid- sperm. 7.12,17.30 If the ficial inguinal ring. (B) Inguinal retention with the testis situated within the ism is linked to the scrotal tesus .rea uni- inguinal canal. (C) Incomplete or partial abdominal retention; the testis fails sex chromosomes~4,7.~7 to pass through the vaginal ring, but the nil and part of the body of the lateral cryptorchid Cryptorchidism has epididymis descend through the vaginal ring and into the inguinal canal. stallion is removed, been associated with (D) Complete abdominal retention; the testis and epididymis fail to pass the testis through the vaginal ring intersexuality and mayhypertrophytoa ...... ------, - with abnormal kary- size comparable to ~t~pes,~'-~Osuggest- that of a normal scro- ing that normal de- tal testis.13 scent of the testis is controlled by multiple genes.4 In The histologic appearance of abdominal retained one study, only a small percentage (9 of 5018 horses) of testes differs from that of inguinal retained testes.12 cryptorchid stallions were actually intersexes.' Genetic Spermatogenesis in abdominal retained testes does not factors that cause cryptorchidism may be expressed as proceed beyond the A- or B-spermatogonia (Figure 7) abnormalities associated with hormone secretion or the and ceases after production of the primary spermato- improper development of structures that are important cytes in inguinal retained testes." Retention of the in the normal descent of the testis. Because of the testis also impedes the development of the seminiferous hereditary possibilities of cryptorchidism, the use of tubules. The extent of development of the tubules in an unilateral cryptorchid stallions in breeding programs abdominal retained testis is similar to that of a 3- to 4- should be di~couraged.~.~~ month-old foal; the development of the tubules in an IHormone s play a role in the normal descent of the inguinal retained testis is comparable to that of a 9- to testes.22*25 1Iescent is believed to be associated with 12-month-old foal.I7 Generalized hyperplasia of the in- gollauuLluyln-induced--J -----: androgen stimulation," and the terstitial cells may be prese nt in the retained t estis."~~~ changes in size and shape of the gubernaculum are be- Neoplastic or cystic e.nlargeme nt of tht retainecd lieved to be controlled by hormones originating from testis has been reported.31.33-36 Va rious tumors-..~. (e.g.,/. . within the fetal testis.17~20*22In young boys, hormonal terat~mas,~'.'"'~interstitial cell tumors,37 and semino- imbalance as a cause of cryptorchidism is suggested by mas3'.") have been associated with cryptorchid testes. the fact that testicular descent may occur after human Such congenital defects as splenic-gonadal fusion,40 chorionic gonadotropin (hCG) is admini~tered.~ fused abdominal testes:' and elongation of the suspen- Mechanical causes of cryptorchidism are often difi- sory ligament of a testis4*have been associated with re- cult to establish. Faults in the development of the guber- tained abdominal testes. Torsion of the spermatic cord naculum, vaginal process, vaginal ring, inguinal canal, of abdominal retained testes affected by a seminoma ha s or testis may have a genetic basis and may in turn im- -7 been reported in two Crypl torchid stallions.38( ,ongenita tI pec de the descent of the testes. The most obvious of the monorchisrn is r;are in hol.ses, 18~43.44 and we c;m find nc hy ~othesizedmechanical causes of cryptorchidism are reDorts of anorchls~~l.- - or- - polyorchidism- - in hors undue stretching of the gubernaculum; inadequate ab-

------. ------. NONDESCENDED TESTES .CYSTIC ENLARGEMENT. ROLE OF HORMONES m= == mpendium November 1997 Equine 1285

domind pressure for proper hazardous to owners and evagination of the vaginal I trainers.'.' process; inadequate expan- - - sion of the gubernaculum Visual Examination and tail of the epididymis to and Palpation enlarge the vaginal ring and To determine whether a inguinal canal; and displace- horse has a retained testis, ment of the testis within the the scrotum is initially exam- abdomen, where the testis ined visually. The scrotum is held by organ pressure and superficial inguinal ring (which prevents it from should be palpated external- reaching or passing through ly.2e4The scrotum and in- the inguinal canal).19 guinal region should be ex- In horses, the left testis has Lined for the presence of been observed to be slightly Fiuure 7A an incisional s&, which in- larger and to lag s~&be- dicates that castration was hind the right testis during attempted. In unilateral descent."*19s25Either factor cryptorchids, digital palpa- could prevent the left testis tion of the descended testis from passing through the and associated spermatic vaginal ring or reaching the cord can indicate whether vaginal ring before it begins the left or right testis is re- to constrict (shortly after tained. parturition). These factors Palpation of a testis that lies may explain the higher fre- 1 in the in@ anal is often difficult.sedation Tranquilizationmay make an in- or quencytion associated of abdominal with the reten- left testis.25 guinal testis more accessible by relaxing the cremasrer DIAGNOSIS dm muscle. Intravenaus seda- Identifying a retained tes- Figure 78 tion with either xylazine tis can be as simple as ob- Fig~rU-(A) Histologic cross-section of a seminiferous (0.5 mg/kg) or detomihe serving the horse's behavior, tubule from a scrod testis; normal spermatogenesis is evi- (0.025 mg~kg),done or in inspecting the scrotum, and dent. (B) Histologic cross-section of a seminiferous tubule wit. butor- obtaining a castration his- from an abdominal retained testis; alterations in spermato- phanol (0.02 mg/k@, relax- genesis are evident. tory. A recently purchased ...... es the cremaster muscle. gelding with an unknown Palpation per rectum can castration history that ex- facilitate identification of a hibits stallionlike behavior may be a bilateral cryp- retained testis or evaluation of the exrent of testicular torchid or a unilateral cryptorchid that has had its des~ent.~.'~~~~'Because of the risk of redtears, cau- descended testis removed (i.e., a hemicastrate). The vet- tion is necessary when palpating stallions per rectum.235 erinarian must determine whether the horse is truly They are usually unaccustomed to the procedure; a cryptorchid and, if so, which testis is retained (or young stallions miiy be more predisposed to rectal tears whether both are retair~ed).~ because of their smaller stature.14 The masculine behavior displayed by cryptorchid Palpation of the vaginal ring and the structures that stallions is often enough to suggest that a horse has a enter it may help in determining whether the testis has retained testis. Cryptorchid stallions generally have the entered the inguinal canal.10*"During palpation per ' physical characteristics of an entire sdion (i.e., one rectum, the examiner should use the lefi hand to deter- ! with both testes located in the scrotum) because the an- mine whether the rght testis is retained and the right 1 dr~gen-~roducin~interstitial cells (Leydigs cells) of the hand to determine whether the left testis is retained.% 1 testis remain f~nctional.'~Like entire stallions, cryp- The vaginal ring is located 8 to 12 cm from the mid- torchid stallions can be nervous and irritable, attempt line, just cranial to the brim of the pelvi~~,~,'~(Figure 8). E breed nearby mares, and have dispositions that are The easily palpated ductus deferens enters the caudo- medial aspect of the vaginal such tiss~e.~'In the same ring and can be used as an study, stallions younger aid in locating the ring. The than 18 months of age usu- testicular vessels that enter ally had serum concentra- the vaginal ring can be diffi- tions of testosterone less cult to palpate and identify than 100 pglml. In another per rect~m.~ study, the presence of testic- Palpation of the ductus def- ular tissue was identifir-' erens at the vaginal ring does when serum concentratio not help in distinguishing of testosterone were great between complete and in- than 44 pglml; the absen.- complete abdominal reten- of testicular tissue was iden- tion. An inability to identify tified when concentrations the vaginal ring and the duc- were less than 24 ~glml.~" tus deferens may indicate Figure 8-Lateral and cran iocaudal views of palpation per The hCG stimulation test rectum of the vaginal ring. that the testis and epidid- ...... is used to identify cryp- ymis are retained in the ab- torchidism when measure- d~men.~An abdominal ment of basal concentra- testis is often difficult to pal- tions of testosterone alone pate per rectum because it is smaller and more flaccid yields inconclusive information.29~32~58~60~62~63~65"7In one than a normal scrotal testis. Because of its mobility, an study, the hCG stimulation test was 94.6% accurate in abdominal testis is difficult to identify in the caudal identifying cryptorchidism in horses.58The intravenous abd~men.~.'~.'~ administration of 6000 to 12,000 units of hCG stimu- lates the production of testosterone from the intersritial Ultrasonographic Examination cells of the testi~.~~.~~Serum is collected before hCG is Ultrasonographic examination of the caudal portion administered, and a second sample is usually collected of the abdomen per rectum via a 5-MHz probe may be 30 to 120 minutes after hCG is given.29,45.58,65There are useful in identifying an abdominal testis.56Abdominal greater increases in serum concentrations of testos- testes are less echogenic than scrotal testes.56Scans per terone in response to hCG if the second sample is col- rectum should begin at the brim of the pelvis and con- lected 24 hours (or even 72 hours) after the initial sam- tinue cranially in a sweeping pattern between the mid- line and the lateral abdominal wall. In one study, serum concentrations of testosterone in Ultrasonography can be helpful in distinguishing cryptorchid stallions were greater than 100 ~~Imland between inguinal fat, vessels, the ductus deferens, and increased after hCG was adrnini~tered.~'Castrates have other confusing structures that may be palpated per a low basal concentration of testosterone (less than 40 rectum. Ultrasonographic examination of the inguinal pglml) and exhibit no response to the administration of canal and surrounding tissue can be performed exter- hCG. nally to identify an inguinal retained testis.30 Trans- Hormonal assays that measure serum concentrations inguinal and transabdominal ultrasonography have of conjugated estrogens have been used to identify been used successfully at the Veterinary Teaching Hos- cryptorchid horses.2"32*5840~63~64~67Assays are routinely pital at Auburn University to identify retained testes performed for estrone sulfate. Measurement of serum within or closely associated with the inguinal canal. concentrations of estrogen was 95% to 96% accurate in differentiating cryptorchid stallions from true castrates Hormonal Assays if the horses were older than 3 years of age.58The Hormonal assays for concentrations of testosterone serum concentrations of estrogen in geldings were less and estrogen can be useful in distinguishing cas- than 50 pglml, but the concentrations in horses with trates from cryptorchid stallions with no scrotal tes- testicular tissue exceeded 400 pglml. The serum con- te~.'~,~~,~~,~~*~~-~Serum concentrations of testosterone are centration of conjugated estrogens in donkeys of all reportedly 86% to 95% accurate in identifying the ages and in horses younger than 3 years of age was presence of testicular tiss~e.~',~'In one study, serum much less than that in horses older than 3 years age.58 concentrations of testosterone over 100 pglml were as- A recent study evaluated the ability to analyze the sociated with the presence of testicular tissue; concen- concentrations of unconjugated estrogens in the feces trations less than 40 pglml indicated the absence of as a method for determining the presence of testicular

------.------.- - ---.--- INCOMPLETE ABDOMINAL RETENTION ULTRASONOGRAPHY W TESTOSTERONE tissue.68 Cryptorchid and entire stallions had increased North Am Equine Pract 4:493-513, 1988. concentrations of fecal unconjugated estrogens; in cas- 4. Varner DD, Schumacher J, Blanchard TL, et al: Diseases of the testes, in Varner DD, Schumacher J, Blanchard TL, trated horses, concentrations of unconjugated estrogens Johnson L (eds): Diseases and Management of Breeding Stal- were much lower. Following are advantages of using fe- lions. Goleta, CA, American Veterinary Publications, 199l, cal samples: The samples are collected by noninvasive pp 193-232. means, estrogens are stable in feces for at least 1 week, 5. Hobday FTG: The castration of cryptorchid horses, in Hob- and it is not necessary to perform a stimulation test.68 day FTG (ed): The -Castration ofCyptorchid Horses and the For hormonal assays, it is crucial to use a laboratory Ovariectomy of Troublesome Mares. New York, William R. that has established an accurate reference range for Jenkins, 1903, pp 17-64. 6. O'Connor JJ: Operations-Castration of cryptorchids, in serum concentrations of equine testosterone and estro- O'Connor JJ (ed): Dollar; Veterinary Surgey, ed 2. London, gen.2,3,30Normal serum concentration ranges of these Bailliere, Tindall & Cox, 1930, pp 322-336. enzymes in other species may be spurious when applied 7. Leipold HW, DeBowes RM, Bennett S, et al: Cryp- to horses and should be interpreted cautiously.30 torchidism in the horse: Genetic implications. Proc AAEP 3 1:579-589, 1986. Laparoscopic Examination 8. Teigland MB: Medical examination of horses at auction sales. Vet Clin North Am Equine Pract 8:4 13-420. 1992. Laparoscopic techniques can be used to diagnose and 9. Hayes HM: Epidemiological features of 5009 cases of equine identify an abdominal testis.69Such a testis is usually vi- cryptorchidism. Equine Vet J 18:467-471, 1986. sualized near the vaginal ring; identifying the structures 10. Stickle RL, Fessler JF: Retrospective study of 350 cases of that enter the ring can help in distinguishing abdomi- equine cryptorchidism. JAW 172:343-346, 1978. nal and inguinal retention. Laparoscopic techniques are 11. Cox JE, Edwards GB, Neal PA: An analysis of 500 cases of 'atively noninvasive, are associated with few compli- equine cryptorchidism. E$uine Vet J 11: 113-1 16, 1979. 12. Coryn M, DeMoor A, Bouters R, et al: Clinical, morpholog- :ions, and can be performed in a standing h~rse.~' ical and endocrinological aspects of cryptorchidism in the horse. Theriogenology 16:489-496, 1981. uJNCLUSION 13. Cox JE: Factors affecting testis weight in normal and cryp- Cryptorchidism is a common developmental defect torchid horses. J Rqrod Fertil (Suppl] 32: 129-1 34, 1982. encountered by equine practitioners. Faults in the de- 14. Ashdown RR: The anatomy of the inguinal canal in the do- scent of the testis are believed to result from genetic, mesticated mammals. Vet Rec 75: 1345-1351, 1973. hormonal, or mechanical factors or from a combina- 15. Sack WO, Habel RE: Pelvis-Pelvic inlet, in Sack WO, Ha- be1 RE (eds): Guide to the Dissection of the Horse. Ithaca, NY, tion of these factors. A thorough physical examination Veterinary Textbooks, 1988, pp 63-73. and an understanding of the available diagnostic proce- 16. Varner DD, Schumacher J, Blanchard TL, et al: Reproduc- dures are important in identifying a retained testis or a tive anatomy and physiology, in Varner DD, Schumacher J, horse with a retained testis. Blanchard TL, Johnson L (eds): Diseases and Management of Breeding Stallions. Goleta, CA, American Veterinary Publica- ACKNOWLEDGMENT tions, 1991, pp 1-60. The authors thank Lisa Makarchuk of Biomedical Com- 17. Bishop MWH, David JSE, Messervy A: Some observations on cryptorchidism in the horse. Vet Rec 76:1041-1048, munications, Auburn University, for providing the figures. 1964. 18. Trotter GW, Aanes WA: A complication of cryptorchid cas- tration in three horses.JAVMA 178:246248, 1981. About the Authors 19. Bergin WC, Gier HT, Marion GB, et al: A developmental Drs. Rodgerson and Hanson are affiliated with the De- concept of equine cryptorchidism. Biol Reprod 3:82-92, partment of Large Animal Surgery and Medicine, College 1970. 20. Noten DM, De Lahunta A: Derivatives of the intermed- ;, of Veterinary Medicine, Auburn University, Auburn, Alaba- iate mesoderm: Reproductive organs, in Noten DM, De j: ma. Dr. Hanson is a Diplomate of the American College Lahunta A (eds): The of Domestic Animals. Balti- f of Veterinary Surgeons. more, Williams & Wilkins, 1985, pp 322-342. I 21. Noten DM, De Lahunra A: Cytogenedcs and sex decermina- tion, in Noten DM, De Lahunta A (eds): The Embyohgy of REFERENCES Domestic Animls. Baltimore, Williams & Wilkins, 1985, pp 1. 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-. . ------. - ENTIRE STALLIONS W ESTROGEN CONCENTRATIONS cryptorchidectomy in the horse, using inguinal extension of 48. Constant SB, Larsen RE, Ashbury AC, et al: XX male syn- the gubernaculum testis. JAW 174: 11 10-1 112, 1979. drome in a cryptorchid stallion. JAVMA 205:83-85, 1994. 25. Arthur GH: The surgery of the equine cryptorchid. Vet Rec 49. Dunn HO, Vaughan JT, McEntee K: Bilaterally cryptorchid 73:385-389, 1961. stallion with female karyotype. Comell Vet 64:265-275. 26. Wright JG: The surgery of the inguinal canal in animals. Vet 1974. Rec 75:1352-1363, 1963. 50. McIlwraith CW, Owen RAR: An equine cryptorchid with 27. Cox JE: Cryptorchidism, in Robinson NE (ed): Current testicular and ovarian tissue. Equine Vet J 8: 156-160, 1976. Therapy in Equine Medicine, ed 2. Philadelphia, WB Saun- 5 1. Ganjam VK, Kenney RM, Gledhill BL: Increased concentra- ders Co, 1990, pp 571-573. tion of androgens in cryptorchid stallion testes. J Steroid 28. 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Noakes DE, White RAS: Splenic-gonadal fusion in the mal, cryptorchid and castrated male horses. Equine Vet J horse. Vet Rec 98:382-383, 1976. 5:85-90, 1973. 41. Sherman K, Myhre G, Wells R: Abdominal fused 63. Ganjam VK: An inexpensive, yet precise, laboratory diagnos- in a miniature horse: A case report. J Equine Vet Sci 9: tic method to confirm cryptorchidism in the horse. Pr 191-192, 1989. AAEP 23:245-248, 1978. 42. Wilson DG, Nixon AJ: Case of equine cryptorchidism re- 64. Ganjam VK, Kenney RM: Androgens and oestrogens in nc sulting from persistence of the suspensory ligament of the ma1 and cryptorchid stallions. J Reprod Fertil [Suppl] 2 gonad. Equine Vet J 18:412413, 1986. 67-73,1975. 43. Parks AH, Scott EA, Cox JE, et al: Monorchidism in the 65. Stelmasiak T: The nonsurgical diagnosis of cryptorchidism horse. Equine Vet J21:215-217, 1989. in horses (testosterone and LH response to HCG injection). 44. Santschi EM, Juzwiak JS, Slone DE: Monorchidism in three NZ VetJ27:50, 1979. colts. JAVMA 194:256266, 1989. 66. Cox JE: Diagnostic test for equine cryptorchidism. Vet Rec 45. Vaughan JT: Surgery of the male equine reproductive sys- 98:204, 1976. tem, in Jennings PB (ed): The Practice of Large Ani- 67. Silbenahn P, Pouret EJM, Zwain I: Androgen and oestro- mal Surgery. Philadelphia, WB Saunders Co, 1984, pp gen response to a single injection of ~cGin cryptorchid 1083-1 108. horses. Equine Vet 121: 126-129, 1989. 46. Technical Development Committee: Cryptorchidism with 68. Palme R, Holzmann A, Mitterer T: Measuring fecal estro- special reference to the condition in the dog. Vet Rec 66: gens for the diagnosis of cryptorchidism in horses. Theri- 482483, 1954. ogenology 42: 138 1-1387, 1994. 47. Blanchard TL, Schumacher J, Taylor TS, et al: Detecting 69. Wilson DG: Laparoscopy as an aid in the surgical manage- unilateral and bilateral cryptorchidism in large animals. Vet ment of the equine hemicastrate. Proc AAEP 35:347-353, Med 85:395403, 1990. 1990. ARTICLE #4 REVIEW QUESTIONS 8. Histologic section of a retained testis will demonstrate The article you have read qualifies for 112 hour of a. spermatogenesis. Continuing Education Credit from the Auburn b. signs of hyperplastic seminiferous tubules. University College of Veterinary Medicine. Choose c. inhibition of spermatogenesis. d. enlarged Sertoli's cells. only the one best answer to each of the following questions; then mark your answers on the test 9. Comparison of left- and right-sided testicular reten- form inserted in The Compendium. tion indicates a. a greater frequency on the left. b. a greater frequency on the right. 1. Abdominal retention of the testis c. a greater frequency on the left in horses up to 3 a. is most common on the right side. years of age. b. is most common on the left side. d. nearly equal frequency on both sides. c. is equally common on both sides. d. does not occur. 10. The cranial, caudal, and ventromedial borders of the deep inguinal ring are the 2. The testis usually enters the scrotum a. caudal edge of the external abdominal oblique mus- a. at day 100 to 150 of gestation. cle, the pelvis and inguinal ligament, and the rectus b. at day 275 of gestation to 10 days before birth. abdominis muscle and prepubic tendon. c. at day 3 15 of gestation to 10 days after birth. b. caudal edge of the internal abdominal oblique mus- d. 3 weeks after birth. cle, the pelvis and inguinal ligament, and the exter- nal abdominal oblique muscle and prepubic ten- 3. The fetal mesenchymal attachment from the caudal don. aspect of the fetal testis to the scrotum is the c. caudal edge of the internal abdominal oblique mus- a. inguinal canal. cle, the pelvis and inguinal ligament, and the rectus b. gubernaculum. abdominis muscle and prepubic tendon. c. epididymis. d. caudal edge of the rectus abdominis muscle, the d. vaginal process. pelvis and inguinal ligament, and the rectus abdo- minis muscle and prepubic tendon. 4. Cryptorchidism is caused by a. mechanical factors. b. hormonal factors. c. genetic factors. d. mechanisms that are not precisely known.

5. The superficial inguinal ring is a. slit in the aponeurosis of the external abdominal oblique muscle. b. slit in the aponeurosis of the internal abdominal oblique muscle. c. bound cranially and caudally by the rectus abdomi- nis muscle. d. none of the above

6. Geldings generally have a serum testosterone concen- The combined 1995 and 1 996 tration of how many pglml? / COMPENDIUM CD-ROMis llere! a. 200 to 300 b. 100 to 200 Quahfiecl subscril~ersreceive the c. greater than 75 /CD-ROM absolutely FREE. d. less than 40 Please contact our Sul~scription '. The hCG stimulation test stimulates testosterone pro- Deparhnent to REQUEST your duction by which cells of the testis? CD-ROM or for more hIf'o1mati~n. a. Leydig's / b. cortical C. Sertoli's d. none of the above