EQUINE VETERINARY EDUCATION / AE / MARCH 2016


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bilateral. Seventy-one testes were retained on the left and 70 on the right. Breed distribution was 32 Warmblood, 28 Cobs, 18 Icelandic, 18 Standardbred, 13 pony, 4 Thoroughbred, 3 Irish Draught and crosses, 4 cross breeds, 3 Friesian, 2 Quarter Horse, one Appaloosa, and one Coldblood. Horse age ranged from 1 to 12 years with a mean of 3 years and median 2 years.


Diagnosis Six of the 127 horses (5%) underwent endocrine blood testing prior to presentation: 4 testosterone assay, one oestrone sulfate assay and one testosterone stimulation test. No horses had a history of previous attempted surgery, even though some were found to have previously undergone surgery, and 8 underwent supplementary rectal examination on presentation. Eighty-five testes (59%) were identified inguinally, 46 right


Fig 1: Under standing sedation, a 2–4 MHz curvilinear ultrasound probe is used to scan the inguinal area on the missing side using alcohol as the coupling agent.


systematically examined. Testicles have a characteristic appearance, with a uniform grey stroma, bright acoustic signal on the tunica albuginea and a central vein (Fig 2). Testicular tissue identified in the inguinal region was considered to indicate inguinal retention; if none was identified, abdominal retention was diagnosed.


Surgery The actual location of the hidden testis was confirmed at surgery. In brief, horses with inguinal retention were castrated under general anaesthesia in dorsal recumbency using a modified scrotal approach (Cox et al. 1975); if descended, the contralateral testis was removed using a standard closed or semi-closed technique. Abdominally retained testes were removed using a standing laparoscopic method (Hendrickson 2002) with a bipolar vessel-sealing device (Ligasure Atlas)1. The normally descended contralateral testis was then removed under standing sedation using an open technique (Turner and McIlwraith 1989), or under general anaesthesia using a closed technique. The location of retention (inguinal or abdominal) of the testis was confirmed and recorded in all cases; complete and incomplete abdominal retention was not routinely differentiated on preoperative ultrasound.


Statistics Data were collated on a spreadsheet (Microsoft Excel 2007)2 and statistical tests carried out using separate software (Medcalc)3. Except where otherwise stated, descriptive statistics were calculated as median and range. Data were tested for normality using the D’Agostino-Pearson test. Fisher’s exact test was used to compare the proportion of abdominal and inguinal testes at the 3 hospitals, and to identify any possible differences between the locations of left and right- retained cryptorchid testes. Significance was set at P<0.05. The results of inguinal ultrasound determination of location were compared with the results of surgery to calculate sensitivity, specificity, negative and positive predictive values.


Results


In total, 127 horses with 141 cryptorchid testes were identified: 113 horses were unilateral cryptorchids and the remaining 14


and 39 left; 56 (41%) were diagnosed as abdominal based on being absent on ultrasound scan (25 right and 31 left). Two inguinally retained testes were not observed on ultrasound (false negatives) in one Welsh Cob and one Irish Draught cross. Two testes were considered inguinal but subsequently had to be removed from the abdomen (false positives) in one Welsh Cob and a Warmblood. These errors cancelled each other out in the descriptive statistics, meaning that the same numbers of inguinal and abdominal testes were subsequently removed at surgery, 85 and 56 respectively. There was no difference in the proportion of left and right


testes retained abdominally and inguinally, with 25 (45%) right and 31 (55%) left testes being abdominal, P>0.99. There was no significant difference in proportion of abdominal and inguinal retained testes at the hospitals, P = 0.25. Sensitivity of inguinal ultrasound to predict the location of


inguinal testes was 98% (95% confidence interval 92–100%) and specificity 97% (95% confidence interval 88–99%). The probability that positively identifying a testis inguinally correctly indicated inguinal retention (positive predictive value) was 98% and the chance that not seeing a testis indicated abdominal retention (negative predictive value) was 97%. The low rate of false positives and negatives prevented meaningful comparison between centres.


Discussion


The use of inguinal ultrasound provided a very reliable and accurate diagnostic tool to determine the location of cryptorchid testes before surgery, allowing cost effective surgical intervention with minimal morbidity. Both curvilinear and linear ultrasound probes proved efficacious. We hypothesise that the percutaneous use of a rectal ultrasound probe, readily available in practice, should also be practical. Jann and Rains (1990) first described the use of preoperative transrectal ultrasound in 11 horses to locate cryptorchid testes, obtaining a 100% correlation with surgical findings. Schambourg et al. (2006) described a technique of scanning 2 additional zones on the flank of the horse to visualise the abdominal testis in situ. Despite many attempts, we infrequently visualise abdominal testes using this method (Fig 4). This may be because horses had not been starved in many of the early cases attempted, and the authors noted that prior starvation greatly facilitated visualisation. Our calculated sensitivity and specificity values of 98% and 97% respectively in 127 horses compare favourably with 93% and


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