THERIOGENOLOGY 6. Transrectal US Exam


Before transrectal US, always perform a manual examination “per rectum.” A pelvic urethra is identified first, followed by both ampullae of the vasa deferentia that are located at the neck of the bladder, and the vaginal rings are identified last. Carefully examine the vaginal rings for the presence of any palpable structures that enter the inguinal canals. Once palpation “per rectum” is completed, the linear US transducer is introduced into the rec- tum, and a longitudinal image of the pelvic portion of the urethra is visualized. Next, the transducer is moved cranially and laterally to assess the size and ultrasonographic appearance of the prostatic lobes located on both sides of the neck of the urinary bladder. A small and inactive prostate is charac- teristic of long-term geldings,9 whereas a large pros- tate with numerous spaces filled with prostatic secretions is found in intact stallions,10,11 as well as in the majority of cryptorchid horses. In order to localize the retained abdominal testis, the vas defer- ens is traced using ultrasonography.1 At first, vi- sualize the ampulla of the vas deferens on top of the urinary bladder, as previously described.11 Then, trace the ampulla as a guide toward the retained testis. In the intact stallion, inguinal cryptorchid, or incomplete abdominal cryptorchid, the ampulla gradually bends ventrally toward the vaginal ring, while in complete abdominal cryptorchids, it runs cranially and without bending. Slowly follow the vas deferens with the US transducer, visualizing longitudinal or cross-sectional images (Fig. 2). While the ampulla is relatively easy to trace, the narrow portion of the vas deferens is more challeng- ing; tracing this portion requires some practice and good-quality equipment. Higher frequencies, 7–9 MHz, are preferred in this part of the examination. In horses with complete abdominal cryptorchidism, the vas deferens runs straight forward, craniolater- ally, or craniodorsally. Therefore, the direction for tracing the vas deferens may need several correc- tions. The result of successful tracing is to first visualize the retained epididymis and, right behind it, the retained testis (Fig. 3). This vas-tracing technique is particularly useful in horses with re- tained testes localized deep in the abdomen, at the caudal pole of the kidney. However, this technique is also helpful in localizing and visualizing inguinal (Fig. 4) and incomplete abdominal testes. The most challenging task is to find an abdominally retained testis after an unsuccessful surgery that led to the removal of the epididymal tail only, since the vas deferens is then disconnected from the testis and may become more mobile within the abdominal cav- ity. Surprisingly, the authors have found the re- tained testis in close proximity to the transected vas deferens in several horses using the described vas- tracing technique (Fig. 5).


Fig. 4. US images illustrating the transrectal US vas-tracing technique of identifying the retained inguinal testis. A, Narrow portion of the vas deferens bends down toward the vaginal ring. B, Small hypoechoic testis is visualized under musculature of the abdominal wall.


7. Transabdominal US Exam


If the retained testis is not found using the previ- ously described technique, perform transabdominal US as previously described.7 In addition to the in- guinal area, evaluate the caudal aspect of the abdo- men, from the midline to the fold of the flank, and the lateral aspect of the flank. For this examina- tion, use a curvilinear 3.5-MHz transducer first aimed at the urinary bladder. Move the transducer cranially while scanning from the midline to the lateral aspect of the abdomen. Perform this exam- ination slowly, meticulously, and in a well-organized fashion. Distinguishing between the retained tes- tis, which is quite mobile, and the continuously mov- ing intestines is not easy and requires patience. Most testes are visualized on the ventral abdominal wall, near the urinary bladder, lying between the intestinal loops or colon haustra (Fig. 6). Other testes are identified in the caudal aspect of the mid-abdomen.7


AAEP PROCEEDINGS  Vol. 64  2018 233


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