Clinical Findings in 10 Horses Diagnosed with Monorchidism Following Exploratory Laparotomy or Standing Laparoscopic Surgery

SummaryMonorchidism describes the complete absence of one testis and is rare in horses. This study reports the clinical findings in 10 horses diagnosed as monorchids by standing laparoscopy or exploratory laparotomy. Hospital records for all horses undergoing cryptorchidectomy (2000–2016) in four centres were reviewed from which horses diagnosed with monorchidism were identified. Surgery was by either standing flank laparoscopy or an inguinal exploration and subsequent exploratory laparotomy under general anaesthesia. Ten horses were diagnosed as monorchids, five by laparoscopy (one bilateral laparoscopy) and five by laparotomy. Nine horses had a normally descended scrotal testicle, which was also removed at surgery. The right testicle was absent in three horses, and the left testicle was absent in seven horses. Anatomical findings were recorded in each case; the vaginal process was present in all horses, ductus deferens and epididymis were present in 80% of horses and the ligament of the tail of the epididymis and testicular vessels were present in 50% of horses. Laparoscopy allowed easy identification of spermatic structures enabling a prompt diagnosis of monorchidism. In conclusion, when monorchidism occurs, most other associated spermatic structures are likely to be present. A diagnosis of true monorchidism is reliant on hormonal testing and absence of testicular tissue on histopathology and so some of these horses may strictly be somewhere on the spectrum of testicular degeneration. This information is particularly useful in the surgical situation when it is not clear whether the testicle is present or not.