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ischaemia can lead to these structures becoming disrupted and degenerative, and their ends can adhere together, end separately, or regress altogether. This theory would explain why the presence and gross appearance of the epididymis, vas deferens and testicular vessels varied amongst cases within this study and also between studies. The presence of a teratoma in Horse 5 was an anomaly. Although teratomas tend to occur in the gonads, they are nonfunctional and do not produce hormones so one could argue that this horse was actually an anorchid. The most important weakness in our case selection is that


Fig 2: Horse 8. Presumed to be a bilateral abdominal cryptorchid was diagnosed with monorchidism after standing laparoscopy. A 15 cm teratoma was identified on the right side and all structures associated with spermatic tissue except for testicular tissue were identified on the left side.


et al. 1989; Santschi et al. 1989) or after birth in an abdominal testis (Parker and Rakestraw 1997), resulting in degeneration (Parks et al. 1989; Santschi et al. 1989) or complete testicular necrosis (Gardner et al. 2017). The morphological changes of fibrous connective tissue,


haemosiderophages and mineralisation of necrotic cells seen in the microscopic histopathology of Horse 8 are similar to those previously described in monorchid horses (Kelmer et al. 2006; Brommer et al. 2011; Gardner et al. 2017). This is very similar to the pathology of testicular regression in man (Lamesch 1994; Spires et al. 2000) where the vas deferens, epididymis, and calcification or haemosiderin pigmentation have been noted in almost 90% of cases, which is characteristic, if not specific, for atrophy resulting from ischaemia. Performing histopathology in more cases would have been beneficial for clarifying the nature of the abnormal tissue and for further implicating ischaemic injury as the cause of equine monorchidism (Fig 5). In light of the study by Brommer et al. (2011), one could argue that the cases, which relied on histopathology for identification of necrotic testicular tissue, should be more accurately described as ‘anomalous cryptorchids’. It was decided to term them as monorchids for this study because of the absence of an obvious testicular structure during surgery. Their inclusion is clinically useful when trying to understand and explain how the surgical appearance of these horses can vary so much. As Brommer et al. (2011) suggests, it may be associated with the testicle being somewhere along the spectrum of ischaemic testicular degeneration. In equine fetal development, the tail of the epididymis,


proper ligament of the testis, vas deferens and ligament of the tail of the epididymis are in close proximity at the caudal aspect of the testicle (Noden and De Lahunta 1985). Brommer et al. (2011) hypothesised that varying degrees of


the history since birth for each horse was taken on trust. Although owner assurances were given, there remains the possibility that the owners may not have declared the horse having undergone previous surgery and been incompletely hemi-castrated whereby some residual epididymis or other spermatic tissue was left behind. This may be more likely to occur if carried out illegally by persons without using sufficient restraint or without veterinary qualification/expertise. Incomplete previous castration may complicate the diagnosis of monorchidism and should be considered a differential diagnosis, although arguably academic rather than clinically relevant. The signalment and history of these cases did not indicate any reason to suspect previous unilateral castration, due to trauma, inguinal herniation or for any other reason. It is important to recognise that in the cases of incomplete hemicastration however, the veterinarian would tend to inadvertently remove just the epididymis and part of the proper ligament, leaving the testis in the abdomen. As a result, it is unlikely that previous incomplete castration would result in a monorchid appearance. Horses in this study were successfully castrated using either


laparoscopy or laparotomy without complications. The choice of surgical approach was attributed to surgeon preference and also to the availability of laparoscopic equipment. The advantages of laparoscopy over traditional laparotomy techniques have been described (Searle et al. 1999; Kelmer et al. 2006; Joyce 2008). Laparoscopy enables good visualisation when searching for an intra-abdominal testis, which was evident in Horse 3 and Horse 4 which underwent previously unsuccessful laparotomy and inguinal exploration respectively. Laparoscopy can also help with identifying testicular remnants or adhesions from previous attempts at surgery, uses smaller and less invasive incisions, reduces manual tissue handling and does not disrupt the deep and superficial inguinal rings. This is in direct contrast to the complications associated with traditional laparotomy techniques, which include difficulty in identifying the testis, incisional infection and hernias, eventration, adhesions and peritonitis (French et al. 2002). Laparotomy also has the added risks associated with general anaesthesia (Wagner 2008) but standing open-flank laparotomy can be performed under sedation and local anaesthesia (Kelmer et al. 2013). As a result, surgical morbidity and post-operative complications are reduced and recovery is quicker with laparoscopy (Hendrickson 2006, 2007; Graham and Freeman 2014). Cribb et al. (2015) however, documented more post- operative complications with laparoscopy when compared to conventional inguinal and parainguinal approaches for cryptorchidectomy. There must also be consideration given in these


laparoscopy cases to the 20% prevalence of post-operative complications associated with standing castration of the


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