8


EQUINE VETERINARY EDUCATION / AE / JANUARY 2017 Since the horse did not seem to be hampered in his


function and had no health issues with the structure, and since any of the therapeutic approaches would be rather aggressive and invasive, the gelding was left untreated and is still in good health and competing at the same level.


Discussion


In the present case, mesenchymal proliferation with low numbers of fibroblasts and without signs of malignancy led to the diagnosis of a preputial fibroma. A fibroma of the preputium has not yet been described unequivocally, and it seems likely that other neoplastic enlargements are more likely to occur on the preputium. A fibroma is a benign neoplasm rarely seen in mature


horses and accounts for 2.1–17.1% of all skin neoplasms (Scott 2007). This large variation is probably due to the fact that in earlier days there was no agreement on a single definition differentiating equine sarcoids from fibromas (Baker and Leyland 1975; Valentine 2006). There is no breed predisposition for fibromas. Fibromas most commonly occur on the extremities, ventral body wall or on the head (Baker and Leyland 1975; Bostock and Owen 1975; Colitz et al. 2000; Scott and Miller 2003). Microscopically, a fibroma consists of a solitary, well-


defined, mass in the dermis or subcutis (Scott 1988). The overlying epidermis is intact in most cases, although when excessive growth occurs, alopecia, hyperpigmentation or even ulceration can be seen (Scott and Miller 2003; Scott 2007). Histologically, a fibroma is characterised by a low number


of fibroblasts with collagenous fibres woven in between. These fibroblasts are fusiform with a hyperkeratotic nucleus and a low mitotic index. Collagenous fibres are mostly variable in maturation and haphazardly oriented. When this mass has a firm structure and on microscopic examination a dense growth of mature fibrocytes and collagenous tissue, it is called a fibroma durum. When soft and microscopically less dense collagenous tissue visible, it is called a fibroma molle (Weiss 1974; Bostock and Owen 1975; Scott 2007). When foci of mucinous deposits are present, fibromas are more diagnosed as being fibromyxomas or myxofibromas. Some essential characteristics to differentiate a fibroma


from a sarcoid are the long and slender extensions of the overlying epidermis into the proliferating dermal fibroblasts (so called rete pegs). This organisation is typical for equine sarcoids except when ulceration occurs or in occult sarcoid lesions (Martens et al. 2000). Fibromas usually do not have an epithelial component or only in a limited area and with short rete pegs at the tumour surface. Moreover, sarcoids are most often characterised by the ‘picket fence’ pattern, in which superficial fibroblasts are orientated perpendicular at the basal membrane. In cases with an unclear histopathological diagnosis, detection of bovine papilloma virus (BPV) DNA by


PCR can help to discern sarcoids (positive for BPV) from fibromas (negative for BPV) (Martens et al. 2000, 2001; Bogaert et al. 2008, 2010). In addition to dermal and subcutaneous fibromas, other


types of fibromas have been described: an exceptional type of fibroma is the juvenile mandibular ossifying fibroma (Morse et al. 1988; Kodaira et al. 2010) seen in juvenile horses where dense fibrous tissue with fibroblasts transform into osteoblasts (Robbins et al. 1996). Musculoaponeurotic fibromatosis is a disorder where fibroblast proliferation occurs in the muscles


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(Valentine et al. 1999). In this case fibroblasts transform into myofibroblasts. In rare cases, an abdominal localisation is described leading to colic (Wilson and Stykes 1981; Tafti and Oryan 1998). Other causes of enlarged preputium include: equine coital


exanthema (caused by equine herpes virus 3) (Kleiboeker and Chapman 2004; Seki et al. 2004; Tibary and Fite 2007; Smith 2009; Ferreira et al. 2010) or Trypanosoma equiperdum infection (Claes et al. 2005; Sellon 2007; Vulpiani et al. 2013). These are easily differentiated from a fibroma by their clinical signs, disease progression or, in the case of Trypanosoma, its region bound prevalence or absence (the present case describes a Belgian Warmblood competing at national level that had never travelled to a Trypanosome endemic region). Identifying habronemiasis by its clinical appearance can be more challenging since the granulomatous proliferative lesions can be quite similar to fibromas on macroscopic evaluation. Ulceration, haemorrhage and serosanguinous discharge are common in habronemiasis lesions. Larvae, eosinophils, mast cells, foci of coagulation and necrosis, caseous granules, and calcification are visible on histopathology of these lesions (Scott and Miller 2003; Tibary and Fite 2007; Down et al. 2009). Finally, a chronic irritation of the preputium, as seen in older debilitating geldings, caused by intrapreputial urination may lead to fibrosis and phimosis as well, but accompanying clinical signs, such as odour, pain, erythema and ulceration, allow differentiation of this condition easily from the previously mentioned diseases (Brinsko et al. 2011). In this case, possible therapeutic approaches should aim


at a total elimination of the tumour preserving all natural functions of the penis (extension and urination in case of a gelding) (Van den Top et al. 2010). Choice of therapy is dependent on the extension of the tumour and (although rare) presence of inguinal metastases. Hyperthermia (Klein et al. 1991; Schumacher 2006),


cryotherapy (Brinsko 1998; May et al. 2002; Van den Top et al. 2008a;), laser therapy (McCauley et al. 2002), radiotherapy (Robbins


et al. 1996), bacillus Calmette-Gu erin-


immunotherapy (Van den Top et al. 2010), chemotherapy (Brinsko 1998; May et al. 2002; Hewes and Sullins 2006; Schumacher 2006; Van den Top et al. 2008b, 2010), penile sheath ablation (Doles et al. 2001), and surgical segmental posthectomy or posthioplasty (Brinsko 1998; May et al. 2002; Van den Top et al. 2010) are all described with various success. When considering a therapeutic approach, one must


consider not only the method of choice depending on feasibility, availability and financial constraints, but also possible complications post therapy have to be considered in advance. In the present case, since the enlargement was very extensive and enveloping the whole circumference of the preputium, the risk of a preputial constriction and as a consequence para- and phimosis was too high. The gelding was left untreated and is still in good health and competing at national level.


Authors’ declaration of interests No conflicts of interest have been declared.


Ethical animal research


Since the case only involved diagnostic procedures, ethical requirements are not applicable.


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