A Rare Ureteral Tumour, What We Know from the Human Side

Ureteral fibroepithelial polyps are rare, benign, mesodermal tumours that primarily affect the urinary tract. There have been few reports of this tumour in animals and most of what we know of the tumour and tumour behaviour comes from the human literature. Cystoscopy or ureteroscopy is the best way to locate the tumours and excision is generally curative. This type of tumour should be suspected whenever there is pain associated with the urinary tract that cannot be attributed to a urolith or cystitis. Ureteral fibroepithelial polyps are rare, benign, mesodermal tumours that frequently occur in the proximal ureter (but can develop along any portion of the urinary tract) and are the most common type of rare benign tumour to form within the urinary tract (Kim et al., 2022). Most of the information we have on these masses comes from the human literature. These polyps are described as having a smooth, long, slender, finger-like or frond projections with one or more projections originating from a common base located in the submucosal connective tissue of the ureter and projecting into the lumen (Gozalo et al., 2006; Lam et al., 2003). They typically occur as a solitary tumour, however, there are documented cases where both ureters are affected and cases where more than one tumour is encountered (Gozalo et al., 2006). Fibroepithelial polyps have a predilection for the left ureter and have a higher occurrence in males (Ludwig et al., 2015). In contrast, females tend to develop renal pelvic polyps that occur within the right side of the urinary tract (Lam et al., 2003). Furthermore, fibroepithelial polyps tend to occur in adults between the ages of 30 and 40 years old and are rarely found in children (Lam et al., 2003; Ludwig et al., 2015). According to Gozalo et al. (2006), clinical cases in animals have been identified in an owl monkey and four dogs where in each case the polyp behaved similarly to and exhibited characteristics that mirrored cases reported within the human population. The pathophysiology of these tumours is still uncertain but they are thought to be congenital in origin or an effect of chronic inflammation, infection, obstruction or trauma (Gozalo et al., 2006). The most common signs associated with fibroepithelial polyps ar abdominal or flank pain, haematuria and urinary tract infections (Gozalo et al., 2006; Lam et al., 2003). Hydronephrosis is variably present depending on the amount of obstruction the polyp creates within the lumen of the ureter (Gozalo et al., 2006). Dysuria, pyuria, polydipsia and pollakiuria were signs that were less commonly reported but still associated with the presence of a ureteral fibroepithelial polyp (Gozalo et al., 2006; Lam et al., 2003). Kim et al. (2022) credit flank pain to be a byproduct of obstructive hydronephrosis. Ureteral fibroepithelial tissues are classified as hamartomas and defined by their non-epithelial, mesodermal origin (Kim et al., 2022; Lam et al., 2003). This classification becomes important when considering the malignant transitional cell and squamous cell tumours that arise from the epithelium and are an important differential when diagnosing fibroepithelial polyps (Kim et al., 2022; Ludwig et al., 2015). Histologically, fibroepithelial polyps are defined by their transitional epithelial layer that is well-differentiated layering over a fibrovascular stroma that emerges from the mucosa of the ureteral lining, lacking papillary formation and having varying degrees of lymphoplasmacytic inflammation (Gozalo et al., 2006; Lam et al., 2003). The main diagnostic imaging used in identifying fibroepithelial polyps is succinctly summarised by Kim et al. (2022) as intravenous urography (IVU), ultrasound, imputed tomography (CT) (with or without contrast), or retrograde pyelogram. Each of these modalities excels in highlighting different diagnostic views of the polyp, however, due to their non-specificity, ureteroscopy is essential for direct visualisation and biopsy of the tumour needed to make a definitive diagnosis (Kim et al., 2022). Ureteroscopy is likely the best option in horses as the other diagnostic techniques are not feasible in the horse. Excision of ureteral fibroepithelial polyps can be accomplished via endoscopic means or via percutaneous approach (Lam et al., 2003). Endoscopic resection is accomplished using holmium: yttrium aluminium garnet (YAG) laser with a long pulse setting (Kim et al., 2022). Laser removal offers long term results with low morbidity, less tissue damage leading to fewer clinical side effects (i.e. ureteral strictures) and provides the added benefit of haemostasis when the polyp is excised (Kim et al., 2022). The percutaneous approach offers an advantage over the laser by allowing the surgeon to directly visualise the base of the stalk, allowing for a safe and complete removal of the entire polyp (Lam et al., 2003). The decision for which approach is better suited varies but fibroepithelial polyp size and location along with patient status should be considered (Lam et al., 2003). It is worth mentioning that as stated in a systematic literature review performed by Ludwig et al. (2015) polyps up to 16 cm were successfully resected via ureteroscopic procedure but most larger polyps were removed in open surgery while smaller polyps not located in the proximal ureter were removed endoscopically. According to Lam et al. (2003), regional or general anaesthesia can be used for an endoscopic removal while general anaesthesia is warranted for the percutaneous procedure. Lam et al. (2003) discuss the challenges of endoscopic removal as largely correlated to the size of the polyp. Some of the specific complications seen with polyps removal are elongation of the stalk with pedunculation making the base difficult to reach, the polyp growing to the size of the lumen blocking any access to the base of the stalk and the small working space making the visualisation poor and differentiation of the polyp and the ureteral wall difficult and therefore dangerous (Lam et al., 2003). The polyp in this associated article (Rikart & Rijkenhuizen, 2024) was removed with an electrocautery snare and a small stock was left behind. Perhaps it would have been valuable to treat the stock with further electrosurgery or laser ablation. Ureteral fibroepithelial polyps, while rare in the veterinary community, are seemingly becoming commonly identified. This is perhaps due to better diagnostic techniques and more awareness of the tumour type. These tumours are defined by their non-epithelial, mesodermal origin. Identification of these tumours is achieved via different imaging modalities that are useful in identifying key characteristics of the tumour. Ureteroscopy is pivotal for the visualisation and biopsy needed to make the diagnosis. Endoscopic resection of these cases has proven to be effective with long-lasting results and minimal side effects from treatment. Laura Mena: Conceptualization; writing – review and editing. Dean A. Hendrickson: Conceptualization; writing – review and editing. None. No conflicts of interest have been declared. Not applicable to this clinical commentary.