Ureterolithiasis is characterized by the formation of uroliths in the upper urinary tract, specifically within the ureters, resulting from the precipitation of minerals in the urine (Little, 2017). In most cases, these calculi are composed of calcium oxalate and struvite (Gomes et al., 2018). Ureteral obstructions can be classified as intraluminal, intramural, or extramural, with the intraluminal type being the most common (Shipov; Segev, 2013). This type of obstruction leads to increased intraluminal pressure, with subsequent release of vasoactive mediators, leukocyte influx, and renal fibrosis, ultimately reducing the glomerular filtration rate (Defarges; Berent; Dunn, 2013).

Ureteral calculi are considered the primary cause of ureteral obstruction in felines and have shown a significant increase in incidence, a trend that has persisted over recent decades (Geddes et al., 2023). Clinical signs are generally subtle and nonspecific, which hinders early diagnosis and compromises therapeutic prognosis (Jericó; Andrade Neto; Kogika, 2023; Cuddy, 2018). Prolonged obstructions result in progressive renal damage, including atrophy of the affected kidney and compensatory hypertrophy of the contralateral kidney (Shipov; Segev, 2013). Chronic kidney disease may arise as a consequence of acute kidney injury secondary to obstruction, which can be fatal if adequate renal decompression is not achieved (Hsu et al., 2022; Vrijsen et al., 2021).

Conventional surgical techniques, such as ureterotomy, neoureterocystostomy, and ureteronephrectomy, are associated with high morbidity and mortality rates, including complications such as uroabdomen and strictures that compromise the ureteral lumen (Vrijsen et al., 2021). In this context, less invasive methods have been developed to restore urinary flow, including the use of ureteral stents and subcutaneous ureteral bypass (SUB) systems (Horowitz et al., 2013). Among these, SUB stands out for offering shorter surgical time, lower complication rates, reduced need for reintervention, and increased patient survival (Deroy et al., 2017).

The choice between ureteral stents and SUB should be individualized, taking into account ureteral anatomical integrity, the etiology of the obstruction, and the patient’s clinical condition. In general, stents are more suitable for simple intraluminal obstructions, where the ureter remains patent and there is no significant stenosis, whereas SUB is preferred in cases of ureteral stenosis, complex or recurrent obstructions, non-catheterizable ureters, and previous stent failure (Berent et al., 2018; Deroy et al., 2017). In felines, however, the use of stents presents important practical limitations, primarily due to the small diameter of the ureteral lumen, making the procedure technically challenging (Kulendra et al., 2014). Additionally, it is associated with complications such as stranguria, pollakiuria, hematuria, and cystitis due to bladder irritation (Deroy et al., 2017), as well as long-term encrustation, which may lead to device obstruction (Deroy et al., 2017).

In specific clinical scenarios, such as the presence of chronic kidney disease (CKD), bilateral obstructions, or ureteral stenosis, SUB tends to be the preferred technique, as it provides more stable and long-lasting renal decompression, better preservation of renal function, and increased survival (Butty; Labato, 2021; Berent; Weisse, 2018). In this context, its impact on surgical decision-making is significant, as SUB is associated with shorter operative time, fewer reinterventions, and improved long-term outcomes compared to ureteral stents (Deroy et al., 2017). It is particularly indicated in patients with greater clinical severity or anesthetic limitations (Berent et al., 2018), whereas stents, although useful in selected cases, require greater technical expertise and are more prone to complications, limiting their applicability in routine feline clinical practice (Kulendra et al., 2014; Deroy et al., 2017).

Thus, this article aims to review the literature on ureterolithiasis in felines and to evaluate the role of SUB as a less invasive technique, highlighting its advantages and the main complications reported in the literature.

This study consists of a narrative literature review based on scientific articles, reviews, and consensus statements published between 2010 and 2025. The search was conducted in the PubMed, SciELO, and Wiley Online Library databases using the descriptors feline urolithiasis, ureteral obstruction in cats, subcutaneous ureteral bypass, and ureterolithiasis in cats.

Studies addressing the etiology, pathophysiology, diagnosis, and treatment of ureterolithiasis in felines were included, with emphasis on minimally invasive surgical approaches, particularly SUB, as well as comparisons with ureteral stents. Review articles, retrospective studies, and international consensus statements published in Portuguese and English were considered.

Duplicate studies, studies focusing on other species, publications addressing exclusively conventional surgical techniques, and studies not directly related to ureteral obstruction in felines were excluded.

The selected studies were critically analyzed regarding clinical relevance, applicability of findings, and level of evidence, prioritizing more recent publications with greater impact on clinical practice. Approximately 25 studies were ultimately deemed eligible and were organized according to the evolution of knowledge on the topic.

Understanding renal anatomy and physiology is essential for elucidating the mechanisms involved in feline urolithiasis and the complications associated with ureteral obstructions. The urinary system consists of two kidneys, two ureters, the urinary bladder, and the urethra-structures responsible for blood filtration, urine formation, transport, storage, and excretion (König; Liebich, 2021; Dyce; Sack; Wensig, 2019). The right kidney is positioned more cranially than the left, and both are located in the retroperitoneal space, lateral to the aorta and caudal vena cava, surrounded by a fibrous capsule (Fossum et al., 2021). Renal vascularization originates from the renal artery, a direct branch of the abdominal aorta, which divides into dorsal and ventral branches and may present anatomical variations (König; Liebich, 2021). Urine formed in the renal pelvis is transported through the ureters, muscular tubes that run along the dorsal wall of the abdominal cavity and enter the bladder obliquely (König; Liebich, 2021).

From a physiological perspective, the nephron represents the functional unit of the kidney, composed of the glomerulus, Bowman’s capsule, and renal tubules. Urine formation involves three fundamental processes: glomerular filtration, tubular reabsorption, and tubular secretion, all regulated by glomerular pressure and osmotic gradients (Reece et al., 2019). Alterations in these mechanisms may lead to imbalances in urinary solute concentration, resulting in supersaturation and subsequent crystal formation, which constitutes the initial event in urolithiasis (Little, 2017).

Urolithiasis is a globally distributed condition characterized by the presence of uroliths throughout the urinary tract. Ureteral obstruction caused by calculi or other factors leads to acute kidney injury in cats, with incidence increasing significantly between 1984 and 2002 (Etedali; Reetz; Foster, 2019). The main causes of ureteral obstruction include calculi, stenosis, circumcaval ureters, neoplasia, mucus plugs, blood clots, fibrosis, and surgical trauma (Gomes et al., 2022). Ureterolithiasis is the leading cause of ureteral obstruction in felines, accounting for approximately 82% of cases and is typically associated with calcium oxalate uroliths (Geddes et al., 2023).

The literature indicates a predominance of specific breeds, such as Ragdoll, Tonkinese, Persian, British Shorthair, and Birman, with a higher incidence in middle-aged to older animals. This suggests that genetic factors, combined with metabolic and dietary predispositions, play a central role in the occurrence of ureterolithiasis (Geddes et al., 2023; Jericó; Andrade Neto; Kogika, 2023). These epidemiological data support the hypothesis that the interaction between genetic and environmental determinants-including diet composition and water intake habits-contributes to urinary supersaturation and urolith formation, predominantly composed of calcium oxalate and struvite (Little, 2017; Etedali; Reetz; Foster, 2019; Gomes et al., 2018).

The ureteral obstructive process, often intraluminal, compromises renal hemodynamics by increasing intraluminal and pelvic pressure, directly affecting the renal tubules and Bowman’s space, thereby reducing the glomerular filtration rate (Shipov; Segev, 2013). This pathophysiological phenomenon is further amplified by the activation of vasoactive mediators and leukocyte recruitment, culminating in progressive renal fibrosis (Defarges; Berent; Dunn, 2013). The progression of obstruction not only impairs the affected kidney through fibrosis but also imposes an increased functional burden on the contralateral kidney as a compensatory mechanism, predisposing to chronic kidney disease, particularly in subclinical conditions in which renal function is compromised prior to the onset of evident clinical signs (Hsu et al., 2022; Santos; Alessi, 2022).

The clinical presentation of ureterolithiasis is often nonspecific, typically characterized by anorexia, weight loss, and vomiting, which complicates early diagnosis and reduces therapeutic effectiveness (Jericó; Andrade Neto; Kogika, 2023; Cuddy, 2018). In cases of chronic unilateral obstruction followed by acute contralateral obstruction, felines may present with uremia, acute abdominal pain, and distension of the renal capsule, conditions that require urgent intervention to prevent renal necrosis and progression to anuria (Jericó; Andrade Neto; Kogika, 2023).

Diagnosis should integrate clinical, laboratory, and imaging findings. A detailed clinical history-including information on diet, home environment, and prior medical history, often marked by nonspecific manifestations-must be correlated with complementary diagnostic results. Particular attention should be given to biochemical alterations such as hyperkalemia, hyperphosphatemia, hypercalcemia, and azotemia, as well as changes in urinary density and pH, which are critical for diagnostic clarification (Gomes et al., 2022; Little, 2017; Jericó; Andrade Neto; Kogika, 2023).

As clinical signs are not always evident, upper urinary tract urolithiasis may contribute subclinically to cases of chronic kidney disease of unknown origin. The high prevalence of this condition suggests that it may itself be a causative factor for CKD, as obstruction by nephroliths or ureteroliths can result in significant renal injury, particularly in unilateral cases and in the absence of pre-existing renal disease (Hsu et al., 2022).

Imaging studies are essential for the diagnosis and monitoring of urolithiasis in felines. Abdominal radiography and ultrasonography are key tools for the localization and characterization of uroliths, allowing assessment of their number, shape, contour, density, and anatomical position, as well as the identification of secondary changes such as hydronephrosis and hydroureter, and monitoring of the affected kidney (Jericó; Andrade Neto; Kogika, 2023). Although radiography enables the detection of calculi, ultrasonography is considered the modality of choice, as it allows evaluation of pyelectasia and ureteral dilation associated with obstructive lesions (Cuddy, 2018). In inconclusive cases or when conventional imaging methods are insufficient, percutaneous antegrade pyelography-preferably ultrasound-guided-remains indicated as a complementary method, enabling detailed visualization of the renal pelvis and ureter and contributing to diagnostic confirmation (Etedali; Reetz; Foster, 2019; Lulich et al., 2016).

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In summary, the reviewed literature demonstrates that ureteral obstruction in felines is a condition of increasing clinical relevance, requiring early diagnosis and appropriate intervention to preserve renal function. Minimally invasive techniques, particularly the SUB, have shown greater safety and long-term efficacy, with lower morbidity and mortality rates compared to traditional methods such as surgical extraction and ureteral stents. Despite these advances, gaps remain, including the scarcity of long-term comparative studies and variability in clinical protocols. Therefore, the choice of technique should be guided by its capacity to relieve obstruction, ensure procedural safety, preserve renal function, and optimize survival outcomes in feline patients.