Introduction

Ureteral pseudodiverticulosis is a rare lesion, with <50 human and only 2 canine cases reported.^1,2

The term “diverticula” refers to the congenital form of the lesion, in which the wall of the invagination includes all the wall layers. The acquired form, pseudodiverticulosis, consists of multiple outpouchings of the mucosa through the wall of the ureter without crossing the tunica muscularis.³ The pathogenesis of ureteral pseudodiverticulosis is unclear. It may develop following a chronic urinary obstruction such as ureteral lithiasis, stenosis, or neoplasia.³

The purpose of this paper is to describe the first feline case of ureteral pseudodiverticulosis associated with bilateral pyelonephritis and unilateral retrocaval ureter.

Case Report

A 6 yr old intact female Birman weighing 2.8 kg was referred to the National Veterinary School of Alfort Hospital for azotemia. The owners reported weight loss and recent development of pollakiuria. The cat had no medical history.

The cat was prostrate and mildly dehydrated. Abdominal palpation was unremarkable. A biochemistry panel confirmed marked azotemia (creatinine 5.6 mg/dL, reference interval 0.52–1.78 mg/dL; blood urea nitrogen 140 mg/dL, reference interval 18.7–37.4 mg/dL). Hematologic analyses showed mild normocytic hypochromic anemia (29%, reference interval 31–51%) and moderate neutrophilia (31.2 × 10³/µL, reference interval 1.2–11.5 × 10³/µL). Serum electrolytes and systolic blood pressure as measured by Doppler were normal. Urine was obtained via cystocentesis. Urinalysis revealed minimally concentrated urine (specific gravity 1.013), microscopic hematuria, and proteinuria. Cytology demonstrated pyuria and bacteriuria.

An abdominal ultrasound examination showed bilateral renal pelvic dilation. The left pelvic cavity was markedly enlarged (23 × 13 mm, kidney axis length 3.8 cm) and contained nonobstructive calcified material. The left ureter was slightly twisted and dilated (8 mm) from the renal pelvis insertion to the uretero-vesical junction (UVJ). The left ureteral lumen was filled with anechoic content.

The right pelvic cavity and the proximal ureter were mildly dilated (8 × 2 mm and 2 mm, respectively). The urinary bladder displayed signs of cystitis with sediments. The UVJs were unusually located between the bladder neck and the urethra.

The association of clinical signs, neutrophilic leukocytosis, azotemia, and pelvic dilation led us to perform a pyelocentesis. An inflammatory, septic liquid with numerous bacilli was obtained. Urine culture revealed Escherichia coli colonies that were resistant to amoxicillin and cefalexin but sensitive to marbofloxacin.

During hospitalization, intravenous fluid therapy was administered together with ranitidine^a (1 mg/kg subcutaneously q 8 hr), maropitant^b (1 mg/kg subcutaneously q 24 hr), sucralfate^c (per os q 8 hr), and buprenorphine^d (0.03 mg/kg IV q 6 hr). Marbofloxacin^e (4 mg/kg IV q 24 hr) was initiated and continued according to the patient’s results.

After mild improvement, the patient’s clinical condition declined on the fourth day of hospitalization. Azotemia persisted (creatinine 4.4 mg/dL; blood urea nitrogen 206 mg/dL). A second abdominal ultrasound examination revealed minor increases in size for both renal pelvic cavities. Based on these results and the guarded prognosis, the owner requested euthanasia.

Necropsy revealed significant lesions only in the urinary system. Both kidneys appeared smaller than normal. The cortex was irregular and retracted with multiple chronic infarcts. The left kidney showed mild pyelonephritis associated with crest necrosis, and the right kidney showed mild hydronephrosis. The position of the proximal right ureter was abnormal, passing dorsal to the vena cava with an acute angulation, consistent with a right retrocaval ureter (Figure 1A). Sectioning of the left ureter revealed numerous 5 mm diameter outpouchings arising from the mucosa that disseminated throughout the entire length of the ureter (Figure 1B). The ureters did not display any serosal deformation and did not contain any material in the lumen. The UVJ malposition was confirmed. The urinary bladder wall was thickened and presented several ulcerations. An ectopic vein that branched from the left renal vein to the caudal abdomen was observed (Figure 1A).

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Histological examination revealed bilateral pyelonephritis. In the right kidney, there was also papillary necrosis.

The left ureter displayed severe and chronic transparietal but mostly serosal pyogranulomatous inflammation. Rare gram-negative bacteria could be seen in the cytoplasm of macrophages. The above-mentioned outpouchings corresponded with multiple epithelial invaginations into the tunica muscularis. The lumen of the outpouchings was empty. This lesion was consistent with ureteral pseudodiverticulosis (Figure 2A).

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The right ureter, which did not present any macroscopic outpouchings, showed microscopic ureteral pseudodiverticulosis (Figure 2B).

Discussion

Ureteral pseudodiverticulosis is rare.^1,3–6 Only two cases have been described in dogs, both in cases of chronic urinary obstruction (ureteral and vesical urolithiasis and vesical hemangiosarcoma).²

Several hypothetical mechanisms have been put forward to explain pseudodiverticulosis formation. Mucosal herniation could be a consequence of the submucosal urothelial hyperplasia by creating crypts and subsequent cysts.⁷ These changes may be triggered by either chronic inflammation or chronic urinary obstruction.³ Human patients developed pseudodiverticulosis in cases of chronic obstruction as a result of distal ureteral lithiasis, benign prostatic hypertrophy, ureteral strictures, or neoplasia.^1,3,5,6 As in the human cases, a subobstructive mechanism was likely present in both canine cases. The canine lesions were small, <5 mm in width, and there were ∼3 or 4 lesions per cm.²

To our knowledge, the present report is the first to document a case of feline ureteral pseudodiverticulosis.

Because ureteral pseudodiverticulosis does not necessarily deform the serosal surface, it is difficult to diagnose. The classic ultrasound exam did not reveal these lesions in either our or the two canine cases. In the human cases reported, radiological imaging, together with retrograde pyelography, was the mainstay for diagnosis. This technique is associated with increased intraureteral pressure, which facilitates visualization of the lesions. Patients often have an unremarkable intravenous urogram.^1,6 The two canine cases, however, were diagnosed from an excretory urogram.² Use of computed tomography scans has been reported, but their sensitivity is not perfect. In our case, anterograde pyelography could have been performed.^8,9 However, considering that the entire length of both ureters was visualized and lithiasis was absent, this procedure was not performed, but in retrospect, it should have been.

Our patient also presented with a right retrocaval ureter (or right circumcaval ureter [RCU]). This congenital anomaly was first described by Huntington and McClure in 1920.¹⁰ Two recent articles reported a higher prevalence, between 14 and 30%.^11,12 In our case, we questioned if the RCU could have participated in a chronic obstruction as well as if this lesion could have enhanced pseudodiverticulosis. The clinical implication of RCU in cats was investigated in two studies, and RCU did not seem to predispose to ureteral obstruction.^12,13

Vesico-ureteral reflux, an abnormal flow of urine from the bladder into the upper urinary tract, is supposed to be a predisposing factor for pyelonephritis in both dogs and humans.¹⁴ It usually results from an abnormal maturation of the UVJ or a short distal ureteric submucosal tunnel in the bladder that alters the function of the valve mechanism.¹⁵ It could be that urinary anomalies can predispose to this vesico-ureteral reflux. Two human cases presenting with an RCU and a reflux have been described.^16,17 This kind of functional anomaly had to be considered for our patient, who was presented as both an RCU and an abnormal UVJ.

Finally, two possible chains of events can be proposed to explain the development of the lesions in our patient. First, congenital lesions (retrocaval ureter and abnormal UVJ) may have caused or predisposed to a ureteral reflux, which in turn predisposes patients to ascending infection and pyelonephritis. This chronic inflammation may have led to ureteral pseudodiverticulosis.

The second possibility is that the simultaneous presence of subobstructive urinary lesions (abnormal UVJs and right retrocaval ureter) caused an obstruction of the urinary flow followed by pseudodiverticulosis. This latter lesion would have enhanced urinary retention and subsequent chronic ascendant urinary tract infection.

Conclusion

To our knowledge, this is the first feline case of ureteral pseudodiverticulosis. This lesion was not seen during the ultrasound scan but was revealed upon necropsy and confirmed histologically. It would be interesting to do a prospective search for this anomaly, as it could be associated with ureteral lithiasis, which is a major concern for feline patients.