• The right kidney is small (3cm length) but with almost complete hydronephrosis and only a thin rim of enhancing renal parenchyma. The cranial portion of the ureter is moderate-markedly dilated (up to 7.5mm), which abruptly tapers to a lesser degree of distention (2.6mm): see second post contrast series, images 37 through 44 to see the change in ureteral diameter. On dorsal reformats, the course of this segment of ureter has a “fish- hook” (see image 34 for example). At the level of L4, the ureter narrows to <2mm and is seen coursing ventrally and towards the left, ventral to the caudal vena cava/aorta. Caudal to this point, the ureter is again slightly dilated to a point (at the level of L5-6) where a small elongated enhancing mass lesion is present (4.5mm diameter, 14mm length): see first post contrast series, images 55-60, or dorsal reformatted series, image 31 for example. Distal to this point, the right ureter is not distended. Mild mural thickening is noted in some portions of the ureter proximal to the mass lesion. No contrast entered the renal pelvis or ureter on this side during the duration of the scan.
• The left kidney is larger than the right at 4cm length but the margin is irregular. There is flat mineralization/nephrolith in the pelvis. Mild pyelectasia is also present. The left ureter is mildly tortuous in its cranial to mid aspects (see dorsal reformatted series for best evaluation) and is slightly distended, up to 1.7mm. There is normal passage of iodinated contrast through the ureter, seen on the later post contrast scan.
• The bladder is unremarkable.
• A splenorenal shunt is present and the caudal vena cava is distended cranial to the shunt.
• The left adrenal gland is enlarged and slightly lobular, up to 7.2mm thick. A small focus of mineral is present in the gland. The right adrenal is normal.
• There is subjective thickening of the small intestinal walls. There is a large amount of luminal gas.
• The pancreas is irregularly margined in some areas.
• The liver is mildly enlarged. Bile ducts are prominent.
• Caudal mesenteric lymph nodes are mildly enlarged, up to 4.4mm thick.
• In the visible lung field, there is a mild bronchial pattern, some thin parenchymal bands, a few ground glass nodules, and a small cavitated lesion in the left caudodorsal lung lobe.
• No significant osseous lesions are present.

CT conclusions:

1. Right-sided hydronephrosis and segmental hydroureter secondary to ureteral obstruction from mass-like ureteral thickening at the level of L5-6 + contribution to ureteral obstruction by a possible stricture cranial to the mass (level of L4). Lesser degrees of ureteral wall thickening cranial to the mass.
   – The mass is concerning for neoplasia, such as transitional cell carcinoma, leiomyosarcoma or possibly lymphoma (given the species, lymphoma was considered, though this has not been reported in cats to date). Inflammatory ureteritis with marked mural mass-like thickening was also considered given the rareity of ureteral neoplasia.
   – The mural thickening in the ureter cranial to the mass may be a similar process, eg additional site of neoplastic infiltration similar to the larger mass lesion or ureteritis +/- ureteral stenosis/stricture
2.  Left sided chronic renal change but with suspect compensatory hypertrophy (since kidney seems large considering patient age and evidence for chronic disease). Pelvic mineralization/nephrolith. Mild pyelectasia may be due to fluid therapy and/or chronic renal disease; cannot rule out pyelonephritis. Mild tortousity and distention of the proximal to mid ureter may be secondary to ureteritis (inflammation, cannot rule out infection), but is of unknown significance (no evidence of obstruction).
3. Left adrenomegaly. May be benign (eg hyperplasia) vs neoplastic (eg primary adrenal tumor or metastatic neoplasia if the ureteral mass is TCC)
4. Intestinal changes; caudal mesenteric lymphadenopathy; irregular pancreas; hepatomegaly; prominent biliary tree; Changes could be secondary to triaditis (IBD, cholangiohepatitis/cholangitis, chronic pancreatitis). Small cell lymphoma is an alternative for the intestinal changes. Hepatic involvement (lymphoma) is possible for the hepatomegaly vs. metabolic hepatopathy or lipidosis. Age-related pancreatic changes could also explain pancreatic irregularity.
5. Splenorenal portosystemic shunt: Likely incidental vs. secondary to hepatic disease.
6. Pulmonary pattern may be due to chronic lower airway disease, age-related changes. Suspect small bulla, left caudal lung lobe (although bullae are rare in cats) vs. cavitated granuloma or other benign lesion. The few ground glass nodules could be neoplastic (eg metastatic) but may also be benign (eg foci of pneumonia or inflammation, granuloma, fibrosis, other).

Outcome:

• The patient went for exploratory laparotomy. At surgery, the proximal right ureter was tortuous and showed hydroureter secondary to strictured, diseased areas of the ureter. The mass region was seen as a thickened, white-ish area of mural proliferation and cranial to this, the ureteral wall was also thickened (but less so) with a similar gross appearance as the mass. There were also adhesions of the broad ligament to the right and left kidneys and fibrosis of the right kidney. Due to the possibility of ureteral neoplasia in 2 different areas of the ureter, complete nephrectomy was performed. Biopsy of other areas (eg liver or intestinal tract) was not performed. No comments were made on the surgery report regarding the other CT abnormalities (splenorenal shunt, etc.).
• Histologic diagnosis
  Histologic diagnosis on the ureteral mass: CHRONIC LYMPHOPLASMACYTIC URETERITIS WITH FIBROSIS. Examined are multiple sections of ureter in which there is an epithelial lining comprised of a single layer of urothelial cells. The subepithelial stroma is composed of dense fibrous connective tissue (fibrosis). Within the subepithelial stroma there are aggregates of lymphocytes and plasma cells, as well as multiple ectatic, cystic spaces (likely invaginated urethral mucosa) containing sloughed, rounded, individualized urothelial cells. This sample represents an area of mild inflammation with moderate fibrosis and abnormal urethral mucosa. This may represent an area of chronic inflammation and healing by fibrosis leading to the stricture noted on CT. There is no evidence of neoplasia within the sections examined.
• Histologic diagnosis of the dilated ureter cranial to the mass area: HYDROURETER. Examined are multiple transverse sections of ureter in which the central lumen is markedly ectatic and lined by intact, regionally attenuated urothelium. Along the adventitial border with the surrounding adipose tissue are small aggregates of lymphocytes and plasma cells. The lumen contains numerous enlarged sloughed urothelial cells. No evidence of neoplasia is present in the sections examined.

Follow-up: At the time of suture removal, the owners reported that the cat was doing well and previous clinical signs (anorexia, vomiting, lethargy, lumbar pain) had resolved.

Discussion: This case demonstrated an obstructive ureteral mass-like lesion that was secondary to chronic inflammatory ureteritis with fibrosis leading to luminal stricture/stenosis. While mild ureteral wall thickening is not uncommon in cats (or dogs) with various conditions such as infection, ureteral calculi, inflammatory ureteritis, and ureteral strictures, the mass-like nature of the thickening in this particular case was unusual. Although ureteral neoplasia is very rare and there are only 2 reports in cats (1 leiomyosarcoma and 1 transitional cell carcinoma) (1-2), the imaging findings and patient age made neoplasia seem more likely in this case. In humans, there are reports of idiopathic segmental ureteritis and inflammatory pseudotumor of the ureter (may be one in the same) presenting with obstructive mass lesions of the ureter that can be misdiagnosed as malignancy on radiological examination.(3-5)  Histologically, lymphoplasmacytic inflammatory cell infiltrates and fibrosis are present in the ureter, similar to our case. In humans, idiopathic ureteritis/inflammatory pseudotumor, along with other causes for hydronephrosis, can cause abdominal/flank pain, so this was presumably the cause for the lumbar pain (referred abdominal pain) that this cat presented with, which is supported by the fact that the cat was clinically back to normal post operatively.

The “fish- hook” course of the ureter as seen on the dorsal reformats is similar to that described in previous studies on circumcaval ureter/preureteral vena cava in cats (6,7)  and in humans with a Type 1 (“low loop”) circumcaval ureter. (8)  This cat, however, did not have a circumcaval ureter (ureter did not course dorsal to the vena cava) so the course of the ureter was presumably secondary to its distention/tortuosity +/- being secondary to adhesions, which were noted in the region at surgery.

The unrelated splenorenal shunt may be secondary to underlying liver disease (e.g., cholangiohepatitis) with the potential for portal hypertension, as described in a previous report where 42% of cats with a splenosystemic shunt had clinicopathologic evidence of a hepatopathy. (9) Or, these shunts may be incidental and completely unrelated to liver disease (since other signs of portal hypertension, such as ascites, are lacking). (10) Since they are usually seen in female spayed cats (91-100%), (9,10)  there is potentially some relationship between previous spay procedure and development of this shunt type. The exact cause for these shunts, however, remains unknown and in our case, while the hepatic enzymes were elevated, a liver biopsy was not obtained so further conclusions cannot be made.

References:

1. Speakman CF, Pechman RD, Jr, D’Andrea GH. Aortic thrombosis and unilateral hydronephrosis associated with leiomyosarcoma in a cat. J Am Vet Med Assoc 1983;182:62–63.

2. Cohen L, Shipov A, Ranen E, et al. Bilateral ureteral obstruction in a cat due to a ureteral transitional cell carcinoma. Can Vet J 2012;53:535–538

3. Joo M, Chang SH, Kim H, et al. Idiopathic segmental ureteritis, misdiagnosed as ureteral cancer preoperatively: A case report with literature review. Pathology International 2010; 60: 779–783

4. Tripp BM, Huttner I, Chu F, Taguchi Y. Idiopathic segmental ureteritis: clinicopathological definition. Can J Urol. 1997 Feb;4(2):381-385.

5. Hiroyuki A, Morikawab T, Araki A, et al. IgG4-related periureteral fibrosis presenting as a unilateral ureteral mass. Pathology – Research and Practice 207 (2011) 712– 714

6. Steinhaus J, Berent AC, Weisse C, et al. Clinical Presentation and Outcome of Cats with Circumcaval Ureters Associated with a Ureteral Obstruction. J Vet Intern Med 2015;29:63–70

7. Pey P, Marcon O, Drigo M, et al. Multidetector-row computed tomographic characteristics of presumed preureteral vena cava in cats. Vet Radiol Ultrasound, Vol. 56, No. 4, 2015, pp 359–366

8. Salonia A, Maccagnano C, Lesma A, et al. Diagnosis and treatment of circmcaval ureter. Eur Urol Suppl 2006;5:449–462.

9. Palerme J-S, Brown JC, Marks SL, Birkenheuer AJ. Splenosystemic shunts in cats: A Retrospective of 33 Cases (2004–2011). J Vet Intern Med 2013;27:1347–1353

10. Specchi S, Panopoulos I, Adrian AM et al.  A“Spaghetti sign” in feline abdominal radiographs predicts spleno-systemic collateral circulation. Vet Radiol Ultrasound 2017; 59: 13-17.