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The urachus is the fetal communication between theurinary bladder and the allantois and allows urine

to pass from the urinary bladder into the allantoic sacof the placenta. At birth, the urachus is nonfunctional,but mechanisms responsible for its atrophy are notclearly defined.1,2 Four types of congenital urachalanomalies have been identified in humans and other

animals: persistent urachus, urachal cyst, urachalsinus, and vesicourachal diverticulum.2,3 Vesicourachaldiverticula are the most commonly recognized urachalanomaly.4,5

By definition, a diverticulum is a circumscribedpouch or sac of variable size occurring normally or cre-ated by herniation of the lining mucous membranethrough a defect in the muscular coat of a tubularorgan. A vesicourachal diverticulum is described as atriangular, circular, or rectangular appendix to the uri-nary bladder vertex.2,6 Its appearance may be classifiedas microscopic or macroscopic, and its location may beclassified as intramural or extramural.2,3 Microscopicvesicourachal diverticula are defined as islands of tran-sitional epithelium of various sizes with a microscopiclumen that may not always be identified. Macroscopicvesicourachal diverticula are grossly visible on posi-tive-contrast radiographs and are limited to the thick-ness of the bladder wall (intramural) or protrudebeyond the serosal surface of the urinary bladder(extramural).3

Vesicourachal diverticula have been identified indogs with chronic or recurrent bacterial cystitis,1,7,8 sug-gesting that there may be an association between vesi-courachal diverticula and urinary tract disease. To our

knowledge, however, the prevalence of vesicourachaldiverticula in dogs without urinary tract disease hasnot been determined. Therefore, the purpose of thestudy reported here was to determine prevalence andradiographic and histologic appearance of vesi-courachal diverticula in dogs without clinical signs ofurinary tract disease.

Materials and MethodsAnimalsFifty dogs without any clinical signs of uri-

nary tract disease that were euthanatized for reasons unrelat-ed to the present study were examined. Reasons for euthana-sia included cardiac insufficiency (n = 11), osteoarthritis (9),vertebral neoplasia (2), mammary neoplasia (1), nasal neo-plasia (1), cerebral neoplasia (2), appendicular neoplasia (3),

splenic neoplasia (1), gastric torsion (1), neuromuscular dis-ease (1), peripheral neuropathy (1), pyometra (1), aggression(2), glaucoma (2), trauma (hit by car; 3), and pyoderma (1).Five dogs were euthanatized at the owners request; forthe remaining 3 dogs, the reason for euthanasia was notobtained.

For all dogs, a history was obtained and a physicalexamination was performed by 1 of 2 individuals (KG or TT)prior to euthanasia; however, a urinalysis was not performed,and urine samples were not submitted for bacterial culture.None of the dogs had any clinical signs of dysuria, polyuria,oliguria, anuria, stranguria, or hematuria, and signs of painwere not evident during abdominal palpation. Owners didnot report any clinical signs of urinary tract disease at thetime of euthanasia.

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Prevalence and radiologic and histologicappearance of vesicourachal diverticula in dogswithout clinical signs of urinary tract disease

Karin Groesslinger, DVM; Tanja Tham, DVM; Monika Egerbacher, DVM, PhD; Dragan Lorinson, DVM, PhD

ObjectiveTo determine prevalence and radiologicand histologic appearance of vesicourachal diverticulain dogs without clinical signs of urinary tract disease.

DesignOriginal study.

Animals50 dogs between 4 months and 17 yearsold representing 22 breeds that had been euthana-tized for unrelated reasons; none of the dogs had ahistory or clinical signs of urinary tract disease.

ProcedureRetrograde positive-contrast radiographywas performed, and radiographs were examined formacroscopic diverticula. Necropsy specimens fromthe urinary bladder vertex were examined by meansof light microscopy for diverticula and signs of inflam-mation.

Results17 of the 50 (34%) dogs had vesicourachaldiverticula, and 1 additional dog had a urachal cyst.Fifteen of the 17 diverticula were macroscopic; sur-face area of the diverticulum could be measured radi-ographically in 13 of these dogs and ranged from 1 to90 mm2. The remaining 2 diverticula were microscop-ic. Sixteen diverticula were intramural and 1 wasextramural. Light microscopic signs of bladder wallinflammation could be detected in 5 dogs, 4 of whichhad macroscopic diverticula.

Conclusions and Clinical RelevanceResults sug-gest that a high percentage of dogs without clinicalsigns of urinary tract disease may have vesicourethraldiverticula. Further studies are needed to determinethe clinical relevance of vesicourethral diverticula indogs. (J Am Vet Med Assoc2005;226:383386)

From the Departments of Surgery and Ophthalmology (Groesslinger,Lorinson) and Histology and Embryology (Egerbacher), Universityof Veterinary Medicine, Vienna, Veterinrplatz 1, 1210 Vienna,Austria; and the Veterinary Hospital Neulinggasse, Neulinggasse32, 1030 Vienna, Austria (Tham). Drs. Groesslinger and Lorinsonspresent address is Small Animal Surgical Center, Neulinggasse 32/3,1030 Vienna, Austria.

Presented in part at the Voorjaarsdagen, Amsterdam, April 2003; theAnnual Meeting of the European College of Veterinary Surgeons,Glasgow, Scotland, July 2003; and the Annual Meeting of theDeutsche Veterinaergesellschaft (German Veterinary Association),Leipzig, Germany, November 2003.

The authors thank Monika Skalicky for assistance with statisticalanalyses.

Address correspondence to Dr. Groesslinger.

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Dogs were euthanatized by means of IV administrationof thiopental sodium (10 mg/kg [4.5 mg/lb]). Immediatelyafter dogs were euthanatized, a flexible urinary catheter wasplaced to completely empty the urinary bladder. Grossappearance of the urine was normal in all dogs.

Radiologic examinationTo fix the urinary bladder insitu, a 1:4 mixture of the water-soluble positive contrastmedium iopamidola in 4% formalin was instilled into the uri-

nary bladder through the urinary catheter. Volume of fluidinstilled in milliliters was equal to body weight of the dog inkilograms. Following fluid instillation, the catheter wasclosed or kinked to prevent the mixture from escaping and alateral radiographic view of the abdomen was obtained.

All radiographs were examined by a single individual(TT). Radiologically apparent diverticula were classified asmacroscopic vesicourachal diverticula. For urinary bladderswith triangular vesicourachal diverticula, surface area of thediverticulum was calculated by use of the following formula:surface area = 0.5 X length Xbase width.

Light microscopic examinationA caudal midlineceliotomy was performed, and the urinary bladder was grosslyexamined. A 2 X2-cm piece of the cranial part of the bladdercentered on the bladder vertex was taken within 15 minutesafter euthanasia and immersion fixed in buffered 4% formalin.Tissue samples were embedded in paraffin, and 4-m-thicksections of the samples were obtained and stained with H&E.

Sections were examined by means of light microscopyby a single individual (ME). Diverticula identified only bymeans of light microscopy were classified as microscopicvesicourachal diverticula. Light microscopy was also used todifferentiate between intramural and extramural macroscop-ic diverticula.

Statistical analysesSummary data were calculated.Age and sex distributions for dogs with diverticula were com-pared with distributions for dogs without diverticula bymeans of 2 tests. Standard statistical softwareb was used.Values ofP < 0.05 were considered significant.

Results

SignalmentNineteen of the 50 dogs were ofmixed breeding, with the remaining 31 dogs represent-ing 21 breeds. There were 4 German Shepherd Dogs, 3Yorkshire Terriers, 2 Collies, 2 Rottweilers, 2Dachshunds, 2 Bernese Mountain Dogs, 2 Pekingese, 1Great Dane, 1 Schnauzer, 1 Bobtail, 1 Golden Retriever,1 Leonberger, 1 Irish Setter, 1 Airedale Terrier, 1Entlebucher, 1 Mnsterlnder, 1 Kaukasian Htehund,1 Akita Inu, 1 Spaniel, 1 Lhasa Apso, and 1 Poodle.Twenty-nine dogs were male and 21 were female. Dogsranged from 4 months to 17 years old, with 4 dogs< 12 months old, 14 dogs between 1 and 9 years old,

and 32 dogs > 10 years old. Mean SD age of the dogswas 10.4 4.4 years.

Radiologic findingsFifteen of the 50 (30%) dogshad radiographic evidence of a macroscopic vesi-courachal diverticulum. Mean SD age of dogs withmacroscopic vesicourachal diverticula was 10.1 5.0years; 9 were male and 6 were female. Age distributionof dogs with macroscopic diverticula was not signifi-cantly different from age distribution of dogs without.The vesicourachal diverticulum was triangular in 14dogs (Figure 1). In the remaining dog, the diverticu-lum had a teardrop shape (Figure 2), indicating extra-mural protrusion of the diverticulum.

Surface area of the diverticulum could be calculat-ed in 13 of the 14 dogs with a triangular diverticulum.Mean SD surface area was 30.4 30 mm2 (range, 1to 90 mm2). In the remaining dog, surface area of thediverticulum could not be calculated because the mix-ture of iopamidol and formalin was not uniformly dis-tributed in the diverticulum.

Light microscopic findingsSeventeen of the 50(34%) dogs were determined to have vesicourachaldiverticula by means of light microscopic examination ofbladder specimens. Fifteen of these were the dogs withmacroscopic diverticula evident on positive-contrastradiographs; the remaining 2 dogs had microscopicdiverticula that were evident only during light micro-scopic examination. In addition to these 17 dogs, 1 doghad an intramural urachal cyst. The 2 dogs with micro-scopic diverticula were 12 and 15 years old; the dog withthe urachal cyst was 4 months old. Again, age distribu-tion of dogs with vesicourachal diverticula was not sig-nificantly different from age distribution of dogs without.

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Figure 2Lateral positive-contrast radiographic view of theabdomen in a dog. Notice the cystic macroscopic vesicourachaldiverticulum.

Figure 1Lateral positive-contrast radiographic view of theabdomen in a dog. Notice the triangular macroscopic vesi-courachal diverticulum.

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Only 1 of the 17 vesicourachal diverticula was

classified as extramural. In this dog, the protrusion wascontinuous throughout the bladder wall with a vesicu-lar appendage, confirming the radiologic results(Figure 3). The remaining vesicourachal diverticulawere intramural. They consisted of a ductlike indenta-tion that protruded into the muscle layer.

Signs of chronic inflammation, as evidenced by dif-fuse lymphocytic infiltration and lymph follicles in thelamina propria and submucosa of the bladder mucosabut not in the muscularis propria, were seen in 5 of the50 dogs. Four of these 5 dogs had a macroscopic intra-mural vesicourachal diverticulum (Figure 4). In thesedogs, lymphocytic infiltration was found in close prox-imity to the diverticulum. The remaining dog with lym-

phocytic infiltration did not have any evidence of a vesi-courethral diverticulum.

Discussion

Although several veterinary textbooks912 refer to theexistence of vesicourachal diverticula in dogs, to theauthors knowledge, there is a lack of information on theirprevalence. In the present study, 17 of 50 (34%) dogs with-out any clinical signs of urinary tract disease had radi-ographic or light microscopic evidence of vesicourachaldiverticula, suggesting that they are not uncommon.

Vesicourachal diverticula have been associatedwith chronic inflammatory diseases of the urinarytract in cats,2,13 dogs,1,7,8 and people.14 Three case

reports1,7,8 describedvesicourachal diver-ticula in dogs withchronic cystitis, andanother case report15

cited persistenturachal ligaments asa reason for recurringcystitis in a BerneseMountain dog and aGolden Retriever.However, the con-comitant presence ofvesicourachal diver-ticula and chronicinflammatory disor-ders of the lower uri-nary tract does notprove a cause-and-effect relationship.One aim of the pre-

sent study was todetermine whethervesicourachal diver-ticula could be foundin dogs without clin-ically apparent uri-nary tract disease.For this reason, dogswith a history of uri-nary tract diseasewere excluded fromthis study.

Light microscopic evaluation of bladder diverticu-la (but not vesicourachal diverticula) in humans

revealed chronic inflammation in 81% of resecteddiverticula.16 The inflammation was attributed to poorcontractility of the diverticulum, resulting in urine sta-sis. In the present study, light microscopic signs ofchronic inflammation were seen in 5 dogs, 4 of whichhad macroscopic intramural diverticula. Escape ofnoninfectious antigenic substances normally confinedto urine into the tissues at the site of the vesicourachaldiverticulum could have resulted in the microscopicinflammation that was seen.

The design of the present study did not permit usto determine whether macroscopic diverticula wereacquired or congenital. A study3 of the biologicalbehavior of vesicourachal diverticula in cats suggested

that microscopic urachal remnants that persist in theurinary bladder vertex after birth are usually silent, butrepresent a risk factor for development of macroscopicvesicourachal diverticula. An abnormal or sustainedincrease in bladder intraluminal pressure associatedwith lower urinary tract disorders may cause enlarge-ment or tearing of microscopic diverticula, leading todevelopment of macroscopic vesicourachal diverticula.

The population of dogs included in the presentstudy was quite diverse. The large number of dogs > 9years old probably resulted from the fact that moreolder dogs are euthanatized. The small number ofyoung (< 1 year old) and middle-aged (between 1 and9 years old) dogs did not allow us to detect a statistical

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Figure 4Photomicrograph of a section of the bladder from adog with a macroscopic diverticulum. Notice the large numberof lymphoid follicles below the epithelium (black arrowheads).H&E stain; bar = 1 mm.

Figure 3Photomicrograph of a sectionof the bladder from the dog in Figure 2.Notice the ample lumen of the diverticu-lum reaching through the full width ofthe bladder wall. H&E stain; bar = 1 mm.

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association between age and the presence of diverticu-la. In a previous study,6 vesicourachal diverticula werefound in 27% of male and 14% of female cats, and aseparate study11 suggested that male cats are twice aslikely to acquire vesicourachal diverticula as arefemales. In the present study, 10 of 17 dogs with vesi-courachal diverticula were male and 7 were female.

Detection of macroscopic vesicourachal diverticu-la by means of positive-contrast radiography is a reli-able technique.2 In human medicine, vesicourachaldiverticula were often serendipitously detected duringabdominal ultrasonography or computed tomogra-phy.17 Both excretory urography and contrast-enhancedcystography are able to reveal disorders of the urinarybladder vertex in animals.3,6,7,9,10With our technique forpositive-contrast radiography, the urinary bladderswere well filled, but not overdistended, with sufficientcontrast medium for identification and classification ofvesicourachal diverticula.

Whereas vesicourachal diverticula reportedly canbe triangular, circular, or rectangular, most of thediverticula in the present study were triangular.Variability of surface area measurements in the presentstudy may be related to variations in degree of urachusatrophy, differences in bladder wall thickness, andfibrosis subsequent to chronic inflammation. A differ-ence in filling pressures between dogs is another possi-ble explanation for the different sizes of vesicourachaldiverticula. In addition, type, severity, and duration ofinitiating diseases may have contributed to differentmeasurements of vesicourachal diverticula. The pre-sent study did not concentrate on measuring the fillingpressure before euthanasia and during contrast radiog-raphy.

Two diverticula in the present study were detected

only by means of light microscopy and were not visibleon contrast radiographs. The reason for this was mostprobably related to the fact that these dogs had a thinbladder wall and a diverticulum with a conelike open-ing toward the bladder lumen. Therefore, filling thebladder with contrast medium could have spread thediverticulum so that it was not macroscopicallydetectable.

Determining the clinical relevance of the results ofthe present study requires additional study to deter-mine whether the findings are coincidental or have acause-and-effect association with chronic urinary tract

infection. Further studies in dogs with urinary tractdisease are necessary to underline the clinical impor-tance of vesicourachal diverticula in dogs with chronicor recurrent infectious or noninfectious cystitis.

a. Jopamiro, Gerot Pharmazeutika, Vienna, Austria.b. SPSS, version 11.5 for Windows, SPSS Inc, Chicago, Ill.

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tion of infection-induced struvite uroliths and vesicourachal diver-ticulum in an immature dog.J Small Anim Pract 1989;30:613617.

2. Osborne CA, Kruger JM, Johnston GR. Feline vesicourachaldiverticula. In: Kirk RW, ed. Current veterinary therapy X. Small ani-mal practice. Philadelphia: WB Saunders Co, 1989;11531157.

3. Osborne CA, Johnston GR, OBrien TD, et al. Etiopathogenesisand biological behavior of feline vesicourachal diverticula. Vet Clin NorthAm Small Anim Pract 1987;17:697733.

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8. Wilson JW, Klausner JS, Stevens JB, et al. Canine vesi-courachal diverticula. Vet Surg 1979;8:6367.

9. Waldron DR. Urinary bladder. In: Slatter D, ed. Textbook ofsmall animal surgery. Philadelphia: WB Saunders Co, 1993;14501462.

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11. Grauer GF. Feline lower urinary tract inflammation. In:Nelson RW, Couto CG, eds. Small animal internal medicine. St Louis:Mosby, 1998;650658.

12. Osborne CA. Bacterial infections of the canine and felineurinary tract. In: Bojrab MJ, ed. Disease mechanisms in small animalsurgery. Philadelphia: Lippincott Williams & Wilkins, 1993;426463.

13. Hansen JS. Urachal remnant in the cat: occurrence and rela-tionship to the feline urological syndrome. Vet Med Small Anim Clin1977;72:17351746.

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15. Eich K, Hess M. Persistent urachal ligament in two juvenilefemale dogsdiagnosis and therapy. Kleintierpraxis 1997;42:903910.

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