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CLINIC AND SURGERY • Cienc. Rural 55 (10) • 2025 • https://doi.org/10.1590/0103-8478cr20240349 linkcopy

Open-access Vesicourachal diverticulum in a Santa Ines lamb: a rare congenital anomaly

Divertículo vesicouracal em um cordeiro Santa Inês: uma anomalia congênita rara

AuthorshipSCIMAGO INSTITUTIONS RANKINGS

ABSTRACT:

The urachus is a canal that connects the urinary bladder with the allantoic sac through the umbilical cord in the prenatal period, transporting urine from the embryo or the fetus to the placenta and involuting after birth. Vesicourachal diverticulum occurs when the obliteration of the urachal lumen is incomplete, resulting in a discontinuity in the muscular layer of the bladder. A 3-month-old male Santa Inês lamb, weighing 20.5 kg, presented bilateral ventral abdominal distension, inappetence, severe apathy, mixed dyspnea, bruxism and an estimated degree of dehydration of 10%. On ultrasound examination, a marked accumulation of free fluid was observed in the abdominal cavity, and paracentesis revealed uroperitoneum. Due to the severity of the clinical condition the animal was euthanized. Necropsy revealed 8 liters of peritoneal fluid and a conical structure with approximately 1 cm diameter located at the apex of the bladder that was ruptured. The histopathological evaluation was consistent with a vesicourachal diverticulum. This congenital anomaly is considered rare in small ruminants, and this is the first report in the literature of a vesicourachal diverticulum in a lamb.

Key words:
bladder; congenital defect; small ruminant; urachus; uroperitoneum.

RESUMO:

O úraco é um canal que conecta a vesícula urinária com o saco alantoidiano por meio do cordão umbilical no período pré-natal, transportando a urina do embrião ou feto para a placenta e involuindo após o nascimento. O divertículo vesicouracal ocorre quando a obliteração e a regressão do lúmen uracal não são completas, resultando em descontinuidade na camada muscular da bexiga. Um cordeiro Santa Inês, macho, com três meses de idade, pesando 20,5 kg, foi atendido por apresentar distensão abdominal ventral bilateral, inapetência, apatia grave, dispneia mista, bruxismo e um grau estimado de desidratação de 10%. Na avaliação caracterizou-se acúmulo acentuado de líquido livre na cavidade abdominal cuja centese revelou uroperitônio, e em razão da gravidade da condição clínica o animal foi eutanasiado. Durante a necropsia, foram recuperados 8 litros de líquido peritoneal, e uma estrutura cônica com aproximadamente 1 cm de diâmetro localizada no ápice da bexiga estava rompida. A avaliação histopatológica foi consistente com divertículo vesicouracal. Essa anomalia congênita é considerada rara em pequenos ruminantes, e esse é o primeiro relato na literatura de divertículo vesicouracal em um cordeiro.

Palavras-chave:
vesícula urinária; defeito congênito; pequenos ruminantes; úraco; uroperitônio

Urachus is a tubular extension of the allantois that connects the urinary bladder with the allantoic sac via the umbilical cord in the prenatal period, transporting urine from the embryo or fetus to the placenta. In sheep, urachal patency begins to decrease after the first half of gestation, when the flow of fetal urine through the urethra increases, going into the amniotic sac. Thus, fetal urine mixed with amniotic fluid is continually swallowed by the fetus and recycled (NODEN & LAHUNTA, 1985; WINTOUR et al., 1996; SHANDLEY et al., 1997).

After birth, the urachus undergoes a passive retraction into the abdominal cavity, where it transforms into the median ligament of the bladder (CONSTABLE et al., 2017). This anatomophysiological metamorphosis renders the urachus non-functional. When this regression process does not unfold in the typical manner, congenital anomalies that can persist into adulthood may arise (STEINER & LEJEUNE, 2009; WILSON et al., 2019).

Urachal abnormalities encompass various conditions, including patent urachus, umbilical-urachal sinus, urachal cysts, and the vesicourachal diverticulum (WILSON et al., 2019). This latter condition develops when there is incomplete obliteration of the urachal lumen proximally to the bladder, resulting in disruption of the smooth muscle layer of the bladder (OSBORNE et al., 1987). The diverticulum can vary in size, typically assuming a conical shape and primarily manifesting in the cranioventral region of the bladder wall, near the bladder’s apex. Urachal anomalies often go asymptomatic. However, if a rupture of the vesicourachal diverticulum occurs, clinical signs emerge as a result of uroperitoneum (MARQUES et al., 2010).

This study reported the case of a male Santa Inês lamb with congenital vesicourachal diverticulum, describing the clinical and pathological findings as it is a rare abnormality, poorly described in small ruminants. Furthermore, the study highlighted the importance of distinguishing this condition from the more prevalent obstructive urolithiasis, given its clinical and diagnostic relevance.

A three-month-old male Santa Inês lamb, weighing 20.5 kg, was referred to the Veterinary School Hospital “Professor Ricardo Alexandre Hippler” with a reported history of apathy, anorexia, and mild abdominal distention in the left dorsal region over the course of approximately four days. Two days prior to referral, the lamb began exhibiting a progressive ventral abdominal distention and hyporexia, ultimately leading to anorexia and severe apathy. Furthermore, during the previous days, there was an absence of urinary output within the stall, and fecal output was notably diminished.

In the physical examination, the animal presented apathy and had a body condition score of 3 (scale from 1 to 5). Its heart rate was 145 beats per minute (bpm), respiratory rate of 40 breaths per minute (rpm), rectal temperature of 38.5 ºC, non-reactive lymph nodes, capillary refill time of 4 seconds, pale ocular mucosa, skin tent of 4 seconds and enophthalmos, with an estimated degree of dehydration of 10%. Bilateral ventral abdominal distension with a pendulous appearance was present (Figure 1). The lamb also exhibited mixed dyspnea and bruxism. During abdominal auscultation, a liquid interface was detected when the ballooning test was performed, in addition to ruminal atony.

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Figure 1
Lateral and ventral view of Santa Inês sheep with bilateral ventral distention. (A) Distention of the lower quadrants of the abdomen. (B) Position imposed on the animal to facilitate and provide relief during breathing.

Transabdominal ultrasonography with a 7.5 MHz linear transducer showed anechoic areas characterizing a marked accumulation of free fluid in the abdominal cavity. After antisepsis of the left ventral flank region, paracentesis was performed to collect peritoneal fluid. In addition, blood samples were collected for evaluation of complete blood count and serum biochemistry profile.

The physical examination of the peritoneal fluid revealed an odorless, reddish, slightly cloudy fluid, and specific gravity of 1.014. The cell count was 90,000 red blood cells/µL, 1,600 leukocytes/µL and in the cytological examination, few mesenchymal cells and moderate amounts of macrophages and neutrophils were identified. In the chemical examination, the protein content was 2.1 mg/dL, concentration of urea was 198.0 mg/dL and of creatinine was 17.8 mg/dL. The peritoneal fluid was classified as modified transudate.

The complete blood count showed the following results: erythrocytes 15.9 mi/µL, hemoglobin 11.5 g/dL, hematocrit 46%, plasma proteins 8.6 g/dL and fibrinogen 600 mg/dL. All values found in the leukogram were within the reference range. In the serum biochemical analysis, there was an increase in the activity of aspartate aminotransferase (106 IU/L), gamma glutamyltransferase (29 IU/L), total protein levels (8.4 g/dL), with hyperglobulinemia (5.8 g/dL), and increased levels of urea (234 mg/dL) and creatinine (6.4 mg/dL). The peritoneal creatinine to serum creatinine ratio was 2.78, characterizing uroperitoneum.

Due to the severity of the clinical condition and unfavorable prognosis, humane euthanasia was performed. During the subsequent necropsy, 8 liters of peritoneal fluid were recovered, and a conical-shaped prominence, measuring approximately 1 cm in diameter, was identified at the apex of the bladder. This prominence was found to be ruptured and with hemorrhagic areas around it (Figure 2). The entire urinary tract was meticulously evaluated for the presence of sediments and urinary calculi; however, none were detected.

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Figure 2
Macroscopic images of the urinary tract of the lamb. (A) Anatomical regions of the urinary tract: kidneys (1), ureters (2), bladder (3), urethra (4), penis (5) and glans (6). (B) Presence of a conical-shaped prominence, located in the region of the apex of the bladder, approximately 1 cm in diameter (thin arrow) and with surrounding hemorrhagic areas (thick arrow). (C) Site of rupture in the region of the apex of the bladder (arrow).

No macroscopic lesions were observed in the other organs, and there were no indications of any communication between the bladder apex and the umbilicus. Additionally, plastic bags that had been ingested were retrieved from the rumen. Fragments of the bladder were collected and preserved in 10% formaldehyde for histopathological analysis.

The histological examination of the bladder fragment at the rupture site revealed marked multifocal to coalescing hemorrhage, accompanied by epithelial ulceration, with a focally extensive region without a muscular layer observed, consisting mainly of abundant fibrovascular connective tissue. This feature rendered the demarcation between the lamina propria and serosa indistinct. Adjacent to this alteration, layers of smooth muscle were identified (Figure 3). Based on the combined macroscopic and microscopic findings, the diagnosis for the animal was established as vesicourachal diverticulum. According to the clinical history, the animal had never presented any clinical signs, and the elimination of urine was normally done through the penile urethra.

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Figure 3
Photomicrograph of the histopathological analysis of the bladder. A) Photomicrograph of an intact part of the bladder, showing mucosa lined by transitional epithelium (1), lamina propria made up of loose connective tissue (2) and bundles of smooth muscle tissue (3). B) Photomicrograph of the vesicourachal diverticulum showing a focally extensive area lacking a muscular layer and consisting of an abundant amount of fibrovascular connective tissue (arrow) with hemorrhagic areas (asterisk). C) Photomicrograph of the ruptured region of the vesicourachal diverticulum demonstrating multifocal to marked coalescing hemorrhage with the epithelium showing ulceration (arrowhead), loose connective tissue (asterisk) and smooth muscle tissue (arrow). Objective 4x.

Urachal pathologies can be infectious or inherently congenital, which stem from deficiencies in the luminal closure process (SCHELLIN & LEITE, 2019). The precise etiology of the incomplete urachus regression in this case remains uncertain. However, OSBORNE et al. (1987) have proposed potential contributing factors, which include premature umbilical cord rupture, umbilical inflammation and/or infection, and excessive physical manipulation of the neonate.

The observed data corroborated the findings of MARQUES et al. (2010) and SOUSA et al. (2017), who documented that urachal abnormalities generally remain asymptomatic and are usually detected only after the onset of clinical signs of uroperitoneum. This condition arises from urine leakage into the abdominal cavity due to the rupture of the vesicourachal diverticulum.

The muscular discontinuity results in incomplete bladder emptying, leading to the permanence of residual urine within the vesicourachal diverticulum. This persistent accumulation of urine exerts a continuous pressure on the lumen, causing distension of the diverticulum wall and rendering it thin and fragile (MARQUES et al., 2010; PERONDI et al., 2020). Urinary stasis results in a persistent inflammatory process, which further contributes to the structural wall’s fragility. When this fragility is coupled with elevated intraluminal pressure stemming from urinary obstructive disorders or increased intra-abdominal pressure, it can lead to rupture of the diverticulum (MARQUES et al., 2010).

Prior to the occurrence of uroperitoneum, the animal exhibited distension in the upper left flank, potentially attributed to ruminal tympanism secondary to cardia obstruction, likely caused by the ingestion of plastic bags discovered during the necropsy. This ingestion could have contributed to an increase in intra-abdominal pressure (MARQUES et al., 2010).

According to SCULLY (2021), the primary cause of urinary bladder rupture in small ruminants is urethral obstruction, often induced by uroliths, which was excluded in this case, since the entire urinary tract of this lamb was thoroughly assessed, with no calculi or signs of obstruction identified and no crystals found in urinalysis.

Renal function was assessed by quantifying serum creatinine and urea levels, which revealed azotemia. According to MORRESEY (2015), azotemia is a hallmark characteristic of uroperitoneum, as urea nitrogen - which is in high concentrations in retained urine - permeates through the peritoneum and is subsequently reabsorbed into the bloodstream. Creatinine, however, is a comparatively large molecule and exhibits slower diffusion into the bloodstream.

According to CONSTABLE et al. (2017), uroperitoneum is confirmed when the concentration of creatinine in the peritoneal fluid is twice as high as the serum creatinine levels. In the present case, the creatinine concentration of the peritoneal fluid exceeded the serum creatinine level by almost threefold, confirming uroperitoneum.

The analyzed peritoneal fluid was categorized as modified transudate. As reported by VALENCIANO & RIZZI (2020), the presence of urine within the peritoneal cavity can induce chemical irritation and peritonitis, potentially instigating an exudative response. This exudative process may manifest with a nucleated cell count of less than 6,000 cells/μL, and a protein content of less than 3 g/dL, contingent on the dilution effect of the urinary volume.

BRAUN & NUSS (2015) asserted that dehydration results from the influx of substantial liquid volumes into the peritoneal cavity, primarily driven by the osmolarity gradient discrepancy. Urine, with an osmotic gradient three times higher than the peritoneal fluid, plays a pivotal role in this process.

In addition to the clinical signs of dehydration, the animal presented hematocrit and plasma protein levels above the reference interval for the species. This finding indicated hemoconcentration, which stems from the loss of body fluids into the abdominal cavity. Consequently, this loss contributes to severe ventral abdominal distention, as a result of the accumulation of approximately 8 liters of peritoneal fluid within the cavity.

As outlined by PORTELA et al. (2018), and SCHELLIN & LEITE (2019) the preferred diagnostic modality for vesicourachal diverticulum is cystography, which effectively highlights structural wall alterations. Nevertheless, ultrasound can also serve as a diagnostic tool, as indicated by PERONDI et al. (2020).

Due to the unfavorable prognosis, humane euthanasia was performed. Consequently, the diagnosis was primarily established through a comprehensive assessment that included the animal’s medical history, clinical signs, laboratory results, as well as the macroscopic and microscopic findings obtained during post-mortem examination.

The histopathological examination of the bladder prominence revealed areas characterized by marked multifocal to coalescing hemorrhage, concomitant with epithelial ulceration. Furthermore, a focally extensive region lacking a muscular layer was identified, and it was predominantly composed of an abundant fibrovascular connective tissue. These findings corroborated with the observations of OSBORNE et al. (1987) who, in their evaluation of thirty-three vesicourachal diverticula in cats, described the structural microanatomy of this pathology as featuring mucosa lined with transitional epithelium encompassed by a substantial amount of connective tissue that disrupts the normal continuity of the smooth muscle layer of the bladder.

This is the first report in the literature of a vesicourachal diverticulum in a lamb, an urinary tract anomaly that has been infrequently documented and is considered rare in small ruminants. Given the asymptomatic progression until the development of uroperitoneum, it is plausible that this condition is underdiagnosed in the species. The rupture of a vesicourachal diverticulum can instigate severe complications by provoking the development of the uroperitoneum, which can lead to death. This condition should be included in the differential diagnosis of uroperitoneum in small ruminants along with obstructive urolithiasis.

ACKNOWLEDGEMENTS

This report was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasil - Finance code 001.

REFERENCES

  • CR-2024-0349.R1
  • BIOETHICS AND BIOSECURITY COMMITTEE APPROVAL
    We authors of the article entitled “Vesicourachal diverticulum in a Santa Ines lamb: a rare congenital anomaly” declared, for all due purposes, the project that gave rise to the present data of the same has not been submitted for evaluation to the Ethics Committee of the Universidade Vila Velha, but we are aware of the content of the Brazilian resolutions of the National Council for Control of Animal Experimentation - CONCEA <http://www.mct.gov.br/index.php/content/view/310553.html> if it involves animals. Thus, the authors assume full responsibility for the presented data and are available for possible questions, should they be required by the competent authorities.
  • DECLARATION OF USE OF ARTIFICIAL INTELLIGENCE
    Artificial intelligence tools were used to improve the quality of the manuscript.

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Publication Dates

  • Publication in this collection
    04 Aug 2025
  • Date of issue
    2025

History

  • Received
    25 June 2024
  • Accepted
    12 Mar 2025
  • Reviewed
    16 May 2025
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This is an open-access article distributed under the terms of the Creative Commons Attribution License
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