Bladder duplication (BD) is a rare and congenital anomaly that occurs mostly in infancy and childhood in both humans and companion animals [4, 9]. Currently, the literature on BD in humans is limited to case reports and case series with no more than 90 cases since 2015 [4, 10]. For companion animals, cases reported in cats and dogs are extremely rare, with only one case in cats and 12 cases in dogs illustrating BDs and other urogenital duplications. In this case, the cat was diagnosed with complete bladder duplication with two accessory tubular tissues according to Abrahamson [11]. Complete duplication has been reported in dogs and one cat [5, 12–14]. In our patient, the morphology of the accessory bladder was an obstructed chamber, which was joined to the primary bladder by tubular tissue. The tubular tissue with one side tightly connected to the accessory bladder and the other side of the tube branched off and attached to the dorsal neck of the primary bladder (Fig. 6).
Figure 6 Diagram of bladder duplication in a cat. The pink region of the Hermosa ovary is the primary bladder, and the green region is the accessory bladder and the attached tubular tissue (arrow).
The pathogenesis of BD is still unclear. Researchers have investigated this kind of urogenital anomaly in humans since abnormal primordia develop during the foetal period. The theory that ‘twinning of the embryo tail’ conceivably refers to the concurrence of duplicated bladders and other duplications, such as colons and genitalia, in the presence of a normal vertebral column [6]. Another theory given by Satter and Mossman, named the “double allantoic duct” [7], explains that the anomaly is initiated by the urogenital sagittal septum, doubling the original endodermal allantoic. However, neither of the two classical theories implies that skeletal duplication relatively rarely occurs in BD patients [6, 7, 15, 16]. The embryogenesis of other duplicated organs is illustrated. The development of uterus didelphys is due to the failure of the fusion of paramesonephric structures, which are called the Mullerian and Wolffian tubes [8]. It is known that ureteral sprouts also originate from Wolffian tubes [17], which suggests a possible association between the development of the urinary system and the ‘Mullerian ducts and Wolffian tubes system’. The generation of the urinary system is highly associated with the reproductive system, and a high incidence of anomalies associated with BDs, which is merely 85%, has been reported in humans [6, 18, 19]. Statistically, 40–56% of BD patients have colon duplication and other anorectal anomalies. Nearly 90% of BD females have duplicated vaginas. Approximately 10–15% of BD patients intend to have spinal malformations [15]. A dog was diagnosed with bladder duplication along with duplication of the urethra, cervix, and vaginal canal [9]. It was also observed in a cat with posterior duplication of the alimentary and urogenital system as well as the vertebral column and spinal cord [16]. In this case, the tubular tissues were associated with anomalies, which simultaneously occurred in BD patients. Moreover, the history of right undescended testis in our patient was similar to that of cryptorchidism in BD patients, both humans and dogs [6, 13, 14].
In this patient, vomiting and constipation were the only clinical symptoms. Without further imaging diagnostic tools, we were unable to diagnose BD and other urogenital anomalies. Like other BD cases in humans, the clinical signs are usually nonspecific if no underlying infection occurs. In many cases, it is only recognized and diagnosed when an external anomaly such as a duplicated genitalia or anus is present. An 18-month-old girl who presented with external anomalies of a cloacal exstrophy variant with an imperforate anus was subsequently diagnosed with BD by computer tomography (CT) [20]. The patient was a 4-year-old boy with a chronic history of intermittent abdominal pain and stunted growth for 2 years. He was not initially diagnosed with any specific disease until an advanced imaging diagnostic tool was used [21]. Generally, BD has no pathognomonic or specific signs, and for a majority of time, it can be a disease of incidental diagnosis both in humans and companion animals.
Congenital urogenital malformations can be hard to diagnose, and special investigations are commonly performed to establish anomalies. In fact, various diagnostic methods have been used in human medicine for further study of congenital urinary anomalies [4, 20, 22]. Some of these materials have been used in veterinary medicine. Many radiographic techniques for diagnosing BD patients in humans and companion animals have been reported. Cystography is a contrast radiographic technique that uses X-rays or CT to assist in the detection of abnormal bladder morphology in cats [23]. A female cat with complete BD underwent negative contrast cystography to determine the location of the bladder and its integrity [5]. It further identifies whether the bladder is duplicated or the ureter is dilated [5]. Cystoscopy is applied to effectively assess the vagina, urethral opening, urethra, bladder, and ureteral openings in most cats [24]. In humans, cystoscopy was performed on urethras to determine the BD [7, 15, 22]. However, it has not been utilized to diagnose BD in animals before this case. Moreover, vaginocystourethrograms are helpful for diagnosing BD caused by duplication of the urethra, cervix, and vaginal canal in both humans and companion animals [5, 9]. Voiding cystourethrography (VCUG) is most often used to diagnose BD and several other urogenital anomalies in human infants and children [4, 20]. Due to the high morbidity of duplicated ureters in BD patients, subsequent intravenous urography (IVU) of BD patients is recommended for further investigation [9, 11, 16]. IVU has been applied in cats with urinary incontinence to reveal the renal function and morphology of the ureter [5, 11, 25–27]. However, this technique has been largely replaced by CT urography in human medicine [28]. In our patient, we performed cystography to locate the urinary bladder, which was confirmed to be the primary bladder after exploratory laparotomy and histopathological diagnosis. We considered CT a preferable exam for the diagnosis of accessory bladder and blind ending tubular tissues. Because there is no way for contrast agent to enter the duplicated bladder, the duplication is not visualized. We suggest using more advanced diagnostic tools to provide veterinarians with a more comprehensive surgical plan.
The principle of BD treatment needs to be individualized to each patient, depending on the patient’s symptoms and associated conditions. In human patients, surgical treatment for those with complete bladder duplication should be postponed until the patients reach the age at which their bladders become more functional to identify [4]. In general, the goal of surgical intervention is to optimize bladder function and drainage as well as minimize incontinence and the risk of infection. To date, the most common surgical treatment for complete BD is to excise the duplicated bladder. The open approach for excision has been the most common choice both for humans and for companion animals [22]. Laparoscopic excision of complete bladder duplication was applied on a 1-year-old male in 2018 [22], suggesting that this technique is a desirable minimally invasive approach utilized for complex urinary anomalies in children. For the affected cat in our patient, excision of the accessory bladder was properly implemented due to inflammation and compression of other organs. Therefore, the cat can eradicate all sources of infection and restore its urogenital tract as anatomically and physiologically normal as possible. The prognosis depends on several factors, including the degree of obstruction and where the anomaly has been impaired, associated anomalies and secondary infections [11]. Canine patients have a good prognosis if they do not have any other skeletal or urogenital anomalies identified and if surgical corrections are to be performed [9].