Mystery Mass in a Maltese: The Hidden Urothelial Cyst

Journal of Veterinary Science 2025

Author

Obi Veterinary Education
March 28, 2026

Soobin Kim, Minjung Kang, Jihee Hong, Youngsuk Kim, Jaehwan Kim, Kidong Eom

Background
Cystic abdominal masses near the vaginal region in dogs can originate from multiple structures, but urothelial cysts—known in human medicine—had not previously been documented in dogs. These cysts may arise from periurethral glands and are often misdiagnosed due to nonspecific imaging and anatomical proximity to the bladder, uterus, or vagina. This case report presents the first confirmed occurrence of a urothelial cyst in a dog, emphasizing the need for differential consideration in similar clinical presentations.

Methods
An 18-year-old intact female Maltese dog was evaluated for a mammary nodule. Imaging studies—including radiographs, ultrasonography, and computed tomography (CT)—revealed a large cystic mass in the pelvic and abdominal cavity. Surgical excision was performed, followed by fluid analysis, cytology, and histopathology to characterize the lesion.

Results
Imaging showed a well-defined, large cystic mass with no direct connection to surrounding organs such as the bladder, urethra, or vagina. CT revealed a hypoattenuating fluid-filled mass with a contrast-enhanced smooth wall. Fluid analysis excluded urine as the source. Cytology showed exfoliated epithelial cells without malignancy. Histopathology confirmed the cyst was lined by transitional and stratified squamous epithelium, consistent with a urothelial cyst. The dog recovered uneventfully post-surgery.

Limitations
Hormonal assays (e.g., estradiol, progesterone) were not conducted, limiting insight into potential endocrine contributions. The rarity of the condition precludes generalization, and embryological origin could not be conclusively determined. This single case limits the scope for establishing prevalence or standardized management protocols.

Conclusions
This report establishes the urothelial cyst as a differential diagnosis for cystic masses near the vaginal region in dogs. Accurate diagnosis relies on advanced imaging and histopathology, as misidentification may lead to inappropriate treatment or complications. Complete surgical excision is recommended for definitive management and prevention of recurrence. This case underscores the need for heightened awareness and further research into such rare urogenital anomalies in veterinary practice.

Computed tomographic and intraoperative imaging features of a urothelial cyst. Postcontrast computed tomography images in the sagittal plane (A), dorsal plane (B) using a soft tissue window, and intraoperative image (C). A cystic mass (yellow asterisk) occupied the abdominal and pelvic cavities. The mass was in contact with the urethra (yellow arrow), vagina (red arrow), and bladder (red asterisk), but no direct connection to these structures was identified. Displacement of the adjacent organs caused by the mass was observed. The cystic mass (yellow asterisk) adhered to the bladder (red asterisk). A blunt dissection was successfully performed, revealing no connections between the mass and other structures, including the vagina, urethra, or bladder.

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