Liza Maria Mulder, Allan Beenakkers, Camille De Ley, Sofie Maes, Marianne De Ridder & Sarah van Rijn
Background
Extraskeletal osteosarcoma is a rare and aggressive neoplasm in cats, occurring outside the skeletal system in atypical locations such as the orbit, intestines, and subcutaneous tissues. It shares histological features with skeletal osteosarcoma but differs in clinical behavior and prognosis. This report describes the first documented case of ESOSA in the urethra of a cat, emphasizing the importance of considering neoplasia in the differential diagnosis of urethral obstructions.
Methods
A 9-year-old neutered male domestic shorthair cat presented with stranguria, dysuria, and haematuria. Initial imaging suggested a urethral urolith. Abdominal ultrasound revealed a calcified S-shaped structure near the proximal urethra. Surgery was attempted to remove the presumed urolith, but the lesion was embedded in the urethral wall. Due to poor prognosis, the cat was euthanized during surgery. Tissue samples were submitted for histopathological analysis.
Results
Histopathology revealed a non-encapsulated, moderately cellular mass with osteoid and cartilaginous matrix, diagnosed as a mixed osteoblastic/chondroblastic osteosarcoma. The tumor caused transmural expansion and necrosis of the urethral wall. No evidence of metastasis was found on imaging or during exploratory surgery. The neoplasm likely arose de novo in the urethra, representing an extremely rare presentation of feline ESOSA.
Limitations
The diagnosis was confirmed post-mortem, and no advanced imaging such as CT was performed preoperatively, which might have clarified the lesion’s nature and extent. Lack of surgical treatment or longitudinal follow-up prevents insights into therapeutic efficacy or progression.
Conclusions
This case highlights ESOSA as a rare but significant differential diagnosis in cats with urethral obstruction not consistent with urolithiasis. Advanced imaging is recommended when standard diagnostics yield atypical findings. The report underscores the diagnostic and therapeutic challenges posed by ESOSA and calls for further case documentation to enhance understanding of its behavior and optimal management.
Radiographs caudal abdomen. Radiographs of the caudal abdomen in left lateral (a) and ventrodorsal (b) projections, submitted by the referring veterinarian, show normal serosal detail in the caudal abdomen. A large, mineral-opaque structure is visible in the caudoventral abdomen, located between the urinary bladder and pelvic inlet, positioned on the right side of the midline. The ventral margin of this structure appears oval and well-defined, while the rest of the structure is irregular and poorly defined. In the ventrodorsal projection, the structure is partially obscured by the bony structures of the pelvis. All other aspects of the radiographs are within normal limits
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