GENERAL CONSIDERATIONS

Pathophysiology

•rhabdomyosarcoma is a very rare tumor which arises from pluripotential mesodermal cells of the urogenital ridge or similar cells in the Müllerian and Wolffian ducts during embryogenesis

•rhabdomyosarcoma is characterized by local invasion with metastasis either rare or late in the course of disease

•subtypes of rhabdomyosarcoma: embryonal, alveolar, and pleomorphic

•subtypes are difficult to differentiate histologically and electron microscopy, immunohistochemistry (i.e., myoglobin and desmin) ± DNA ploidy may be required for definitive diagnosis

•gross appearance: friable grape-like cluster or polypoid mass in the trigone or neck of the bladder causing urinary tract obstruction, hydronephrosis, and hydroureter

•hypertrophic osteopathy without pulmonary metastasis is a common paraneoplastic syndrome

•metastatic sites include mesentery, omentum, regional lymph nodes, adrenal gland, and liver

DIAGNOSIS

Signalment

•young, large breed dogs < 2 years

•no sex predilection in dogs

•breed predisposition: Saint Bernard

 

Clinical Signs

•dysuria, hematuria, pollakiuria, and stranguria

•vaginal discharge

•urinary obstruction

•incontinence

 Urinalysis and Urine Sediment Cytology

•hematuria and proteinuria are consistent findings on urinalysis due to ulceration of the urothelial mucosa

•bladder wash cytology may improve diagnosis capabilities by reducing contaminants

Blood Tests

•hematology and serum biochemistry findings are usually normal or non-specific

•mild to moderate normochromic, normocytic anemia can be caused by either hematuria or bone marrow suppression secondary to chronic disease

•uremia may result from neoplastic obstruction of urinary outflow or age-related renal failure

Imaging Studies

Survey Radiographs

•imagining techniques include survey abdominal and thoracic radiographs, contrast radiography, and CT

•survey radiographs: sublumbar lymph node enlargement, renomegaly, and metastatic disease in the pulmonary parenchyma or skeleton, particularly lumbar vertebrae and pelvis

•positive contrast cystography is useful for identification of mucosal abnormalities and space occupying lesions

•excretory urogram is indicated to determine the location and extent of obstructive urinary tract disease when the urethra cannot be catheterized

Ultrasonography

•ultrasonography is recommended to determine the location and extent of bladder involvement, regional lymph node size and appearance, and involvement of adjacent anatomical structures such as the colon

Biopsy

•biopsy is required for definitive diagnosis of urinary tract tumors

•biopsy techniques include FNA, needle biopsy, catheter biopsy, cystoscopic, and open surgery

•percutaneous biopsy procedures are not recommended due to the risk of tumor seeding

•catheter biopsy techniques correlate with surgical biopsy results in 73% of urethral and bladder tumors

•inflammation secondary to necrosis and ulceration is common and may result in false-negative findings

Clinical Staging

•Intergroup Rhabdomyosarcoma Study Committee Clinical Classification (postoperative staging system):

TREATMENT

Surgery

•surgical techniques for management of bladder tumors include:

•palliative procedures: tube cystostomy ± partial cystectomy

•curative-intent procedures: partial cystectomy and total cystectomy with urinary diversion

•cystostomy tube can be placed percutaneously or with either laparoscopic or open surgery

•complications: stranguria, pollakiuria, hematuria, urine leakage around the stoma, and vesicoureteral reflux which predisposes to ascending UTI and tumor seeding of the upper urinary tract

Chemotherapy

•rhabdomyosarcoma is treated with a combination of surgery, radiation therapy, and chemotherapy in humans

•chemotherapy agents include vincristine, actinomycin-D, and cyclophosphamide

•prolonged clinical remission has been reported in 1 dog treated with partial cystectomy, cyclophosphamide, and doxorubicin

•partial response has been observed with vincristine, doxorubicin, and cyclophosphamide, but single agent doxorubicin was ineffective in another case

Prognosis

•prognosis for dogs with rhabdomyosarcoma is poor due to infiltrative growth and urinary tract obstruction

•multimodality treatment, especially chemotherapy, has improved the prognosis in children with rhabdomyosarcoma

•prognostic factors in humans include histologic type and grade, DNA ploidy, and clinical staging

•diploid embryonal rhabdomyosarcoma are more sensitive to chemotherapy and radiation therapy than aneuploid embryonal rhabdomyosarcoma