Veterinary Society of
Surgical Oncology

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
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