Case Number 12-114902
An Enlarging Pectoral Mass in a Thoroughbred Horse
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Stephanie M. Shrader, DVM1
Richard C. Weiss, VMD, PhD1
Fred Caldwell, DVM, DACVS2
1Department of Pathobiology2Department of Clinical Sciences Auburn University College of Veterinary Medicine
• 9-year-old, male castrated, Thoroughbred horse
• Firm mass extending from the right pectoral region to the right thoracic wall
• Kicked in this region by another horse several months prior to presentation
• Size of mass waxes and wanes • Painful on palpation• Starting to cause abduction of the scapula and
gait alteration
Signalment and History
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Image courtesy of Fred Caldwell, DVM, MS,
DACVS
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Image courtesy of Fred Caldwell, DVM, MS,
DACVS
• Ultrasound of the mass – mixed echogenicity• rDVM submitted samples for culture:
• Acinetobacter baumannii• Alpha hemolytic Streptococcus• Raoultella planticola
• Incisional biopsy diagnosed as a possible soft tissue sarcoma
• Corynebacterium pseudotuberculosis titer was negative @1:8
Other Diagnostics Performed
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1x, H&E
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1x, Trichrome
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20x, H&E
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20x, Trichrome
Musculoaponeurotic fibromatosis (desmoid tumor), diffuse, marked, chronic
Morphologic Diagnosis
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• First reported in a horse in 1983 (Ihrke et al., JAVMA, 183:10;1100-1102)
• Prior to that, reported as a rare non-metastasizing fibrous neoplasm in people
• Occurs in mid-cervical region of the neck and pectoral region
• Intralesional fluid-filled cavities associated with sterile inflammation have been described
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Musculoaponeurotic fibromatosis (desmoid tumor)
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• Criteria for diagnosis in people:• Hypocellular, unencapsulated, infiltrative mass• Composed of bands of mature fibrous tissue • Deep location and relationship to a musculoponeurotic
system• Diffuse growth with engulfment of muscle fibers
• Unknown etiology• Possibly secondary to trauma
• Prognosis• Variable
Musculoaponeurotic fibromatosis (desmoid tumor)
• Pool, R.R. (1990): Tumors and tumor-like lesions of joints and adjacent soft tissues. In Moulton, J.E. (ed). Tumors in Domestic Animals. 3rd ed. University of California Press, Berkley, 129-30.
• Cooper, B.J. and Valentine, B.A. (2002): Tumors of Muscle. In Meuten, D.J (ed). Tumors in Domestic Animals. 4th ed. Iowa State Press, Blackwell Publishing Company, Ames, 360-1.
• Ihrke P.J., et al, Fibromatosis in a Horse. JAVMA. 1983;183:1100-2.
• Valentine, B.A., et al., Intramuscular Desmoid Tumor (Musculoaponeurotic Fibromatosis) in Two Horses. Veterinary Pathology. 1999;36(5):468-70.
References
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• Dr. Weiss• Dr. Caldwell• Histopathology
laboratory• My fellow residents
And a Special Thanks To…
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