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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