title: Canine orbital rhabdomyosarcoma: a report of 18 cases.
abstract: OBJECTIVE
  To describe clinical and pathological features of canine orbital rhabdomyosarcoma (COR).
  
  
  METHODS
  Retrospective review of patients with COR from the archives of the Comparative Ocular Pathology Laboratory of Wisconsin and the University of Wisconsin Veterinary Medical Teaching Hospital (1983-2014).
  
  
  RESULTS
  Eighteen cases of COR were identified, all diagnosed in an 8-year period (2006-2014). Affected dogs were typically young (range 1-8; median 2 years), and both sexes were equally represented. Common clinical signs included exophthalmos (16/18) with dorsolateral deviation of the globe (10/18) and elevation of the nictitans (12/18). Ultrasonography, performed in nine cases, revealed an orbital mass with mixed echogenicity and posterior globe indentation. Advanced imaging, performed in nine cases, demonstrated a soft tissue mass with variable contrast enhancement and lysis of the orbital bones (5/9). Histologically, all tumors were subclassified as embryonal rhabdomyosarcoma. All neoplasms demonstrated positive immunohistochemical labeling for desmin, and 14/18 were positive for skeletal muscle actin. Follow-up information was available for 15/18 cases. Older dogs, aged 6-8 years, had no clinical signs of recurrence or metastasis 8-13 months postdiagnosis (4/4). Most younger dogs (9/11), aged 1-4 years, were euthanized within 6 months (median 2.5 months) of diagnosis due to recurrence at the surgical site (5/9) and/or metastasis (5/9).
  
  
  CONCLUSIONS
  Canine orbital rhabdomyosarcoma is a highly malignant neoplasm in juvenile dogs, but may be amenable to surgical resection in older dogs. This duality in biologic behavior may reflect differences in tissue of origin between juvenile onset tumors and adult onset tumors.
authors.affiliation: Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Scott
authors.affiliation: Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, USA.
authors.forename: Leandro B C
authors.identifier: http://orcid.org/0000-0001-9960-678X
authors.initials: LB
authors.lastname: Teixeira
authors.forename: David J
authors.initials: DJ
authors.lastname: Flanders
authors.affiliation: Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, USA.
authors.forename: Richard R
authors.initials: RR
authors.lastname: Dubielzig
authors.affiliation: Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, USA.
authors.forename: Gillian J
authors.initials: GJ
authors.lastname: McLellan
mesh_terms: D000818:Animals; D004283:Dog Diseases / Q000000981:diagnostic imaging; D004285:Dogs; D005260:Female; D008297:Male; D009918:Orbital Neoplasms / Q000000981:diagnostic imaging / Q000662:veterinary*; D012208:Rhabdomyosarcoma / Q000000981:diagnostic imaging / Q000662:veterinary*
keywords: canine; neoplasia; orbital; retrobulbar; rhabdomyosarcoma