From Dog
Microscopic appearance of a cardiac rhabdomyoma in a dog, showing variably-sized ovoid to irregular, swollen myocytes[1]

Rhabdomyomas are benign solitary or multiple neoplasms that originate from striated muscles and characterized by heart disease or laryngeal tumors in young to middle-aged dogs[2].

Rhabdomyomas can occur in the myocardium of the heart and skeletal muscles of the larynx[3], tongue[4] and head, but are commonly reported in the left or right ventricle with lesser involvement of the atria[5].

Dogs clinically affected with cardiac rhabdomyomas usually present with signs related to heart disease, ranging from progressive lethargy, ascites, exercise intolerance, auscultatable murmurs to cardiomyopathy, congestive heart failure and sudden death[1].

Dogs with laryngeal rhabdomyomas usually present with progressive dyspnoea, exercise intolerance and stridor. A palpable tumor is often felt in the throat region[6].

Diagnosis is difficult antemortem, and usually relies on cardiac biopsy for definitive diagnosis. However, ultrasonography of cardiac rhabdomyomas usually reveal cardiomegaly, lactescent pericardial and serosanguineous pleural effusions as well as a visible intracardiac mass[7].

Histologically, these tumors appear as tightly arranged, large, variably sized, ovoid to irregular, swollen myocytes. Individual cells have variably distinct cell borders with a deeply eosinophilic cytoplasm and varying degrees of cytoplasmic vacuolation due to cytoplasmic glycogen accumulation.

Immunohistochemistry is usually negative for periodic acid-Schiff and strongly positive for myoglobin, desmin and phosphotungstic acid-hematoxylin[8].

Differential diagnosis include hemangiosarcoma, heartworm disease, oncocytoma[9], chemodectoma and lymphoma.

With laryngeal rhabdomyomas, complete surgical extirpation is usually curative[10].

A guarded to poor prognosis is associated with cardiac rhabdomyomas.


  1. 1.0 1.1 Radi ZA & Metz A (2009) Canine cardiac rhabdomyoma. Toxicol Pathol 37(3):348-350
  2. Meuten, DJ (2002) Tumors of muscle. In Tumors in Domestic Animals (D. J. Meuten, ed.), pp:319–363. Iowa State University Press, Ames, Iowa
  3. Liggett AD et al (1985) Canine laryngopharyngeal rhabdomyoma resembling an oncocytoma: light microscopic, ultrastructural and comparative studies. Vet Pathol 22(6):526-532
  4. Rivera RY, Carlton WW (1992) Lingual rhabdomyoma in a dog. J Comp Pathol 106(1):83-87
  5. Szuperski, T (1951) Rare case of cardiac rhabdomyoma in a dog. Med Weter 7(2):120-121
  6. Clercx C et al (1998) Laryngeal rhabdomyoma in a golden retriever. Vet Rec 143(7):196-198
  7. Mansfield CS et al (2000) Intra-atrial rhabdomyoma causing chylopericardium and right-sided congestive heart failure in a dog. Vet Rec 147(10):264-267
  8. Dunbar MD et al (2012) Laryngeal rhabdomyoma in a dog. Vet Clin Pathol 41(4):590-593
  9. Meuten DJ et al (1985) Canine laryngeal rhabdomyoma. Vet Pathol 22(6):533-539
  10. O'Hara AJ et al (2001) Laryngeal rhabdomyoma in a dog. Aust Vet J 79(12):817-821