From Dog
A smooth-surfaced, multinodular myxosarcoma fills the lumen of the left atrium and is adherent to the interatrial septum[1]

Myxosarcoma are a locally invasive and metastatic tumor of canine connective tissue.

These are a malignant tumor of primitive pleomorphic fibroblasts that produce excess mucin.

These slowly growing tumors will cause clinical signs only when they impinge on adjacent structures. Primary tumors have been reported in the long bones, subcutaneous connective tissue, vertebrae[2], skull[3], brain[4], heart[5], pericardium[6] and lungs (endobronchial polyposis)[7].

Clinically affected dogs often present with cardiac or pulmonary involvement, and symptoms include pyrexia, dyspnoea and tachycardia. Regional lymphadenopathy may be observed with cutaneous myxosarcomas.

Diagnosis is based on clinical presentation with supportive histopathology examination of biopsied material.

These tumors commonly appear as atypical mesenchymal cells in a dense eosinophilic background, interpreted as consistent with the presence of a matrix-secreting tumour[8].

A variant form involves myxosarcoma with adrenal adenoma and pituitary hyperplasia (Carney syndrome)[1].

A differential diagnosis would include osteoma, giant cell tumor, bone cyst, fibrosarcoma, osteochondroma, chondrosarcoma, polyostotic lymphoma and Spirocerca lupi.

Treatment usually involves wide-margin surgical resection with or without radiation therapy.

The prognosis is usually good but recurrence is common.


  1. 1.0 1.1 Adissu HA et al (2010) Cardiac myxosarcoma with adrenal adenoma and pituitary hyperplasia resembling Carney complex in a dog. Vet Pathol 47(2):354-357
  2. Kunkel KA et al (2007) Imaging diagnosis - spinal myxosarcoma in a dog. Vet Radiol Ultrasound 48(6):557-559
  3. Dennis R (2008) Imaging features of orbital myxosarcoma in dogs. Vet Radiol Ultrasound 49(3):256-263
  4. Richter M et al (2003) Myxosarcoma in the eye and brain in a dog. Vet Ophthalmol 6(3):183-189
  5. Briggs OM et al (1997) Right atrial myxosarcoma in a dog. J S Afr Vet Assoc 68(4):144-146
  6. Foale RD et al (2003) Left ventricular myxosarcoma in a dog. J Small Anim Pract 44(11):503-507
  7. Hill RC et al (2008) Endobronchial polyp derived from a myxosarcoma in the lung of a dog. J Am Anim Hosp Assoc 44(6):327-334
  8. Sommerey CC et al (2012) Intrathoracic myxosarcoma in a dog. J Comp Pathol 147(2-3):199-203