A four-year-old, male, Labrador retriever was referred for removal of a
spindle cell sarcoma involving the right jugular vein. A post-contrast CT scan showed a seven-centimeter subcutaneous mass originated from the right external jugular vein, which was partially obstructed and showing contrast stasis, suggested a primary intravascular
tumor of the jugular vein. The mass was resected, and histological evaluation was consistent with grade II intravenous
spindle cell sarcoma of the jugular vein. Immunohistochemical positivity for
vimentin,
desmin, and αSMA antibody and negativity for
S-100 protein confirmed venous
leiomyosarcoma. The dog received five doses of intravenous
doxorubicin, and there was no recurrence of the
tumor 30 months post treatment. In dogs, primary intravascular
sarcomas are rare and primary venous
leiomyosarcoma has not been described. A venous
tumor may be considered as a differential diagnosis in dogs with ventral neck swelling.