Congenital Fetal Rhabdomyoma in a Thoroughbred Filly Foal

• Congenital fetal rhabdomyoma is a differential diagnosis for a proximal cervical mass in the foal.
• Diagnosis is confirmed using desmin immunohistochemistry on biopsy samples.
• Surgical excision is curative with an excellent prognosis for full recovery.

A Thoroughbred filly foal was presented 12 hours after birth for evaluation of a cranioventral cervical mass. A congenital tumor was suspected after ultrasound examination, fine needle aspirate, and biopsy of the mass. Desmin immunohistochemistry on a section of the mass after surgical excision confirmed a diagnosis of fetal rhabdomyoma, a rare congenital tumor only reported once before in a foal. In the short term, wound complications occurred, but the filly had no long-term complications and subsequently raced successfully. This report outlines the differential diagnoses for cranioventral cervical masses in the foal, the approach to diagnosis, and outlines the difficulties encountered in the removal of masses in this region.