Primary cardiac T‐cell rich large B‐cell lymphoma causing aortic stenosis with metastasis in a Warmblood

Summary An 18‐year‐old Warmblood mare was presented to the Royal Veterinary College Equine Referral Hospital for investigation of progressive periocular and facial swelling, weight loss and tachycardia. Physical examination additionally identified bilateral pansystolic (grade 5/6 basilar left‐sided, 2/6 right‐sided), cardiac murmurs, submandibular lymph node enlargement and mucopurulent ocular and nasal discharge. Echocardiography identified heterogeneity and thickening of the cardiac valves and interventricular septum. Computed tomography revealed periocular soft tissue swelling but no convincing mass lesion. The mare was euthanised following deterioration in her cardiovascular status. Post‐mortem examination revealed extensive infiltration of all cardiac valves (pulmonic, aortic, mitral and tricuspid), interventricular septum and pulmonary artery. This case report describes a primary cardiac T‐cell rich B‐cell lymphoma manifesting in aortic stenosis‐induced forward failure, and highlights the importance of lymphoma as a differential for periocular swelling in the horse.