Abstract
Background:
Only 27 cases of equine conjunctival haemangiosarcoma have been reported in the literature over the past 37 years. Out of these, 22% of cases were lost to follow-up, 52% were euthanised and 26% survived. A scarcity of cases and information is available for this rarely seen conjunctival tumour.
Aim:
To describe the clinical features, management, and outcome for conjunctival hemangiosarcoma in seven horses in the UK.
Methods:
Optivet medical records were reviewed for equine cases seen, or advised on, with a histopathological diagnosis of conjunctival haemangiosarcoma between January 2013 and March 2023. Medical records were accessed for details of signalment, history, management, and follow-up. Histopathology was used to confirm the diagnosis of haemangiosarcoma and assess the surgical margins. Immunohistochemistry was performed in a minority of cases with poorly differentiated solid tumours to support vascular lineage.
Results:
Seven eyes from 7 horses (5 geldings and 2 mares) with a mean age of 16 years and median of 18 years (range 10-21 years) met the criteria. Serosanguinous discharge was seen in 6 eyes. All eyes were managed surgically; 4 by exenteration and 3 by conjunctivectomy/keratectomy. Adjunctive cryotherapy was performed in 2 eyes. Metastatic disease in the ipsilateral parotid salivary gland, confirmed with histopathology, was seen in 1 horse. Surgical margins were clear in all but 1 eye. Solar elastosis was noted in 5 eyes. All horses were healthy at the last follow-up (0.2 – 5 years, mean 2.9 years, median 2 years).
Conclusion:
Equine conjunctival haemangiosarcoma is rare. Serosanguinous ocular discharge is a common clinical sign. Early surgical excision is highly effective. Solar elastosis is a common histopathological feature, suggesting a role for UV-light in the pathogenesis.

Key words: Haemangiosarcoma, Solar elastosis, Vascular tumour, Ocular tumour, Conjunctival tumour