Enlarged ovary in a mare: review of the literature and a case report

Mares regularly have an enlarged ovary. The main causes are haematomas, anovulatory follicles, abscesses, and neoplasia. The granulosa-theca-cell tumour is by far the most common neoplasia of the ovary (about 97%) and accounts for 2.5% of all equine tumours. In this article the differential diagnosis of an enlarged ovary and the background of granulosa-theca cell tumours are reviewed. A case is described of a mare with a very large granulosa-theca cell tumour in the left ovary, which was discovered 1 month after delivery of a healthy foal. This case is special not only because the tumour was enormous (diameter 60 cm) but also because the contralateral ovary was functional and there were no behavioural changes. The fact that a haematoma had been found 2 years earlier made the diagnosis even more difficult.