Case report of granular cell myoblastoma arising within the medial rectus muscle.

A rare case of granular cell myoblastoma is reported in a 37-year-old man where the tumour was situated within the medial rectus muscle. Histological, cytochemical and ultrastructural examination showed it to have features typical of granular cell myoblastoma. It also reacted with chorioembryonic antigen antisera, a sign of primitive cell origin. The findings add further weight to the idea of the histiogenesis of these tumours from primitive mesenchymal cells.