Granular cell tumours of the orbit.

Granular cell tumours are uncommon benign tumours, occurring in various sites in the body, and very rarely in the orbit or ocular adnexa. Four cases of orbital granular cell tumour are described, with detailed light and electron microscopic description of one tumour arising in the orbital apex of a child. The histogenesis of granular cell tumour is uncertain, with many authors proposing an origin from Schwann cells. In central nervous system granular cell tumours, an astrocytic cell origin has been proposed. Evidence is presented for an origin from astrocytes in a child whose tumour arose in or adjacent to the optic nerve.