What could casuse a fleshy mass growing behind the optic nerve?

Multiple things. Jerry and carol shields presented data on orbital tumors at the 2002 montgomery lecture. A variety of tumors and pseudotumors can involve the orbit. In this series of 1264 lesions, 64% were benign and 36% were malignant. The percentage of malignant tumors increased with age, with malignancies being common in older patients because of the higher incidence of lymphoma a metastasis.