Primary orbital meningioma: a review of 41 patients investigated radiologically.

The X-ray features in 41 patients with histologically verified primary meningiomas in the orbit are reviewed. These tumours arise from the sheath of the optic nerve (78%) or extradurally within the orbit, remote from the nerve (22%). Sheath meningiomas occur predominantly in middle-aged women. Characteristically they give little sign of their presence on plain X-rays, but may show minor variations in the size of the optic canal (22%) or calcification in the tumour (12.5%). The radiological diagnosis is based upon the computed tomography (CT) findings. Visual deterioration in a middle-aged or elderly patient with obvious optic nerve enlargement on CT and minimal or no enlargement of the optic canal is virtually diagnostic of a sheath meningioma. Primary extradural meningiomas in the orbit usually present with proptosis before compressing the optic nerve. The majority of these show some plain X-ray evidence of their presence such as localised or generalised orbital enlargement, hyperostosis of the orbital walls, or changes in the adjacent sinuses. In this group the tumour may be located inside or outside the rectus muscle cone and the CT changes are usually non-specific.