Axial hypocycloidal tomography of the orbits.

Axial hypocycloidal tomography has been applied to the investigation of 168 patients with suspected pathology in the orbit. Of these 75 had histological or angiographic confirmation of a space occupying lesion, and 55 patients showed positive evidence of abnormality. The X-ray changes observed include osteolysis and hyperostosis of the bony walls of the orbit, enlargement of the orbit-local and generalized, soft tissue abnormalities, and changes in the optic canal and superior orbital fissure. The most important evidence of the presence of a tumour or granuloma in the orbit was given by a positive "medial wall sign". This consists of a flattening or incurvation of the medial boundary of the orbit, best demonstrated by axial tomography. The sign was seen in 36.6 per cent of patients with proven intra-orbital space occupying lesions in the series. Axial hypocycloidal tomography is now an indispensable part of the diagnostic evaluation of patients with suspected orbital tumours and the procedure is complementary to other non-invasive investigations of the orbit, such as axial computerized tomography and ultrasonography.