A preliminary evaluation of fine matrix computerized axial tomography (Emiscan) in the diagnosis of orbital space-occupying lesions

Abstract

The application of fine matrix computerized axial tomography (Emiscan) to the diagnosis of orbital space-occupying lesions is described. In this preliminary study 24 patients have been examined for a suspected orbital tumour with verification of the type of lesion present in 17. These comprised a wide variety of pathological states in the orbit, including examples of meningiomata, haemangioma, neuri-lemmoma, pseudotumour, melanoma and lacrimal gland tumours. A single example of an arterio-venous malformation, confirmed by arteriography, was included in the series. These patients were also examined by other techniques of orbital investigation, viz. orbital venography, axial hypocycloidal tomography and ultrasonography (B scan and holography). A comparison of these various investigations showed a diagnostic accuracy for Emiscan of 76·5 per cent, orbital venography 76·5 per cent, axial hypocycloidal tomography 75 per cent, and ultrasound 62·5 per cent. Preliminary results show that Emiscan is a very accurate new method of investigating the orbit. Modification of the original scanner by employing a matrix of 160×160 cells has greatly increased the diagnostic potential of the method, and has brought optic nerve abnormalities well within the diagnostic range of the apparatus. The Emiscan is complementary to existing procedures and should be combined with other non-invasive methods of examination such as axial hypocycloidal tomography and ultrasonography. This study has also shown that routine orbital venography is still a necessary investigaton in patients with suspected intraorbital space-occupying lesions, and because of the high proportion of vascular anomalies found in the orbit, carotid angiography is also required in selected cases for complete diagnosis.