CT findings in orbital tumours of nerve sheath origin

The clinical and CT features of orbital nerve sheath tumours (13 neurofibromas and 17 neurilemmomas, including one malignant neurilemmoma) have been reviewed. The commonest clinical findings were proptosis, mild impairment of visual acuity and disorders of eye movements. No significant correlation with intra- or extraconal location and these symptoms was found. The two types of tumour were morphologically similar, most being smooth retrobulbar masses, elongated in the long axis of the orbit; lobulation was slightly more common with neurofibromas. The neurilemmomas were generally larger than the neurofibromas. The distribution of neurilemmomas in the retrobulbar space, and in its intra- and extraconal compartments appeared random, but most neurofibromas occurred in the upper orbit and three quarters lay extraconally. The apex of the orbit was seen to be clear of tumour in all intraconal neoplasms (except the one case of malignant neurilemmoma); this observation may be useful in differentiation from intrinsic optic nerve tumours and pseudotumour. Focal or generalised enlargement of the bony orbit was common, being seen in four-fifths of neurilemmomas and three-quarters of neurofibromas. Tumour density was homogeneous for all the neurilemmomas and in the majority of neurofibromas: attenuation coefficients were slightly higher for the neurofibromas. Subcutaneous extension was more common in neurofibromas, occurring in approximately one third of cases but was observed in about a tenth of the neurilemmomas. Enhancement with intravenous contrast medium was variable; contrast medium was helpful in showing intracranial extension. Although the CT findings did not allow unequivocal presurgical diagnosis, they were suggestive in many cases and facilitated biopsy.