254 NMR Imaging in the Evaluation of Orbital Tumors R. C. Hawkes,1 G. N. Holland ,'·2 W. S. Moore, ' S. Rizk,3 B. S. Worthington, 4 and D. M. Kean 4 The application of nuclear magnetic resonance (NMR) imaging to the diagnosis of orbital space-occupying lesions was studied in group of 28 patients with a wide range of pathology . The NMR findings in six patients are illustrated. The results of the NMR scans are compared with the information that can be derived from conventional neuroradiologic procedures , including com- puted tomography. The value of the multiplanar facility of NMR is emphasized . It provides accurate volumetric information and establishes the precise topographical relationships of tumors to normal structures . The muscle cone and the optic nerve can be identified in the axial , coronal , and sagittal planes. Current limitations of the method and possible future developments to improve diagnostic precision are discussed. Proton nuclear magnetic resonance (NMR) imaging has under- gone a rapid evolution. Techni ca l advances no w a ll ow production of images with quality rivaling that of the earlier ge nerations of comput ed tomogr aphic (CT) scanners. NMR also reveals tissue properties hitherto in accessible to study . These capa bilitie s, to- gether with the total avoidance of ionizing radiation and the absence of any demonstrable hazard, make it an espec ially attr act ive imaging techiqu e. The multi planar f ac ility is part icularl y valuable in the study of orbital disease, avoiding as it does the time and radiation dose penalty of reformatting techiques . Materials and Methods Using a Pi cker resistive NMR unit, we studied a series of 24 pa ti ents who presented with unilateral proptosis , and fo ur patient s with intraocular tumors (melanoma). Among the 24 there were nine case of dysthyro id proptosis, thr ee of intraco nal tumors, six of extraconal tumors, five of tumors invading the orbit , and one per i- orb ital lesion. The sca ns were obtained in a st eady-s tate fr ee- precession sequence. Eac h sect ion took 2 min to produce and was 1 cm thick. Results and Discussion In NMR as in CT, or bital examinations display th e orbs , extr aoc u- lar muscles, and opt ic nerves co ntrasted aga inst the high signal of the retrobulbar fat. Di sadvantges of NMR imaging are th at ca lcifi- cation is not seen, and that the margins of co rtical bone are on ly 1 Department of Physics. University of Nottingh am. En gland. 2Present address: Pi cke r International. Highland Heights . OH 44 143. 'Depar tm ent of Ophthalmology . University of Nottingham. England. defined where it in ter faces with soft tissue. In transverse sections in a normal subj ect look ing left and right, the change in size of the medial and lateral rec ti and the movement of the optic nerve are clea rl y shown (fig. 1). In a few patients, unilateral proptosis may be due to an intracra- nial cause. The first patient we examined by NMR had a large parasellar aneur ysm, ca using proptosis , which was associated with nerve III palsy and retrobulbar pain [1]. Occasionally, giant pituitary tumors may encroach on the orbit; we had one case where this was clearly depicted on co ronal sect ions. More frequently, the extraorbital ca use of proptosis is to be found in the paranasal sinuses or nasopharynx, and is usually the result of tumor , infection, or mucoce le. In a case of Ewing sarcoma arisin g from the ethmoidal sinuses the tumor encroac hment on the orbit was demonstrated together with the co nsequent lateral dis locati on of the orb. En croac hment on the orbit by an intrinsic abnormality of the bone forming its bound aries is a rare cause of proptos is, but one in w hi ch NMR proved most useful. In a patient with fibrous dysp lasia, gross bone thickening prec luded an adequate examination of the orbit al co ntents by CT; however, as the abnormal bone is practic all y invisible on NMR, a mor e satisfac tory examination was therefore possible using this technique. Another impor tant practical prob lem is the identification of those patients with dysthyroid disease, the most co mmon ca use of prop- tosi s. Although most cases can be recognized clinica ll y and th e diagnosis co nfirmed by immunologic test s, there is a minority for which diagnosis is unclear. These patients must be separated from those who have impalpable tumors in the muscle cone causing axial proptosis. In NMR as in CT, the thi ckened r ect us muscles arE clearly shown in a ll thr ee planes, but th e coro nal plane shows th e extraocular mu sc les most co mpletely, and is the most useful for distinguishing cases of dysthyroid proptosis from tumor- cause d proptosis . Occasionally (as in the patient shown in fig. 2) there is selec ti vE in volvement of the muscles, and a discrepancy is visible betweer the enlarged inferior rectus mu sc le and the norma l super ior rectu, mu sc le. Both NMR and CT ca n take the diagnosis beyond thE indi ca ti on of the presence of an o rbit al mass by identifying the si ll of or igin of the mass, and, in part icular, whether it is intraconal 0 extraco nal. The shape and sharpness of the bounda ri es of the mas'. and its density provide import ant diagnostic feat ures. Tumors as soc iated with the op ti c nerve (both intr insic and sheath tumors) cal be clear ly identified as arising from the nerve. For example, in ou ' Department of Academic Radiol ogy , Queen's Med ica l Centre. University of Nottingham. Nottingh am, NG7 2UH, England. Address reprint requests to B. !' Worthington. AJNR 4: 254-256, May / June 1983 0195 -6108 / 83 / 0403-0254 $00.00 © American Roentgen Ray Society