ABSTRACT
Objective To investigate HR-MR imaging characteristics of non-Hodgkin lymphomas (NHL) of the orbits in extraconal compartment. Methods The HR-MR images of 16 patients with NHL of the orbits identified pathologically were retrospectively analyzed. MRI of the orbit at a 1.5 T scanner was performed with 4-cm surface coil, thin slice, suitable bandwidth, small FOV, and large matrix. T1-weighted (before and after i.v. bolus injection of contrast medium) and fast spin-echo T2-weighted sequences were acquired in all patients. All cases were performed with fat suppression techniques. The analyzed criteria of imaging appearance included location, number, size, shape, margins, extension, adjacent structures, and signal intensity of the lesions. Results The lesions in 13 of 16 cases located in anterior part of extraconal compartment, posterior to the orbital septum, and with irregular cast shape. The other 3 patients showed diffuse lesions with infiltration in extraconal compartment and with irregular shape. Eleven lesions had the large volume above 3.0 ml, 4 lesions with medium volume ranging from 1.0 to 3.0 ml, and only one with small volume less than 1.0 ml. 13 cases had a poor-defined margin with infiltration of extraocular muscles, but without mechanical shift of the muscles. 7 patients had infiltration of eyeball, but only 3 cases with exophthalmos. Destruction of orbital bone was evident in 2 cases with diffuse lesions but never in isolated orbital lymphoma. On the T_1-weighted images, the signal intensity of the lymphoma was isointense compared with that of the muscle in all patients. The T_2-weighted fast SE images showed a hyperintense signal in 13 cases and intermediate in 3 cases. All lesions enhanced after intravenous Gd-DTPA administration, 15 cases with homogeneous enhancement, and 10 cases with reliably visible enhancement in the T_1-weighted fat-suppressed sequences. Conclusion Most NHL of the orbits in extraconal compartment have the characteristic findings on HR-MR imaging, including anterior part of extraconal compartment location, posterior to the orbital septum, irregular cast shape, large volume, poor-defined margin with infiltration but without mechanical shift of extraocular muscles, uniform signal characteristics and marked enhancement after injection of contrast medium, and without bony destruction in isolated orbital lymphoma. The understanding of HR-MRI features of orbital NHL in extraconal compartment is very useful for making the differential diagnosis with other orbital diseases.