ORBIT AND OPTIC-NERVE

The optic nerve is a fiber tract of the brain, and is not a true crani al nerve. Primary pathologic processes seen in the central nervous sys tem and its linings can therefore affect the optic nerve. Along their course the fibers of the visual pathways are also susceptible to secon dary extrinsic processes. The MR appearance of many of the primary and secondary processes that affect the optic nerve are characteristic. W here the imaging features of a process are not characteristic, a fairl y narrow differential diagnosis can be suggested depending on the imag ing appearance and anatomic location of the pathologic entity. This ar ticle is a categorical overview of the disease entities that may affec t the optic nerve and tracts. Pathologic processes are organized accor ding to the typical sites of involvement along the visual pathways, fr om the retina to the occipital cortex. Medical imaging, pathologic, cl inical, and epidemiological highlights are presented.