Skull base erosion in nasopharyngeal carcinoma: detection by CT and MRI.

It is generally accepted that computed tomography (CT) is superior to magnetic resonance imaging (MRI) in demonstrating bony erosion while MRI is better in delineating soft tissue abnormality. The ability to detect skull base erosion by CT and MRI was compared in a retrospective study of 114 patients with nasopharyngeal carcinoma (NPC). Involvement of the following structures was demonstrated on CT and MRI: pterygoid plates [CT--10 (9%) patients, MRI--8 (7%) patients]; pterygoid process [CT--22 (19%) patients, MRI--22 (19%) patients]; clivus [CT--17 (15%) patients, MRI--26 (23%) patients]; petrous apex [CT--20 (18%) patients, MRI--34 (30%) patients]; sphenoid body/sinus [CT--31 (27%) patients, MRI--32 (28%) patients]; sphenoid wing [CT--12 (11%) patients, MRI--16 (14%) patients]. Erosion of the foramen ovale could be seen on CT in 19 (17%) patients but tumour was noted in the foramen in 28 (25%) patients using MRI. Contrary to common belief, MRI appears to be more sensitive in detecting bony involvement in the petrous apex, the clivus and the sphenoid wing. MRI is, therefore, the preferred technique in demonstrating skull base involvement.