RÉSUMÉ
<p><b>OBJECTIVE</b>To investigate the influence of MRI on the T, N staging system, 5(th) edition, UICC and the 92 staging system, China by comparing CT and MRI of the nasopharyngeal carcinoma (NPC).</p><p><b>METHODS</b>From 1993 to Dec. 2000, fifty-six NPC patients proved by pathology underwent CT and MRI examination with Philip T5-II ultra-magnetic system (0.5T) and Elscient CT twin flash. Routine axial scans by CT and SE sequence with axial, sagittal and coronal scans by MRI from oral pharynx (lower border of second cervical vertebra) to supracellar cistern were done with enhancement (50/56).</p><p><b>RESULTS</b>The tumor beyond the nasopharyngeal cavity was accurately defined because the pharyngobasilar fascia could be seen by MRI which appeared to be more sensitive than CT in revealing the invaded soft tissues surrounding the nasopharyngeal cavity, such as longus colli (14 by CT and 26 by MRI), tensor veli palatini and levator veli palatini (17 by CT and 42 by MRI), the skull base erosion (15 by CT and 23 by MRI) and enlargement of retropharyngeal lymph nodes (13 by CT and 24 by MRI). As a result, 28.6% (16/56) of NPC staging system, UICC and 33.9% (19/56) of the 92 staging system of China should undergo changes.</p><p><b>CONCLUSION</b>MRI is able to reveal the invasion extent into the structures around the tumor mass more accurately than CT, with the pharyngobasilar fascia readily seen and the infiltration and/or destruction of the skull base more easily visualized by MRI than by CT. The impact of MRI upon the 92 staging system of China lies in the differentiation of direct infiltration by the tumor from the enlargement of the retropharyngeal lymph node and the early detection of skull base erosion. The Influence of MRI on the staging system of NPC is more pronounced than that of CT.</p>