Background & objective: With the general using of computed tomography (CT) and magnetic resonance imaging (MRI), it is important to determine which method is more sensitive in detecting the skull base encroachment in clinic. This article was designed to investigate the diagnostic value of CT and MRI in detecting the skull base erosion in nasopharyngeal carcinoma patients.
Methods: Sixty-one cases pathologically proven as nasopharyngeal carcinoma were selected from August 1993 to September 2001. three-dimensional reconstruction with spiral CT thin slices scan were performed in 8 cases. CT scan was performed with Elscient CT Twin Flash; axial scan was parallel to the OM line routinely from soft palate to the suprasellar cistern. There were 13 cases with enhancement scan. MRI scan was performed by Philips T5-II super-conducting magnetic resonance imaging system (0.5T). The standard quadrature head coil was used. Routine axial, sagittal, and coronal image with SE sequences were obtained. Scanned field ranged from the soft palate to the suprasellar cistern. After plain scan, enhanced scan was performed in 55 of 61 cases.
Results: MRI discovered the skull base encroached more precisely than CT, 17 cases by CT and 26 cases by MRI, respectively. The early bone marrow infiltration was seen at clivus, basilar pterygoid, and basilar sphenoid in 6 cases by MRI scan while CT scan showed no abnormal lesion at these sites. In addition, MRI revealed nasopharyngeal carcinoma tissue infiltrated along the mandibular nerve (3 cases) while CT scan showed no change of these structures.
Conclusion: Both CT and MRI can reveal that the tumor encroaches on the skull base by either destroying the bony structure or breaking through the natural foramen. MRI is more sensitive than CT in detecting the skull base encroachment. MRI could reveal the early infiltration of the bone marrow and tumor infiltration along the mandibular nerve. MRI confirms the dimension of nasopharyngeal carcinoma more precisely than CT. The three dimension reconstructional spiral CT was directer in discovering the dimension of the tumor.