PURPOSE: The purpose of this study was to describe the MR imaging and CT findings of intracranial inflammatory pseudotumors. MATERIALS AND METHODS: We reviewed the MR imaging (n=8) and CT (n=4) studies of eight patients (M:F = 4:4, mean age: 41 years) with pathologically proven intracranial inflammatory pseudotumor. The findings were then evaluated with regard to location, shape, MR signal intensity, CT density and degree of contrast enhancement of the lesion, surrounding parenchymal edema, adjacent bone change and the location of accompanying extracranial lesion. RESULTS: In two patients, the parietal convexity was involved unilaterally, with no extracranial mass, and in the other six, the middle cranial fossa was involved unilaterally and extracranial mass was present. The lesion also involved the tentorium in four cases, the cavernous sinus in four, the anterior cranial fossa in one, and the posterior cranial fossa in one. The location of extracranial mass was the mastoid and middle ear cavity in two cases, the infratemporal fossa in two, both the infratemporal fossa and paranasal sinuses in one, and the orbit in one. MR images showed diffuse dural thickening in all eight cases, leptomeningeal thickening in four, and focal meningeal-based mass in two. As seen on T1-weighted images, the lesions were isointense to gray matter in eight cases, and on T2-weighted images were hypointense in seven cases and isointense in one. Marked homogeneous contrast enhancement was seen in all eight cases. The lesions seen on brain CT, performed in two cases, were isodense. Adjacent brain parenchymal edema and the destruction of adjacent bones were each seen in five cases. CONCLUSION: The characteristic MR findings of intracranial inflammatory pseudotumors are(1) diffuse dural thickening;(2) a focal meningeal-based mass which on T2-weighted images is seen as hypointense; and marked (3) contrast enhancement : these findings are, however, nonspecific. In order to differentiate these tumors, an awareness of these findings is, however, useful.