OBJECTIVE. This report illustrates the contrast enhancement characteri
stics on MR imaging of three patients with hypertrophic pachymeningiti
s and provides an explanation for the observed imaging findings. CONCL
USION. A differential pattern of enhancement, consisting of intense en
hancement of the peripheral margin of the abnormal pachymeninges, was
present in all cases. In two patients, much of the remaining abnormal
pachymeninges did not enhance at all. On the basis of the microscopic
pathology of hypertrophic pachymeningitis, the physiology of normal me
ningeal enhancement on MR imaging, and the described MR appearance of
other pachymeningeal lesions, this differential pattern of enhancement
should strongly suggest the diagnosis of hypertrophic pachymeningitis
.