T 1 and T 2 Measurements of Meningiomas and Neuromas Before and After Gd - DTPA 463

Seven patients with meningiomas and five patients with neuromas were examined with spin-echo sequences on a 0.35-T imaging system. Signal enhancement and relaxation rate increments with gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) were evaluated, as well as relaxation rate contributions, indicators of Gd-DTPA accessibility to the tissue water. The average signal enhancement rate with Gd-DTPA was higher in neuromas than in meningiomas, 148% and 84%, respectively, but this difference was poorly appreciated on enhanced images because of similar average postcontrast T1 values in both tumors. However, the average T1 relaxation increment was almost twofold higher in neuromas than in meningiomas, 318% and 162%, respectively, mainly deriving from longer intrinsic T1 values in neuromas. Also, there was a 25% increase in the average T2 relaxation rate in neuromas after Gd-DTPA together with a higher T2 contribution by Gd-DTPA, while such effects were hardly discernible in meningiomas, suggestive of greater accessibility of Gd-DTPA to the tissue water in neuromas. By electron microscopy, endothelial fenestration and open gap junctions are commonly found in capillaries of both tumors, functioning as the routes into the extracellular space where the major contrast effect' of Gd-DTPA can be expected. However, the open gap junctions are short and straight in neuromas, while they are tortuous and sinusoid in meningiomas. This may provide greater access for contrast material into relatively larger extracellular spaces in neuromas and may cause a greater T1 relaxation rate increment with Gd-DTPA. Although of limited clinical value, the different T1 and T2 relaxation rate increments with Gd-DTPA occasionally may provide useful information in the differential diagnosis, especially with mass lesions in the cerebellopontine angle and skull base. Gd-DTPA was found to provide useful information about T1 relaxation effects in meningiomas and neuromas and may help distinguish between them.