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.(ABSTRACT TRUNCATED AT 250 WORDS)