Diffuse cerebral and leptomeningeal astrocytoma in dogs: MR features.

Magnetic resonance (MR) imaging has increased sensitivity in detection of nonenhancing brain tumors and may show the extent of CNS neoplasia with greater detail than CT. Magnetic resonance images of the canine brain were acquired in two dogs with diffuse leptomeningeal and cerebral low grade astrocytoma. Abnormalities were identified with MR imaging when CT and CSF analysis were noncontributory. Changes seen with MR included decreased signal on T1-weighted images and increased signal on T2-weighted images consistent with vasogenic edema. Neither MR nor CT showed post-contrast enhancement. Magnetic resonance did not show the full extent of cellular infiltration, however. This was attributed to the diffuse submacroscopic distribution and absence of corresponding edema and contrast enhancement in certain regions of brain.