Foci of MRI signal (pseudo lesions) anterior to the frontal horns: histologic correlations of a normal finding.

Review of all normal magnetic resonance (MR) scans performed over a 12-month period consistently revealed punctate areas of high signal intensity on T2-weighted images in the white matter just anterior and lateral to both frontal horns. Normal anatomic specimens were examined with attention to specific characteristics of this region. Three unique features typify the brain tissues that correspond to the foci of high signal. First, this region of the brain is notable for its loose network of axons with low myelin content. Second, pathologic scrutiny revealed an entity called "ependymitis granularis," which represents patchy loss of the ependyma in the frontal horns with astrocytic gliosis. Third, flow of interstitial fluid within this region of the brain tends to converge at the dorsal-lateral angle of the frontal horns. All these factors contribute to increased water content locally, which results in foci of high signal intensity anterior to the frontal horns in all normal MR scans.