High-field, High-resolution MR Imaging of the Human Indusium Griseum

In the March 1999 issue of the AJNR, Nakada (1) indicates that one or more elevations medial to the superior surface of the corpus callosum represent the indusium griseum (Fig 1). I believe he is incorrect because these elevations represent the medial longitudinal striae of Lancisii (Fig 1, 2). A lateral longitudinal stria of Lancisii also exists, as can be seen on the left laterally in Figure 1B. These medial and lateral longitudinal striae are believed to be rudiments of the fornices proper that remain dorsal to the corpus callosum during embryogenesis. Together with the indusium griseum, the longitudinal striae form the supracallosal hippocampal rudiments. The medial and lateral longitudinal striae are small bundles of myelinated fibers that primarily originate in the hippocampi in the temporal lobes and run forward underneath the thin layer of gray matter of the indusium griseum to project mainly in the septal area. Fibers arising from the indusium griseum itself and fasciola cinerea also run within these longitudinal striae. The exact subregional origin(s) and precise termination(s) of the majority of fibers in the medial and lateral longitudinal striae of the Lancisii is not known with certainty. Similarly, the functional aspects of these hippocampal rudiments is unclear (2–7).

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fig 1.

Representative MR images of the IG classical, symmetric two-strip (A), symmetric, but centrally fused (B), lateralized, single-strip (C), and thin-layer (D) patterns.fig 2. The medial and lateral longitudinal striae of Lancisii. Schematic of the superior aspect of the anterior extent of the supracallosal hippocampal remnants with cut edge (arrowheads) shows: 1) medial longitudinal stria; 2) lateral longitudinal stria; and 3) indusium griseum. (Reprinted from: Nieuwenhuys R, Voogd J, van Huijzen C. The Human Central Nervous System. Berlin: Springer-Verlag 1988:300, with permission.)