Curvilinear and tubulonodular varieties of lipoma of the corpus callosum: an MR and CT study.

Until recently all callosal lipomas were grouped together. However, these lipomas can be clearly separated into two groups having different morphologies and associated brain anomalies. One group consists of anteriorly situated round or cylinder-shaped lipomas, termed tubulonodular. These lipomas are generally greater than 2 cm in diameter and have a high incidence of corpus callosum dysgenesis, frontal lobe anomalies, and frontal encephaloceles. The second group comprises thin, posteriorly situated lipomas curving around the splenium and are termed curvilinear. The curvilinear lipomas are generally associated with a normal corpus callosum and otherwise have a low incidence of associated anomalies. When anomalies do occur, they tend to be less severe than with the tubulonodular lipomas. We present four cases of curvilinear lipomas and review similar cases in the literature to explain why lipomas of the callosal region have such a variety of associated anomalies and morphologies. Our findings support the idea that both groups of lipomas develop in the region of the origin of the corpus callosum but form at different times during gestation, with the tubulonodular ones forming earlier and thus being associated with more severe cerebral anomalies.