Prenatal diagnosis of pericallosal curvilinear lipoma: specific imaging pattern and diagnostic pitfalls

We report the first series of five cases of prenatal diagnosis of pericallosal curvilinear lipoma (CL) and underline limitations and pitfalls in identifying a specific prenatal imaging pattern using ultrasound and MRI. On ultrasound, the main referring feature was a short corpus callosum in all cases. This subtle callosal dysgenesis was associated with a band of hyperechogenicity surrounding the corpus callosum, which can mimic the pericallosal sulcus, and increased in size over the third trimester in three out of four cases in which sonographic follow-up was obtained. This band showed typical hypointensity on T2-weighted images in all cases, whereas, on T1-weighted images, no hyperintensity, suggestive of fat, as shown typically in the postnatal period, was found in any of the cases except one. Finally, with regards to outcome and prenatal counselling, we underline that recognition of CL is crucial when facing mild corpus callosum dysgenesis and that one should be aware of subtle diagnostic findings such as a thin band of echogenicity surrounding the corpus callosum, which may increase during gestation, identified as a band of hypointensity on T2-weighted fetal MR images.