Piglet sign (osmotic demyelination)

The piglet sign is seen in osmotic demyelination syndrome. It refers to the appearance of the upper pons in axial T2 and FLAIR images. The areas of coalescent T2 signal increase are reminiscent of a pig's snout, with other features on axial MR images resembling the rest of the face of a piglet with the temporal lobes representing ears, the carotid arteries represent the eyes and the fourth ventricle as the mouth .

The area of abnormally increased T2 signal is perhaps better known as the trident sign.