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Cleft sign

Dr Jeremy Jones and Dr Frank Gaillard et al.

The cleft sign can be used to distinguish an extra axial lesion from an intra axial lesion and is typically used in the description of a meningioma.

Classically, the cleft was regarded as representing a thin rim of CSF between tumour and brain parencyma. However, it often is of high signal on FLAIR imaging and most likely represents a non-CSF tumour-brain interface.

Nevertheless, it remains a good sign that a mass is extraaxial and is typically made up of:

high T2 signal : (?) CSF (?) other
vessels - pial or as in case 1, larger vessels.
hypointense dura (on both T1 and T2 on the surface of the mass. (if extra dural)