‘CSF’ Cleft Sign

csf cleft sign

The ‘cleft sign’ is useful in distinguishing extraaxial from intraaxial lesions, typically meningiomas as in this case. Although the cleft traditionally has been regarded as representing a thin rim of CSF (as seen around the posterior edge of the lesion) it has been contended that as that rim is often high signal on FLAIR imaging (see green arrow) it in fact represents non-CSF tumour-brain interface. Nonetheless it remains a good sign of a mass being extraaxial and is typically made up of:
high T2WI signal – (?) CSF (?) other;
vessels – pial vessles or as seen posteriorly larger vessels;
hypointense dura (on both T1 and T2WI) over the surface of the mass.

For more images of the same case please visit Radiopaedia.org here.

References:
1. Takeguchi, T. et al “Evaluation of the Tumor-brain Interface of Intracranial Meningiomas on MR Imaging including FLAIR Images” Magnetic Resonance in Medical Sciences Vol. 2 (2003) , No. 4 pp.165-169 pdf here

Credit: Dr Frank Gaillard