Sixth Nerve Palsy and The Clival Marrow Sign

Sixth nerve palsy is a common manifestation of neoplastic infiltration of the clivus. Even if the lesion does not expand the clivus, sixth nerve palsy occurs because the nerve is trapped in Dorellos canal lying on the clival edge. Clival marrow is adipose-rich in adults and therefore hyperintense on pre-contrast T1 MRI. Infiltrating neoplastic disease causes loss of this high signal (clival marrow sign). We believe that this telltale sign is often overlooked, not only by clinicians, but also by radiologists. We describe three examples in which the clival marrow sign occurred as an isolated imaging finding or in combination with loss of high T1 signal in calvarial or vertebral marrow.