Background

This atlas is to illustrate the use of MRI in the diagnostic work-up of patients with abducens nerve paraly-sis of non-traumatic origin. The abducens nerve (the sixth cranial nerve) is a motor nerve that controls the movement of the lateral rectus muscle of the eye. The abducens nucleus is situated in the pons, on the floor of the fourth ventri-cle, close to the midline. The nerve enters the subarachnoid space when it emerges from the brain stem and runs upward in the prepontine cistern towards Dorello’s canal, lateral to the dorsum sellae of the sphenoid bone. In the cavernous sinus it runs along-side the internal carotid artery and enters the orbit through the superior orbital fissure to innervate the lateral rectus muscle of the eye (1). Complete interruption of the peripheral sixth nerve causes diplop-ia (double vision), due to the unop-posed action of the medial rectus muscle. Partial damage to the sixth nerve causes weak or incomplete abduction of the affected eye. Abducens nerve paralysis of non-traumatic origin is discussed here. Imaging findings A wide variety of lesions is seen, and for each of the four segments (pontine segment, prepontine seg-ment, cavernous sinus segment and orbital segment) along the nerve’s course, a limited differential diagno-sis has to be considered. Visualizing all these regions con-sequently has to be included in the standard imaging protocol in such cases. Patients with abducens nerve paralysis are best imaged using T2WI of the brain and T1WI of the Other processes that can damage the sixth nerve include hydro-cephalus, hemorrhage, edema that exerts downward pressure on the brainstem, causing the nerve to stretch along the clivus.The prepon-tine segment of the abducens nerve orbit. The cisternal course of the nerve is well studied using 0.5-1.0 mm thick 3D-T2WI. After gadolin-ium injection axial and coronal T1WI are performed. Pending on the pres-ent problem additional sequences are considered: DWI (elderly), FLAI