Fig. 4

Axial Fast imaging employing steady-state acquisition (FIESTA) MRI image (a) showing the CNIII (yellow arrows) entering the cavernous sinus (asterix). From here, CNIII courses anteriorly in the dura of the cavernous sinus to enter the orbit through the superior orbital fissure (SOF), supplying the extra ocular muscles except the superior oblique and lateral rectus muscles. Axial FIESTA MRI image (b) shows the normal abducens nerves (red arrow) entering Dorello’s canal (green arrow). From here, CN VI courses anteriorly through the cavernous sinus to enter the orbit through the SOF, supplying the lateral rectus muscle. The white arrows show the general direction of travel of CN III and VI (a, b). A 73-year-old male presenting complaining of double vision. Axial fused PET/CT (c), PET (d), and coronal PET (e) images showing a large peripherally ossified hypometabolic expansile mass centered in the left petrous apex extending to the cerebellopontine angle and middle cranial fossa (long green arrow). Note the lower activity in the left lateral rectus muscle (green short arrow) compared to the right one (red arrow) and the overcompensating hypermetabolic left medial rectus muscle, indicative of left abducens nerve paresis which was confirmed clinically. f Zoomed in Axial FIESTA MRI imaging shows the normal right abducens nerve (red arrow) entering Dorello’s canal (green arrow). On the left side, the mass is seen involving the expected location of the left CN VI