Trochlear nerve palsy and contralateral internuclear ophthalmoplegia: an unusual crossed syndrome

Clinical Reasoning: A 45-Year-Old Man With Vertical Diplopia

“…A single lesion affecting the MLF and trochlear nerve nucleus or fibers prior to decussation would present with INO and a contralateral SO palsy. 3,4 But in this case, there were likely two lesions, one involving the left MLF resulting in a left INO and the second lesion involving the post-decussation left trochlear nerve fibers in the left dorsal midbrain, originating from the right trochlear nucleus, resulting in a left SO palsy (Figure 2A).…”

“…A combination of INO and trochlear nerve palsy has been rarely reported in the literature. 3,4 The typical presentation is that of INO with a contralateral superior oblique palsy as explained by a single lesion affecting the MLF and trochlear nucleus or the intraparenchymal fibers of trochlear nerve prior to decussation in the dorsal midbrain. 3,4,5 What is unusual in our case is the co-occurrence of INO with ipsilateral SO palsy.…”

“…3,4 The typical presentation is that of INO with a contralateral superior oblique palsy as explained by a single lesion affecting the MLF and trochlear nucleus or the intraparenchymal fibers of trochlear nerve prior to decussation in the dorsal midbrain. 3,4,5 What is unusual in our case is the co-occurrence of INO with ipsilateral SO palsy. This combination can only be explained by two separate lesions: one affecting the MLF and the other affecting the post decussation trochlear nerve fibers, originating from the contralateral trochlear nucleus, in the ipsilateral dorsal midbrain (Figure 2A).…”

“…3,4 The typical presentation is that of INO with a contralateral superior oblique palsy as explained by a single lesion affecting the MLF and trochlear nucleus or the intraparenchymal fibers of trochlear nerve before decussation in the dorsal midbrain. 3-5…”