Editing Trochlear nerve (section)

=====Chronic palsy=====
{{Main|Congenital fourth nerve palsy}}
The most common cause of ''chronic'' fourth nerve palsy is a congenital defect, in which the development of the fourth nerve (or its nucleus) is abnormal or incomplete. Congenital defects may  be noticed in childhood, but minor defects may not become evident until adult life, when compensatory mechanisms begin to fail. Congenital fourth nerve palsies are amenable to surgical treatment.