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A 14 year old girl suffers head trauma in an automobile accident. When she recovers consciousness, she reports diplopia. Examination shows a right hypertropia in primary gaze position that increases on left gaze but converts to a left hypertropia on right gaze.
The responsible lesion is likely to be in the
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When the right eye is higher in left gaze and the left eye is higher on right gaze, you are looking at BILATERAL fourth nerve palsies, especially in the setting of head trauma. In concussive head trauma, the brain
moves more than its coverings, including the dura. As a result, the dorsal midbrain slams into the rigid, knife-like inner margin of the tentorium cerebelli at exactly the place where the crossing fourth nerves exit
from the brainstem. The fourth nerves are often injured together, although usually asymmetrically.
Bilateral fourth nerve palsies create this pattern of “alternating hypertropia,” a large (at least 10 degrees) excyclodeviation, and an esotropia in downgaze. Imaging generally does not show a pertinent
abnormality, although sometimes there is hemorrhage in the caudal dorsal midbrain.
Recovery is delayed for months and is of variable degree. Eye muscle surgery may eventually be necessary.
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