[Isolated trochlear nerve paralysis following head trauma].

39 cases with isolated trochlear nerve palsies of traumatic origin have been analyzed retrospectively. 18 patients (46%) had had cerebral contusion, 15 (39%) cerebral concussion, and 6 patients (15%) a minor head trauma. 33 patients had unilateral trochlear nerve palsies and 6 (all of them with cerebral contusion) bilateral. The degree of the palsies did not correlate with the severity of the head trauma. Essential pathogenetic mechanisms were frontal or occipital blows. We emphasize a fact hitherto underestimated in the literature, that even a relatively mild head trauma (cerebral concussion or minor head trauma) can cause isolated trochlear nerve palsies. This was the case in 21 of our 39 patients (54%). Simple clinical examination techniques are described (Bielschowsky phenomenon, pencil test), which allow detection of trochlear nerve palsies in most cases.