Isolated Syndrome of the Medial Longitudinal Fasciculus in Man

THE DIAGRAM makers have provided two schemes for the connections through the medial longitudinal fasciculus (MLF) to explain the MLF syndrome in man. Some authorities depict a wiring diagram with internuclear axons running ipsilaterally in the MLF from the 6th to the 3rd nerve nucleus, 1 while other authorities depict a decussation at the 6th nerve level to run in the contralateral MLF. 2 In the macaque monkey the problem has been resolved. 3,4 The internuclear MLF fibers decussate at the 6th nerve level to run contralaterally. Thus, unilateral MLF lesions cause ipsilateral paralysis of the adducting eye and contralateral horizontal nystagmus in the abducting eye. The situation in man has been obscure because of the lack of suitable clinicopathologic material. In the few anatomically studied cases the clinical picture was beclouded by multiple signs, and the anatomic correlation was beclouded by multiple or extensive lesions. 5-7 The present