[Lesion of the bilateral MLF and unilateral paramedian pontine reticular formation, caused by an infarction in the midbrain tegmentum]

A 71-year-old man with bilateral medial longitudinal fasciculus (MLF) syndrome and paralytic pontine exotropia caused by an infarction of the midbrain tegmentum was reported. He suddenly noticed a diplopia and gait disturbance, and visited our clinic. Neurological examination revealed that this right eye was slightly abducted in the primary position. On horizontal gaze, outwardbeating nystagmus of the abducted eyes was observed, bilaterally. The adduction of the bilateral eyes was severely disturbed and the abduction of the left eye was slightly restricted, while the convergence was normal. T2-weighted magnetic resonance imaging revealed high signal intensity area in the medial portion of the midbrain tegmentum, which indicated an infarction. Several cases showing bilateral MLF syndrome with exotropia have been reported, but a case whose lesion was shown in the midbrain has not been reported so far. The present case suggests that paramedian pontine reticular formation (PPRF) is not confined to pons but expands to midbrain.