Saccadic lateropulsion and upbeat nystagmus: disorders of caudal medulla. 
A patient developed a primary position upbeat nystagmus and a left saccadic lateropulsion.  Magnetic resonance imaging demonstrated a probable cavernoma at right caudal paramedian medullary level.  Anatomical correlations are discussed.  Saccadic lateropulsion is attributed to olivocerebellar pathway impairment but usually is described in more rostral medullar lesions.  Our case would still support this hypothesis because the lesion could have involved the olivocerebellar pathway at its very caudal level.  Upbeat nystagmus could be attributed to impairment of the nucleus intercalatus and/or cell groups of the paramedian tract.