[Aberrant pyramidal tract: a study with Sudan III stain]

The aberrant pyramidal tracts in the pontine medial lemnisci were studied, using standard Sudan III stain, in six cases of chronic pyramidal tract degeneration. Three of the six cases had bilateral or unilateral cerebral destructive lesions, one cervical hematomyelia with rare retrograde pyramidal tract degeneration, one classical amyotrophic lateral sclerosis, and one atypical motor neuron disease with striatonigral degeneration. Except for the latter two cases the aberrant pyramidal tract degeneration was confirmed bilaterally or on the side ipsilateral to the pyramidal tract degeneration in the pontine base. This degeneration could also be found, on careful examination, with other stains, i.e., H & E, Luxol fast blue-periodic acid Schiff and modified Bielschowsky. Significant change was not observed in the medullary medial lemniscus in any case. The different results observed in the aberrant pyramidal tract between the destructive and degenerative disorders might be pathogenetically important. Reservation, however, may be required since the number of the cases of degenerative disorders in this study was limited. A possible factor for this difference is the survival length which might have erased degradation products altogether. Another factor is the sensitivity of Sudan III in comparison with the Marchi's method which might demonstrate more subtle evidence of degeneration but with its intrinsic capricious staining characteristics. The physiological role of the aberrant pyramidal tract, which has been neglected in the recent textbooks of neuroanatomy, may become of clinical interest with high-quality MRI in cases such as isolated cranial motor nerve palsy without concomitant paralysis of the extremities.