Sparing of the Onufrowicz nucleus in sacral anterior horn lesions.

Sacral anterior horns were examined with special reference to the Onufrowicz nucleus in 3 patients with Werdnig-Hoffman disease, 2 with healed anterior poliomyelitis, and 1 who had undergone amputation of both legs above the knee. None of these patients showed symptoms of either urethral or anal sphincter disturbances. The Onufrowicz nucleus of the second sacral anterior horn appeared normal in all the patients examined, though the lateral portion of that horn and the medial nuclear group of the third sacral segment were frequently involved. These findings support the view that the Onufrowicz nucleus may be innervating the external sphincter muscle of the urethra and the anus.