Objective:The authors evaluated rectal manometry of children with sacral root abnormalities secondary to isolated sacral agenesis.Methods:The anorectal manometric recordings of seven patients with isolated sacral agenesis (four with partial agenesis and three with complete agenesis) were retrospectively evaluated and compared with tracings from healthy control subjects. Characteristics of the internal anal sphincter (IAS), the rectoanal inhibitory reflex (RAIR), voluntary external anal squeeze pressure, and threshold of rectal sensation to distension were analyzed. Characteristics of the patients' neurologic function with attention to urinary and fecal continence were obtained by chart review.Results:All seven patients had urinary and fecal incontinence. IAS resting pressure was the same in patients and control subjects. In the three patients with total sacral agenesis, IAS relaxation was more complete and lasted longer after balloon distention of the rectum. These patients also had significantly lower voluntary external anal squeeze pressure and blunted sensation of rectal distension.Conclusions:Abnormal parasympathetic innervation associated with sacral agenesis is associated with changes in anorectal function. Manometric findings suggest that there is modulation of the RAIR by extrinsic innervation, which may explain the fecal incontinence in these patients.