Sacral aplasia (agenesis).

Abstract

Congenital absence of part or all of the sacrum is of infrequent occurrence. Gross aplasia (frequently called agenesis) of the caudal portion of the spine from the mid-thoracic level or higher is probably incompatible with life at an early stage of fetal development and would therefore tend to be unreported. Absence of the terminal part of the coccyx would also be likely to remain undetected unless found during unrelated roentgen studies. An analysis of spinal roentgenograms of 700 children was made by Shands and Bundens (1) in 1956. In a group of 169 anomalies, there were 5 cases of absence of spinal segments, 3 of congenital absence of all or part of the lumbar spine, sacrum, and coccyx, and 1 of solitary coccygeal absence. In 1852, Hohl (2) reported absence of the sacrum for the first time. The first complete review of this subject, however, was presented by Freedman (3) in 1950. By that time, 54 cases had been reported, to which Freedman added a fifty-fifth. An excellent and comprehensive review by Blumel, Evans, and Eggers, recently published (4), presents data on 50 new cases, of which 8 were personally observed and the remaining 42 were collected by correspondence with 300 orthopedic surgeons in the United States. In this series 32 cases showed complete absence of the sacrum and 18 partial absence. Our purpose is to describe and emphasize the clinical and roentgen findings of sacral aplasia. It is important that the clinician and radiologist be made aware of the existence of this conditon and of its relationship to cord bladder, fecal urinary incontinence, infection, and abnormalities of gait. We shall present 3 new personally observed cases of sacral aplasia, of which 2 were complete and 1 partial. Anatomy and Morphogenesis Gray's Anatomy (5) adequately describes the development of the sacrum and coccyx from nine separate segments, and the detailed discussion of the embryology of these spinal segments may best be read in the original. Briefly, after development, the large triangular bone known as the sacrum is situated in the lower part of the vertebral column at the upper and posterior portion of the pelvic cavity. The sacrum is inserted between the two hip bones as a wedge articulating superiorly with the last lumbar vertebra and at its lower margin with the coccyx. Clinical Material Case I: A. W., a 3 1/2-year-old white boy, was admitted to Montefiore Hospital on June 12, 1957, with a history of fecal and urinary incontinence since birth. Motor activity was reported to be unimpaired, and the family had not been aware of any sensory deficits. On examination, the pertinent findings included a protuberant abdomen, a soft-tissue mass over the sacral area, atrophic glutei, absence of natal creases, and thin, atrophic legs. Positive neurologic findings consisted of the inability to stand on either foot, absence of ankle jerks, and bilateral Babinski reflexes. Rectal tone was absent.