Sacral agenesis

Sacral agenesis (or hypoplasia of the sacrum) (also more commonly called caudal regression syndrome) is a little known and rather infrequent congenital condition of spinal deformity affecting the sacrum - the caudal partition of the spine. It occurs at a rate of approximately 1 per 25,000 live births.

Etiology
The condition arises from some factor or set of factors present during approximately the 3rd week to 7th week of fetal development. Formation of the sacrum/lower back and corresponding nervous system is usually nearing completion by the 4th week of development. While the exact etiology is unknown, it has been speculated that the condition may be associated with certain dietary deficiencies including a lack or insuffient amounts of folic acid or other developmental aids. The condition may also be associated with or resultant of maternal diabetes. However, it's important to note that the correlation between onset of sacral agenesis and the above-mentioned possible causes is weak. The dominant inherited sacral agenesis (also referred to as Currarino syndrome) is very often correlated with a mutation in the Hb9 (also called HlxB9) gene (shown by Sally Ann Lynch, 1995, Nature Genetics).

Prognosis
There are four levels (or "types") of malformation. The least severe indicates partial formation (unilateral) of the sacrum. The second level indicates a billateral (uniform) deformation. And the most severe types involve a total absence of the sacrum.

Depending on the type of sacral agenesis - bowel or urinary bladder deficiencies may be present. A permanent colostomy may be necessary in the case of imperforate anus. Incontinence may also require some type of continence control system (e.g. self-catheterization) be utilized. Occasionally if deformities of the knees, legs or feet would prove unresponsive to corrective action - amputation at the knee may be proposed.

Before more comprehensive medical treatment was available, full amputation of the legs at the hip was often performed.