Sacral Agenesis


The sacrum is a bone at the base of the spinal column that is formed following the fusion of five vertebrae. It sits near the top of the buttocks and just below is another small series of bones called the coccyx.

Nerves from the spinal cord pass through a bony canal within the sacrum and exit the sacrum in a number of places to provide nerve supply to the bowel, anus, bladder, and to the muscles and sensory organs in the lower limbs.

Sacral agenesis is a condition that exists when either part or all of the sacrum is missing. It is possible for two of the five sacral segments to be missing without causing problems. If three or more of the sacral segments are missing, there is likely to be some abnormality of the nerves coming out of the sacrum.

Sacral agenesis may occur in isolation or be associated with other abnormalities -such as problems with the development of the anus, rectum or the bones or joints of the lower limb.


Medical text written May 2001 by Mr P Malone. Last updated January 2018 by Mr Feilim Murphy, Consultant Paediatric Urologist, St George’s Hospital, London UK.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

What are the symptoms?

If there is damage to nerve function in sacral agenesis, problems can include:

  • constipation (reduced bowel movement) due to the bowel and the bowel sphincters being affected  
  • faecal incontinence (where a person is unable to control the removal of faeces from the body) due to the bowel and the bowel sphincters being affected  
  • urinary incontinence and urinary tract infections due to the bladder and the urinary sphincters being affected
  • kidney damage could occur as the bladder may store and empty urine at abnormally high pressure
  • there can be varying degrees of paralysis affecting the lower limbs if the nerves coming from the sacrum are abnormal. This can vary from minor problems with gait (the pattern of movement of the limbs) to total paralysis.

What are the causes?

Although in the majority of cases there is no clear cause of sacral agenesis, there is a clear association with insulin-dependent diabetes in the mother. Sacral agenesis may also be associated with abnormal development in other organs such as the anus/rectum, the bones and joints of the leg and the other bones in the spine. When these occur together this is referred to as Caudal Regression syndrome.

How is it diagnosed?

Most cases are only detected after birth. Sometimes the condition may be discovered later when the child is older and has problems with constipation, incontinence, urinary tract infections or abnormalities with gait.

All patients with sacral agenesis will need to be assessed by a medical specialist with an interest in bowel and bladder problems, the neurology of the lower limbs and, probably, a specialist paediatric orthopaedic surgeon. A simple X-ray of the spine will usually diagnose the condition. Once the diagnosis is confirmed, all patients will require a magnetic resonance imaging (MRI) scan.

How is it treated?

There are a wide variety of treatments available to improve and control all of the problems arising due to sacral agenesis. It is now possible to achieve both faecal and urinary continence. It is also possible to safely protect the kidneys from damage due to the abnormal bladder.

Inheritance patterns and prenatal diagnosis

Inheritance patterns

There is an increased association between the development of sacral agenesis and diabetes in the mother. However, most cases of sacral agenesis arise sporadically (with no previous family history).

Like all abnormalities of the development of the spine and spinal cord, if a parent has one child affected, there is an increased risk of further children being affected. Affected families should be referred to a genetics service for further information and support.

Prenatal diagnosis 

Prenatal diagnosis is possible, but is unusual. Affected families should be referred to their local genetics centre for further information and support.

Is there support?

Sacral Agenesis Contact Group

Tel: 02380 842 661

The Group offers information and support to anyone affected by Sacral Agenesis. 

Group details last updated December 2014.

Back to A-Z Conditions