Description, Causes and Risk Factors:
Sacral agenesis is a congenital disorder in which there is abnormal fetal development of the lower spine — the caudal partition of the spine. There are four main types of sacral agenesis, some more severe than others. The first involves the partial formation of the sacrum. This means that some of the lower back is developed, but certain components are missing. Another type is the deformation of the sacrum, and the two additional types involve the total failure of sacrum formation.
Although it is unknown why exactly this occurs, it is speculated that a lack of certain vital nutrients during pregnancy may be a factor. For example, folic acid taken in sufficient amounts may help prevent this and other spinal defects in newborns.
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. Due to abnormal gastrulation, the mesoderm migration is disturbed. This disturbance results in symptoms varying from minor lesions of the lower vertebrae to more severe symptoms such as complete fusion of the lower limbs. While the exact etiology is unknown, it has been speculated that the condition may be associated with certain dietary deficiencies including a lack or insufficient amounts of folic acid.
Sacral agenesis syndrome is a well-established congenital anomaly associated with maternal diabetes mellitus (not gestational diabetes). However, other etiologic factors are presumably involved, as demonstrated by the rare incidence of sacral agenesis (1:60,000) compared to diabetes. Certainly not all children born with sacral agenesis have diabetic mothers.
The dominant inherited sacral agenesis is very often correlated with a mutation in the Hb9 (also called HlxB9) gene.
Those who are born with sacral agenesis may suffer from small lesions on the lower spine or more serious effects, including fusion of the lower limbs. If there is an abnormality of the nerves coming out of the sacrum, this can have a number of different effects. It may affect the bowel and the bowel sphincters, which can give rise to constipation and/or faecal incontinence. It may affect the bladder and the urinary sphincters and this may give rise to urinary incontinence and urinary tract infections. It is possible that in patients with sacral agenesis the bladder will store urine at abnormally high pressure and thus may pose a risk of causing kidney damage. The final problem that may exist, if the nerves coming from the sacrum are abnormal, is varying degrees of paralysis affecting the lower limbs. This can vary from minor problems with gait to total paralysis requiring the permanent use of a wheelchair.
The major orthopedic problems associated with sacral agenesis are spinopelvic instability, scoliosis, myelomeningocele, hip dislocation and contracture, knee contracture and foot deformities. Nearly all individuals with sacral agenesis have disorders of the genitourinary tract - the most common being neurogenic bladder (a urinary problem in which the bladder does not empty properly). Depending on the type of neurological disorder causing the problem, the bladder may empty spontaneously (incontinence) or may not empty at all (retention with overflow leakage).
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 orthopedic surgeon.
Prenatal diagnosis of sacral agenesis is unusual - the condition is usually detected after birth. Often times, a parent may not know something is wrong with their child until they have an incontinence problem or an abnormal gait. If a problem is noticed at birth, diagnosis is confirmed with a radiographic exam. Then a panel including a neurologist, pediatric orthopedic surgeon, neurosurgeon, and a development expert may be consulted.
Because there are varying degrees of severity in sacrum agenesis, the prognosis is equally varied. Some children may go on to live ordinary lives with surgery combined with physical therapy. Others may have fully malformed legs and hips, making walking or even crawling impossible. These children will likely be confined to a wheelchair. Sometimes the lower limbs are even removed.
In some very severe cases, bladder and bowel function are inhibited. This may necessitate the use of permanent colostomy to prevent bowel incontinence as well as catheterization for urine passage. Despite these limitations, the prognosis is improving for these patients as more efficient surgeries and physical therapies are developed; along with more technologically advanced wheelchairs and mobility aids.
To prevent sacral agenesis from occurring, all women in their childbearing years are encouraged to take a daily multivitamin that contains folic acid. Maintaining a healthy diet and lifestyle is also beneficial by preventing the onset of type 2 diabetes. Quality prenatal care is also important so care providers can spot any abnormalities, and treatment options can be made available the moment of birth.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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