Spina Bifida Occulta and Spinal Dysraphism
Types
of occult spinal dysraphism (OSD)
Initial
signs and symptoms of OSD
Developmental signs and symptoms of OSD
Pes
Cavus
(Source of statistical information: Asbah fact sheet)
Spinal Dysraphism is a generalised term for a group of congenital abnormalities that can cause progressive neurological damage and therefore the deterioration of neural and physical function. The abnormalities are also sometimes known as neural tube defects. The feature common to all the conditions is an anomaly in the midline structures of the back, especially the absence of some of the neural arches (outward facing bony parts of the vertebrae), and damage to the skin, filum terminale, nerves and the spinal cord itself. It is therefore a congenital condition in most cases rather than acquired by injury.
Spina Bifida Occulta can also occur without a tethered cord. It is known that 5-10% of the general population may have mild spina bifida but in most cases the damage is limited to one or two vertebrae, the defect is invisible and overall it causes no neurological, musculo-skeletal, or bladder and bowel problems. Some people may suffer from backache which may be investigated through their GP and perhaps x-rays taken, and the condition may be detected by accident.
Neural tube defects and spinal dysraphism can be classified under two main categories:
Open forms: these are called myelocele, meningocele and myelomeningocele and are often associated with hydrocephalus and Arnold Chiari Malformation I and II. These forms are classified as spina bifida cystica if their form includes a sac containing neural elements. Brief details can be found here.
Closed forms
Spina
bifida occulta: simple forms (as in second paragraph above)
Spina bifida occulta with tethered cord
Some 1 in 1000 people have the additional complication of a tethered spinal cord. This means the cord is restricted within the vertebral column by further congenital abnormalities such as a thickened filum terminale, fibrous bands of tissue, dermal sinus tracts, longitudinal bony spurs within the spinal canal (diastematomyelia) and lipomae (lipomyelomeningocele) lying within the spinal canal and overlying unbroken skin. Each of these cases is dealt with in greater detail in the section on Tethered Cords.
Titles of types of occult spinal dysraphism
| Tight filum terminale | Syringomyelia |
| Diastematomyelia | Diplomyelia |
| Dermal sinus tracts | Caudal agenesis |
| Lipomyelomeningocele | Intraspinal lipoma |
| Neurenteric cysts | Myelocystocele |
| Meningocele manque | Terminal Syrinx |
This section outlines the initial and developmental signs and symptoms of occult spinal dysraphism with a tethered cord.
The word "occult" means "hidden" in this context and the majority of signs indicating the underlying dysraphism may not be immediately visible in the newborn, except the form known as lipomyelomeningocele. At birth babies also rarely exhibit neurological deficiencies but on closer examination and as the child grows the effects of the dysraphism become apparent. It is also an unfortunate fact that if the dysraphism and associated cord tethering is neglected there is the risk that urological and neurological damage may be irreversible and permanent [Satar et al., 1995]. There is an argument that babies should have their cords detethered before any physical symptoms of deterioration become apparent, but babies and younger children are at a greater risk of recurrent tethering. It therefore becomes a consideration of the individual circumstances as to whether and when surgery should take place. Retethering also depends on the original type of tethering, the operative skill of the surgeon, and the individual patient's body's reaction to surgery.
Overall in all cases the management of dysraphism and tethered cord syndrome becomes an ongoing lifelong process and its treatment becomes individualised, according to the type, severity and progress of the condition.
Initial
signs and symptoms of occult spinal dysraphism
Initial signs on examination can include:
The presence of dysraphism can cause a deterioration in the condition of the tethered cord as a result of:
Developmental signs and symptoms of deteriorating occult spinal dysraphism
Developmental signs and symptoms of occult spinal dysraphism may appear as the child grows, as more tension is put on the tethered spinal cord. Physical symptoms may initially be relatively painless, although nerve, muscle and bone damage may be evident, such as foot deformities (see below) or scoliosis. Eventually, however, the nerves emanating from the cord and those in the legs and feet cannot take further stretching and begin to emit warning pain signals (tingling and pins and needles) or may even stop sending signals altogether causing reduced or poor sensation (numbness of toes and feet). Progressive abnormalities in organ (bladder and bowel) function may also occur, depending on the point and type of tethering.
Developmental signs can include:
Bowel or bladder problems
Orthopaedic problems
Gait problems
Adult patients may exhibit some or all of the developmental signs detailed above. The deterioration in an adult's tethered cord is due to the degree of tethering, "the cumulative effect of repeated microtrauma during flexion and extension" [Gupta et al., 1999], general wear and tear, hypoxia and ischaemia, and the stretching of the vulnerable nerves relating to the bladder and bowel.
The most common warning sign of deterioration in adults is the appearance and exponential increase of pain, particularly in the lower back and legs, and the further tightening of feet and leg tendons. Gupta concluded that after surgery the pain was relieved in 90% of his patients but that only a few had improved bladder control. This is therefore a strong argument to have detethering surgery as soon as possible, in order to maintain continence.
Neurological impairment as a result of spinal dysraphism can lead to the abnormality known as pes cavus, literally "hollow foot". It is caused by the nerve roots at the level of the spinal abnormalities sending out distorted signals to the muscle groups of the legs and feet (usually from the lumbar and sacral nerve roots) as the child grows, thereby causing distorted growth and muscle imbalance. People with this condition often refer to it as "classic feet and legs" (or "chicken legs") and it usually develops by the age of five. It is important to stress that if pes cavus develops in a previously symptomless child the underlying situation should be investigated by a qualified medical professional.
The components of pes cavus may include some or all of the following:
Legs can also be affected by
Various surgical procedures can be undertaken to correct the most problematic symptoms of pes cavus, although the surgeries may not completely eradicate the problem. See http://www.medmedia.com/ for some details on this subject.
After surgery to release a tethered cord, the tightness on the feet tendons may be released. You may be delighted to see that your toes may un-claw and the exaggerated arches may drop slightly, but "feet and tendon contractures may not fully loosen if they have been present for many years" (words courtesy of Mr Pople) or in adult patients due to the ossification of bone structures.
Since my detethering my feet have continued to contract, especially on the right side, which is not very encouraging. However, Mr Pople has advised me that despite the release of the tension on the tethered cord, which should ordinarily result in less tight feet, sometimes the damage to the nerve roots is so extensive and long-standing that the feet continue to tighten or show signs of deterioration. This can be disappointing but it is important to note that the true tension on the cord, which was doing the potentially disabling damage, is now released.
Unfortunately pes cavus feet cause major problems for fitting of shoes. I usually wear kids' open-toed sandals for the summer but in 2001 I was fortunate to find some "Kickers" shoes in Marks and Spencer which fit like a glove. For the first time in 35 years, my feet look smart and fashionable. As they are also so small, friends now think they are "cute"!
If anyone has suggestions on getting better fitting shoes, names of shoemakers, suppliers, brand names etc., please email me on nina.bunton@bristol.ac.uk. I will post this information on the feedback page.