Spinal Dysraphism
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Spinal = to do with the spine
Dysraphism = incomplete fusion
Spinal dysraphism is an umbrella term that describes a number of conditions present at birth that affect the spine, spinal cord, or nerve roots.
- Spine: the bony structure also known as the spinal column. Made up of individual vertebrae (bones), the spine protects the spinal cord.
- Spinal cord: the bundle of nerves and other tissue that connects brain and body. Inside the spine, the spinal cord is also protected by a series of membranes (coverings). The spinal cord relays sensory information from the body to the brain, and movement instructions from the brain to the body.
- Nerve roots: nerves that branch off the spinal cord to reach the rest of the body.
All forms of spinal dysraphism result from an event very early in an embryo’s development. In about the third week of development, a sheet of cells called the neural plate folds up to form a structure called the neural tube. The top of the neural tube develops into the brain, and the rest of the neural tube develops into the spine and spinal cord. Spinal dysraphism results when a section of the neural tube that will become the spine and spinal cord does not close completely.
Types of spinal dysraphism include myelomeningocele (also known as spina bifida aperta or open spina bifida), spina bifida occulta, split cord malformation (diastematomyelia), spinal cord lipoma (lipomyelomeningocele), dermal sinus tract, tight filum terminale, and tethered spinal cord. A person with spinal dysraphism may have more than one type.
- Myelomeningocele, or spina bifida aperta: a condition in which the spinal cord and its membranes are not contained within the spinal column, but protrude into a sac outside the body
- Spina bifida occulta: a condition in which one or more vertebrae (bones of the spinal column) has a slight defect, but the spinal cord and its membranes are not affected
- Split cord malformation (diastematomyelia): a complex type of spinal dysraphism in which the spinal cord splits lengthwise into two distinct cords. Often, the split is caused by a thin segment of bone or cartilage that protrudes from the spinal column into the spinal cord space. Sometimes there is only one protective membrane or sleeve (the dura) around both parts of the spinal cord. Sometimes each part has its own dural sleeve.
- Spinal cord lipoma (lipomyelomeningocele): a condition in which an abnormal growth of fat attaches to the spinal cord, its membranes, and the space outside the spinal canal.
- Dermal sinus tract: a channel in the skin that may reach all the way to the spinal cord. Dermal sinus tracts are often associated with tumors in the space around the spinal cord called dermoids or epidermoids.
- Benign (non-cancerous) tumors and cysts can be found along with any type of spinal dysraphism. Tumor types include lipoma (a fatty tumor), dermoid (a tumor containing tissue of hair, bone, or cartilage), and epidermoid (a tumor of skin layers). These tumors are not cancerous and will not spread. However, they may compress the spinal cord or cause a tethered spinal cord.
- Tethered cord: a condition that may occur as a result of any spinal dysraphism, or as a result of other conditions (e.g. tumor, infection, or scar tissue formation). In this condition, the spinal cord is restricted at its base and cannot move freely in the spinal column. The resulting “stretch” on the spinal cord tissue can cause damage to the spinal cord leading to neurological problems (weakness, sensory loss), urological problems (incontinence), orthopedic problems (scoliosis and foot, ankle or leg deformities) and pain (see below). Accumulations of fluid in the spinal cord can also occur.
Symptoms
The symptoms of spinal dysraphism vary by type:
- Myelomeningocele: Can cause incontinence, hydrocephalus, tethered cord, sensory loss, orthopedics deformities, leg weakness, and/or or paralysis.
- Spina bifida occulta: Rarely causes symptoms and most often does not require treatment.
- Split cord malformation (diastematomyelia): Symptoms include structural scoliosis (spinal curvature) and tethered cord. Cases where each part of the cord has its own dura are usually associated with more severe symptoms.
- Spinal cord lipoma (lipomyelomeningocele): Sometimes cause no symptoms for a time. Symptoms are usually caused by the tethered spinal cord, and may include problems with bowel and bladder function, frequent urinary tract infections, spasticity, back and leg pain, weakness, and sensory loss.
- Dermal sinus tract: Sometimes cause no symptoms. However, these tracts often lead to tethered cord, and can also be a pathway for infection.
- Dermoid and epidermoid spinal cysts: May cause no symptoms at all, or may cause neurological symptoms like weakness, clumsiness, and incontinence if they compress the spinal cord and nerve roots.
- Tethered cord: Symptoms vary, but often include leg weakness, sensory loss, orthopedic deformities, low back and leg pain, and bowel or bladder incontinence. Symptoms can progress to become quite severe.
Diagnosis
The more severe forms of spinal dysraphism are diagnosed early in life. Myelomeningocele, for example, is often diagnosed before birth by ultrasound. It is visible to the naked eye, and can be diagnosed immediately in newborns.
A dermal sinus tract is generally visible as a channel, pit or dimple in the skin directly over the spine. However, the naked eye cannot determine whether the channel reaches the spinal cord, whether it may tether the spinal cord, and whether there are masses in the spinal cord. Only an imaging test like a magnetic resonance (MR) scan can provide these answers. A dermal sinus tract should almost always be evaluated by imaging scan. Prompt diagnosis can improve patient outcomes.
Lipomyelomeningocele can sometimes be diagnosed before birth by ultrasound. It can usually be tentatively diagnosed at birth by a pad of fat beneath the skin over the spine.
Spina bifida occulta, diastematomyelia, and dermoid and epidermoid cysts themselves are not visible to the naked eye, but they sometimes cause visible skin signs: a thick patch of hair, a growth of extra skin, or a difference in skin pigment directly over the defect, for example. When these conditions cause neurological symptoms like scoliosis, leg weakness, pain, or incontinence, they usually do so in the early years of life. Therefore they are usually diagnosed in childhood. Cysts may be found while investigating the spine if they occur along with other forms of dysraphism.
However, in rare cases, these conditions are not diagnosed until adulthood. In other rare cases, they are diagnosed in childhood but cause few symptoms and, depending on the age of the child, may not need treatment. Symptoms can progress in adulthood, at which point the conditions may require treatment.
Spinal ultrasound is a common screening study in newborns, but MR (magnetic resonance) imaging is the most useful diagnostic tool for diastematomyelia or tethered cord. MR scans use radio waves and a large magnet to produce detailed images of soft tissues like the spinal cord.
Risk Factors
The causes of spinal dysraphism are not yet completely understood. Genetic and environmental factors both seem to play a role.
The spinal cord arises very early in fetal development–in the first several weeks of gestation. Many forms of spinal dysraphism develop during this time. Robust maternal nutrition early in pregnancy, especially adequate levels of a vitamin called folate, seems to protect against some forms of spinal dysraphism.
Treatments
Surgical treatment for spinal dysraphism varies by type.
In myelomeningocele, the defect that exposes the spinal cord to the outside world is repaired in the first days of life. The surgeon protects the spinal cord from further damage, removes as many problematic elements as possible, restores as much normal structure as possible, then closes the membranes and skin over the spinal cord. This operation cannot reverse damage that has already occurred. However, it prevents further damage and dramatically reduces the risk of infection.
Spina bifida occulta does not need surgical repair if it causes no symptoms.
The most common surgery for diastematomyelia, called decompression surgery, involves removing the thin piece of bone or cartilage that divides the spinal cord. Removing this piece provides more room for the spinal cord within the spinal column. In many cases, removing this piece also “un-tethers” the spinal cord, allowing it to move freely once again. Sometimes the dura, the sleeve around the spinal cord, is also repaired at the time of surgery.
Lipomyelomeningocele is treated by freeing the spinal cord from its attachment to the lipoma, removing as much of the lipoma as safely possible, and closing the membranes over the spinal cord.
The goals of surgical treatment of dermal sinus tract are to remove the tract, untether the spinal cord, and to prevent any loss (or any further loss) of neurological function. The tract must be removed because it provides a conduit from the spinal canal to the outside world.
Tumors and cysts may be removed from the spinal cord with microsurgical resection. This type of surgery uses an operating microscope and very fine tools to remove masses from the spinal cord.
Surgery for tethered cord is tailored to the cause of the tether. In general, the spinal column is opened from behind via a laminectomy to reveal the location of the tether. The surgeon then works carefully to release the constriction.