The “cord” in tethered cord refers to the spinal cord. The “tether” refers to a sticking point. The spinal cord normally hangs down between the bones of the spine, called vertebrae. A sheath of tissue surrounds the cord, enclosing it along with fluid, called cerebrospinal fluid (CSF). As your child grows, so do the spinal cord and its surroundings.
Occasionally, the spinal cord is restricted and cannot grow. This can happen when the cord or its sheath becomes affixed to the surrounding bony structures. Initially, this causes no problems. But as a child grows, the stuck cord cannot stretch. Instead, the nerves of the cord are slowly pulled taut. Eventually, the nerves cannot perform their usual functions, such as transmitting impulses to muscles in various parts of the body.
The symptoms of a tethered cord really depend on where along the spine the cord is stuck. This location will determine which nerves are pulled. By far the most common place for a tether to occur is toward the bottom of the spine, at the L4-L5 level. The L is short for lumbar, the section of the spine that goes (approximately) from the bottom of the ribs to the hips. The numbers refer to vertebrae, which you can feel as you run your hand up and down your child’s back. The vertebrae are counted from top to bottom, so LI is at the top of the lumbar section of the spine, closer to the ribs, and L5 is at the bottom, near the hips.
A tether in the lower lumbar region is especially significant because the nerves that travel to the bowel and bladder exit the spinal cord at that level. Therefore, when the cord tethers there, the symptoms usually involve the bowel and bladder: constipation, urinary retention, or urinary tract infection (UTI). Nerves that exit the spinal cord below the level of the tether also become impaired. This means that nerves traveling to the legs and feet are usually involved when a cord becomes tethered. The result is a tingling sensation (“pins and needles”) or weakness in the feet or legs, but no symptoms in the back, where the tether actually exists.
What causes a cord to tether? Usually there is an underlying anatomical irregularity. Sometimes the sheath that encases the spinal cord gets trapped between vertebrae during fetal development. When only the sheath is involved, the condition is called a meningocele. When both the sheath and the cord beneath it are involved, it is called a meningomyelocele. Cysts or other masses also may develop along the inside of the spinal column. These masses may create sticking points for the spinal cord. Or the spine may curve, as is the case with scoliosis, trapping the spinal cord.
In toddlers, it can be very difficult to diagnose a tethered cord. Whereas adults can describe tingling in their toes and numbness in their legs, toddlers usually cannot. Toddlers are also more likely just to keep on going despite new sensations or increased difficulty moving. Therefore, a tethered cord is suspected when a constellation of symptoms appears: changes in gait or foot coordination; complaints of feeling funny tingling or “sleepiness” in the toes, feet, or legs; changes in urinary patterns and bowel patterns; and recurrent UTIs.