Spina bifida occulta is a small gap in one or more bones of the spine that forms before birth. It’s the mildest and most common type of spina bifida, and most people who have it never know. The word “occulta” means hidden, which fits: the gap is entirely internal, covered by skin, and typically causes no symptoms at all. Many people only discover it as adults when a spine X-ray is taken for an unrelated reason, like a car accident or a fall.
How It Differs From Other Types of Spina Bifida
Spina bifida is a spectrum of conditions where the vertebrae don’t fully close around the spinal cord during fetal development. What separates spina bifida occulta from the more serious forms is that the spinal cord and nerves are not involved. The gap in the bone is there, but everything underneath stays protected and in place.
In the most serious type, myelomeningocele (also called open spina bifida), the spinal canal is open across several vertebrae and part of the spinal cord actually pushes through the opening, forming a visible sac on the baby’s back. Tissues and nerves are exposed, leading to significant neurological problems. In a middle-ground type called meningocele, a sac of spinal fluid bulges through the opening, but no nerves are affected. Spina bifida occulta sits at the far mild end of this spectrum: no sac, no exposed tissue, no nerve involvement in the vast majority of cases.
Skin Markers That Can Signal It
Because the bone gap is hidden beneath the skin, there are sometimes subtle surface clues over the lower back. These include a small dimple or pit in the skin over the spine, a tuft or patch of hair in an unusual location (sometimes called a “faun tail”), a port-wine stain or hemangioma birthmark, a small fatty lump (lipoma), or an off-center gluteal crease. Not everyone with spina bifida occulta has these markers, and having one doesn’t automatically confirm the condition. But when a pediatrician notices a midline dimple or hair tuft on a newborn’s lower back, it can prompt further investigation.
How It’s Diagnosed
Most cases are found incidentally. You go in for an X-ray after a back injury, and the radiologist spots the incomplete vertebral arch. That’s the typical story for adults. An X-ray, MRI, or CT scan can all show the gap clearly, revealing where the bone didn’t fully form during fetal development.
Unlike the more serious forms of spina bifida, which are usually detected during prenatal ultrasound, spina bifida occulta is mild enough that it often slips through prenatal screening entirely. Many cases go undiagnosed for a lifetime simply because there’s never a reason to image the spine.
Symptoms Most People Don’t Have
The majority of people with spina bifida occulta experience no symptoms whatsoever. They live completely normal lives, often unaware of the condition. The spinal nerves aren’t affected, so there’s no pain, weakness, or loss of function attributable to the gap itself. If you’ve just learned you have it from an incidental X-ray finding, chances are excellent that it will never cause you a problem.
When It Does Cause Problems: Tethered Cord
In a small number of cases, spina bifida occulta is associated with a condition called tethered cord syndrome. This happens when fatty tissue or a thickened band at the base of the spinal cord attaches it abnormally to the wall of the spinal canal. Normally, the spinal cord hangs loosely and can move freely as you grow and bend. When it’s tethered, growth and movement put tension on the cord, which can gradually damage nerves.
Tethered cord syndrome is uncommon, but its symptoms are worth knowing about. They can appear in childhood or not until adulthood, and they tend to develop slowly:
- Leg or back pain that may extend into the groin or rectal area
- Numbness or weakness in the legs
- Difficulty walking or changes in gait
- Bladder or bowel control problems, including incontinence
- Scoliosis (curvature of the spine)
- Loss of muscle mass in the legs
- Foot deformities that develop over time
The presence of skin markers like a dimple, lipoma, or birthmark on the lower back can be an early clue that tethered cord may be present alongside spina bifida occulta. If any of these neurological symptoms develop, an MRI can confirm whether the cord is tethered, and surgery to release it is typically effective at preventing further damage.
Treatment for Spina Bifida Occulta
If you have no symptoms, no treatment is needed. The bone gap itself doesn’t weaken your spine in a meaningful way, and it doesn’t progress or get worse over time. There is nothing to fix, and no restrictions on activity are necessary for the typical asymptomatic case.
Treatment only becomes relevant if a related problem like tethered cord develops. In that situation, the focus is on addressing the complication rather than the vertebral gap itself. For the overwhelming majority of people who learn they have spina bifida occulta, the appropriate response is simply knowing it’s there and understanding that it’s a common anatomical variation rather than a disease requiring management.
What Causes It
Spina bifida occulta develops very early in pregnancy, during the first month, when the neural tube (the structure that becomes the brain and spinal cord) is forming. The vertebrae that should fully enclose the spinal cord don’t completely close. The exact cause isn’t always clear, but low folate (vitamin B9) intake before and during early pregnancy is the best-established risk factor for all forms of spina bifida. This is why prenatal vitamins containing folic acid are recommended before conception and throughout the first trimester. Genetic factors also play a role, as the condition can run in families.