Mildest form of spina bifida (a neural tube defect) where the bony vertebral arches fail to fuse, leaving a "hidden" gap. It results from incomplete neural tube closure (around days 17-30 of gestation) but has no exposed neural tissue.
Occulta means "hidden" - it's extremely common (10-20% of people) yet usually asymptomatic. It's often discovered incidentally (e.g. on spine X-ray/MRI for another reason) but is a classic high-yield topic. A sacral tuft of hair, dimple, or birthmark is a key exam clue. Most cases are benign, but some patients have tethered cords, so recognition is important.
Often an incidental radiographic finding (e.g. a spine X-ray or MRI done for another reason).
Physical exam may show a sacral skin marker (hairy patch, dermal sinus, lipoma, hemangioma, pigmented nevus, or small dimple).
Neurologic exam is usually normal. If present, symptoms are subtle (mild leg numbness/weakness or occasional back pain).
Suspect SBO when you see a sacral tuft/dimple on exam or an incidental vertebral cleft on imaging.
Screen infants with spinal ultrasound (<6–9 months old) or older kids with MRI to evaluate the spinal cord (look for lipoma or thickened filum).
If imaging is normal and no symptoms, reassure. If cord tethering signs appear, or imaging is abnormal, refer to pediatric neurosurgery.
Identify sacral skin markers or incidental spine cleft → if age <6mo do spine ultrasound, if older do MRI.
If imaging shows isolated SBO with normal cord → routine follow-up. If filum thickening/low conus or symptoms → neurosurgery eval.
Remember: most SBO cases don't need surgery unless tethering symptoms develop.
Pelvic X-ray of an asymptomatic teen showing absence of the S1 spinous process (arrow).
Toddler with a sacral tuft/dimple and normal neurology – likely SBO (diagnosed by imaging; just observe if no tethering).
Case 1
A 2-year-old boy is found to have a small tuft of hair and a dimple at his lower back during a well-child exam. He has normal leg strength and no neurologic deficits.
