Which spina bifida form is typically invisible externally?

• A. Spina bifida occulta
• B. Meningocele
• C. Myelomeningocele
• D. Myeloschisis

Answer: (A)

Spina bifida occulta is defined by a defect in the vertebral arches without herniation of the spinal cord or meninges. Because there is no sac or exposed tissue protruding through the opening, the skin surface often looks normal, so the condition is typically invisible externally. Many cases are found later only on imaging or when subtle skin clues appear over the spine, such as a tuft of hair, a dimple, or pigmented birthmark, lipoma, or other markers that hint at the underlying vertebral anomaly.

In contrast, forms like meningocoele and myelomeningocele involve herniation of meninges with or without neural tissue through a vertebral defect, creating a visible bulge or sac on the back at birth. Myeloschisis presents with an open neural tube defect and exposed neural tissue, which is also clearly externally apparent. Because occult spina bifida lacks those outward signs, it’s the form most commonly invisible at first glance.