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Spina bifida, tethered cord and closed dysraphism
Neural tube defects divide into open ones — myelomeningocele, closed within 48 to 72 hours of birth and almost always accompanied by Chiari II and hydrocephalus — and closed ones under the skin, whose clue is a cutaneous marker over the spine and whose danger is a tethered cord.
Why it matters in the exam
In myelomeningocele the lesion is usually lumbosacral, and motor and sensory deficit below the lesion, a neurogenic bladder and foot deformities are expected. Closure within 48 to 72 hours reduces infection. The MOMS trial showed that prenatal repair (before week 26) reduced the need for a shunt to 40% versus 82% with postnatal repair and improved motor function, at the cost of preterm birth and uterine risk. Almost all children with open myelomeningocele have Chiari II, and many need a shunt. Latex allergy is common, so care is latex-free. Prevention: folic acid 0.4 mg daily for every woman before pregnancy, and 4 mg daily after a previous affected pregnancy.
Closed defects: lipomyelomeningocele, dermal sinus, a thick tight filum and split cord malformation. In split cord type 1 there are two dural sacs and a bony or cartilaginous septum that needs surgery; in type 2 one dural sac and a fibrous septum. In tethered cord the conus lies below L2 and the filum is thicker than 2 mm; symptoms: back and leg pain, gait disturbance, bladder dysfunction, foot deformity and worsening scoliosis, and they worsen during growth spurts. Cutaneous markers that need work-up: a hair tuft, haemangioma, subcutaneous lipoma, or a dimple above the gluteal fold or more than 2.5 cm from the anus. A dermal sinus can cause meningitis and is therefore operated on early. A simple dimple under 5 mm, within 2.5 cm of the anus and with a visible base, needs no work-up. Work-up: ultrasound in an infant up to 3 to 6 months, and MRI after that.
Key points
- Myelomeningocele — closure within 48 to 72 hours; Chiari II almost always.
- MOMS: shunt 40% versus 82%.
- Tethered cord — conus below L2, filum over 2 mm.
- Cutaneous marker over the spine — ultrasound or MRI.
- Folic acid 0.4 mg, and 4 mg after a previous defect.
Summary table
| Condition | Finding | Work-up | Treatment |
|---|---|---|---|
| Myelomeningocele | Open sac with neural tissue, Chiari II | Head ultrasound, urological assessment | Closure within 48 to 72 hours; shunt as needed |
| Tethered cord | Conus below L2, filum over 2 mm | MRI | Untethering |
| Dermal sinus | Skin opening with a tract, recurrent infection | MRI | Early excision |
| Split cord type 1 | Two sacs and a bony septum | MRI and CT | Septum removal and untethering |
| Simple dimple | Under 5 mm, close to the anus | — | No work-up needed |
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Sources
- Management of Myelomeningocele Study (MOMS), 2011 — Prenatal versus postnatal repair
- Congress of Neurological Surgeons guidelines on myelomeningocele, 2019 — Timing of closure, hydrocephalus and tethered cord
- Israeli Ministry of Health recommendation on folic acid supplementation before and during pregnancy, current — Neural tube defect prevention
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.