Neural tube defects and spinal dysraphism: Viva

Branch 1: Classification and definition

The candidate should define neural tube defects as the failures of the neural tube to close during the third and fourth week of embryogenesis, and give the open and closed classification. The open defects expose neural tissue to the amniotic fluid and include anencephaly, the encephalocele, and the myelomeningocele. The closed defects cover the malformation with skin and include the meningocele, the spina bifida occulta, and the occult dysraphic states. [1]

If the examiner presses for the occult dysraphic states, the candidate should name the lipomyelomeningocele, where a lipoma tethers the conus, the diastematomyelia, where a bony spur splits the cord, the dermal sinus tract, where an epithelial track runs to the spinal canal, and the tethered cord syndrome, where a thickened fatty filum anchors the cord. A strong candidate explains that the open lesion is the neonatal emergency while the tethered cord is the childhood problem, and that the Chiari II malformation and the hydrocephalus belong almost exclusively to the myelomeningocele phenotype. [1]

Branch 2: Prevention and prenatal screening

If asked about the prevention, the candidate should state the periconceptional folic acid doses. All women of reproductive age take 400 to 800 micrograms daily, and the United States Preventive Services Task Force reaffirmed the grade A recommendation in 2023 that the supplement is started at least one month before conception and continued through the first trimester. The high-risk woman, with a previous affected pregnancy or diabetes, takes 4 milligrams daily, established by the Medical Research Council Vitamin Study of 1991, which showed the 4 milligram dose reduced the recurrence by about 72 percent. [5][3]

For this infant, whose mother took no periconceptional vitamins, the candidate should note that the neural tube closes before the missed period, so the supplement started after the positive test is too late. The candidate should describe the mandatory food fortification of flour with folic acid as the public health measure that lowers the population prevalence by a quarter to a half. For the prenatal diagnosis, the candidate should give the maternal serum alpha-fetoprotein above two and a half multiples of the median at 15 to 20 weeks as the threshold for an open defect, and the fetal ultrasound at 18 to 20 weeks showing the lemon and banana signs of the Chiari II and the ventriculomegaly of the hydrocephalus. [5]

Branch 3: Neonatal management and the closure

If the examiner moves to the neonatal management, the candidate should run the structured emergency. Handle the baby in a latex-free environment from the first contact, because the latex sensitisation that complicates spina bifida begins with the early exposure. Place the baby prone or lateral and cover the lesion with a sterile saline-soaked dressing. Start the broad-spectrum antibiotics that cover the skin flora, and call the neurosurgical team for the closure within 24 to 72 hours. [1]

The candidate should describe the motor and the sensory level as the central bedside finding, because the lowest functioning muscle group predicts the ambulation potential. Examine the head for the macrocephaly and the full fontanelle of the hydrocephalus, and watch for the stridor, the swallowing difficulty, and the apnoea of the Chiari II. The candidate should describe the closure, where the surgeon frees the neural placode, reconstructs the neural tube, closes the meninges, and brings the skin over the defect, and the placement of the shunt for the hydrocephalus when the ventriculomegaly progresses. [7]

Branch 4: The lifelong complications and the fetal surgery option

If asked about the complications, the candidate should name the shunt malfunction, the Chiari II brainstem compression, the renal failure from the neurogenic bladder, and the latex anaphylaxis. The shunt malfunction is the commonest shunt emergency in this group, and a child who presents with the headache, the vomiting, or the drowsiness has a malfunction until proven otherwise. The neurogenic bladder is managed with the clean intermittent catheterisation and the anticholinergics, started early to protect the kidneys. The latex-free environment from birth prevents the sensitisation that produces the anaphylaxis. [7]

A strong candidate closes by describing the Management of Myelomeningocele Study, reported in 2011, which showed the prenatal repair before 26 weeks reduced the need for the shunt from 82 percent to 40 percent and improved the motor function, with the risks of the preterm birth and the uterine dehiscence. The candidate should name the cutaneous stigmata of the occult dysraphism and the spinal magnetic resonance imaging criteria for the tethered cord, including a conus below L2 and a filum thicker than 2 millimetres, and the lifelong multidisciplinary follow-up across neurosurgery, urology, orthopaedics, and rehabilitation as the standard of care. [6][8]