Management of neural tube defects: prevention, embryology, and surgical approaches
With Dr. Francesco T. Mangano
Chapter 3 of 10
Dimple evaluation
Clinical Evaluation: Dimples and Dermal Sinus Tracts
Cued at 9:41 · press play
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What the experts said
Global prevalence of neural tube defects is roughly 20 per 10,000 live births, with US incidence of 7 per 10,000 and some countries like Algeria reaching 96 per 10,000
Folate supplementation can have a significant reduction of the incidence of neural tube defects, and countries that have adopted fortification mandates have done much better than others in preventing this problem
The pathophysiology of tethered cord is primarily related to a lack of blood flow and oxidative metabolism to the cord
Benign sacral dimples in the intergluteal fold are relatively common in newborns and typically have no consequences; these patients typically do not have a tethered cord and do not have any reason to have any further imaging or workup
Any lesions occurring above the gluteal fold should be considered to be potentially abnormal and warrant investigation
X-rays are not necessary in evaluating any type of cervical, lumbar, or sacral dimple; ultrasound is beneficial for young patients and MRI is the gold standard for older patients
In many parts of the world, patients that have a fatty filum as a tethered cord finding on imaging are just observed and do not undergo prophylactic detethering; this is more of a North American trend in some institutions
Dr. Mangano does not typically detether patients that have an asymptomatic tethered cord, but follows them; the risk is that they could deteriorate at some point, but that is typically not the case
Lipomyelomeningoceles result from primary and secondary neurulation defects; patients usually present very early in life and prophylactic resection and detethering is typically recommended because they will become symptomatic
In lipomyelomeningocele surgery, the dura typically is not normal, so the dural dissection is extended out as laterally as possible to enable watertight closure without a patch; it is rare to require a dural patch
In type 1 diastematomyelia with a midline bony spur, the spur is the tethering lesion; prophylactic detethering occurs at the level of the bony spur, not necessarily at the bottom of the canal where the filum is located
Fetoscopic myelomeningocele repair has become what is primarily done at Cincinnati in 2022
Myelomeningocele is a primary problem of primary neurulation, with most lesions in the thoracolumbar region and primarily more distal
The majority of myelomeningoceles are associated with hydrocephalus requiring shunts when repaired postnatally, and more than 90% of patients have a Chiari 2 malformation
The morbidity associated with myelomeningocele is not typically related to the cord itself, but usually to the hindbrain issue and compression of the cervical medullary junction
Most patients with postnatal myelomeningocele repair will have a relatively low normal IQ and can function in community quite well
The downside of prenatal repair are the associated maternal and fetal risks
Adult tethered cord presentation is rare but when it happens with symptoms should be managed surgically; the clinical presentation can differ from the pediatric population, especially with incontinence
Folate supplementation is the best resource to prevent neural tube defects and leads to better outcomes than surgical outcomes
In Kenya, neural tube defects particularly spina bifida are common in some parts of the country; open repair with the technique Dr. Mangano described is standard, though some centers perform distal cordectomy when there is no lower limb function on neurostimulation
The challenge in Kenya is that spina bifida patients often present when the lesion has ruptured and is leaking, sometimes with significant burden of infection
In Kenya, most myelomeningocele patients undergo two-stage surgeries: repair the spina bifida first, then after healing give an appointment to return for VP shunt placement; for most this is adequate
In Kenya, patients who get early myelomeningocele repair and VP shunting tend to do well, particularly with long-term multidisciplinary follow-up for urinary incontinence and mobility issues
For postnatal myelomeningocele repair, the goal is to get to the patient within the first 48 to 72 hours of birth if possible
If there is evidence of the myelomeningocele leaking at birth, it is wrapped with Tegaderm and material that looks like Saran wrap to keep it moist so it doesn't dry out and scar quickly, and the patient is placed on intravenous antibiotics
Dr. Mangano does not typically place a shunt at the same time as myelomeningocele repair; he waits with daily ultrasounds to see what happens, as the great majority will require a shunt but delaying a few days to a week allows the lumbosacral region to heal
Sometimes hydrocephalus creates pressure on the myelomeningocele repair, in which case it is better to place a shunt to take CSF pressure off the lumbosacral repair
Adults with myelomeningocele tend to do worse as they get older rather than better, because as they age their muscles cannot keep up with the size of their bodies; patients may go from walking with braces to needing more assistance to eventually being wheelchair bound despite being able to move their legs
In the multidisciplinary spina bifida clinic, the goal is to optimize patients for social continence and get them to a place where they can be as independent as possible
The conus medullaris above L2 or above is considered to be normal, and anything below that level is considered to be abnormal
Tethered cord syndrome has been described in patients that have a normal conus medullaris, with roughly 50% of patients with occult tethered cord having a normal conus position
Dr. Yamada's experiments demonstrated that the greatest effect of pathology from tethering was in the lower set of nerves, with the dentate ligaments providing some protection to the rostral cord
Filum terminale lipomas have been reported in cadaveric studies to occur in as many as four to six percent of the population, with MRI prevalence up to four percent
Patients that have a conus below at or below the level of L4 tend to be those that present with symptoms, while those patients between L2 and L4 are less likely to present with symptoms (50% threshold)
Dr. Pang describes the ideal patient for lipomyelomeningocele repair as someone who is asymptomatic, less than two years of age, without a history of previous lipoma surgery
Three types of lipomyelomeningoceles: dorsal (lipoma not affecting the conus, easily dissected), transitional (lipoma extends into conus, difficult to achieve gross total resection), and chaotic (lipoma includes ventral roots, creating further difficulty in dissection)
The MOMS trial was stopped early because there was a clear demonstration of efficacy shown in the prenatal repair group
Prenatal myelomeningocele repair showed reduced need for shunting (40% versus 82%), improved composite score for mental development and motor scores at 30 months, improved hindbrain herniation at 12 months, and improved ambulation at 30 months
MOMS trial inclusion criteria required myelomeningocele between T1 and S1, grade 3 hindbrain herniation on MRI, gestational age between 19 and 27 weeks, normal fetal genome and echocardiography, and singleton pregnancy
Exclusion criteria for prenatal repair included significant fetal anomalies, lumbosacral kyphosis greater than 30 degrees, incompetent cervix, and significant morbid obesity by the mother