Meningomyelocele

Article Author:
Mitali Sahni
Article Editor:
Abhinav Ohri
Updated:
9/16/2019 5:06:49 PM
PubMed Link:
Meningomyelocele

Introduction

Meningomyelocele or myelomeningocele, commonly known as open spina bifida is a devastating congenital malformation of the central nervous system and is associated with significant morbidity. Neural tube defects are of two types: open and closed. Open neural tube defect means that the defect is either not covered at all or just covered by a membrane. Open neural tube defects comprise 80% of all neural tube defects. Myelomeningocele is the most common open neural tube defect. It is characterized by failure of the neural tube to close in the lumbosacral region during the embryonic development (fourth-week post-fertilization) leading to the herniation of the meninges and spinal cord through a vertebral defect.[1] The neural tube fusion starts at the level of the hindbrain (medulla and pons) and progresses rostrally and caudally. Incomplete fusion caudally leads to the formation of meningomyelocele around day 26 of gestation.[2]

Etiology

Most open neural tube defects occur sporadically, however, they are believed to have a multifactorial etiology. Two to 16% of them are associated with a single gene or chromosomal anomalies. Trisomy 18 is the most commonly associated aneuploidy with open neural tube defects. Other genetic disorders associated with it include Meckel-Gruber syndrome, Roberts, Jarcho-Levin, HARD (Hydrocephalus, agyria and retinal dysplasia), trisomy 13, PHAVER syndrome, VATER syndrome, and X-linked neural tube defects among others.[3][4] If a prenatal diagnosis of myelomeningocele is suspected, karyotype and genetic consultation should be obtained.[5] Various maternal and environmental factors are also associated with an increased risk for neural tube defects. Maternal alcohol use, caffeine use, elevated glycemic index, and gestational diabetes mellitus increases the risk of myelomeningocele. Similarly, low maternal folate and methionine intake, low levels of zinc, vitamin C, vitamin B12, and choline levels also increases its risk. Maternal smoking, low socioeconomic status, infections, obesity, stress, and valproic acid use also increases its risk. Various folic acid antagonists like valproic acid, carbamazepine and methotrexate have been linked to neural tube defects. Environmental factors contributing to increased risk include air pollution, disinfectant byproducts in drinking water, exposure to organic solvents, pesticides, nitrate-related compounds, and polycyclic aromatic hydrocarbons.[1] Amniotic bands may be another risk factor for the development of neural tube defects as they may disrupt normal neural tube development. Maternal fever or hypothermia from febrile illness or external sources like sauna, hot tub especially during the first trimester has been linked to increased neural tube defects.

Epidemiology

Myelomeningocele is the most common disorder of neurulation that results in viable infants. Its incidence in the United States is about 0.2 to 0.4 per 1000 live births. However, its incidence is up to 20-times higher in some regions of China.[1] Within the United States, rates are higher in the Latino population. Females are affected up to 3- to 7-times more than males. The incidence also increases with lower socioeconomic status and increasing maternal age. The recurrence rate in subsequent pregnancies is about 2% to 3%.[6]

Pathophysiology

Failure of closure of the neural tube leads to exposure of the neural tube to amniotic fluid. Although the neuroepithelium initially develops normally with neuronal differentiation and function, over time these neurons die because of toxicity from exposure to amniotic fluid. Hence it is often described as a "two-hit" process. First is failed neural tube closure and second is neurodegeneration in utero.[7]

History and Physical

The diagnosis in a newborn is usually obvious because of the grossly visible lesion in the back. A protruding membrane covered sac-containing meninges, cerebrospinal fluid (CSF) and nerve tissue is seen through a defect in the vertebral column. The clinical features of myelomeningocele depend on the level of involvement, the presence of hydrocephalus and other associated brain abnormalities. Newborns may remain asymptomatic up to 6 weeks of age. If hydrocephalus is present and worsens, clinical signs of increased intracranial pressure may be present. These include an increase in head circumference, irritability, lethargy and limited upward gaze (sun-setting sign).[8] Impairment in sensory, motor and sphincter function is present depending on the level of lesion. Bowel and bladder function is impaired in almost 97% of the population with spina bifida. Loss of function in antigravity muscles like iliopsoas and quadriceps leads to problems with ambulation and may progressively worsen with age. Most individuals with myelomeningocele have complete paralysis and loss of sensation in their lower extremities and trunk, below the level of the lesion.[9]

Spina bifida can also be associated with Chiari-II malformation which is characterized by downward displacement of the cerebellar tonsils and medulla. This malformation leads to obstruction of the CSF flow through the posterior fossa leading to hydrocephalus.[10] These associated neurological abnormalities are responsible for most of the major neurological morbidity and mortality. If brainstem dysfunction is present, these patients can have swallowing difficulties, vocal cord paresis leading to apnea and stridor.[11][12]

Evaluation

Most neonates are diagnosed prenatally by maternal screening with the help of ultrasound and/or serum levels of alpha-fetoprotein. The screening test of choice is a high-quality second-trimester ultrasound as it is more accurate in detecting neural tube defects as compared to serum levels of alpha-fetoprotein. All pregnant women should be offered screening for neural tube defects as selective screening is ineffective in detecting all cases of neural tube defects. If there is a positive screen, a comprehensive evaluation is done, including a complete anatomy scan, genetic testing like fetal karyotype and fetal magnetic resonance imaging if ultrasound imaging is indeterminate. Once the diagnosis is confirmed, extensive prenatal counseling must be undertaken to discuss the natural history of spina bifida, offer additional prenatal testing and provide choices for management including termination of pregnancy, postnatal surgery or fetal surgery if available. Serial ultrasounds are also done to monitor head growth, ventricular size, and help with delivery planning.[13]

Treatment / Management

Fetal surgery has increasingly become common in the treatment of myelomeningocele. The rationale for doing fetal surgery comes from animal studies where it has been shown that by intrauterine closure of the myelomeningocele lesion, the progressive intrauterine damage of the neural tissue due to exposure to amniotic fluid can be prevented. [14] A randomized control trial comparing the efficacy of prenatal surgery vs. postnatal repair was done and was stopped early due to better outcomes with prenatal surgery. The trial showed that prenatal surgery was associated with a decreased rate of shunt placement (40% in the prenatal group and 82% in the postnatal surgery group). It also showed that children who underwent prenatal surgery had improved mental development and motor function at 30 months. Complications associated with prenatal surgery were increased risk of prenatal delivery and uterine dehiscence at time of delivery.[15]

When the infant is born, careful assessment of the lesion should be done while laying the infant in the lateral or prone position, to avoid pressure on the lesion. Non-latex gloves should be used to avoid latex sensitization[16] and the lesion should be covered by a moist dressing or plastic wrap to prevent heat loss. The dressing should ideally be removed only in presence of the neurosurgeon. In postnatal surgery, closure of myelomeningocele should be done as early as possible to reduce the risk of infection (ideally within the first 48 hours after birth).[17] In patients with associated Chiari II malformation, presenting with brainstem dysfunction decompressive upper cervical laminectomy may be needed to reduce brainstem and cerebellar tonsillar decompression.[18] Most of these patients benefit from a multidisciplinary team approach for coordinating their management. In patients with urinary dysfunction, daily catheterization is needed to prevent urinary tract infections. Orthopedic follow up should be done to prevent, monitor and treat contractures and scoliosis.[19] Delivery should preferably be done at a center with a level III neonatal intensive care unit or above along with accessibility to pediatric neurosurgery services. Delivery should be performed at term to prevent complications related to prematurity. When in utero surgery was performed, delivery should be planned via early term or late preterm cesarean section as there is a risk for uterine rupture.

Differential Diagnosis

  1. Caudal regression syndrome (sacral agenesis)
  2. Sacrococcygeal teratoma
  3. Multiple vertebral segmentation disorder
  4. VACTERL (vertebral anomalies, anal atresia, cardiac abnormalities, tracheoesophageal atresia/ esophageal atresia, renal anomalies and limb defect).
  5. Spine segmental dysgenesis[20]

Prognosis

Patients with spina bifida have a mortality rate of about 1% per year from the age of 5 to 30 years. The higher the lesion, the greater the mortality rate. Among survivors, their quality of life is massively impacted by their diagnosis. Psychosocial issues like increased incidence of depression, anxiety, and risk-taking behaviors are common in this group. Studies have shown that the areas most likely to be affected are employment, romantic relationships, and financial independence.[13]

Complications

Various complications associated with myelomeningocele are-

  • Learning disabilities and cognitive impairments
  • Tethered cord
  • Seizures
  • Hydromyelia
  • Paralysis and loss of sensation below the site of the lesion
  • Arnold-Chiari Malformation of the brain, associated with hydrocephalus
  • Abnormalities of the corpus callosum
  • Decreased mobility as a function of the height of the lesion and associated muscle weakness
  • Neurogenic bladder and frequent urinary tract infections
  • Bowel dysfunction
  • Pressure ulcers due to sensory loss
  • Orthopedic problems associated with paralysis, for example, scoliosis, contractures, hip dislocation among others[21] 

Deterrence and Patient Education

Spina bifida is a type of congenital disability in which the backbone or spine does not typically form in a baby, while they are developing in the mother’s womb. It is also known as myelomeningocele or open neural tube defect. As a result of this defect when the baby is born, they have an opening in their skin on their back through which part of the spine and nerve tissue can protrude out.

It can cause various long-term problems in your child, and they depend on how severe the defect is. Many babies with spina bifida can have the following:

  • Weakness of their leg and may not be able to walk
  • Loss of feeling below their waist
  • Problems controlling their urine and stools
  • Problems with learning or memory
  • Problems with joints and legs
  • Some children may also develop too much fluid in their brain and may need surgery to relieve the pressure on their brain

After receiving a prenatal diagnosis of spina bifida, some parents chose to terminate the pregnancy, while others chose to continue their pregnancy. If you chose to continue the pregnancy, some centers can offer fetal surgery to correct the defect or a planned cesarean section near term can be offered with a surgical plan to correct the congenital disability immediately after birth. After the initial treatment, your baby will need medical management throughout their life.

They may need:

  • Wheelchair or assist devices to help them walk
  • Other surgeries to fix their bones
  • They may have learning problems and need additional testing and help at school
  • If their bladder does not work, they may need a tube to empty their bladder from time to time.

A child’s diagnosis will affect their quality of life. The best way to support the child will be to take them to a multidisciplinary team of medical professionals who specialize in taking care of patients with this diagnosis.

Enhancing Healthcare Team Outcomes

Problems with urinary continence are common in patients with myelomeningocele. They are at increased risk of urinary tract infections because of the need for frequent catheterization. Early initiation of intermittent catheterization reduces the risk of renal disease. These patients also have an increased risk of bowel incontinence and issues with bowel motility. A comprehensive bowel management routine including routine use of laxatives, enemas, and suppositories should be adopted to avoid complications.

Routine surveillance in an orthopedic clinic also helps promote ambulations, prevent and manage deformities like scoliosis and contractures and maximize mobility. Worsening scoliosis could be a sign of complications like tethered cord, shunt malfunction, hydromyelia, among others and must trigger immediate evaluation.

Almost 75% of patients with spina bifida survive to early adulthood. A multidisciplinary, patient-centered, team-based approach to provide medical, educational, social and developmental services, can enhance the quality of life of these patients by improving their overall health and functioning.[22]


References

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