Meningocele

Etiology

The definitive etiology of meningoceles remains poorly understood. Most isolated neural tube defects appear to be caused by folate deficiency, likely combined with genetic and environmental risk factors. Folate deficiency may be related to inadequate oral intake, folate antagonist use, or genetic factors causing abnormal folate metabolism. Meningoceles may also be associated with chromosomal anomalies or single-gene disorders.

Genetic syndromes associated with meningoceles include HARD (hydrocephalus, agyria, and retinal dysplasia), Meckel-Gruber syndrome, and trisomy 13 or 18. Anterior and lateral meningoceles can be associated with neurofibromatosis type 1 and Marfan syndrome.[7] Lateral meningocele syndrome is a rare genetic disorder of the connective tissue, which leads to meningoceles protruding through the neural foramina. Other features of lateral meningocele syndrome include craniofacial dysmorphic features, such as hypertelorism, ptosis, midface hypoplasia, and micrognathia. These patients can also have other neurological conditions, including hydrocephalus and Chiari I malformation. Mutations in the NOTCH3 gene, inherited in an autosomal dominant manner, characterize this disorder.[8]

Maternal factors associated with an elevated risk for neural tube defects include advanced and young maternal age, low socioeconomic status, maternal alcohol use during pregnancy, smoking, caffeine use, obesity, high glycemic index, and gestational diabetes. Maternal use of antiseizure medications, including valproic acid and carbamazepine, may lead to the development of neural tube defects. The elevation of maternal core temperature in the first trimester from febrile illness or other sources may be associated with the development of meningoceles. Environmental factors like agrochemicals and polycyclic aromatic hydrocarbons can also cause neural tube defects.[9][6]

Epidemiology

The incidence of neural tube defects ranges from 1 to 10 per 1000 births worldwide. The prevalence of neural tube defects in the United States and many European countries is around 0.5 to 0.8 per 1000 births, and the risk in subsequent pregnancies is upwards of 5%. Spinal meningoceles are less common than myelomeningoceles. Most meningoceles occur in the lumbar spine, although they can occur throughout the entire neural axis.

The prevalence of neural tube defects has variable rates among differences in geography, ethnicity, gender, and countries. The prevalence is higher among White patients compared to Black patients and in females compared to males. The risk of neural tube defects for some ethnic groups (eg, European and Hispanic) is higher than for others (eg, White and Asian).[6][10][11]

Pathophysiology

Although skin-covered, meningoceles are grouped into disorders of primary neurulation. During neurulation, a coordinated series of events gives rise to a neural plate and folds, forming the neural tube. The neural tube eventually forms the brain and spinal cord. Neural tube defects arise from the anterior (ie, anencephaly) and posterior neuropores (ie, myelomeningoceles) as they are last to close.

Meningoceles result from a failure to develop the caudal end of the neural tube, causing a protrusion that contains cerebrospinal fluid and meninges and does not contain neural tissue. Anterior meningoceles, a subset of lumbosacral meningoceles, are usually presacral in location and are often asymptomatic throughout childhood. These meningoceles are primarily present as abdominal complaints such as bowel and bladder disturbances, abdominal pain, and even infertility.[12] Intrathoracic meningoceles are fluid-filled sacs with the spinal meningeal wall's protrusion into the thoracic cavity through an enlarged intervertebral foramen.

Neurologic manifestations of meningoceles depend on their size and location and may include back pain, neurogenic bladder, paresthesias, and paraparesis. Other neurologic findings can include syringomyelia, Chiari I malformation, and, rarely, hydrocephalus. Neural tube defects are complex multifactorial defects involving both environmental and genetic factors.[13][14][5][15][16]

Meningocele manque is characterized by dorsal intradural bands that tether the spinal cord. The classical theory of the development of these bands stems from meningoceles that failed to form during development and eventually atrophy. However, some propose that these bands form due to abnormal regression of the caudal neural tube. Meningocele manque has a strong association with split cord malformations and intradural lipomas.[17] 

Histopathology

On microscopic examination, meningoceles demonstrate a thick fibrous wall lined by flattened arachnoid cells.

History and Physical

Prenatal screening for neurological defects includes measuring maternal serum alpha-fetoprotein and performing high-quality second-trimester ultrasound to detect fetal anomalies. Defects can present throughout the spine, with the lumbar region being the most common. Neurological involvement and deficits are rare in meningocele. On clinical examination, a fluctuant midline mass that transilluminates is present. The newborn's initial assessment is essential at birth. A detailed examination of the head and neck should include the size and shape of the head, skull, and anterior fontanelle. A complete neurological exam should be performed at birth to exclude neurological abnormalities.

The clinical manifestations of a thoracic meningocele are related to its size and proximity to the surrounding structures. This condition can present with back pain, shortness of breath, coughing, and palpitations when accompanied by lung and mediastinal structure compression.[3][13] Meningoceles can be seen in patients with neurofibromatosis and can occur within the thoracic cavity or cervical spine. When these occur within the thoracic spine, they are most often found incidentally; however, patients can present with dyspnea secondary to direct compression or intrathoracic rupture.[18] When occurring within the cervical spine, patients may present with dyspnea, changes in voice, or dysphagia.[19] Others have reported anterolateral meningoceles in the cervical spine, causing radiculopathies presenting with weakness and paresthesias.[7] Cases of anterior cervical meningoceles with craniovertebral junction instability have also been reported.[20] Though rare, double meningoceles have been reported, with cervical meningoceles being seen in addition to lumbosacral myelomeningoceles.[21]

Evaluation

All patients with a suspected meningocele must be assessed radiologically after birth. Plain x-rays may show associated skull defects, bone abnormalities, and spine deformities. Magnetic resonance imaging (MRI) is the best diagnostic test to assess the lesion and evaluate for underlying hydrocephalus. Ultrasonography can also be used to quickly assess ventricular size if patients are too unstable for an MRI.

Treatment / Management

The management of meningoceles is primarily surgical. However, counseling the family regarding treatment's immediate and long-term effects is a vital component of meningocele management. Surgery is preferred as soon as feasible on large meningoceles. In suspected central nervous system infection or meningitis, treatment is started immediately with prophylactic antibiotics and anticonvulsants. Patients require monitoring in the neonatal intensive care unit with an assessment of electrolytes and blood counts.

The association of meningocele with tethered cord syndrome is high. Active surgical treatment is suggested immediately after a definitive diagnosis. During surgery, the surgeon should explore the spinal canal and release the tethered cord after repairing the protruded meninges.[3][4] Patients with anterior or lateral meningoceles may benefit from genetic counseling if neurofibromatosis type 1, lateral meningocele syndrome, or Marfan syndrome are suspected. 

Differential Diagnosis

The differential diagnoses of meningoceles are primarily other types of spina bifida, including myelomeningocele, lipomyelomeningocele, and sacrococcygeal teratomas. Cystic hygromas, dermoid cysts, hemangiomas, and branchial cleft cysts are among the differential diagnoses of cervical meningoceles.[22][23] Noonan syndrome shares some similar characteristic facial features as lateral meningocele syndrome, which has arched eyebrows, ptosis, flat midface, thin upper lip, low-set and posteriorly angulated ears, and low posterior hairline, hands with wide and short distal second and third fingers (ie, pseudo-clubbing).[16][24]

Prognosis

Meningocele usually has no neural involvement or acute neurological complications, hence a favorable prognosis. Spina bifida aperta usually presents a skin defect with the looming risk of cerebral spinal fluid leak, whereas the occult forms have no visible skin opening. The prevalence of spina bifida at birth has decreased by 23% over 10 years between 1995 and 2004 after the Food and Drug Administration mandated fortification of all cereal and grain products with folic acid. In clinical practice, the prognosis of patients with meningocele is excellent, and simple surgical repair is adequate.[3][6][4][6][4]

Complications

Compression of the meningocele can cause symptoms of increased intracranial pressure due to the displacement of extra spinal cerebrospinal fluid into the intracranial cavity. Raised intracranial pressure may cause erosion of the skull base and may result in a cerebrospinal fluid leak. Results from recent reports indicate that meningoceles are often associated with tethered cord syndrome, and the symptoms of tethered cord syndrome occur in a considerable proportion of children who had meningocele repair.[2][4][2][25]