Abstract
In this chapter, the common pediatric conditions of Myelomeningocele and Hydrocephalus are reviewed. The pathophysiology of spina bifida is discussed in relation of both post-natal and fetal surgical management. The author covers the surgical interventions and the related complex anesthetic considerations for both the primary repair of myelomeningocele as well as for ventriculoperitoneal shunt placement. The presentation of patients with raised intracranial pressure in the setting of hydrocephalus is considered.
A four-year-old child presents for replacement of her ventriculo-peritoneal (VP) shunt. She has spina bifida diagnosed postnatally and has mild developmental delays. Over the last day, she was lethargic at home and “not acting herself” prompting a trip to the emergency department by her parents.
In the preoperative area, she is responsive but very sleepy. Vitals include: Temp 37.60C, BP 107/62, HR 67 bpm, SpO2 100%. She is your next case to follow.
Two hours later, the nurse in the preoperative holding area calls you concerned that she seems “sleepier” and not very arousable. She is also concerned that the patient’s heart rate is only 49.
What Are the Types of Spina Bifida?
Spina bifida is a broad term encompassing defects of the skin (spina bifida occulta), vertebrae, meninges (meningocele), and spinal cord (myelomeningocele [MMC]).
What Are the Predisposing Risk Factors Related to Spina Bifida?
Maternal folate deficiency has been associated with a two- to eight-fold increased risk for developing spina bifida. Other maternal factors include vitamin B12 deficiency, pregestational diabetes, obesity, and antiepileptic use (carbamazepine and valproic acid). History of previous pregnancy (with the same partner) complicated by spina bifida affords significant increased risk.
What Prenatal Studies Are Performed to Assess for Spina Bifida and the Degree of Neurologic Involvement?
Elevated levels of maternal serum alpha-fetoprotein are suggestive of spina bifida or anencephaly. Amniocentesis allows for measurement of alpha-fetoprotein in the amniotic fluid and fetal karyotyping for associated chromosomal abnormalities. When the diagnosis is suspected, ultrasound or fetal MRI can assess for neurologic defects and presence of a Chiari malformation. Ultrasound of the lower extremities is used to assess fetal leg and foot movement and associated limb deformities.
What Is the Incidence of Myelomeningocele (MMC)?
The incidence of MMC is around 0.5–1:1,000 live births.
What Are the Etiologies of MMC?
The exact etiology of MMC remains unknown. Failure of closure of the neural tube or mesenchymal closure of the caudal neuropore during development has been suggested. Exposure of unprotected neural tissue may result in traumatization of the spinal cord. In addition, it is thought that prolonged exposure of the spinal cord tissue to amniotic fluid throughout gestation leads to damage.
What Is the Defect That Occurs with a MMC?
A defect in the vertebral arches leads to protrusion of the meninges and spinal cord (neural tissue).
What Are the Most Common Locations of MMC Defects?
Most commonly, the defect occurs in the lumbar region, although it can occur at any location along the spinal cord. Anencephaly occurs when the cerebral portion of the primary neural tube fails to close.
What Are the Potential Causes of Neurologic Morbidity in Patients with MMC?
Long-term sequelae relate to immobility leading to pressure-related ulcerations, venous thrombosis leading to deep venous thrombosis/pulmonary embolism, urinary tract infection from frequent bladder catheterizations, and issues relating to hydrocephalus and shunt function.
Hydrocephalus is common in children with MMC especially in the presence of Chiari malformations and may be related to obstruction of CSF flow by the herniated cerebellum (Figure 35.1).
What Are the Associated Neurologic Disabilities Attributed to a MMC?
Neurologic manifestations include: varying degrees of mental retardation, bowel and bladder dysfunction, and orthopedic-related disability. The degree of bowel and bladder dysfunction and extremity paralysis correlates with the level of herniated spinal cord tissue.
What Is the Rationale for Midgestation Fetal Repair of MMC?
Prolonged fetal exposure of the developing spinal cord to amniotic fluid is thought to contribute to significant neurologic morbidity. Fetal correction via a midgestational procedure has been shown to significantly improve neurologic function and reduce the morbidity from hydrocephalus and the Arnold–Chiari malformation. Fetal repair lends a significant reduction in the need for VP shunt, a major cause of morbidity for these patients. The considerations for fetal intervention are discussed in Chapter 46.
What Other Conditions Are Associated with a MMC?
Patients with spina bifida have a high incidence of Arnold–Chiari II malformation. The Chiari II malformation is herniation of the hindbrain (cerebellum and brainstem) through the foramen magnum. Fetal correction of MMC is associated with a reduced incidence of Chiari II malformations. Chiari II malformations are corrected by surgical decompression to remove the bone surrounding the hindbrain. The repair is performed in the prone position, is generally extradural and with the assistance of neurologic evoked potential monitoring.
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