Abstract
This chapter summarizes the common complications associated with myelomeningocele closure. Although cerebrospinal fluid leak and spinal cord tethering/fixation at the closure site and the most common problems, other issues can occur (inclusion dermoids and unrecognized hemimyelia). Appreciation and prevention of these problems is addressed.
Keywords
myelomeningocele, complications, hemimyelia, tethered spinal cord, cerebrospinal fluid leak, inclusion dermoid
Highlights
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Cerebrospinal fluid leak and retethering are two of the more common complications after myelomeningocele repair.
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Watertight dural closure and adequate cerebrospinal fluid diversion are important in preventing and managing cerebrospinal fluid leak.
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Imbrication of the neural placode not only may help prevent retethering, but also may make untethering at a later date, when indicated, easier to perform.
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Retethering typically is caused by scarring of the neural placode or imbrication suture line to the dorsal dura.
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Other causes of tethering are inclusion dermoids or unrecognized concomitant lesions, such as split cord malformation (hemimyelia).
“Le mieux est l’ennemi du bien.” (“The best is the enemy of the good.”) —VOLTAIRE
Background
In the post–folic acid fortification era, an estimated 1500 children in the United States are born with spina bifida every year. The vast majority of patients with myelomeningocele undergo surgical closure within 48 hours after birth. Complications that occur shortly after surgery include worsened neurologic function or level, cerebrospinal fluid (CSF) leak, wound dehiscence, meningitis, and wound infection. Unfortunately, some of these complications may occur concomitantly. Complications that occur in a delayed fashion include symptomatic Chiari II malformation, which can occur within weeks to months of birth, and retethering, which typically occurs years to decades later.
Anatomic Insights
Understanding the anatomy is critical to successful myelomeningocele repair ( Fig. 31.1 ). The neural placode is a flattened, open embryologic form of the caudal aspect of the spinal cord. The dorsal surface corresponds to the unclosed interior of the neural tube. The central canal of the normal, closed spinal cord above is in direct continuity with the primitive neural groove down the midline of the placode. The ventral surface corresponds to the entire exterior pial-lined surface of what should have formed into a closed neural tube. Thus, both the ventral and dorsal nerve roots arise from the ventral surface of the placode, with the dorsal sensory roots lateral to the ventral motor roots.
Surrounding the edge of the placode is the arachnoid membrane, which extends laterally to fuse with the edge of normal skin. Ventral to the placode is an intact subarachnoid space. Although the ventral dura develops normally, rather than fusing in the dorsal midline, the dura fuses with the free edges of the surrounding soft tissue, including the paraspinal musculature, lumbodorsal fascia, and/or periosteum of the incomplete neural arch. What would have been the dorsal dura therefore lies laterally just beneath the surface of the skin.
Due to the incomplete formation of the posterior neural arch, the dorsal paraspinal musculature and lumbodorsal fascia are displaced ventrolaterally and may be attenuated. The underlying vertebral bodies typically are flattened and widened. The pedicles are usually everted, which, in combination with wider vertebral bodies, results in an increased interpedicular distance. The laminae remnants typically are hypoplastic and may also be everted. The spinous processes are absent.
To identify all of the important structures, closure of the myelomeningocele begins with a circumference incision around the myelomeningocele at the junction of the arachnoid and the advancing edge of epithelium. Attention is then turned toward dissection of the neural placode. The nerve roots are dissected free from the arachnoid. The arachnoid and remaining epithelium are then sharply divided away from the neural placode, allowing it to move freely within the CSF. The superior and, to a lesser degree, inferior poles of the placode are technically the most challenging to separate. Although there is some debate about it, the neural placode likely contains residual functional neural elements with a reflex arc especially important for rectal sphincter tone, so it should be handled with care to minimize injury. It is also important to ensure that no epithelium is retained within the neural placode, because it can result in an inclusion dermoid, which not only enlarges over time, but also can cause arachnoiditis and enhance the tethering process.
This idealized description may seem moot when one is faced with significant variation from the individualized patient. Although the goal is the maintenance of neurologic integrity and the exclusion of all dermal elements in the closure of the neural placode, in practice this can prove technically challenging.
Cerebrospinal Fluid Leak
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Large, wide epithelial deficiency for skin closure
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Hydrocephalus
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Kyphotic deformity
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Lesions involving deficient sacral skin
Retethering
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No imbrication of placode at time of initial myelomeningocele closure
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Shallow spinal canal
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Inclusion dermoid
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Thickened filum terminale
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Split cord malformation (hemimyelia)
Prevention
Cerebrospinal Fluid Leak
A meticulous watertight primary dural closure is important to the prevention of a CSF leak. We prefer to use a 6-0 polydioxanone (PDS) suture with a small tapered needle in a running fashion. If care is taken to identify the extreme lateral aspect of the dura, there is almost always adequate material for primary closure without tension. After the dural closure is completed, Valsalva maneuvers should be performed to evaluate the integrity of the closure.
After the primary dural closure, it is desirable to perform a strong, multilayered wound closure. Mobilizing paraspinal musculature and fascia for soft-tissue coverage over the midline can help tamponade and contain small CSF pseudomeningoceles and may help prevent CSF leakage through the skin. With wide areas of absent skin, these tissues may not be available to assist in the closure, leaving only the skin. If the lesion is especially large, it may be prudent to consider requesting assistance from plastic surgery colleagues with the skin closure.
Although dural closure is the surgeon’s primary defense against CSF leak, this must be balanced against tight soft-tissue compression of the neural elements, particularly when they are positioned proud of the skin surface, which can compromise the blood supply to the neural placode.
Postoperatively, keeping the patient prone and relatively flat may also help prevent CSF leak. This decreases pressures within the lumbar thecal sac, allowing any small tears or holes within the dura to heal. At our institution, the more precarious the wound closure, the longer we tend to keep the patient flat. However, this must be balanced with the upright nurturing of the patient by the mother.
Finally, it should be emphasized that CSF leaks cannot be avoided if intracranial pressure (ICP) is elevated and hydrocephalus is not appropriately treated. For lesions with large skin defects and limited soft-tissue coverage that require complex skin closures, an external ventricular drain (EVD) for temporary CSF diversion to allow for better wound healing may be a consideration. Even if it is not present at birth, progressive hydrocephalus may develop over time, especially after closure of a leaking myelomeningocele. Prompt treatment of hydrocephalus with a ventriculoperitoneal (VP) shunt or endoscopic third ventriculostomy (ETV) is important for prevention of CSF leaks and meningitis.
Retethering
Preventing retethering remains a significant neurosurgical challenge. Unfortunately, there are no infallible methods for avoiding retethering, but the stage should be set to minimize this problem during the initial myelomeningocele repair.
Imbrication of the placode, that is, reapproximation of the pial edges of the placode into a tubular structure, may help because it decreases the exposed raw surface area available for retethering. It also makes untethering at a later date easier because the anatomy can be more readily identified. We prefer to use interrupted 7-0 nylon sutures in an inverted fashion to imbricate the placode to minimize the exposed suture line, which is the most common site of tethering after myelomeningocele repair.
After imbrication of the placode, it is important to inspect for the presence of other concomitant tethering lesions. Occasionally, there is a thickened filum terminale that should be sectioned if present. In our institution, the last intact spinal lamina is cut during the initial myelomeningocele repair to inspect for evidence of a split spinal cord malformation, which is present in 6% of patients. Hemimyelia is the presence of a terminal split cord malformation with a myelomeningocele involving only one of the hemicords ( Fig. 31.2 ). These patients often present with asymmetry in lower-extremity neurologic examination, with greater distal dysfunction ipsilateral to hemicord with myelomeningocele. Although these lesions per se do not technically cause retethering, if unrecognized and untreated during the initial repair, they can cause progressive loss of neurologic function over time.
