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Complications After Myelomeningocele Repair
31
Complications After Myelomeningocele Repair: CSF Leak and Retethering IRENE KIM, W. JERRY OAKES
HIGHLIGHTS • Cerebrospinal fluid leak and retethering are two of the more common complications after myelomeningocele repair. • Watertight dural closure and adequate cerebrospinal fluid diversion are important in preventing and managing cerebrospinal fluid leak. • 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. • Retethering typically is caused by scarring of the neural placode or imbrication suture line to the dorsal dura. • 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.1 The vast majority of patients with myelomeningocele undergo surgical closure within 48 hours after birth.2,3 Complications that occur shortly after surgery include worsened neurologic function or level, cerebrospinal fluid (CSF) leak, wound dehiscence, meningitis, and wound infection.4 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.4
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.5 The ventral surface corresponds to the entire exterior pial-lined surface of what 178
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.3,4 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.4 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.3–5 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.2,3,6 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.5,6 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.7
CHAPTER 31 Complications After Myelomeningocele Repair: CSF Leak and Retethering
• Fig. 31.1
179
Photograph of myelomeningocele on left. Illustration of anatomy of myelomeningocele on
right.
RED FLAGS Cerebrospinal Fluid Leak • • • •
Large, wide epithelial deficiency for skin closure Hydrocephalus Kyphotic deformity Lesions involving deficient sacral skin
Retethering • • • • •
No imbrication of placode at time of initial myelomeningocele closure Shallow spinal canal Inclusion dermoid Thickened filum terminale Split cord malformation (hemimyelia)
Prevention Cerebrospinal Fluid Leak A meticulous watertight primary dural closure is important to the prevention of a CSF leak.3,4 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.2–4 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.3,4,6 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.3
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.4 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.4
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.3–6 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.3 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.8 Hemimyelia is the presence of a terminal split cord
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the fresh wound to heal before another attempt is made to wean the EVD.
Retethering
• Fig. 31.2 Myelomeningocele with focal hirsutism on left side due to split cord malformation with hemimyelia (myelomeningocele on only one hemicord).
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.
Management Cerebrospinal Fluid Leak If a patient develops a CSF leak, he or she is also at risk of developing meningitis, wound dehiscence, and/or wound infection. The patient should be started on broad-spectrum empiric antibiotics with meningitis coverage, and attempts should be made to minimize ICP, add reinforcing skin sutures, and avoid stool contamination of the wound. CSF diversion is essential to the management of CSF leaks.4 If not already in place, an EVD may be placed to divert CSF away from the wound to allow it to heal. The height of the EVD can then be adjusted accordingly until there is no further egress of CSF from the wound. After adequate wound healing, the EVD can be raised in an attempt to wean it. It should be noted that with a single CSF leak, some surgeons may prefer to proceed with VP shunt placement rather than a temporary EVD. If CSF leaks persist despite adequate CSF diversion, or if they recur after the EVD is raised, wound exploration may be helpful.4 At the time of surgery, a dural defect can often be identified, which should be repaired primarily. The EVD should be kept in place postoperatively for additional CSF diversion to allow
After repair of the myelomeningocele, nearly all patients will have radiographic evidence of spinal cord tethering or fixation.9 Symptomatic tethering, when it occurs, is delayed for years to decades and rarely occurs within the first five years of life. If symptoms develop early, other causes of neurologic dysfunction are much more common, such as a second expression of neural tube defect (i.e., split cord malformation, second skin-covered lesion, etc.). The brain and entire spine should be imaged. The diagnosis of symptomatic tethered cord is based on clinical symptoms.9 The most common symptoms include progressive motor dysfunction, worsening urologic dysfunction, deteriorating gait, scoliosis and, rarely, spasticity and/or pain.9–11 It is our experience that by 10 years of age, approximately half of ambulatory patients will have some clinical evidence of neurologic decline. The decision regarding whether this deterioration crosses the risks vs. benefits threshold for untethering depends on the severity of these symptoms. Before proceeding with tethered cord release, it is important to ensure that hydrocephalus is adequately treated and that symptoms are not secondary to worsening syringomyelia. To perform a tethered cord release, the patient’s existing incision is used. Although not strictly required, it is often necessary to reopen the entire incision due to extensive tethering. The incision should be extended cranially to expose the inferiormost intact lamina to identify normal anatomic landmarks.11 A laminectomy of the inferiormost intact lamina may be necessary to identify a safe place to open the dura and enter the subarachnoid space above the point of tethering. The dural opening is extended inferiorly toward the site of tethering, which most commonly occurs in the midline along the suture line of the imbrication.11 When the dorsal surface of the neural elements is densely adherent to the overlying dura, it is safest to open just lateral to the point of fixation. After the dura is opened and the subarachnoid space is identified, it is ideal to keep the arachnoid intact and to work in the subdural, extraarachnoidal space for as long as possible. We prefer to use the blunt nerve hook to sweep under the dura from lateral to medial toward the point of tethering, that is, the junction of the dura with scar and neural elements. The dura is then incised sharply just lateral to the nerve hook. This minimizes the risk of injury to the functional sensory roots exiting the placode but adherent to the undersurface of the dura. We use this technique to open the dura laterally around the point of dorsal fixation, working from cephalad to caudad, until the dura is opened circumferentially around the scar, allowing the cord to fall ventrally back into its normal position within the spinal canal. Attention can then be directed to the scar fixed to the dorsal surface of the cord. This maneuver should be performed last, only after all of the nerve roots have been identified and dissected free. This is the point of maximum risk of injury to the underlying cord. This dorsal nonneural mass should then be separated sharply and removed. Once the neural placode is completely free and untethered, the wound should be carefully inspected for any other abnormalities before attention is turned toward the closure. As with the initial repair, a watertight dural closure is important. A dural graft is sometimes required to achieve a primary dural closure.
CHAPTER 31 Complications After Myelomeningocele Repair: CSF Leak and Retethering
181
SURGICAL REWIND
My Worst Cases Cerebrospinal Fluid Leak A full-term infant male was born with a wide upper lumbar myelomeningocele that was significantly elevated relative to the level of the surrounding skin (Fig. 31.3). Preoperative workup including scoliosis x-rays confirmed a significant kyphotic deformity (Fig. 31.4). The patient was taken to the operating room (OR) for myelomeningocele repair. The placode was imbricated and the dura mobilized and closed primarily without difficulty. However, due to the kyphotic deformity, the neural elements and dural sac remained significantly proud relative to the level of the skin. Kerrison punches and rongeurs were used to remove the remaining hypoplastic, splayed lamina and pedicles bilaterally, resulting in a shallow spinal canal. Due to the wide defect, the paraspinal musculature was attenuated and could not be mobilized without significantly compressing the neural elements. Despite adequate dural closure and partially because of the attenuated skin closure, a CSF leak was seen on the third postoperative day. EVD was placed to allow wound healing of the attenuated soft-tissue closure. The patient did not require return to the OR for wound revision, but he did undergo placement of VP shunt after the wound was appropriately healed.
Retethering A 12-year-old male child who had undergone myelomeningocele repair shortly after birth at an outside institution presented to our spina bifida clinic with progressive lower-extremity weakness and worsening gait. Neurologic examination was notable for asymmetric lower-extremity function with intact toe flexion and extension on the right but only iliopsoas and quadriceps function on the left. Physical examination was notable for a well-healed midline incision with hypertrichosis (Fig. 31.5). Computed tomographic myelogram demonstrated a complex split cord with the myelomeningocele occurring on the left hemicord and the right hemicord folded under but with recognizable neural anatomy (Fig. 31.6). Patient was taken to the OR for exploration and tethered cord release. Intraoperative findings confirmed imaging findings of hemimyelia. The bony median septum was rotated, making its excision difficult. The dural sleeve between the two hemicords was removed down to the level of the ventral dural floor. A thickened filum terminale was identified and sectioned on the left hemicord.
A
• Fig. 31.4 Lateral x-ray demonstrating kyphotic deformity in patient with myelomeningocele.
B
• Fig. 31.3
Lateral view (A), and overhead view (B), of myelomeningocele with significant kyphotic
deformity.
Continued
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• Fig. 31.5
12-year-old male who had undergone myelomeningocele repair at birth at outside institution who presents with neurologic deterioration. Focal hirsutism suggests presence of split cord malformation (hemimyelia).
• Fig. 31.6
Computed tomographic myelogram demonstrating split cord malformation with two hemicords and hemimyelia on the left side. The bony septum is deviated to the left, resulting in the right hemicord being slightly more ventral to the left hemicord within the spinal canal. This slight rotation can make it very difficult to identify a split cord malformation intraoperatively.
NEUROSURGICAL SELFIE MOMENT CSF leaks and retethering are among the more common complications after myelomeningocele repair. Care taken during the initial repair can help minimize complications as well as make future operations less challenging. CSF diversion is the key to management of CSF leaks. Treatment of secondary tethering is indicated if clinical symptoms are significant enough that benefits outweigh risks of tethered cord release.
References 1. Parker SE, Mai CT, Canfield MA, et al. Updated national birth prevalence estimates for selected birth defects in the United States, 2004–2006. Birth Defects Res A Clin Mol Teratol. 2010;88(12):1008– 1016.
2. Mattogno PP, Massimi L, Tamburrini G, et al. Myelomeningocele repair: surgical management based on a 30-year experience. Acta Neurochir Suppl. 2017;124:143–148. 3. Caldarelli M, Rocco CD. Myelomeningocele primary repair surgical technique. In: Özek MM, Cinalli G, Maixner WJ, eds. The Spina Bifida: Management and Outcome. Milano: Springer Milan; 2008: 143–155. 4. Pang D. Surgical complications of open spinal dysraphism. Neurosurg Clin N Am. 1995;6(2):243–257. 5. Akalan N. Myelomeningocele (open spina bifida) - surgical management. Adv Tech Stand Neurosurg. 2011;37:113–141. 6. McLone DG, Dias MS. Complications of myelomeningocele closure. Pediatr Neurosurg. 1991;17(5):267–273. 7. Danzer E, Adzick NS, Rintoul NE, et al. Intradural inclusion cysts following in utero closure of myelomeningocele: clinical implications and follow-up findings. J Neurosurg Pediatr. 2008;2(6): 406–413.
CHAPTER 31 Complications After Myelomeningocele Repair: CSF Leak and Retethering
8. Iskandar BJ, McLaughlin C, Oakes WJ. Split cord malformations in myelomeningocele patients. Br J Neurosurg. 2000;14(3):200–203. 9. Mehta VA, Bettegowda C, Ahmadi SA, et al. Spinal cord tethering following myelomeningocele repair. J Neurosurg Pediatr. 2010;6(5): 498–505. 10. Herman JM, McLone DG, Storrs BB, et al. Analysis of 153 patients with myelomeningocele or spinal lipoma reoperated upon for a
183
tethered cord. Presentation, management and outcome. Pediatr Neurosurg. 1993;19(5):243–249. 11. Caldarelli M, Boscarelli A, Massimi L. Recurrent tethered cord: radiological investigation and management. Childs Nerv Syst. 2013;29(9):1601–1609.
Complications After Myelomeningocele Repair: CSF Leak and Retethering IRENE KIM, W. JERRY OAKES
HIGHLIGHTS • Cerebrospinal fluid leak and retethering are two of the more common complications after myelomeningocele repair. • Watertight dural closure and adequate cerebrospinal fluid diversion are important in preventing and managing cerebrospinal fluid leak. • 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. • Retethering typically is caused by scarring of the neural placode or imbrication suture line to the dorsal dura. • 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.1 The vast majority of patients with myelomeningocele undergo surgical closure within 48 hours after birth.2,3 Complications that occur shortly after surgery include worsened neurologic function or level, cerebrospinal fluid (CSF) leak, wound dehiscence, meningitis, and wound infection.4 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.4
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.5 The ventral surface corresponds to the entire exterior pial-lined surface of what 178
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.3,4 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.4 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.3–5 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.2,3,6 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.5,6 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.7
CHAPTER 31 Complications After Myelomeningocele Repair: CSF Leak and Retethering
• Fig. 31.1
179
Photograph of myelomeningocele on left. Illustration of anatomy of myelomeningocele on
right.
RED FLAGS Cerebrospinal Fluid Leak • • • •
Large, wide epithelial deficiency for skin closure Hydrocephalus Kyphotic deformity Lesions involving deficient sacral skin
Retethering • • • • •
No imbrication of placode at time of initial myelomeningocele closure Shallow spinal canal Inclusion dermoid Thickened filum terminale Split cord malformation (hemimyelia)
Prevention Cerebrospinal Fluid Leak A meticulous watertight primary dural closure is important to the prevention of a CSF leak.3,4 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.2–4 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.3,4,6 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.3
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.4 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.4
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.3–6 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.3 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.8 Hemimyelia is the presence of a terminal split cord
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the fresh wound to heal before another attempt is made to wean the EVD.
Retethering
• Fig. 31.2 Myelomeningocele with focal hirsutism on left side due to split cord malformation with hemimyelia (myelomeningocele on only one hemicord).
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.
Management Cerebrospinal Fluid Leak If a patient develops a CSF leak, he or she is also at risk of developing meningitis, wound dehiscence, and/or wound infection. The patient should be started on broad-spectrum empiric antibiotics with meningitis coverage, and attempts should be made to minimize ICP, add reinforcing skin sutures, and avoid stool contamination of the wound. CSF diversion is essential to the management of CSF leaks.4 If not already in place, an EVD may be placed to divert CSF away from the wound to allow it to heal. The height of the EVD can then be adjusted accordingly until there is no further egress of CSF from the wound. After adequate wound healing, the EVD can be raised in an attempt to wean it. It should be noted that with a single CSF leak, some surgeons may prefer to proceed with VP shunt placement rather than a temporary EVD. If CSF leaks persist despite adequate CSF diversion, or if they recur after the EVD is raised, wound exploration may be helpful.4 At the time of surgery, a dural defect can often be identified, which should be repaired primarily. The EVD should be kept in place postoperatively for additional CSF diversion to allow
After repair of the myelomeningocele, nearly all patients will have radiographic evidence of spinal cord tethering or fixation.9 Symptomatic tethering, when it occurs, is delayed for years to decades and rarely occurs within the first five years of life. If symptoms develop early, other causes of neurologic dysfunction are much more common, such as a second expression of neural tube defect (i.e., split cord malformation, second skin-covered lesion, etc.). The brain and entire spine should be imaged. The diagnosis of symptomatic tethered cord is based on clinical symptoms.9 The most common symptoms include progressive motor dysfunction, worsening urologic dysfunction, deteriorating gait, scoliosis and, rarely, spasticity and/or pain.9–11 It is our experience that by 10 years of age, approximately half of ambulatory patients will have some clinical evidence of neurologic decline. The decision regarding whether this deterioration crosses the risks vs. benefits threshold for untethering depends on the severity of these symptoms. Before proceeding with tethered cord release, it is important to ensure that hydrocephalus is adequately treated and that symptoms are not secondary to worsening syringomyelia. To perform a tethered cord release, the patient’s existing incision is used. Although not strictly required, it is often necessary to reopen the entire incision due to extensive tethering. The incision should be extended cranially to expose the inferiormost intact lamina to identify normal anatomic landmarks.11 A laminectomy of the inferiormost intact lamina may be necessary to identify a safe place to open the dura and enter the subarachnoid space above the point of tethering. The dural opening is extended inferiorly toward the site of tethering, which most commonly occurs in the midline along the suture line of the imbrication.11 When the dorsal surface of the neural elements is densely adherent to the overlying dura, it is safest to open just lateral to the point of fixation. After the dura is opened and the subarachnoid space is identified, it is ideal to keep the arachnoid intact and to work in the subdural, extraarachnoidal space for as long as possible. We prefer to use the blunt nerve hook to sweep under the dura from lateral to medial toward the point of tethering, that is, the junction of the dura with scar and neural elements. The dura is then incised sharply just lateral to the nerve hook. This minimizes the risk of injury to the functional sensory roots exiting the placode but adherent to the undersurface of the dura. We use this technique to open the dura laterally around the point of dorsal fixation, working from cephalad to caudad, until the dura is opened circumferentially around the scar, allowing the cord to fall ventrally back into its normal position within the spinal canal. Attention can then be directed to the scar fixed to the dorsal surface of the cord. This maneuver should be performed last, only after all of the nerve roots have been identified and dissected free. This is the point of maximum risk of injury to the underlying cord. This dorsal nonneural mass should then be separated sharply and removed. Once the neural placode is completely free and untethered, the wound should be carefully inspected for any other abnormalities before attention is turned toward the closure. As with the initial repair, a watertight dural closure is important. A dural graft is sometimes required to achieve a primary dural closure.
CHAPTER 31 Complications After Myelomeningocele Repair: CSF Leak and Retethering
181
SURGICAL REWIND
My Worst Cases Cerebrospinal Fluid Leak A full-term infant male was born with a wide upper lumbar myelomeningocele that was significantly elevated relative to the level of the surrounding skin (Fig. 31.3). Preoperative workup including scoliosis x-rays confirmed a significant kyphotic deformity (Fig. 31.4). The patient was taken to the operating room (OR) for myelomeningocele repair. The placode was imbricated and the dura mobilized and closed primarily without difficulty. However, due to the kyphotic deformity, the neural elements and dural sac remained significantly proud relative to the level of the skin. Kerrison punches and rongeurs were used to remove the remaining hypoplastic, splayed lamina and pedicles bilaterally, resulting in a shallow spinal canal. Due to the wide defect, the paraspinal musculature was attenuated and could not be mobilized without significantly compressing the neural elements. Despite adequate dural closure and partially because of the attenuated skin closure, a CSF leak was seen on the third postoperative day. EVD was placed to allow wound healing of the attenuated soft-tissue closure. The patient did not require return to the OR for wound revision, but he did undergo placement of VP shunt after the wound was appropriately healed.
Retethering A 12-year-old male child who had undergone myelomeningocele repair shortly after birth at an outside institution presented to our spina bifida clinic with progressive lower-extremity weakness and worsening gait. Neurologic examination was notable for asymmetric lower-extremity function with intact toe flexion and extension on the right but only iliopsoas and quadriceps function on the left. Physical examination was notable for a well-healed midline incision with hypertrichosis (Fig. 31.5). Computed tomographic myelogram demonstrated a complex split cord with the myelomeningocele occurring on the left hemicord and the right hemicord folded under but with recognizable neural anatomy (Fig. 31.6). Patient was taken to the OR for exploration and tethered cord release. Intraoperative findings confirmed imaging findings of hemimyelia. The bony median septum was rotated, making its excision difficult. The dural sleeve between the two hemicords was removed down to the level of the ventral dural floor. A thickened filum terminale was identified and sectioned on the left hemicord.
A
• Fig. 31.4 Lateral x-ray demonstrating kyphotic deformity in patient with myelomeningocele.
B
• Fig. 31.3
Lateral view (A), and overhead view (B), of myelomeningocele with significant kyphotic
deformity.
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Cranial Complications
• Fig. 31.5
12-year-old male who had undergone myelomeningocele repair at birth at outside institution who presents with neurologic deterioration. Focal hirsutism suggests presence of split cord malformation (hemimyelia).
• Fig. 31.6
Computed tomographic myelogram demonstrating split cord malformation with two hemicords and hemimyelia on the left side. The bony septum is deviated to the left, resulting in the right hemicord being slightly more ventral to the left hemicord within the spinal canal. This slight rotation can make it very difficult to identify a split cord malformation intraoperatively.
NEUROSURGICAL SELFIE MOMENT CSF leaks and retethering are among the more common complications after myelomeningocele repair. Care taken during the initial repair can help minimize complications as well as make future operations less challenging. CSF diversion is the key to management of CSF leaks. Treatment of secondary tethering is indicated if clinical symptoms are significant enough that benefits outweigh risks of tethered cord release.
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CHAPTER 31 Complications After Myelomeningocele Repair: CSF Leak and Retethering
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