Surgical Technique

General anesthesia is used, and the patient is placed in the prone position, with rolls under the chest and hips to allow the abdomen to hang freely (Fig. 5.2). If the sac remains intact, fluid is aspirated and sent for culture. The surgeon gently attempts to approximate the base of the sac or defect vertically, then horizontally, to determine which direction of closure will produce the smallest skin defect. An elliptical incision is made, oriented along that axis, just outside the junction of the normal, full-thickness skin and the thin, pearly zona epitheliosa. Full-thickness skin forming the base of the sac is viable and should not be excised. The incision is carried through the subcutaneous tissue until the glistening layer of everted dura or fascia is encountered. The base of the sac is mobilized medially until it is seen to enter the fascial defect (Fig. 5.3A). The sac is entered by radially incising the cuff of skin surrounding the neural placode. This skin is sharply excised circumferentially around the placode with scissors and discarded (Fig. 5.3B). It is important to excise all of the zona epitheliosa to prevent later formation of an epidermoid cyst. At this point, the neural placode is lying freely above the everted dura (Fig. 5.4).

FIGURE 5.2 Positioning the patient for myelomeningocele closure. The infant is placed in the prone position, with rolls beneath the chest and iliac crests to minimize epidural bleeding. The skin incision is outlined circumferentially on the outside of the zona epitheliosa. A vertical orientation of the elliptical incision is appropriate for most closures.

FIGURE 5.3 A, Mobilizing the sac. The skin is undermined medially until the dural sac is seen to enter the fascial defect. B, Excising the fringe of skin surrounding the placode. A radial cut is used to enter the sac, and it is continued around the placode to excise the skin. A separate circumferential cut amputates the base of the sac.

FIGURE 5.4 Mobilizing and closing the dura. The dura is undermined and closed using a continuous 4-0 nonabsorbable suture.

In some instances it is appropriate to “reconstruct” the neural placode so that it fits better within the dural canal and a pial surface is in contact with the dural closure to prevent tethering. Interrupted 6-0 sutures approximate the pia-arachnoid-neural junction of one side of the placode with the other, folding the placode into a tube. The central canal is closed along its entire length.

Attention is then directed to the dura, which is everted and loosely attached to the underlying fascia. The dura is undermined bluntly and reflected medially on each side until enough has been mobilized to enable a closure (see Fig. 5.4). The dura is closed in a watertight fashion using a running suture of 4-0 neurilon. If possible, the fascia is closed as a separate layer by incising it laterally in a semicircle on both sides, elevating it from the underlying muscle, and reflecting it medially. Like the dura, the fascia is closed with a continuous stitch of 4-0 suture material (Fig. 5.5). The fascia is poor at the caudal end of a lumbar myelomeningocele as well as with most sacral lesions; thus, closure at this level may be incomplete.

FIGURE 5.5 The fascial closure. The fascia is closed with a continuous stitch. The caudal end of the repair may be incomplete. Skin is mobilized by blunt dissection with scissors or a finger.

The skin is mobilized by blunt dissection with dissecting scissors or a finger. It may be necessary to free up the skin ventrally all the way to the abdomen (see Fig. 5.5). In most instances, midsagittal (vertical) plane closure is easiest, but occasionally horizontal closure results in less tension. A two-layer closure using vertical interrupted mattress skin sutures is preferred.

Very large lesions require special techniques. Various types of “Z-plasties” and relaxation incisions have been described and may be necessary in very large or difficult lesions. Large circular defects can be closed using a simple rotation flap (Fig. 5.6). Alternative techniques such as allogeneic skin grafts and tissue expansion may be used in rare circumstances.^9,10

FIGURE 5.6 Simple rotation flap. A, An S-shaped horizontal incision is made, encompassing the circular defect. B, The points are approximated to the hollows, relieving tension both vertically and horizontally. The resulting skin closure has a W shape.

Care of the child with a myelomeningocele is life-long; it only begins with the surgical closure. Any deterioration in neurological function signals a progressive process such as shunt malfunction, hydromyelia, tethered cord, or symptomatic Chiari II malformation. Significant advancements have been made in the treatment of these children over the past two decades, particularly in the widespread use of multidisciplinary teams of specialists to manage their urological, orthopedic, and other needs. Among those who undergo early back closure, 92% will survive to 1 year.¹¹ From prospective outcome cohort data, it is known that the survival rate until age 17 is 78%,¹² but it drops to 46% by the fourth decade of life.¹³ Death is the result of problems associated with the Chiari II malformation, restrictive lung disease secondary to chest deformity, shunt malfunction, or urinary sepsis. A sensory level higher than T11 is associated with increased risk of mortality,¹³ likely due to increased risk of urosepsis.¹⁴ Approximately 75% of children with myelomeningocele are ambulatory, although most require braces and crutches. Approximately 75% of surviving infants will have normal intelligence (defined as IQ > 80), although only 60% of those requiring shunts for hydrocephalus will have normal intelligence.¹⁵ Normal intelligence drops to 70% in surviving adults.¹⁶

In a few centers, the fetus with spina bifida may be a candidate for in utero treatment, because this condition is routinely detected before 20 weeks of gestation. There is evidence that neurological deterioration occurs during gestation.¹⁷ Normal lower extremity movement can be seen on sonograms of affected fetuses before 17 to 20 weeks of gestation, but most late-gestation fetuses and newborns have some degree of deformity and paralysis. Such deterioration could be the result of exposure of neural tissue to amniotic fluid and meconium or direct trauma as the exposed neural placode impacts against the uterine wall. In theory, such deterioration could be reduced or eliminated by in utero closure of the lesion. Animal studies (in which a model for spina bifida is created by laminectomy and exposure of the fetal spinal cord to the amniotic fluid) have demonstrated improved leg function if the lesion is closed before birth.¹⁸ There is also evidence that the Chiari II malformation, which occurs in the vast majority of individuals with spina bifida, is acquired and could potentially be prevented by in utero closure.¹⁹

The first cases of in utero spina bifida repair were performed in 1994 using an endoscopic technique. This technique proved unsatisfactory and was quickly abandoned. In 1997, in utero repair of spina bifida was performed by hysterotomy at Vanderbilt University and at the Children’s Hospital of Philadelphia.^20,21 Fetuses treated in utero are delivered by cesarean section because the forces of labor are likely to produce a uterine dehiscence. The early experience at both institutions suggested that relative to babies treated postnatally, those treated in utero had a decreased incidence of hindbrain herniation, and possibly a decreased need for shunting.^22,23 The combined experience at the Children’s Hospital of Philadelphia and Vanderbilt, indicates that the incidence of hydrocephalus requiring shunting in patients treated in utero is less than in historical control subjects stratified by spinal level who received standard postnatal care.^24,25 It is hypothesized that fetal closure of the spinal lesion reduces the need for shunting by eliminating the leakage of spinal fluid which puts back-pressure on the hindbrain. This allows reduction of the hindbrain hernia and relieves the obstruction of the outflow from the fourth ventricle.²⁶

In utero spina bifida closure appears to be generally well tolerated by the expectant mothers. Approximately 5% of fetuses have died from complications associated with uncontrollable labor and premature birth. An analysis of leg function in children treated prenatally revealed no significant difference from a set of historical control subjects who were treated with conventional postnatal repair.²⁷ However, many of the children evaluated in this series had lower limb paralysis at the time of the surgery, which may have diluted any possible benefit. In contrast, a series from the Children’s Hospital of Philadelphia suggested potentially improved leg function in patients with prenatally confirmed intact leg movement on ultrasound prior to fetal surgery.²⁸ Problems with delayed development of dermoid inclusion cysts and tethered cord may adversely affect outcome in the long term.²⁹ The preliminary experience suggests that children treated in utero have the same urodynamic abnormalities that are seen in conventionally treated children with spina bifida.^30,31 The incidence of the Chiari II malformation, and the need for shunting may be decreased,²³ but there are currently no long-term data.

Prior to the Management of Myelomeningocele Study (MOMS) trial,³² outcomes for spina bifida babies treated in utero were assessed relative to outcomes in conventionally treated, historical control subjects.⁸ Such comparisons are, however, prone to substantial biases because fetuses that undergo in utero closures represent a highly selected subset of cases. In addition, the medical management of spina bifida is continuously improving, making comparisons with historical control subjects particularly problematic.

A consortium of three institutions (Children’s Hospital of Philadelphia, Vanderbilt, and University of California San Francisco) performed an unblinded, randomized, controlled trial of in utero treatment of spina bifida ([MOMS] to obtain definitive answers regarding the benefits of fetal myelomeningocele closure.³²). Pregnant women who receive a prenatal diagnosis of spina bifida between 16 and 25 weeks of gestation were randomized to either in utero repair at 19 to 25 weeks’ gestation or cesarean delivery after demonstration of lung maturity. The primary study end points were the need for a shunt procedure at 12 months, and fetal/infant death. Secondary end points included neurological function, cognitive outcome, and maternal morbidity. The intent to treat analysis demonstrated a significant risk reduction with regard to the primary endpoint, and the study was closed early due to efficacy of prenatal surgery. The prenatal surgery group benefited from decreased shunt requirement (40% versus 82%) and a higher proportion of normal hindbrain anatomy, and it was more likely to ambulate independently at 30 months compared to the postnatal group. There were no maternal deaths, and adverse neonatal outcomes were similar between groups; however, prenatal surgery was associated with more pregnancy complications, increased frequency of pre-term delivery, and a higher rate of respiratory distress syndrome in the neonate. To date, this is the only randomized study that demonstrates clear benefits of in utero treatment of spina bifida. These benefits were realized at experienced centers with strict inclusion criteria and must be carefully weighted against the higher rates of prematurity and maternal morbidity. Longer follow up is required to determine the longevity of these benefits as well as the effect on urinary function.