Our study comparing the radiographic appearance of IUMR and PNMR revealed no significant differences in subcutaneous tissue appearance, or other radiographic characteristics, including presence of syrinx and epidermoid or dermoid cysts. Furthermore, the difficulty in which a blinded neuroradiologist was able to predict repair timing further suggested an absence of differences on radiographic imaging between the two groups.
Important outcomes in IUMR closures include rates of CSF diversion and tethering rates. In the current study, there was not a significant difference in rates of CSF diversion between the IUMR and PNMR groups (58.3% vs. 91.7% respectively). The lack of statistical significance may be attributed to the small cohort in this study. The rates were similar to that of the MOMS cohort.3,13 Consistent with previous literature,14 patients undergoing IUMR were older and weighed more at the time of CSF diversion compared to PNMR patients.
In this, there was not an increase in tethering rates in the IUMR group (16.7%) patients compared to the PNMR group (12.5%; Table 2). Previous literature has noted that the rates of tethering myelomeningocele patients to be between 10 and 30%.7,9,10 While a previous study found a rate of tethering in IUMR patients of nearly 33%,15 a more recent study using the National Spina Bifida Patient Registry demonstrated no difference in the rates of detethering operations between IUMR and PNMR patients (18% vs 16%, respectively), with a mean age at last follow-up of 3.67 years in the IUMR group and 4.08 years in the PNMR group.6 In our cohort, mean age at last follow-up was 6.6 years in the IUMR group and 5.8 years in the PNMR group. It is possible that additional tethering operations will be necessary for this cohort as they age, based on recent studies demonstrating a risk of tethering of approximately 1.8% per year between ages 0–13,7 so continued follow-up and ongoing analysis is necessary.
The appearance of the subcutaneous tissue is a novel variable that could help to assess the consequences of different closure techniques. For example, it is possible that not performing a fascial closure could result in less subcutaneous tissue. While the appearance of tethering on MRI is present in nearly all patients following myelomeningocele closure,8,9 it was important to evaluate the appearance of subcutaneous tissue between the groups to see if the differential closure made a significant difference. There was no difference in the amount of tissue between the skin and neural tissue between the IUMR and PNMR groups. This important in demonstrating that the lack of myofascial flaps does not seem to make a substantial difference in appearance on MRI. The lack of differences is also highlighted by the inability to qualitatively differentiate between IUMR and PNMR on MRI. A board-certified neuroradiologist was only correct 38% of the time when asked to determine if the patient had a IUMR or PNMR accentuating the lack of visible difference between the two groups despite effort to prove otherwise.
There were two IUMR cases (16.7%) that required wound revisions following birth. Neither patient had evidence of CSF leakage or exposure of neural elements, and underwent complex wound closure with plastic surgery. Both of these cases were early in our experience with this technique. Rates of wound dehiscence in IUMR in the literature have been reported between 0%-13%.3,14,16 Additionally, as more experience is gained by both surgeon and field, rates of complications have declined.5
Other modifications from the technique described in MOMS3 have been described. Flanders et al.17 described their results following modification of a technique in which they rotated a myofascial flap over the dural defect and close this layer. The skin is then closed primarily. They report significantly fewer inclusion cysts with this technique compared to their results prior to this modification, as well as lower rates of CSF diversion compared to the MOMS cohort.17 Notably, they did not include the age at last follow-up, which is important to know as many cysts and symptomatic tethers are not reported until later in life.7,9,18
Simplifying the technique while maintaining the benefit of the operation could allow for the further development of less invasive techniques of IUMR. Fetoscopic surgery has recently gained traction with the goal of decreasing morbidity related to an open hysterotomy. A recent analysis of an international registry of centers performing fetoscopic IUMR demonstrated similar rates of hydrocephalus when compared to the MOMS and post-MOMS cohorts.19 Additionally, 32% of children in the fetoscopic group were delivered vaginally, which is not possible following open hysterotomy. There was increased operative time, and rates of preterm premature rupture of membranes and oligohydramnios were higher in the fetoscopic cohort. This technique does require significant training for neurosurgeons and the entire prenatal surgery team.20,21 It is also important to note that the Texas Children’s group, who has pioneered this technique, recently published that moving away from a simpler closure reduced their postoperative immediate take back for CSF leaks after delivery.22
While our study demonstrated no significant differences radiographically or increased tethering rates in prenatal compared to postnatal closure, it is not without limitation. First, the single-institution nature of this study limits the size of the cohort; larger scale studies evaluating different techniques of closure are indicated to more fully understand possible differences in outcomes. Furthermore, the surgery was performed by one team and the radiographic findings in our study were interpreted by a single neuroradiologist. Therefore, subsequent validation of this study should be pursued in order to determine whether the results of this study can be replicated. Despite these limitations, our study is the first to compare intrauterine prenatal closure and postnatal closure of myelomeningocele from a radiographic perspective, showing little difference between the tissue covering the placode between the two operative techniques In addition, there appeared to be no difference in symptomatic tethering rates, bring the opportunity to emphasize the substantial differences in closure techniques that have evolved since MOMS and the idea perhaps that we should begin moving towards adopting the least complex procedure that allows the field to maintain the benefits seen in MOMS and also provides short and longer term protection from returning to the operating room for any reason.