Myelomeningocele is known as the most common Neural Tube Defect (NTD), however the study by Schindelmann K.H. et al. showed that myeloschisis is not as rare as it is believed but rather a common NTD. Contrary to literature, their results showed that myeloschisis (31%) occurred more frequently than myelomeningocele (23%) [14]. Therefore, the distribution and classification of NTDs show significant variations between different studies. Reported incidence of myeloschisis (MS) cases is often lower than actual, likely due to the need for a more detailed neuropathological examination to ascertain the presence of a neural placode [14]. Although the presence of a membrane (MM sac) and cyst surrounding the defect is generally considered a distinguishing feature between MM and MS, the clinical presentation for these two forms of open neural tube defects remains the same [8]. Our study indicates that the presence of a MM sac covering the lesion or evidence of a CSF leak can be determinant factors for postoperative hydrocephalus development.
Numerous studies have acknowledged that the absence of a MM sac significantly increases the risk of developing postoperative hydrocephalus requiring a V-P shunt [11]. In our study, the need for a V-P shunt placement was found in 34% of cases where the sac was notably intact, compared to 94% in cases where it was open, which was statistically significant.
Another important issue in infants with MM or MS is the diagnosis of hydrocephalus and timing of treatment. In historical reports published up until 1990, many opted for a V-P shunt implantation at birth even if the head circumference was within normal limits [5]. Consequently, numerous studies reported high rates of V-P shunt placement, such as Januschek et al. reported an 85% V-P shunt rate, Laskay et al 84.6%, and Marreiros et al. 70% [9, 10]. However, by tolerating larger ventricles and applying beter postoperative wound care, few experienced centers have managed to reduce the V-P shunt rates to 55–65% [13].
The primary concern in the management of infants with detected preoperative ventriculomegaly is the progression, regression, or stability of ventriculomegaly. The long-term neurocognitive impact of allowing larger ventricles is unknown, but it appears to be insignificent in short-term evaluations. On the other hand, these patients may be spared the morbidity associated with repeated operations and complications due to V-P shunt insertion[15].
To monitor the hydrocephalus and evaluate the timing of V-P shunt placement, knowing the volume of the ventricles (VV) is crucial. Data obtained from routine neonatal TFUSGs for identifying intracranial pathologies, or from MRIs for a more detailed understanding, can be used to create VV indices. In their study, Radhakrishnan et al. found that the fronto-occipital horn ratio (FOHR), a VV index derived from TFUSG and MRI, showed a strong correlation between both imaging methods [13], and a clinical FOHR threshold of 0.55 demonstrated high sensitivity in identifying infantile hydrocephalus [13]. Particularly, FOHR can be used to measure the severity of ventriculomegaly [1, 2]. We obtained similar results from preoperative TFUSG and MRI examinations concerning FOHR results. A close relationship was found between values exceeding 0.55 and the likelihood of requiring a V-P shunt insertion.
Another significant factor in determining the need for hydrocephalus treatment and V-P shunt placement is the routine measurement of head circumference. The study conducted by Vonzun L et al. showed that preoperative and/or postoperative head circumference and ventricular measurements were determinants of the need for a V-P shunt in the first year of life [17]. They found that a head circumference above 95 percentile predicts an 80% likelihood of needing a V-P shunt due to late hydrocephalus [17]. We found this rate to be approximately 81% in infants with a head circumference of 37 cm or more which is similar to findings of Protzenko et al. that showed a birth head circumference of 38 cm or above was a significant factor for V-P shunt requirement [12].
We observed that regardless the morphology of the defect, there is a greater need for V-P shunt placement in patients with lesions located in the thoracic level, larger than 5 cm in diameter, and those with more severe deficits, in our study. Some studies have indicated that the development of hydrocephalus is generally not related to the anatomical level or size of the lesion, but rather to myeloschisis [7]. Another study showed that hydrocephalus and the need for a V-P shunt placement were more common in higher spinal level lesions [12]. We believe the possible reason for these differing results might be due to not fully understanding the distinctions between MM and MS.
Additionally, similar to our findings, no significant impact of birth weight and gender has been identified on the need for a V-P shunt [17].
Considering all results, it was observed that knowing parameters such as the size and level of the lesion, the integrity of the sac, head circumference (HC), and Frontal Occipital Horn Ratio (FOHR) can play a role in determining the risk and the need for a V-P shunt due to hydrocephalus that may develop after the MM/MS repair.
This study is limited by being single-centered and involving a relatively small number of patients. The findings could be more definitive when considered by larger groups and various centers, and lead to the development of guidelines or scales.