Hydrocephalus is a condition that arises from an imbalance of cerebrospinal fluid (CSF) dynamics, which induces a pathological accumulation of CSF. This leads to an abnormal expansion of the cerebral ventricles and an increase in intracranial pressure. It is one of the most commonly observed abnormalities in the neonatal brain (1). Ultrasound is the primary imaging modality for evaluating neonatal brain abnormalities, while magnetic resonance imaging (MRI) has been shown to identify additional anomalies in approximately 20%–50% of cases detected by ultrasound (1).

Several etiologies of hydrocephalus have been reported, classified as either congenital or acquired (2). Post-hemorrhagic hydrocephalus of prematurity and congenital anomalies are the most common causes of hydrocephalus in high-income countries, whereas neonatal infections are predominant in developing countries (2). Infants with neonatal hydrocephalus may exhibit an abnormal increase in head circumference, irritability, vomiting, bulging of the anterior fontanelle, or splaying of the cranial sutures (2).

Occlusion of the foramen of Monro (FOM) is a cause of hydrocephalus and may be congenital or secondary to various disorders (3). Intraventricular and choroid plexus tumors can obstruct CSF flow, whereas vascular malformations and infectious etiologies can cause FOM obstruction due to mass effect or scarring (3). However, idiopathic occlusion of the FOM presenting as prenatal ventriculomegaly is extremely rare. In this article, we present a case of a newborn with bilateral hydrocephalus diagnosed during the prenatal period due to congenital and idiopathic occlusion of the FOM. The neonate underwent successful endoscopic septostomy and foraminotomy. To the best of our knowledge, this is the youngest and smallest neonate to have undergone this procedure.

Hydrocephalus has many etiologies, including neoplastic, congenital, inflammatory, infectious, and vascular malformations, which can lead to obstruction of the FOM (4). Among these, congenital and idiopathic obstructions of the FOM are rare, and symptoms may present either in childhood or adulthood (5). Common neurological symptoms in infants and children include seizures, bulging of the anterior fontanelle, abnormal head circumference, and delayed development (5). Congenital obstruction of the FOM during the prenatal period is extremely rare, and according to previous case reports (Table 1), not all cases present initially with an inappropriate head circumference or seizures. Some patients would be considered asymptomatic if not for findings through imaging. Hence, neuroimaging plays a crucial role in the early diagnosis and regular follow-up of hydrocephalus (1). MRI is highly effective in detecting FOM stenosis and ruling out other causes of lateral ventricle dilatation, such as obstructive cysts, tumors, vascular lesions, or meningeal lesions (1). Additionally, cranial sonography is a non-invasive and important tool for routine monitoring of ventricle size and flow pattern in cases with abnormal head circumference as well as asymptomatic patients with stable head circumference.

There is no consensus regarding hydrocephalus treatment timing among neurosurgeons, neonatologists, and pediatric neurologists. The maximum ventricle size in post-hemorrhage dilation preterm infants is related to neurodevelopmental outcomes, according to a previous study (18). Intervention is based on sequential cranial sonography findings and clinical symptoms including increased in ventricle size, splayed sutures, and bulging fontanelles (18). Brain sonography parameters include the ventricular index (VI), AHW, and TOD, where a VI >97th percentile + 4 mm, AHW > 10 mm, or TOD > 25 mm require neurosurgical intervention and treatment. In our case, the patient had no clinical symptoms, but sonography showed abnormal findings that fulfilled the intervention criteria. Therefore, cranial sonography is a valuable tool which can aid in timely surgical interventions for cases of progressive ventriculomegaly.

Previously, ventriculoperitoneal (VP) shunting was the preferred surgical strategy to alleviate symptoms of FOM occlusion (19). However, this procedure can result in complications such as mechanical malfunction and infection. Pediatric patients who undergo VP shunts to treat hydrocephalus are particularly predisposed to complications (20), with a prevalence of 20%, with infants below 1 year of age being the most affected. One study showed that most patients with shunt failure required re-shunting before reaching 2 years of age (21). In the past, isolated septum pellucidotomy was not a routine procedure, although it was sometimes performed together with foraminoplasty or in addition to third ventriculostomy (19). In current practice, minimally invasive endoscopic procedures are the commonly used management procedures. Endoscopic treatment is known to have excellent outcomes in the treatment of idiopathic bilateral FOM occlusion in adults (22). For neonates, a 10-year study demonstrated that endoscopy is a feasible treatment of post-hemorrhage or post-infectious hydrocephalus (23), but it did not include data for FOM occlusion.

Endoscopic septostomy enables CSF circulation between the obstructed and opposing ventricle, allowing communication with the third ventricle to resolve the obstruction and avoiding the need for a VP shunt (24). The patency rate of the initial endoscopic septostomy is 53%, which increased to 81% after repeated septostomy, ensuring improvement in isolated ventricular hydrocephalus in a study involving children (4). In addition, multiple shunt revisions increase the risk and failure rate of septostomy (4). Only a few complications have been reported from endoscopic septostomy, including sterile meningitis, intraventricular hemorrhage, and dehiscence of the operative wound incision (4). Published reviews provided limited data regarding the overall complications of endoscopic surgery in neonate. The advantages of neuroendoscopic techniques include invasiveness and potentially lower risk. However, more clinical experience in needed.

In the case of neonates, the FOM is relatively small and the tissues are fragile. This adds to the technical demands of the surgery, requiring the use of specialized small endoscopes and surgical instruments to ensure accuracy and safety. The limitation of neuroscopic approach include restricted visualization and the small size of instruments, highlighting the requirement for advanced technical expertise in this procedure. The limitation of neuroscopic approach include restricted visualization and the small size of instruments, highlighting the requirement for advanced technical expertise in this procedure.

To the best of our knowledge, our patient is the youngest and smallest neonate compared to other cases involving endoscopic septum pellucidotomy and foraminoplasty for treatment of FOM occlusion (Table 1). The first neonate to receive successful endoscopic treatment for FOM was in 2021 (17). The initial presentation of the first case involves an enlarged cranial suture, which differs from our case where only an enlargement in ventricle size in cranial sonography. Both of these two 2 cases demonstrate successful endoscopic treatment with positive outcomes. Historically, a VP shunt was the predominant treatment for neonates with congenital occlusion of the FOM with hydrocephalus. To avoid shunt complications, endoscopic septum pellucidotomy and foraminoplasty should be considered as primary treatment methods in neonates. However, the success and safety of the surgery depend on the experience and expertise of the surgeon, as these procedures have their limitations and challenges.

In conclusion, endoscopic septostomy and foraminoplasty are valuable treatment options to be considered in cases of congenital occlusion of the FOM with hydrocephalus in neonates.