https://orcid.org/0000-0003-1825-3877
Abstract
Fourth ventricle outlet obstruction is a rare cause of obstructive hydrocephalus in children. Although surgical management has been reported, the diagnostic challenges, differential considerations, and therapeutic strategies remain debated. We report a 5-year-old boy with progressive vomiting, severe headache, gait instability, and incontinence. High-resolution magnetic resonance imaging with T2-CISS sequences confirmed a membranous obstruction at the foramina of Magendie and Luschka. The patient underwent microsurgical fenestration via suboccipital craniotomy, with histopathological confirmation of arachnoid membranes without signs of infection or malignancy. The postoperative course was favorable with complete symptom resolution. Notably, persistent papilledema was observed at 2-month follow-up despite clinical improvement, but showed gradual regression during subsequent visits, underlining the need for cautious postoperative monitoring.
Introduction
Obstructive hydrocephalus due to fourth ventricle outlet obstruction (FVOO) represents a clinical challenge in the diagnosis and the treatment [1]. FVOO arises from blockage at the foramina of Magendie and Luschka, disrupting cerebrospinal fluid (CSF) flow and leading to ventricular dilation [1]. While various etiologies exist, including congenital malformations, infections, and tumors [1, 2], idiopathic membrane formation, as seen in this case, is relatively rare [2]. The nonspecific symptoms—vomiting, headaches, altered gait, and neurological dysfunction—often delay its diagnosis [1]. Prompt recognition and appropriate intervention are crucial to prevent irreversible neurological damage [1]. This case report emphasizes the diagnostic complexities and therapeutic considerations in managing FVOO due to membranous obstruction.
Case presentation
A 5-year-old boy was referred to our institution with suspected obstructive hydrocephalus after a 12-day history of progressive symptoms. Initially, he developed intermittent vomiting, occasionally bilious, which became daily during the four days before admission. He also complained of severe headaches, gait instability, fatigue, urinary incontinence, and reduced oral intake. There was no history of recent infection. His past medical history was remarkable only for a self-limiting febrile illness at the age of three years.
On admission, the patient was drowsy but fully oriented (Glasgow Coma Scale 15). Neurological examination revealed no focal motor or sensory deficits. Gait assessment was not possible because of his clinical condition. Fundoscopic examination demonstrated marked bilateral papilledema.
Magnetic resonance imaging (MRI) was performed under general anesthesia because of the patient’s age and clinical condition. Spinal MRI was unremarkable (Fig. 1a). Cranial MRI demonstrated marked tetraventricular hydrocephalus (Fig. 1b). High-resolution T2-CISS sequences identified a thin membranous obstruction at the foramina of Magendie and Luschka without evidence of tumor or inflammatory disease (Fig. 1c–e), confirming fourth ventricle outlet obstruction.
Preoperative MRI scan. Spine T2 sequences (a), cranial T2 coronal view (b) depicting dilatation of the supratentorial ventricles, and CISS sequences (c–e) illustrating membrane occlusion at the Magendi and Luschka foramina (arrows).
After multidisciplinary discussion, microsurgical membrane fenestration was favored over endoscopic third ventriculostomy (ETV) or ventriculoperitoneal shunting because of the patient’s young age, the possibility of additional prepontine membranes, the accessibility of the obstructing membrane, and the opportunity to obtain tissue for histopathological examination.
The patient underwent a midline suboccipital craniectomy in the semi-sitting position. Intraoperatively, an arachnoid membrane obstructing the foramen of Magendie was identified and microsurgically fenestrated, restoring free CSF flow (Fig. 2). Tissue and CSF samples were obtained for histopathological and microbiological analysis. Early postoperative MRI confirmed restoration of CSF circulation (Fig. 3a).
Intraoperative images. Post-dural opening images showing dilated membranes at the floor of the fourth ventricle (a). Fenestration of the membrane, with the floor of the fourth ventricle no longer visible (b).
Postoperative MRI-scans. Postoperative MRI immediately after surgery (a) and at the two-month follow-up (b), demonstrating restored CSF flow throughout all ventricles and cisterns, as evidenced by flow void signals.
The postoperative course was initially uneventful, and the patient was discharged neurologically intact on postoperative day five. Shortly thereafter, he was readmitted with fever, apathy, and headache. Extensive microbiological investigations, including CSF cultures, blood cultures, inflammatory markers, and leukocyte counts, were negative. Antibiotics were discontinued, and treatment with dexamethasone resulted in complete symptom resolution, consistent with postoperative aseptic (chemical) meningitis.
At the 2-month follow-up, MRI demonstrated marked reduction of ventricular size (Fig. 3b). Although papilledema persisted despite complete clinical recovery, it gradually regressed during subsequent ophthalmological follow-up. Histopathological examination confirmed benign arachnoid membrane without evidence of inflammation, hemorrhage, infection, or malignancy. At the latest follow-up, the patient remained neurologically intact with sustained clinical and radiological improvement.
Discussion
Fourth ventricle outlet obstruction (FVOO) is a rare cause of obstructive tetraventricular hydrocephalus resulting from blockage of the foramina of Magendie and/or Luschka [1]. Diagnosis relies on the combination of characteristic clinical findings and careful radiological evaluation. Typical MRI features include tetraventricular dilatation with a patent cerebral aqueduct, while high-resolution CISS/FIESTA sequences may reveal thin obstructing arachnoid membranes that are often not visible on conventional MRI [1, 2]. Consequently, the diagnosis is frequently established only intraoperatively, making preoperative identification by modern MRI sequences particularly valuable for surgical planning.
The differential diagnosis includes Chiari malformation, posterior fossa arachnoid cysts, postinfectious arachnoiditis, posterior fossa tumors, and congenital malformations such as Dandy–Walker spectrum disorders or Blake’s pouch cyst [1, 3, 4]. These entities can usually be differentiated by characteristic MRI findings, clinical history, and CSF flow assessment. Therefore, high-resolution MRI plays a pivotal role in establishing the diagnosis and planning surgical treatment.
Surgical intervention is generally required to restore CSF circulation and prevent progressive neurological deterioration [1]. ETV has been reported as an effective treatment in selected patients [1, 5–7]. However, its efficacy may be less predictable in young children because it bypasses rather than removes the obstructing membrane and may not fully restore physiological CSF flow. In addition, both ETV and ventriculoperitoneal shunting carry a risk of persistent or isolated fourth ventricle in selected patients [7]. Ventriculoperitoneal shunting also introduces lifelong shunt dependency with risks of infection, obstruction, and revision [8].
Microsurgical fenestration via a suboccipital approach directly addresses the underlying pathology by removing the obstructing membrane, restoring physiological CSF flow, and allowing histopathological confirmation. The procedure also permits direct inspection of the fourth ventricle and cerebral aqueduct, excluding additional obstructive lesions that may not be apparent on preoperative imaging. In our patient, the localized obstruction, young age, and the need for tissue diagnosis favored this approach over ETV or shunting.
This case provides several noteworthy observations. Histopathological examination confirmed a benign arachnoid membrane without evidence of inflammation, hemorrhage, infection, or malignancy, a finding rarely documented in previous reports. Furthermore, the patient developed postoperative aseptic (chemical) meningitis, supported by negative microbiological investigations and complete resolution following corticosteroid therapy. Finally, persistent papilledema despite marked clinical and radiological improvement illustrates that optic disc swelling may regress slowly after successful treatment and should not be mistaken for treatment failure. Together, these findings underline that successful management extends beyond restoration of CSF flow and requires careful interpretation of postoperative clinical and ophthalmological findings to avoid unnecessary interventions. These observations emphasize the importance of long-term clinical, radiological, and ophthalmological follow-up.
Conclusion
Membranous FVOO should be considered in children presenting with tetraventricular hydrocephalus and a patent cerebral aqueduct. High-resolution MRI is essential for identifying subtle outlet membranes and excluding alternative posterior fossa pathologies. Microsurgical fenestration offers direct restoration of physiological CSF circulation while providing tissue for histopathological confirmation. Awareness of postoperative chemical meningitis and delayed regression of papilledema may help avoid unnecessary interventions and improve postoperative management. Long-term multidisciplinary follow-up remains essential to ensure sustained neurological and ophthalmological recovery.
Author contributions
All individuals listed as authors have substantially contributed to the design, execution, and analysis of the study. Prior to its submission, all authors have reviewed and confirmed the accuracy of the whole manuscript.
Conflicts of interest
The authors declare that they have no conflict of interest.
Funding
None declared.
