Discussion:
Only a small number of cases of TFV, often referred to as IFV are documented in the previous studies. [14]. When the cerebral aqueduct of Sylvius and the exit foramina, , are closed, it happens[15]. The choroid plexus produces and secretes CSF and is found at the centre of the brain. Lymph veins and arachnoid granulations collect CSF close to the skull. It implies a lengthy flow pathway. CSF must go from the lateral ventricles to the third ventricle and finally to the fourth through its natural course [16]. When there is any pathology, then cerebrospinal fluid (CSF) will gradually accumulate as a result, first creating a displacement of the cerebellum and then moving on to the brainstem anteriorly.Although the precise process causing the fourth ventricle to become confined is not entirely understood, it is more frequently observed in individuals who have undergone numerous shunt surgeries, post-infectious hydrocephalus, and Youmans’s isolated fourth ventricle (IFV) [17].
Large anatomical spaces, such as the ventricles and subarachnoid cavity, are in close proximity to perivascular regions and nerve sheaths, facilitating systemic circulation and the transfer of solutes [16]. However, the complications associated with fourth ventricle shunting remain insufficiently explored. A recent review by Lee et al. detailed the management of 12 patients with trapped fourth ventricles and associated cysts linked to Dandy-Walker malformations. In three instances, direct damage to the fourth ventricular floor impeded the proper placement of a catheter in the posterior fossa. One individual experienced an intracystic hemorrhage due to shunt failure [18]. Additionally, five of the seven patients in our study exhibited slit lateral ventricles (unilateral or bilateral) connected to an isolated fourth ventricle, a finding consistent with other reports [19–24].. Headache, uncoordinated movements, coma, cranial nerve lesions, anorexia, and vomiting are all indications of an isolated fourth ventricle [23]. The premature newborns treated for hydrocephalus following intraventricular haemorrhage (IVH)  had the most frequent clinical presentation [25].The fourth ventricle cavity’s volume growth and the resulting compression on the surrounding neurological structures—the brainstem, lower cranial nerves, and cerebellum—are linked to the most frequent clinical sequel. The end outcome of that occurrence is a condition known as posterior fossa syndrome, which manifests clinically similarly to an increasing posterior fossa tumour. Patients first experience headaches, emesis, and irritability in addition to cerebellar and bulbar dysfunction [11].
The implications of isolating the fourth ventricle and identifying the signs that make its care critical are two further issues that warrant extra surveillance. The cerebellum’s posterior displacement and compression are the initial signs of growing fourth ventricle dilatation. This is followed by anterior relocation of that entity and the onset of brain stem deformation. The inflated fourth ventricle’s upper herniation is a frequently noticed phenomenon. Common manifestations include deconjugate eye movements, poor eating, truncal instability, and somnolence. Acute or subacute IFV is less frequent and is linked to bleeding or infection during diagnosis [26-28].
Other study results demonstrate that in clinically deteriorating patients with neurosarcoidosis and ventriculoperitoneal shunting, an isolated fourth ventricle must be taken into consideration as a differential diagnosis. Granulomatous inflammation of the periventricular tissue may be the origin of the meningeal contrast enhancement at the fourth ventricle’s outputs. This inflammation ultimately resulted in the establishment of the ailment[29] . After lateral ventricular shunting, the symptoms often go away entirely so ventricle returns to normal and needs to be shunted. It can be distinguished from other pathologies, like cystic tumours, by paying close heed to denseness and presentation on CT [15].
MRI is frequently used to confirm the issue of discrepant dilatation, which is commonly identified by cranial ultrasonography. Diagnosis is confirmed when an enlarged ”ballooned” fourth ventricle is observed. Compression of the surrounding structures, membranous blockade of the aqueduct of Silvius, effacement of the cerebellar tissue, flattening of the posterior aspect of the brainstem, and decreased CSF in the prepontine cistern due to ventral displacement of the brainstem are also frequently present [30, 31]. Furthermore, MRI can be utilised to distinguish between cystic lesions, shunt dysfunction, and a TFV. Compression of the brainstem and cerebellum, herniation through the tentorial notch on preoperative imaging, structures and length of CSF containing parts, all influence treatment choices [32, 27].
Cranial nerve palsy after shunt implantation is rare in an IFV. In some instances of IFV, catheter damage to the nuclei of the brainstem is believed to cause nerve dysfunction. A young patient was reported to develop dysfunction of the abducent, facial and hypoglossal nerves some days after shunt placement[33]. Another study showed that treatable polyneuropathies resulted after acute decompression of the structure[34]. Multiple cranial nerve impairments that affect both sides are extremely rare. As far as we are aware, there has only been one case documented in the literature. In a report of a young patient who had undergone implantation of a low-pressure fourth VP shunt, three months following the procedure a CT scan was done which demonstrated the ventricular shrinking with the child having symptoms like bilateral abducent nerve palsies and vomiting. After switching to ”a medium pressure” system for the valve, these problems subsided [35].The basic principle of the management of a fourth ventricular trap is to facilitate CSF drainage, thereby alleviating compression over vital structures. A wide range of options are available for management, with a variety of non-invasive measures ranging from observation and monitoring, periodic neurological examination and imaging for asymptomatic cases, medical measures like intra-cranial pressure lowering drugs, shunt adjustment and rehabilitative measures. Severe cases might require surgical management, including fourth ventricular shunting, endoscopic third ventriculostomy and aqueductoplasty. In less complicated cases when other procedures are not viable, shunting with a Y connector stands out to be an appropriate choice [36]. Prompt treatment of fourth ventricular trap can ensure relief from features of raised ICP and life-threatening compressive features encompassing nerve lesions, dysphagia and dysarthria, thereby preventing neurological damage. Timely intervention can also prevent regression of developmental milestones in children, minimise irreversible neurological damage and improve surgical outcomes [9, 11].
Treatment of the fourth ventricular trap, whether surgical or non-surgical, poses a risk of certain complications like shunt blockage, over-drainage leading to ventricular collapse, damage to the adjacent structures, CSF leak and risk of infection, in addition to the neurological deficit that might occur due to the progression of the condition [9]. Amongst these, the risk of infection is one of the most common complications, which might be acquired through exogenous or endogenous (haematogenous) routes. Generalised features of fever, irritability, lethargy, signs of inflammation along the shunt track, symptoms suggestive of peritonitis and neurological features suggestive of shunt failure, including signs of raised ICP and altered mental status, can develop. After confirming the diagnosis through blood cultures, CSF analysis and imaging, a shunt is removed, followed by draining, and usage of intravenous bactericidal drugs. Reapplication of a new shunt is planned later on. The prognosis after prompt treatment of trapped fourth ventricles is dependent on multiple factors, including but not limited to the treatment modality employed, time elapsed, presence of an underlying condition, age and overall health status of the patient. Most patients do experience symptomatic relief, particularly marked with respect to headache, vomiting, ataxia and cranial nerve deficits evidenced by the reduction in the length of cavity on imaging. Timely intervention also curtails the risk of long-term neurological deficits and developmental delays, although certain issues such as shunt dependency and infection can arise. Early diagnosis and intervention reduces the chances of irreversible neurological deficits and improves the long-term outcomes, improve survival as well as quality of life in such children, while reducing the risk of complications. In view of the potentially life-threatening complications that can arise, long-term follow-up and monitoring are extremely vital. This will facilitate early detection of complications and thereby a better neurological outcome. Additionally, any recurrence due to scarring, blockage of shunt or infection can be detected before significant symptoms arise. It can be done by serial imaging in addition to monitoring of symptomatic improvement and assessment of developmental milestones attained. The aspect of psychosocial support is indispensable in such cases, more so with complications or neuronal deficits [11].