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].