Introduction
Arachnoid cysts (AC) account for approximately 1% of all intra cranial mass lesions,[1 ] and are more common in the middle cranial fossa followed by posterior cranial fossa.[2 ] They are often incidental and managed conservatively, but the effective treatment
modality still remains controversial. Symptomatic cases are managed by different modalities,
i.e., cyst excision, marsupialization of the cyst, cyst fenestration, cystoperitoneal
shunt, and endoscopic cysto-ventriculostomy.[3 ]
[4 ]
Neuro-endoscopy achieves the fenestration of cyst less invasively, avoids shunt and
open micro surgery-related complication especially in the eloquent areas. We present
a series of eight cases managed with endoscopic trans-aqueductal cysto-ventriculostomy
of fourth ventricular and juxta fourth ventricular arachnoid cyst, which is sparsely
reported.
Description of Cases
This is a prospective analysis of a subset of patients with fourth ventricular and
juxta fourth ventricular ACs and hydrocephalus who underwent transaqueductal cysto-ventriculostomy
with a flexible neuro-endoscope. Of 350 intraventricular neuro-endoscopic procedures
performed on children between 2008 and 2019, 8 were for fourth ventricular and juxta
fourth ventricular arachnoid cysts ([Table 1 ]).
Table 1
Clinical features, imaging, and surgical outcomes
S. No.
Age
Clinical features
Imaging
Procedure
Follow-up
Remarks
1
20 d
Diagnosed on antenatal screening
Right cerebellopontine angle arachnoid cyst with hydrocephalus
ETV + TA CV + CC + RP
10 months
Clinical and radiological improvement
2
8 mo
Progressive increase in head size with raised ICP features
Right cerebellopontine angle arachnoid cyst with hydrocephalus
ETV + TA CV + RP
16 months
Clinical and radiological improvement
3
8 mo
Progressive increase in head size with raised ICP features
Posterior fossa arachnoid cyst with hydrocephalus
ETV + TA CV + RP
17 months
Clinical and radiological improvement
4
15 mo
Raised ICP features
Posterior fossa arachnoid cyst with hydrocephalus
ETV + TA CV + RP
19 months
Had postoperative meningitis; improved neurologically
5
6 mo
Progressive increase in head size with raised ICP features
Posterior fossa arachnoid cyst with hydrocephalus
ETV + TA CV + RP
10 months
Clinical and radiological improvement
6
13 mo
Raised ICP features
Posterior fossa arachnoid cyst with hydrocephalus
ETV + TA CV
Clinical and radiological improvement
7
8 mo
Progressive increase in head size and raised ICP
Retrocerebellar arachnoid cyst
ETV + TA-TM CV + RP
1 year
Developed subdural hygroma; improved with conservative management
8
12 mo
Progressive increase in head size and raised ICP
Retrocerebellar arachnoid cyst
ETV + TA-TMCV + VPS
2 years
Clinical and radiological improvement
Abbreviations: CC, choroid plexus cauterization; ETV, endoscopic third ventriculostomy;
ICP, intracranial pressure; RP, reservoir placement; TA CV, trans aqueductal cysto
ventriculostomy; TA-TM CV, trans aqueductal transmagendal cysto ventriculostomy; VPS,
ventriculoperitoneal shunt placement.
Patients were aged 20 days to 15 months; in the neonate (20 days old), the diagnosis
was established during antenatal screening; others were aged 6 months or older. Progressive
increase in the size of the head with signs of raised intracranial pressure (ICP)
was the clinical feature.
Our surgical goal was to decompress the arachnoid cyst and treat the hydrocephalus
with a single approach.
Surgical Procedure
General Principles
All patients were assessed clinically and radiologically (computed tomography [CT]
and magnetic resonance imaging [MRI]), pre- and postoperatively. Preoperative antibiotics
and other patient safety issues were followed as per the standard hospital protocol.
All were operated under general anesthesia in supine position ensuring the stability
of head. A standard pre-coronal burr hole (Kocher's point) was performed. After incision
of the dura, working sheath of the rigid endoscope with obturator was introduced into
the lateral ventricle. Initially, a standard third ventriculostomy was done with the
help of a rigid endoscope and the stoma was dilated with a Fogarty catheter. The sheath
was stationed at the foramen of Monroe. A 4 mm flexible neuroendoscope/3.2 mm video
neuroendoscope (Karl Storz) was passed through the sheath, with tip maneuvered through
the foramen of Monroe and then through the aqueduct into the fourth ventricle. The
arachnoid cyst bulging into the fourth ventricle was cauterized, shrunken with a low
current flexible monopolar and marsupialized. [Table 1 ] summarizes the clinical features, and procedures done in these patients.
In two (cases 7 and 8), the cyst was retrocerebellar, which required transforaminal,
transaqueductal and transmagendal procedures. In one case (case 8), after the cyst
marsupialization, a shunt catheter was placed into as endoscopic third venriculostomy
(ETV) could not be performed because of narrow prepontine space. The shunt with multiple
fenestration was placed through the aqueduct and foramen of Magendie into the cyst.
This catheter in turn was connected to a routine (ventriculo-peritoneal) shunt. The
neuroendoscope and sheath were removed after completion of the surgery. In two patients,
Ommaya reservoir was placed following the initial procedure, where the opening intracranial
pressure was noted to be very high for controlled tapping of CSF in case of postoperative
raised pressure or impending leak from surgical site wound.
Specific Technical Aspects
All surgeries were performed by an experienced neurosurgeon having more than two decades
of experience in pediatric neurosurgery, expert in neuroendoscopy, specifically with
flexible neuroendoscopy.
All these cases had a naturally dilated aqueduct because of fourth ventricular outlet
obstruction and none required an aqueductoplasty. However, this procedure to be avoided
undilated aqueduct.
A standard rigid endoscope was used for third ventriculostomy followed by a flexible
neuroendoscope/video neuroendoscope (STORZ) with a working channel; standard accessories
such as grasping forceps and monopolar cautery were used for the transaqueductal procedure.
A standard rigid scope was used for ETV. Keeping the sheath in place, the flexible
neuroendoscope was passed through it.
A flexible neuroendoscope with an outer diameter of 4 mm/3.2 mm with a working channel
can easily be maneuvered through the aqueduct with a standard pre-coronal burr hole
without causing any damage to the fornix, with special and extra care particularly
for the neonate.
There were no intraoperative complications. All eight patients improved symptomatically,
clinically, radiologically and are on regular follow-up to date. One patient had postoperative
meningitis, which gradually improved with antimicrobial therapy. None required alternative
form of treatment such as shunt or craniotomy and microsurgical excision.
[Table 2 ] compares the new technique with the existing technique for transaqueductal cysto-ventriculostomy.
Table 2
Comparison between techniques for transaqueductal cysto-ventriculostomy with the existing
technique
Parameters
New technique
Existing technique
Instrumentation
Technical
Approach
Single precoronal burr hole
Suboccipital craniotomy with cyst marsupilization or a cysto + ventriculoperitoneal
shunt
Ventriculostomy
Purely endoscopic technique
Microsurgical technique
Expertise
Requires extensive training
Complications
Minimal, i.e., subdural hygroma
All craniotomy and/or shunt related issues, pseudomeningocele, cerebrospinal fluid
leak
Preoperative/anesthetic
Shorter duration of surgery
Longer duration
Intra-operative
Minimal blood loss
Blood loss in craniotomy is higher
Postoperative
Early recovery and discharge from the hospital
Longer recovery and hospital stay
Advantages
Minimally invasive and access and single burr hole surgery
Conventional surgery and familiar to many
Limitations
Steep learning curve, especially with the use of flexible neuroendoscopy
Cannot address the issue with a single procedure; requirement of craniotomy and ventriculoperitoneal
shunt for the cyst and hydrocephalus
Disadvantage
Risk of injury to periaqueductal structures during a transaqueductal procedure
All complications and risks of craniotomy and/or shunt related
[Figs. 1 ], [2 ], [3 ], [4 ], [5 ], [6 ] depict the important surgical techniques adapted for the new technique.
Fig. 1 Direction of videoneuroendoscope/flexible neuroendoscope transventricular, transformaminal,
transaqueductal into the fourth ventricle.
Fig. 2 Preoperative retrocerebellar arachnoid cyst with hydrocephalus and postoperative
changes: decrease in cyst size and hydrocephalus with bilateral subdural hygroma.
Fig. 3 Visualization of the brain stem and the cyst once the scope is negotiated through
aqueduct and foramen of Magendie, coagulation of AC with a flexible monopolar cautery,
dilation of the cyst openings with Fogarty catheter and visualization of PICA after
coagulation of the cyst in the occipital bone.
Fig. 4 Posterior fossa arachnoid cyst bulging into the fourth ventricle with associated
hydrocephalus (preoperative), well-decompressed arachnoid cyst and ventricles (postoperative).
Fig. 5 Arachnoid cyst bulging into the fourth ventricle, fenestration of arachnoid cyst
with monopolar cautery, coagulated and collapsed arachnoid cyst.
Fig. 6 Shunt being guided into the retrocerebellar cyst transaqueductal transmagendal post
cyst marsupilization, Shunt catheter in position in the posterior fossa–draining the
cyst and the ventricles.
Discussion
Arachnoid (leptomeningeal) cysts are benign, space-occupying lesions within the split
layers of the arachnoid membrane and are filled with cerebrospinal fluid (CSF).[5 ]
[6 ] Only 5 to 10% of these cysts have been found in the posterior cranial fossa, with
the quadrigeminal plate, retro cerebellar area, cerebellopontine angle, fourth ventricle
and clivus being common sites of occurrence. ACs of the fourth ventricle may present
diversely such as normal pressure hydrocephalus,[7 ] raised ICP, and cerebellar dysfunction, which need immediate surgical intervention.
Simple ACs and hydrocephalus are generally approached conservatively with wait and
watch strategy. In our series, all presented with a large cyst and hydrocephalus,
manifestation of pressure effects; so, it was pertinent to treat both in a single
sitting and single approach procedure.
Surgery is indicated to prevent developmental delays associated with asymptomatic
patients. Indications and use of cranial neuroendoscopy, a minimally invasive technique,
are gradually expanding. Intracranial AC is an attractive target for neuroendoscopy.
Flexible neuroendoscope helps to navigate into the remote areas of ventricle, where
a rigid endoscope cannot reach without compromising safely. Novel idea of endoscopic
transaqueductal cysto-ventriculostomy has shifted the difficulty in approach towards
an easy, less laborious procedure; video neuroendoscopy, more precise adjunct causes
minimal damage to the surrounding structures and reduces associated complications.
Success of neuroendoscopy for ACs in infants,[8 ] has demonstrated the practicality in younger patients, which is proven in the 20
day old neonate in our series.
Craniotomy with micro-surgical approach and shunting are the established modalities
of management but are associated with complications such as meningitis, injury to
neuro-vascular structures around the fourth ventricle, shunt infection, malfunction,
and dependence on shunt. Endoscopy avoids life-long shunt dependence, shunt-related
complications and has less chances of recurrence.[9 ] Flexible neuroendoscope is successfully used for trans lamina terminalis third ventriculostomy,
if standard third ventriculostomy could not be achieved safely.[10 ]
Endoscopic cysto cisternostomies and cysto-ventriculostomies are safe and effective
minimally invasive techniques for the treatment of arachnoid cysts.[11 ] In this series, we used flexible neuroendoscopy effectively in the management of
benign fourth ventricular lesions (arachnoid cyst) in a minimally invasive way.
Possible approach for navigating into the fourth ventricle endoscopically are from
the third ventricle through the cerebral aqueduct[12 ] and via the cerebellomedullary cistern through the foramen of Magendie.[13 ] In our series, location of the cyst caused obstruction of the fourth ventricular
outlet, due to which the aqueduct was naturally dilated that allowed easy passage
of the flexible neuroendoscope without causing any brain stem dysfunction or any ependymal
contusion. In our series, we did not use neuronavigation, which is not possible with
flexible neuroendoscope.
Transaqueductal navigation of the fourth ventricle has been considered dangerous.
Neuroendoscopic exploration of the fourth ventricle done using rigid endoscopes in
the past were associated with many sequelae, particularly disturbances of ocular movement.[14 ] In our series, all had naturally dilated aqueduct because of fourth ventricular
outlet obstruction and none required an aqueductoplasty. In the absence of dilation,
navigating a non-stenotic aqueduct has to be avoided.
Decompression/marsupilization of the fourth ventricular cyst through trans-frontal
approach via the third ventricle is reported to be safe, though there is a possibility
of transient complications (hemiparesis, ocular ptosis).[15 ] Approach through sub-occipital craniotomy, transcerebellar endoscopy and fenestration
of cyst in the fourth ventricular AC has been reported as a safe procedure.[2 ]
Fourth ventricle is the common site for neurocysticercosis brain, resulting in CSF
blockage. Available reports state success of endoscopic approach via a frontal burr
hole in patients with hydrocephalus, dilation of aqueduct, and foramen of Monro.[16 ] Exploration through the aqueduct for removal of fourth ventricular neurocysticercosis
is reported by Suri et al.[17 ] Aspiration of cyst contents of fourth ventricular neurocysticercosis by positioning
a rigid endoscope at the opening of cerebral aqueduct is another method described.[18 ]
Successful endoscopic removal of cysticercal cysts in the fourth ventricle through
a midline durotomy between the opisthion and the posterior arch of C-1, advancing
toward the fourth ventricle through the foramen of Magendie, avoiding transductal
pathway using a flexible endoscope has been documented.[15 ]
[19 ]
Neuroendoscopy offers a different outlook for anatomy of the fourth ventricle. Neuroendoscopy
provides a superior and detailed visualization, particularly of the structures located
in the inferior triangle compared to microsurgery. But the experience with trans aqueductal
approach for fourth ventricular lesions is limited even among neurosurgeons who are
well versed with flexible endoscopes; hence, difficulty and procedure related complications
can be expected, though mortality is not reported. We used neuro-endoscopic techniques,
which is considered risky by a few, as simple endoscopic procedures will not address
both pathologies. We performed ETV for hydrocephalus, which was necessary to release
the pressure symptoms; we approached posterior fossa endoscopically as the opening
of the cyst (cyst ventriculostomy) to reduce the size of the cyst and pressure on
the posterior fossa was required. Endoscopic transaqueductal management of the fourth
ventricular AC is rarely reported; a single case of endoscopic treatment of fourth
ventricular AC via the third ventricle has been reported by Martinoni et al[12 ] and a case of transaqueductal trans-Magendie fenestration of arachnoid cyst in the
posterior fossa was described with good outcome by Felliti et al.[20 ]
Longatti et al[21 ] who performed 75 endoscopic explorations for spectrum of disorders reported no deaths
but caution us about the complications (extreme bradycardia [n = 04]; ependymal contusion
[n = 01]). They identified around 20 anatomical structures, consistently by exploring
the fourth ventricle with a flexible neuroendoscope. Hence, endoscopic trans-aqueductal
navigation of the fourth ventricle using a flexible endoscope is safe in expert hands,[21 ]
[22 ] emphasizing the need for training.
We suggest performing a minimum of 20 procedures with flexible neuroendoscope to develop
a good hand–eye coordination, understand the maneuverability of the scope, and get
familiarized with the anatomy of the structures in the third ventricle, aqueduct,
and the fourth ventricle.
The utility of neuro-endoscopy and frameless neuro-navigation in exploring the fourth
ventricle has been investigated. This combination determines the entry point accurately,
helps to plan trajectory, minimize injury to the vital structures and helps surgeon
to orient within the cystic cavity for appropriate fenestration sites. Its applicability
in cases of small ventricles and while using a rigid scope to target the aqueduct
or planning a transaqueductal procedure is the focus area to explore.[23 ]
These posterior fossa arachnoid cyst cause fourth ventricular outlet obstruction and
exert mass effect on posterior fossa structures. Fenestrating the cyst will help not
only in decreasing the size of the cyst and mass effect but also the obstructing pathway.
By performing an additional successful ETV as a back-up, hydrocephalus is also managed
and was considered in few patients in our series. Large cysts causing mass effect
also have to be taken care of and this cyst decompression may not be enough to treat
this hydrocephalus.
Neuroendoscopy confers various advantages; surgery through a small frontal burr hole,
less intraoperative time and minimally invasive are a few. It requires learning, experience
to navigate the flexible neuroendoscope through the aqueduct without causing injury
to brain stem, and vital structures in the floor of fourth ventricle. Intraventricular
bleeding when encountered is managed with continuous copious irrigation or transiently
raising ICP by opening the inlet for irrigation and closing the outlet under strict
hemodynamic monitoring; there were no intraoperative complications including intraoperative
bleeding in the fourth ventricle, bradycardia in our study. In our series, there was
no mortality; post-operative meningitis was reported in one patient, which was managed
appropriately. None of our patients required alternative form of treatment indicating
the success of the procedure.
Conclusion
Transaqueductal neuro-endoscopy helps in managing fourth ventricular and juxta fourth
ventricular arachnoid cysts safely and effectively with minimal invasiveness. It avoids
complications that are associated with the conventional modalities of management.
Our preliminary experience shows transaqueductal navigation of the fourth ventricle
using flexible neuroendoscope is safe in expert hands.
