TECHNICAL NOTE - PEDIATRICS

Suboccipital endoscopic management of the entrapped fourthventricle: technical note

Alaa Raouf & Ihab Zidan

Received: 4 June 2013 /Accepted: 8 August 2013# Springer-Verlag Wien 2013

AbstractBackground Entrapped fourth ventricle is the result of bothinlet aqueduct and outlet fourth ventricular midline and lateralforaminae obstruction. It occurs as a sequalae of intracranialhemorrhagic or inflammatory disease condition. Usually itpresents after previous shunting for communicating hydro-cephalus with a period of improvement, after which manifes-tations of posterior fossa expanding process appear. The diag-nosis of this rare condition is easy considering the patient pasthistory and the recent clinical state, together with the midlineCSF density of the dilated fourth ventricle in either the CT orMR images. The treatment options for this condition includeopen and endoscopic approaches together with the traditionalventricular to extracranial CSF diversionary procedures.Objective The aim of the study was to adopt a procedure fortreatment of entrapped fourth ventricle that carries the advan-tage of the minimally invasive technique thus avoiding thecomplications of the traditional opened and shunt surgeries aswell as decreasing multiple procedures due to aqueduct reste-nosis or stent fall.Methods Thirteen patients with symptomatic entrapped fourthventricle underwent suboccipital endoscopic trans–fourth ven-tricular aqueductoplasty from May 2007 till November 2011.The Gabb endoscopic system was used and aqueductoplastywas performed using 3F Fogarty balloon followed by stentplacement. Nine patients were females. The mean age was3.6 years and the mean follow up period was 23 months. Allcases had a previous one or two supratentorial VP shuntplacement.

Results Short stent was used in eight patients. During thefollow up, stent migration occurred in five of them. Three ofthese five patients developed posterior fossa compressionmanifestations due to aqueduct restenosis. Long stent fromthe aqueduct till the bur hole site for these three patients andthe following five patients was used. All cases showed bothclinical and radiologic improvement. Apart from the stentmigration, no procedure-related complications wereencountered.Conclusion Endoscopic suboccipital paramedian aque-ductoplasty with the use of a stent is a safe and effectivesurgical option that—in our opinion—should stand as the firstline treatment for the entrapped fourth ventricle. Long stent isbetter used after aqueductoplasty to avoid the restenosis if nostent is used or stent fall after short stents. However, good caseselection, familiarity with this fairly common endoscopicapproach and longer follow-up is needed for obtaining anoptimal result.

Keywords Entrapped fourth ventricle . Endoscopic .

Aqueductoplasty . Stent

Introduction

Entrapped fourth ventricle means its isolation from the rest ofthe ventricular system due to obstruction of the aqueduct andfrom the subarachnoid space due to obstruction of the fourthventricle outlet foraminae. Since its first diagnosis in 1968[10], the trapped fourth ventricle still carries many controver-sial issues concerning its both diagnosis and treatment [9].Trapping of the fourth ventricle is not a primary event, butusually complicates an intracranial hemorrhagic, inflammato-ry or infective process resulting in hydrocephalus that wastreated with supratentorial ventricular shunting. The trappedfourth ventricle is not a common clinical entity, in spite therelative high incidence of post hemorrhagic or post

Presentation at a conference: 23rd Congress of the European Society forPediatric Neurosurgery, May 1–5, 2012| Amsterdam, Netherlands.

A. Raouf : I. Zidan (*)Department of Neurosurgery, Faculty of Medicine, AlexandriaUniversity, Champillion St, Elazaritta, Alexandria, Egypte-mail: zidanihab@yahoo.fr

Acta NeurochirDOI 10.1007/s00701-013-1843-5

inflammatory hydrocephalus. The postulations for its patho-genesis failed to explain why it occurs in some and does notoccur in other patients despite having the same disease process[6, 9]. The clinical diagnosis depends mainly on the newappearance of posterior fossa compressive symptoms after arelatively quiescent period in a previously shunted patient[11]. Radiologic diagnosis should differentiate this diseasecondition from other posterior fossa cysts and cystic tumors.The treatment strategies for the trapped fourth ventricle in-clude the classical CSF diversionary procedures, the opensurgical and the minimally invasive endoscopic techniques.The endoscopic approaches entail aqueductoplasty alone—through either precoronal or suboccipital routes—oraqueductoplasty with stenting [9, 20]. Regardless of the cho-sen surgical modality, the Treatment is plagued by a high rateof complications and failure. An ideal treatment would be thatone with low complications and high success rate, meanwhileavoid the need for permanent implants. This aim is usuallyunattainable and more practical goals are to avoid majorcomplications, multiple procedures and complex shunt sys-tems [9]. Endoscopic aqueductoplasty with stenting also has alower rate of restenosis than simple aqueductoplasty [2]. Weaimed in our study to adopt a procedure that carries theadvantage of the minimally invasive technique thus avoidingthe complications of the traditional opened and shunt surger-ies, meanwhile decreasing as much as possible multiple pro-cedures due to aqueduct restenosis or stent fall.

Patients and methods

Between May 2007 and November 2011, 13 children withsymptomatic entrapped fourth ventricle admitted atAlexandria Main University Hospital underwent suboccipitalendoscopic aqueductoplasty with the placement of a stent in theaqueduct. The age ranged between 1 and 10 years. The meanage was 3.6 years. Nine were females and four were males. Allpatients had a previous one or two supratentorial shunt inserted.The hydrocephalus was due to perinatal infection in ten, neo-natal hemorrhage in two and frontal abscess in one patient. Thetime lapse between the insertion of the supratentorial shunt andthe radiologic presentation of the trapped fourth ventricleranged between 1 month and 8 years, while the time passedfrom the radiologic diagnosis till the development of clinicalmanifestations ranged between 4 months and 4 years. None ofour patient was subjected to previous endoscopic surgery. Onepatient had a previous shunt inserted in the trapped fourthventricle and the peritoneal end slipped to the pelvis. Thedecision for surgery was taken when patients presented withrecurrent periodic pouts of non explainable headache, partialunilateral third nerve palsy, unilateral or bilateral six nervepalsy, manifestations of lower cranial nerves affection, frequentattacks of vomiting, lethargy, disturbed conscious level and

irritability with growth failure in patients around 1 year. Thepatients’ relevant clinical data is fully represented in Table 1.Patients with dilated fourth ventricle and stable clinical condi-tion or thosewith evident shuntmalfunctionwere excluded. Forall patients, CT was done both to diagnose the trapped fourthventricle and to exclude malfunctioning supratentorial ventric-ular shunt system.MRI examination was done for all cases withstress on requesting sagittal T1-weighted images with thinmidline cuts to show the morphology of the sylvian aqueduct.A thin membrane occluding the aqueduct was demonstrated inthe 13 patients.We used the conventional ventricular catheter asa stent. Side holes were made in the stent to augment its fluidtransfer capacity, and to guard against its proximal end block-ade. In the first 8 cases a short stent, 2 cm longer than the lengthof the aqueduct was used. During follow up, stent slippage fromthe aqueduct occurred in five cases. Three of these cases neededanother surgery, while two remained stable without a stent. Forthe 3 cases who required resurgery and the next 5 cases, weused a long stent. The follow up period ranged from 42 to7 months with a mean of 23 months.

Surgical technique

Under general anesthesia, the patient was placed prone. Thehead was flexed and resting on the forehead thus securing theeyes and the nose against any compression. The burr hole wasplaced 2–3 cm below the superior nuchal line (In younginfants, the posterior fossa is shallow and the burr hole wasplaced between the superior nuchal line and foramen mag-num) and 2 cm from the midline to be in line with theaqueduct. The dura was opened and a brain cannula was usedto tap the dilated fourth ventricle. A 0° rigid scope wasintroduced through its sheath to the cavity fourth ventricle.Once inside, the anatomy of the dorsal brain stem was iden-tified and the distal aqueduct was localized with the mem-brane occluding it. A 3F Fogarty balloon catheter was used toperforate the obstructing membrane. With gentle and cautiousmild inflation of the balloon catheter, the distal aqueduct wasdilated caring not to injure the periaqueductal structures,meanwhile not to do so much dilatation that may cause thestent to migrate. Application of the stent was as follow;

Short stent placementThe distal end of the stent was grasped with the

endoscopic grasping forceps and guided through the en-doscopic sheath till its proximal end fits the aqueduct andafter securing its location, the endoscope was withdrawnfrom the cavity of the fourth ventricle.Long stent placement

The stent was introduced parallel to the scope whilethe grasping forceps was introduced through the endo-scopic sheath to hold the proximal end of the stent and

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direct it towards the aqueduct. Then the endoscope waswithdrawn from the cavity of the fourth ventricle and theextra length of the stent was cut and its distal end wasfixed to the occipital muscles at the burr hole site using 3/0 silk and tightly closed not to cause gravitationalintermuscular or subcutaneous CSF collection.Reintroduction of the scope to the cavity of the fourthventricle in these cases was done to ensure the accuratelocation of the proximal end of the stent after the manip-ulation on its distal end during fixation.

In trapped fourth ventricle, the aqueduct and tectumare already shortened as they are pushed upward by thedilated fourth ventricle. This could be explained by in-creased fourth ventricular pressure together with de-creased pressure in the lateral ventricle due previousshunting. In all our cases the membrane was found dis-tally in the aqueduct.

We didn’t face any cases with long segment aqueductstenosis.

We did not use image guidance (e.g., ultrasound,frameless stereotaxy, etc.) in our cases as the trajectoryis straight and the fourth ventricle is dilated together withthin cerebellar mantle which facilitates the stent applica-tion under vision.

Results

The suboccipital approach was used in all the patients as thesupratentorial shunt system was functioning and the

ventricular systemwas well drained. In the first 8 cases a shortstent was used (Fig. 1). During the follow-up period, fivestents slipped from their place in the aqueduct to the cavityof the fourth ventricle (Fig. 2). One stent has slipped earlyafter 1 week, while another one has slipped 3 years after thesurgery. For the case that showed early slippage of the stent wewere obliged to reoperate rapidly due to the frequent vomitingand intractable headache of the patient. From this case on-wards we used the long stent (Fig. 2). The other four caseswith stent slippage were followed; two of them did wellwithout the need for reoperation while the other two showedgradual development of pressure manifestations thus necessi-tating long stent placement. During the revision of these 2cases a membrane was found occluding the aqueduct andaqueductoplasty was done again before a long stent wasplaced. Apart from stent slippage, no per or postoperativecomplications were encountered. All cases showed improve-ment of the newly developed manifestations that was ascribedpreoperatively to the trapped fourth ventricle except for thegrowth delay in patient number 8. However all patients withgrowth delay with vomiting and/or cranial nerve palsy showedimprovement. The dilated fourth ventricle did not return to itsnormal size in all patients, despite the marked clinicalimprovement.

Discussion

Entrapment of a ventricle or part of it by occlusion of its outletdue to ependymal reaction after intraventricular infection orhemorrhage is a well known and fully described entity [10].

Table 1 Clinical data of 13 patients with trapped fourth ventricle

Patient Age Sex Causeof HC

No ofVP shunts

Previous shuntfor TFV

Clinical presentation Time from shunt tillradiologic D

Time from radiologic Dtill clinical presentation

1 1 F PI 1 − GD 5 months 6 months

2 3 F PI 1 − Headache vomiting 12 months 18 months

3 3 M PI 1 − Vomiting, gait disturbance 23 months 12 months

4 7 F F ab 1 + 6th n. palsy, headache 3 months 48 months

5 5 F PH 2 − Bilateral 6th n. palsy, vomiting 32 months 24 months

6 6 F PH 1 − Feeding problem, vomiting, headache 42 months 23 months

7 2 M PI 1 − GD, bilateral 6th n. palsy 3 months 15 months

8 1 F PI 1 − GD 1 months 9 months

9 1 F PI 1 − GD, vomiting 2 months 4 months

10 5 M PI 1 − Headache chocking, vomiting 42 months 12 months

11 2 M PI 1 − Partial 3rd n. palsy, vomiting 15 months 5 months

12 2 F PI 1 − Vomiting, gait disturbance 2 months 21 months

13 9 F PI 2 − 6th n. palsy, headache, chocking,disturbed sensorium

96 months 6 months

HC hydrocephalus, TFV trapped fourth ventricle, D diagnosis, PI post infection, PH post hemorrhagic, F ab frontal abscess, GD growth delay

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Entrapment of the fourth ventricle is, however, a recentlyrecognized condition [2]. Post hemorrhagic dilatation of thefourth ventricle occurs only in a minority of infants. In a

review of 1,535 neonatal ultrasonograms, IVH was seen in761(50 %). Of these cases, 229 were severe and 10 of theseacquired significant dilatation of the fourth ventricle before

Fig. 1 a CT scan (axial view)showing hugely dilated fourthventricle with evidentperiventricular permeation. bMRI (T1 weighted image) strictmidline sagittal view of the samepatient showing a membrane inthe aqueduct. The entrappedfourth ventricle is evident withmarked compression and anteriorshift displacement of the brainstem. c , d , e Postoperativefollow-up CT scan (axial andsagittal views) of the same patientafter endoscopic aqueductoplastyshowing short stent in theaqueduct and in the cavity of thefourth ventricle

Fig. 2 a , b CT scan (axial view)showing stent migration to thefourth ventricular cavity afterendoscopic aqueductoplasty withshort stent and the patient showedrecurrence of the pressuremanifestations. c , d , e , fPostoperative follow-up CT scan(Axial views) of the same patientafter endoscopic aqueductoplastyusing long stent showing theposition of the long stent from theaqueduct out to the dura. g , h , iPostoperative follow-up CT scan(sagittal views) of the samepatient

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shunt placement. Trapping of the fourth ventricle manifestedin 6 of these 10 patients after shunting of the lateral ventricle[11]. The incidence of the truly trapped fourth ventricle hasbeen reported to be 2–3 % of the totally shunted patients [20].

The pathogenesis of the entrapment of the fourth ventricleis not fully understood. The obstruction of the aqueduct is thekeystone for the isolation of the fourth ventricle. It has longbeen recognized that shunting of the ventricular system forcommunicating hydrocephalus can cause obstruction of theaqueduct [2, 19]. The delayed presentation of the radiologi-cally and clinically trapped fourth ventricle, reaching to 8 yearsin our study and to a mean of 17 months in Cinalli’s work [2]and 3.1 years in Eder et al. study [5], supports the firstpostulation.

As children with trapped fourth ventricle are previouslyinsulted by intracranial inflammatory or hemorrhagic processthus usually having a fair neurological baseline, it is difficultto diagnose the condition and monitor the improvement [11].Specific symptoms of trapped fourth ventricle may be due tomass effect on brain stem and cerebellum [8, 14] or due toincreased intracranial pressure in a patient with low compli-ance. It must however be emphasized that the newly develop-ing manifestations are actually due to the entrapped fourthventricle and not due to supratentorial shunt malfunction [22].Even with the picture of an isolated large fourth ventricle, theclinical presentation is important, as some children can livewith large fourth ventricle without any clinical manifestations.A key point for the diagnosis of a trapped fourth ventricle isthe establishment of a good functioning previously placedsupratentorial shunt system despite the newly developed pos-terior fossa compressive manifestations. Both CT and MRIcan differentiate adequately the trapped fourth ventricle fromother cystic lesions or neoplasms that might affect the poste-rior fossa. Besides, they can identify the pressure manifesta-tions on both the cerebellum and the brain stem. In all ourpatients the sagittal MRI demonstrated flattening of the pos-terior aspect of the brain stem and diminished CSF in the prepontine cistern. The cerebellum was also compressed andeffaced laterally. Udayakumaran et al. [22] demonstrated thesame sign in their 12 patients.

The management of the trapped fourth ventricle shouldcover two points: the first is the indication for surgery andwhen decided, and the second is the treatment modalitiesavailable and which one will be chosen. Patients who hadbeen operated before for communicating hydrocephalus withnewly developed posterior fossa compressive manifestationsand documented functioning shunt system were our surgicalcandidates. Cases with evidently dilated fourth ventricle, welldrained shunted supratentorial ventricular system and mean-time having a stable clinical condition were excluded from ourstudy. Many authors stress the same criteria as an indicationfor surgery. Teo [20] excluded from his study asymptomaticpatients even having radiologic progression.

The treatment options for symptomatic entrapped fourthventricle include the traditional CSF diversionary procedures,open surgery and the endoscopic techniques. All these man-agement strategies have been fully discussed by Harter [9].

Fourth ventricular shunt placement has been the conven-tional method of treatment for this pathologic entity [10, 17].Shunting procedures can be effective either when it is usedalone or when shared with the lateral ventricular shunt.Morbidity, however, after the placement of fourth ventricularcatheter by whatever route is significant [1, 4, 11, 12, 15] andmostly related to cranial nerves. Complications can occureither at the time of catheter placement or even in a delayedfashion when the brain stem reexpands. The shunting proce-dures can be also associated with the usual shunt complica-tions as infection, obstruction and dislodgement.

Open surgical fenestration of the fourth ventricular outlethas been reported. The aim was to decompress the fourthventricle, while avoiding the use of another shunt. Manyreports of great success and minimal accepted complicationshave been published [11, 18, 22, 23]. Still the procedureshould be addressed as a major cranial surgery with its possi-ble complications.

Endoscopic reopening of the aqueduct leads to communi-cation between the isolated fourth ventricle and thesupratentorial compartment equating intraventricular pressuregradients and allowing a single supratentorial shunt to controlhydrocephalus. It carries the advantages of both being a min-imally invasive procedure (avoids an open surgery) andavoids the patient the application of another shunt with itspossible complications. Endoscopic aqueductoplasty preventsalso the sudden collapse of fourth ventricle. In our work on 13cases with trapped fourth ventricle, we used a rightparamedian suboccipital burr hole to do aqueductoplasty, withthe use of a stent in all cases. Series of aqueductoplasty usingthe precoronal or suboccipital route with or without the use ofstents have been reported [2]. The suboccipital approach wasnot commonly used [2]. Even In cases of non dilated lateralventricles, some advocate upgrading the valve opening pres-sure in case of externally adjustable valves or externalizationof the lateral ventricular shunt for 2 or 3 days for their gradualdilatation [2, 20]. Longatti [13] and associates commenting ontheir experience for managing the trapped fourth ventriclethrough the suboccipital approach that the exploration provedto be very difficult and the anatomy was so deformed that ithad become unrecognizable. Cinalli et al. [2] stated that: thesuboccipital approach has rarely been performed because ofthe higher risk and rarity of the condition making this proce-dure less natural even for experienced neuroendoscopists.Toyota et al. [21] and Gawish et al. [7] used the midlinesuboccipital approach for treating the trapped fourth ventricle.They did a craniocervical skin incision and a smallsuboccipital craniotomy to introduce the endoscope to thedilated fourth ventricle in the midline after elevation of the

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cerebellar tonsils. Cinalli and colleagues [2] used the rightparamedian suboccipital approach in 2 cases with trappedfourth ventricle. They considered the limit of this approachwas the lack of landmarks available for orientation in theunusual and distorted anatomy of the trapped fourth ventricle.Reviewing the literature and from our experience inaqueductoplasty for treating aqueductal stenosis we found thatthe rate of restenosis is somewhat high when a stent is not used[9]. Oi and associates [16] experienced 2 cases of restenosisout of 2 cases operated for aqueduct stenosis without using astent. Teo and colleagues [20] advised that placement of astent in the aqueduct after aqueductoplasty is the rule, aftergetting 2 cases of restenosis out of 3. Stent migration occurredin 5 of our first 8 cases. In one case the stent migrated as earlyas after 1 week and in another case it migrated after 3 years. Incases operated using a long stent from the start or the 3 revisedcases, no stent migration occurred. The longest follow upperiod for these cases was 23 months. There is no availabledata in the literature about aqueduct stent migration or theperiod after which it migrated. Da Silva et al. [3] reported theuse of long stent through the suboccipital approach in fourcases in whom the stent was fixed to the dura at the cisternamagna using 4/0 prolene. The longest period of follow up inthese 4 cases was 29 months with no reports of stent migra-tion. We experienced no per nor postoperative complications.Complications of suboccipital endoscopic aqueductoplastyare not so frequently mentioned in the literature as we haveonly few reports concerning the use of this technique. Also thestraight trajectory and the placement of stent under vision inthis technique lessen the incidence of complication. Transientophthalmoparesis is the most common complication reportedin the literature after endoscopic aqueductoplasty with orwithout stent placement. The anatomic substrates for theseproblems are trochlear nuclei, medial longitudinal fasciculus,tectum, dorsal longitudinal fasciculus, and periaqueductalcentral gray area. Teo et al. [20] had transient dysconjugateocular movements in 2 out of 8 patients.

Conclusion

Endoscopic suboccipital paramedian aqueductoplasty withthe use of a stent is a safe and effective surgical optionthat—in our opinion—should stand as the first line treatmentfor the entrapped fourth ventricle. It helps the avoidance of thecomplications of a second or sometimes a third shunt device inthe same patient as well as prevents the hazards of an openposterior fossa surgery and reduces the incidence of aqueductrestenosis. Long stent is better used after aqueductoplasty toavoid the restenosis if no stent is used or stent fall after shortstents. However, good case selection, familiarity with thisfairly common endoscopic approach, and longer follow-upis needed for obtaining an optimal result.

Conflicts of interest None.

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