Update: Fourth ventricle hydrocephalus

Synonyms: Entrapped fourth ventricle; Isolated fourth ventricle.
Udayakumaran and Panikar reiterate that a Fourth ventricle hydrocephalus or trapped fourth ventricle (TFV) is a functional concept with imaging being at most only corroboratory ¹⁾.
In adults, Ferrer and de Notaris call this condition the functional trapped fourth ventricle because in none of there cases they have found physical obstruction of CSF flow ²⁾.

Fourth ventricle hydrocephalus, or a “trapped” fourth ventricle is a rare and uncommon entity which has been observed as a complication after intraventricular hemorrhage, infection/ meningitis or as a result of chronic shunt overdrainage after hydrocephalic shunting ^{3) 4) 5) 6)}.
A postinfectious occlusion of fourth ventricle outflow (foramen of Luschka and Magendie) and aqueduct of sylvius is the second most common cause for the development of trapped fourth ventricle ⁷⁾.
This condition is caused by blockage of both the outlets (Foramen of Luschka, Foramen of Magendie) and the inlet of the fourth ventricle at the level of the aqueduct of Sylvius ⁸⁾.
Progressive dilation of the fourth ventricle is due to continuing CSF production by the choroid plexus of the fourth ventricle within a closed space.
An increased cerebrospinal fluid (CSF) pressure within the fourth ventricle can lead secondary to the enlargement of the central canal in terms of communicating secondary syringomyelia. The exact pathophysiological mechanism of developing syringomyelia generally is not well established and remains yet controversial although several theories have been postulated ⁹⁾.

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In a follow-up study of 164 hydrocephalic children without tumors treated with ventriculoperitoneal shunts, 46 (28.0%) developed slit ventricle syndrome, 5 (3.0%) developed isolated fourth ventricles, and 4 (2.4%) developed isolated unilateral hydrocephalus. All of the patients with isolated unilateral hydrocephalus and 3 with isolated fourth ventricles had associated slit ventricles, 2 of whom had enlarged ventricles as double-compartment hydrocephalus. Reopening of the foramen of Monro or the aqueduct was achieved in one of the former and two of the latter cases with re-expansion of the slit ventricles. It is suggested that in some cases, the slit ventricle could be a causative factor in post-shunt isolated ventricle ¹⁰⁾.

Such an entrapment may lead to clinical symptoms secondary to distortion of the brainstem and lower CNs. The clinical findings are mostly non localizing, even when there are obvious bulbar signs.

Imaging may corroborate clinical findings but may not be diagnostic by itself.

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The diagnostic and treatment dilemma is to differentiate between a “true” symptomatic TFV and other conditions associated with a large fourth ventricle. This dilemma is especially significant when one is attempting to identify those patients who may benefit from surgery, as opposed to those patients with a well-compensated process that simply have a similar clinical and a radiological picture of a large fourth ventricle.

Posterior fossa cysts are usually divided into Dandy Walker malformations, posterior fossa arachnoid cysts, and isolated and/or trapped fourth ventricles.

Treatment of the TFV remains a formidable challenge. However, prompt recognition and intervention may aid in the preservation of life and neurological function ¹¹⁾.
Treatment extends from placement of fourth ventriculoperitoneal shunt, endoscopic aqueductoplasty and interventriculostomy to open fenestration via suboccipital craniotomy ^{12) 13)}.
Prone position is better compared to the sitting position. Apart from the risk of air embolism and post operative pneumocephalus in the sitting position, the air may get trapped in the ventricle and interfere in intraoperative visualization ¹⁴⁾.
Unfortunately, these techniques showed a high rate of dysfunction and complications.
Standard management of loculated fourth ventricle hydrocephalus consists of fourth ventricle shunt placement via a suboccipital approach. An alternative approach is stereotactic-guided transtentorial fourth ventricle shunt placement via the nondominant superior parietal lobule.

The development of neuroendoscopy has dramatically changed the outcome of these patients and the literature review suggest that endoscopic trans-fourth ventricle aqueductoplasty and stent placement is a minimally invasive, safe, and effective technique for the treatment of TFV and should be strongly recommended, especially in patients with supratentorial slit ventricles ¹⁵⁾.
Aqueduct stent placement is technically feasible and can be useful in selected patients either with endoscopy or open surgery ¹⁶⁾.
Essentially, the main cause of a TFV, namely, the aqueductal obstruction, is addressed using an endoscopic technique, and hence it is the most rational of all surgeries for this condition. The aqueduct can be dilated and kept open using a stent either through a transfrontal (trans-third ventricle) route or through a trans-fourth ventricular route. The latter is a shorter route, but is less commonly used probably due to the lack of familiarity with the endoscopic anatomy of the region of the fourth ventricle.
With either route, the surgeon has to decide whether a simple dilatation of the aqueduct will suffice or to leave a stent in place. The advantage of a stent is that the patency of the aqueduct is ensured in the postoperative period unless the stent migrates. The major disadvantage is that of infection due to the presence of a foreign body. Gallo et al., placed a stent whenever the dilated aqueduct was narrower than the width of the stent. Although theoretically it is possible to produce additional neurological deficits by introducing a wider stent through a narrower aqueduct, in the authors’ series, the complications (two patients with ophthalmoparesis) were equally distributed between those who had a stent placed and those who underwent aqueductoplasty alone. Hence, it appears that fear of additional deficits should not deter a surgeon from using a stent ¹⁷⁾.

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Longatti et al., suggest a very simple method of steering the tip of standard ventricular catheters by using materials commonly available in all operating rooms. The main advantage of this method is that it permits less invasive transaqueductal drainage of trapped fourth ventricles, especially in cases of narrow third ventricle, because the scope and catheter are introduced in sequence and not in a double-barreled fashion. Two illustrative cases are reported ¹⁸⁾.

Stereotactic parietal transtentorial shunt placement may be considered for patients with loculated fourth ventricle hydrocephalus, especially when shunt placement via the standard suboccipital approach fails. It is therefore reasonable to offer this procedure either as a first option for the treatment of fourth ventricle hydrocephalus or when the need for fourth ventricle shunt revision arises ¹⁹⁾.

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In 10 patients, Turner et al., used an alternative technique involving stereotactic and endoscopic methods to place a catheter in symptomatic posterior fossa cysts across the tentorium. Discussion of these cases is included, along with a review of various approaches to shunt placement in this region and recommendations regarding the proposed technique.
No patient suffered intracranial hemorrhage related to the procedure and catheter implantation. All 3 patients who underwent placement of a new transtentorial cystoperitoneal shunt and a new ventriculoperitoneal shunt did not suffer any postoperative complication; a decrease in the size of their posterior fossa cysts was evident on CT scans obtained during the 1st postoperative day. Follow-up CT scans demonstrated either stable findings or further interval decrease in the size of their cysts. In 1 patient, the postoperative head CT demonstrated that the transtentorial catheter terminated posterior to the right parietal occipital region without entering the retrocerebellar cyst. This patient underwent a repeat operation for proximal shunt revision, resulting in an acceptable catheter implantation. The patient in Case 8 suffered from a shunt infection and subsequently underwent hardware removal and aqueductoplasty with stent placement. The patient in Case 9 demonstrated a slight increase in fourth ventricle size and was returned to the operating room. Exploration revealed a kink in the tubing connecting the distal limb of the Y connector to the valve. The Y connector was replaced with a T connector, and 1 week later, CT scans exhibited interval decompression of the ventricles. This patient later presented with cranial wound breakdown and an exposed shunt. His shunt hardware was removed and he was treated with antibiotics. He later underwent reimplantation of a lateral ventricular and transtentorial shunt and suffered no other complications during a 3-year follow-up period ²⁰⁾.

Frassanito et al., report an exceptional case of Descending transtentorial herniation (DTH) complicating the implant of a CSF shunting device in the trapped fourth ventricle of a 17-year-old boy in whom a second CSF shunting device had been implanted for neonatal posthemorrhagic and postinfectious hydrocephalus. The insidious clinical and radiological presentation of DTH, mimicking a malfunction of the supratentorial shunt, is documented. Ultimately, the treatment consisted of removal of the infratentorial shunt and endoscopic acqueductoplasty with stenting. The absence of supratentorial mass lesion and other described etiologies of DTH prompted the authors to speculate on the hydrodynamic pathogenesis of DTH in the present case ²¹⁾.

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Cranial nerve palsy is rarely seen after shunt placement in an isolated fourth ventricle. In the few reports of this complication, neuropathies are thought to be caused by catheter injury to the brainstem nuclei either during the initial cannulations or after shrinkage of the fourth ventricle. The authors treated a child who suffered from delayed, progressive palsies of the sixth, seventh, 10th, and 12th cranial nerves several weeks after undergoing ventriculoperitoneal shunt placement in the fourth ventricle. Magnetic resonance imaging revealed the catheter tip to be placed well away from the ventricular floor but the brainstem had severely shifted backward, suggesting that the pathogenesis of the neuropathies was traction on the affected cranial nerves. The authors postulated that the siphoning effect of the shunt caused rapid collapse of the fourth ventricle and while the cerebellar hemispheres were tented back by adhesions to the dura, the brainstem became the only mobile component in response to the suction forces. Neurological recovery occurred after surgical opening of the closed fourth ventricle and lysis of the basal cistern adhesions, which restored moderate ventricular volume and released the brainstem to its normal position ²²⁾.

Pomeraniec et al retrospectively reviewed 8 consecutive cases involving pediatric patients with TFV following VP shunting for IVH due to prematurity between 2003 and 2012. The patients ranged in gestational age from 23.0 to 32.0 weeks, with an average age at first shunting procedure of 6.1 weeks (range 3.1-12.7 weeks). Three patients were managed with surgery. Patients received long-term radiographic (mean 7.1 years; range 3.4-12.2 years) and clinical (mean 7.8 years; range 4.6-12.2 years) follow-up.
The frequency of TFV following VP shunting for neonatal posthemorrhagic hydrocephalus was found to be 15.4%. Three (37.5%) patients presented with symptoms of posterior fossa compression and were treated surgically. All of these patients showed signs of radiographic improvement with stable or improved clinical examinations during postoperative follow-up. Of the 5 patients treated conservatively, 80% experienced stable ventricular size and 1 patient experienced a slight increase (3 mm) on imaging. All of the nonsurgical patients showed stable to improved clinical examinations over the follow-up period.
The frequency of TFV among premature IVH patients is relatively high. Most patients with TFV are asymptomatic at presentation and can be managed without surgery. Symptomatic patients may be treated surgically for decompression of the fourth ventricle ²³⁾.

Of 1044 aneurysms treated, 3 patients were identified who required fourth ventricular shunting, for the treatment of the isolated ventricle. All 3 patients underwent microsurgical clip obliteration of their aneurysms and had subsequent frontal approach ventriculoperitoneal cerebrospinal fluid diversion. These patients had no evidence of infection of the cerebrospinal fluid as measured by serial cultures. Subsequently, all 3 patients presented in a delayed fashion with symptoms attributable to a dilated fourth ventricle and syringomyelia or syringobulbia. Either exploration or percutaneous tapping confirmed the function of the supratentorial shunt. These patients then underwent fourth ventriculoperitoneal cerebrospinal fluid diversion by the use of a low-pressure shunt system. The symptoms attributable to the isolated fourth ventricle resolved rapidly in all 3 patients after shunting. This clinical improvement correlated with the fourth ventricular size.
Isolated fourth ventricle, in an adult, is a rare phenomenon associated with intracranial posterior circulation aneurysm rupture treated with microsurgical clip obliteration. Fourth ventriculoperitoneal cerebrospinal fluid diversion is effective at resolving the symptoms attributed to the trapped ventricle and associated syrinx ²⁴⁾.

Between February 1998 and February 2007, 12 children were treated for TFV in Dana Children’s Hospital by posterior fossa craniotomy/craniectomy and opening of the TFV into the spinal subarachnoid space. The authors performed a retrospective analysis of relevant data, including pre- and postoperative clinical characteristics, surgical management, and outcome.
Thirteen fenestrations of trapped fourth ventricles (FTFVs) were performed in 12 patients. In 6 patients with prominent arachnoid thickening, a stent was left from the opened fourth ventricle into the spinal subarachnoid space. One patient underwent a second FTFV 21 months after the initial procedure. No perioperative complications were encountered. All 12 patients (100%) showed clinical improvement after FTFV. Radiological improvement was seen in only 9 (75%) of the 12 cases. The follow-up period ranged from 2 to 9.5 years (mean 6.11 ± 2.3 years) after FTFV ²⁵⁾.

Between January 1986 and December 1995, Eder et al., treated 292 children younger than 16 years for hydrocephalus: 7 (2.4%) developed an isolated IV ventricle, and 5 of these were symptomatic with posterior fossa signs. These 5 patients required posterior fossa shunting, after which their neurological status improved. However, 1 week and 6 weeks after surgery, respectively, 2 patients developed new cranial nerve deficits related to a slit-like IV ventricle with secondary irritation of the brain stem by the IV ventricular catheter. Shortening the catheter and replacing the valve eliminated the cranial nerve palsies, implying that these complications were not caused by direct injury of the brain stem during placement of the shunt. Alternative surgical techniques and the use of different (flow-regulating) valves may avoid such complications ²⁶⁾.

Isolated fourth ventricles were diagnosed by computed tomography (CT) in 16 children in a 3 year period. They all had shunting of the lateral ventricles for hydrocephalus, and all needed subsequent shunt revisions. Seven patients without signs of raised intracranial pressure clinically had new posterior fossa signs at different intervals after lateral ventricular shunting. The clinical findings in the other nine patients were much less specific and in some cases the isolated fourth ventricle was an incidental finding. CT is essential for the diagnosis. The isolated fourth ventricle needs to be differentiated from posterior fossa cysts and cystic tumors. Shunting of the fourth ventricle improved the clinical condition in six of 14 children ²⁷⁾.

Signs of cerebellar dysfunction combined with signs suggestive of shunt malfunction developed in three children with obstructive hydrocephalus. Shunt function was normal. In all cases, the cerebellar signs persisted and computerized tomography scans revealed enlargement of the fourth ventricle. Shunting of the fourth ventricle returned the patients to normal function ²⁸⁾.

Trapped Fourth Ventricle With Vasogenic Edema ²⁹⁾.

A 28-year-old female who had previously undergone treatment of intracerebral hemorrhage and meningitis developed a hydrocephalus with TFV. After 3 years she developed disturbance of walking and coordination. Cranial-CT revealed an enlargement of the shunted fourth ventricle as a result of shunt dysfunction. Furthermore a cervical syringomyelia developed. The patient underwent a revision of a failed fourth ventriculo-peritoneal shunt. Postoperatively, syringomyelia resolved within 6 months and the associated neurological deficits improved significantly. An insufficiency of cerebrospinal fluid draining among patients with TFV can be associated with communicating syringomyelia. An early detection and treatment seems important on resolving syringomyelia and avoiding permanent neurological deficits. Ventriculo-peritoneal shunt in trapped fourth ventricles can resolve a secondary syringomyelia ³⁰⁾.

A 4-year-old girl with a ventriculoperitoneal shunt presented with complaints of ataxia and altered consciousness. These symptoms were subacute at onset and progressive in nature.
Radiological evaluation revealed a trapped fourth ventricle with brainstem compression, associated with abnormal diffuse diencephalic signal changes compatible with edema. The entrapment was managed by foramen magnum decompression, resulting in complete symptom resolution and improvement in the abnormal magnetic resonance findings.
While trapped fourth ventricle is a well-described entity, we could not find a similar reported case where such an acute clinical syndrome was associated with such a distinct radiological picture ³¹⁾.

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A 20-year-old man with complex hydrocephalus and trapped fourth ventricle underwent a suboccipital placement of a VP shunt. Postprocedure patient developed double vision. Magnetic resonance imaging showed that the catheter was penetrating the dorsal brainstem at the level of the pontomedullary junction. Patient was referred to our Neuroendoscopic Clinic. Physical exam demonstrated pure right VI cranial nerve palsy. Patient underwent flexible endoscopic exploration of the ventricular system. Some of the endoscopic findings were severe aqueductal stenosis and brainstem injury from the catheter. Aqueductoplasty, transaqueductal approach into the fourth ventricle, and endoscopic repositioning of the catheter were some of the procedures performed. Patient recovered full neurological function. The combination of endoscopic exploration and shunt is a good alternative for patients with complex hydrocephalus. A transaqueductal approach to the fourth ventricle with flexible scope is an alternative for fourth ventricle pathology ³²⁾.

Cranial nerve palsy is rarely seen after shunt placement in an isolated fourth ventricle. In the few reports of this complication, neuropathies are thought to be caused by catheter injury to the brainstem nuclei either during the initial cannulations or after shrinkage of the fourth ventricle. The authors treated a child who suffered from delayed, progressive palsies of the sixth, seventh, 10th, and 12th cranial nerves several weeks after undergoing ventriculoperitoneal shunt placement in the fourth ventricle. Magnetic resonance imaging revealed the catheter tip to be placed well away from the ventricular floor but the brainstem had severely shifted backward, suggesting that the pathogenesis of the neuropathies was traction on the affected cranial nerves. The authors postulated that the siphoning effect of the shunt caused rapid collapse of the fourth ventricle and while the cerebellar hemispheres were tented back by adhesions to the dura, the brainstem became the only mobile component in response to the suction forces. Neurological recovery occurred after surgical opening of the closed fourth ventricle and lysis of the basal cistern adhesions, which restored moderate ventricular volume and released the brainstem to its normal position ³³⁾.

The first reported case was a patient with cysticercosis meningitis and communicating hydrocephalus in whom signs of a posterior fossa mass developed a few months after shunting of the lateral ventricles . Air studies and posterior fossa exploration demonstrated an encysted fourth ventricle due to occlusion of its outlets as well as of the aqueduct ³⁴⁾.