Obstruction Of Cerebrospinal Fluid Flow Research Articles

Analysis of cerebrospinal fluid flow dynamics and morphology in Chiari I malformation with cine phase-contrast magnetic resonance imaging

To determine cerebrospinal fluid (CSF) dynamics and morphology in Chiari I malformation (CMI) and assess the response to surgery of the posterior cranial fossa, we examined midsagittal imaging along with anterior cervical 2-3 (AC2-3), posterior cervical 2-3 (PC2-3), and aqueduct CSF flow hydrodynamics in axial imaging by using cine phase-contrast magnetic resonance imaging (PCMR). We examined 52 patients with CMI, both with and without syringomyelia (SM), pre-/post-surgery, and compared them to 17 healthy volunteers. Statistical analyses included paired t-tests, independent-samples t-tests, binary logistic regression, and crosstab with MedCalc software. Patients with CMI had significantly shorter clivus length and larger tentorial angle than the healthy controls (P = 0.004, P = 0.019, respectively). The AC2-3 cranial/caudal peak velocity (PV), PC2-3 cranial/caudal PV and aqueduct cranial peak PV of patients with CMI were significantly lower than healthy volunteers pre-surgery (P = 0.034 AC2-3 cranial PV, P = 0.000002 AC2-3 caudal PV; P = 0.046 PC2-3 cranial PV, P = 0.015 PC2-3 caudal PV; P = 0.022 aqueduct cranial PV) and increased after surgery (P = 0.024 AC2-3 cranial PV, P = 0.002 AC2-3 caudal PV; P = 0.001 PC2-3 cranial PV, P = 0.032 PC2-3 caudal PV; P = 0.003 aqueduct cranial PV). The aqueduct caudal PV of patients with CMI was higher than that of healthy controls (P = 0.004) and decreased post-surgery (P = 0.012). Patients with pre-surgery PC2-3 cranial PV >2.63 cm/s and aqueduct cranial PV >2.13 cm/s, respectively, experienced primary symptom improvement after surgery. The innate bony dysontogenesis in patients with CMI contributes to tonsilar ectopia and exacerbates CSF flow obstruction. A pressure gradient that existed between SM and SAS supports the perivascular space theory that is used to explain SM formation. Our findings demonstrate that PCMR maybe a useful tool for predicting patient prognosis.

Paradoxical migrating cyst: An unusual presentation of intraventricular neurocysticercosis with a coincidental pituitary adenoma

Intraventricular neurocysticercosis is an uncommon entity which may become symptomatic due to cerebrospinal fluid flow obstruction. Migration of intraventricular cysts through the ventricular spaces is a rare occurrence. This phenomenon is poorly understood but may be due to pressure changes within the ventricular cavities. We present a patient with intraventricular neurocysticercosis with paradoxical transaqueductal migration of the cyst from the cerebral aqueduct to the fourth ventricle shortly after ventricular drain placement for acute hydrocephalus. The patient also presented with a coincidental sellar and suprasellar mass, later pathologically proven to be a pituitary adenoma. The migration of this cyst resulted in spontaneous relief of obstruction at the cerebral aqueduct, thus restoring normal cerebrospinal fluid pathways and avoiding permanent shunting. We discuss the possible mechanisms and implications of cyst migration, and the diagnostic challenges of concomitant findings of a pituitary mass and neurocysticercosis. Although the presence of a sellar and suprasellar mass in a patient with known neurocysticercosis should raise clinical suspicion for the possibility of sellar neurocysticercosis, pituitary macroadenoma is a more common entity and a more likely etiology for a sellar lesion.

Severe second-trimester obstructive ventriculomegaly related to disorders of diencephalic, mesencephalic and rhombencephalic differentiation

By review of a series of cases, we set out to identify sonographic features suggestive of an obstructive mechanism in second-trimester fetuses with ventriculomegaly and describe developmental disorders related to pathological differentiation of the diencephalon, mesencephalon and rhombencephalon that lead to obstruction of cerebrospinal fluid flow. We studied retrospectively 11 fetuses referred for severe second-trimester ventriculomegaly of undetermined origin. Neurosonography was performed with detailed analysis of the third ventricle, thalami, cerebral aqueduct and cerebellum. The cerebral imaging data were compared with neuropathological data in eight patients, with a focus on the level and etiology of the obstruction. Parenchymal thinning and reduction of the pericerebral spaces were highly suggestive of ventriculomegaly due to an obstructive mechanism. The ventriculomegaly was related to diencephalosynapsis (thalamic fusion and third ventricle atresia) in five cases and partial/complete aqueduct stenosis in six; it was associated with cerebellar hypoplasia in six cases, including rhombencephalosynapsis in two cases. In nine patients, disorders of the diencephalon, mesencephalon and rhombencephalon were present. In cases of severe isolated ventriculomegaly in which sonographic features are suggestive of an obstructive mechanism, close examination of the third ventricle, thalami, aqueduct of Sylvius and cerebellum may reveal pathological differentiation of the diencephalon, mesencephalon or rhombencephalon, often in combination.

Usefulness of Intraoperative Magnetic Resonance Ventriculography During Endoscopic Third Ventriculostomy

Endoscopic third ventriculostomy (ETV) is the preferred method for the treatment of noncommunicating hydrocephalus. The different success rates of ETV indicate the difficulties in predicting the success of this procedure. To show the usefulness of intraoperative ventriculography performed by the low-field 0.15-T magnetic resonance imager Polestar N20 during ETV. The study was conducted in 11 patients with noncommunicating hydrocephalus caused by tumors or cysts of the third ventricle (n = 5), nontumoral stenosis of the sylvian aqueduct (n = 3), and fourth ventricle outlet obstruction (n = 3). Intraoperative magnetic resonance (iMR) ventriculography was performed before and after the ETV. In each case, iMR-ventriculography was a safe procedure and determined the exact site of obstruction of cerebrospinal fluid flow. In all cases, iMR-ventriculography performed after ETV showed with the greatest accuracy the patency of the performed fenestrations, demonstrating in 9 patients good flow of the contrast from the third ventricle to the basal cisterns, restricted flow in 1 patient, and no flow in 1 patient. The results of ventriculography were consistent with the postoperative neurological status of operated-on patients. In 3 patients, the opinion of the surgeons about the patency of endoscopic fenestration, based on intraoperative observation of the third ventricle floor, was inconsistent with the results from iMR-ventriculography. Low-field iMR-ventriculography is a safe procedure that can be successfully applied during ETV to determine the site of obstruction in hydrocephalus and the patency of performed ventricle fenestration.

Dyke-Davidoff-Masson syndrome: case report of fetal unilateral ventriculomegaly and hypoplastic left middle cerebral artery

Prenatal ultrasonographic detection of unilateral cerebral ventriculomegaly arises suspicion of pathological condition related to cerebrospinal fluid flow obstruction or cerebral parenchimal pathology. Dyke-Davidoff-Masson syndrome is a rare condition characterized by cerebral hemiatrophy, calvarial thickening, skull and facial asymmetry, contralateral hemiparesis, cognitive impairment and seizures. Congenital and acquired types are recognized and have been described, mainly in late childhood, adolescence and adult ages. We describe a female infant with prenatal diagnosis of unilateral left ventriculomegaly in which early brain MRI and contrast enhanced-MRI angiography, showed cerebral left hemiatrophy associated with reduced caliber of the left middle cerebral artery revealing the characteristic findings of the Dyke-Davidoff-Masson syndrome. Prenatal imaging, cerebral vascular anomaly responsible for the cerebral hemiatrophy and the early clinical evolution have never been described before in such a young child and complete the acquired clinical descriptions in older children. Differential diagnosis, genetic investigations, neurophysiologic assessments, short term clinical and developmental follow up are described. Dyke-Davidoff-Masson syndrome must be ruled out in differential diagnosis of fetal unilateral ventriculomegaly. Early clinical assessment, differential diagnosis and cerebral imaging including cerebral MRI angiography allow the clinicians to diagnose also in early infancy this rare condition.

Interhemispheric transcallosal route for resection of anterior third ventricular lesions

Anterior third ventricular lesions present with a variety of symptoms related to cerebrospinal fluid flow obstruction and mass effect. Colloid cysts are among the most common lesions in the region. They usually present with ventriculomegaly, leading to headaches, vertigo, or, rarely, decreased mental status due to the development of acute hydrocephalus. Many patients become aware of their asymptomatic colloid cysts during imaging evaluation related to other conditions. Symptomatic cysts require removal, and larger asymptomatic colloid cysts (> 1cm) in younger patients may also need to be excised despite a lack of symptoms. A variety of surgical routes have been described to access and remove colloid cysts. Endoscopic approaches are least invasive and provide adequate decompression and removal of the cyst wall. However, presence of ventriculomagaly may be necessary to provide adequate working space for endoscopic resection. Transcallosal interhemispheric and transcortical routes are typically reserved for patients with symptomatic or large asymptomatic cysts without any significant hydrocephalus. Transcortical route may carry a slightly increased risk of seizures due to cortical disruption. Interhemispheric transcallosal approach with the use of microsurgical techniques minimizes injury to normal structures. In this video, the author describes his technique for transcallosal resection of a large colloid cyst in the absence of significant ventriculomegaly. Methods to minimize complications are reviewed. The video can be found here: http://youtu.be/KzC8QYsTKeg. (http://thejns.org/doi/abs/10.3171/2013.V1.FOCUS12340)

MRI appearances of tuberculous meningitis in HIV-infected children: a paradoxically protective mechanism?

Immune suppression predisposes HIV-infected children to opportunistic infections including Mycobacterium tuberculosis. HIV infection increases the risk of progression to active disease and also increases the risk for extrapulmonary involvement, including tuberculous meningitis (TBM). Brain injury in TBM is the consequence of an immune-mediated vasculopathy. HIV-related immune dysfunction prevents the production of thick exudates that cause parenchymal infarctions and cerebrospinal fluid flow obstruction. It could be postulated that HIV may be ‘protective’ from some of the common complications related to TBM. The aim of this paper is to highlight the ‘protective’ features of HIV-related immune suppression observed on MRI in children with TBM and promote the use of MRI for detecting subtle and atypical meningeal enhancement in HIV and TBM coinfected children.

Development of Neurological Symptoms in Patients with Asymptomatic Cerebral Cysticercosis Undergoing Albendazol Therapy for Intestinal Parasites

Intraventricular neurocysticercosis is an uncommon entity which may become symptomatic due to cerebrospinal fluid flow obstruction. Migration of intraventricular cysts through the ventricular spaces is a rare occurrence. This phenomenon is poorly understood but may be due to pressure changes within the ventricular cavities. We present a patient with intraventricular neurocysticercosis with paradoxical transaqueductal migration of the cyst from the cerebral aqueduct to the fourth ventricle shortly after ventricular drain placement for acute hydrocephalus. The patient also presented with a coincidental sellar and suprasellar mass, later pathologically proven to be a pituitary adenoma. The migration of this cyst resulted in spontaneous relief of obstruction at the cerebral aqueduct, thus restoring normal cerebrospinal fluid pathways and avoiding permanent shunting. We discuss the possible mechanisms and implications of cyst migration, and the diagnostic challenges of concomitant findings of a pituitary mass and neurocysticercosis. Although the presence of a sellar and suprasellar mass in a patient with known neurocysticercosis should raise clinical suspicion for the possibility of sellar neurocysticercosis, pituitary macroadenoma is a more common entity and a more likely etiology for a sellar lesion.

Microsurgical fenestration of retrocerebellar cysts as a treatment for syringomyelia

Abnormal posterior fossa cerebrospinal fluid (CSF) collections (PFC) are a constituent feature of several welldescribed disorders [1, 25]. These include retrocerebellar arachnoid cysts and the continuum of Dandy Walker pathology described by Barkovich and coworkers (including Dandy Walker malformation, Dandy Walker variant, and Blake’s pouch cyst) [4]. It is thought that similar to Chiari malformations, posterior fossa cysts adjacent to the foramen magnum can herniate and cause impaction of the foramen magnum. Although rare, such impaction may lead to secondary syringomyelia, probably secondary to obstruction of CSF flow between the posterior fossa and the cervical spinal subarachnoid space [2, 6, 9, 10, 15, 17, 19–21, 23, 24, 26–28]. We report our experience treating two children with PFC causing secondary syrinx and review the literature on this topic.

Endoscope-Assisted Surgery of Spinal Intradural Adhesions in the Presence of Cerebrospinal Fluid Flow Obstruction

Prospective cohort study. To investigate whether the adjunctive use of endoscopy of the subarachnoid space (arachnoscopy) can improve the success of microsurgery for spinal arachnoid adhesions. Intradural adhesions that obstruct pulsatile cerebrospinal fluid (CSF) flow are a typical spinal cause of syringomyelia. Phase-contrast magnetic resonance imaging (MRI) allows CSF flow obstructions to be reliably localized. The treatment of choice is the microsurgical removal of CSF flow obstructions caused by adhesions. Microsurgery, however, does not lend itself to assessments of further adhesions beyond the borders of the exposed area. In this study, we therefore investigated whether endoscopic assistance allows adhesions in the vicinity of the exposed area to be detected. From 2006 to 2009, a single neurosurgeon performed 27 consecutive microsurgical procedures with endoscopic assistance in 25 patients with spinal arachnoid adhesions. A MurphyScope endoscope was used for this purpose. CSF flow was studied before and after surgery in all patients using phase-contrast MRI in the region of the craniocervical junction, the cervical spine, the thoracic spine, and the lumbar spine. In all 27 procedures, CSF flow obstructions were detected at the level identified by phase-contrast MRI. In 25 procedures, image quality was sufficient for an inspection of the adjacent subarachnoid space. In six cases, the surgeon detected further adhesions that obstructed CSF flow in the adjacent subarachnoid space not visualized with the microscope. In all cases, these adhesions were identified and removed during microsurgery.Postoperative MRI scans demonstrated free CSF flow in all patients and a decrease in syrinx size in six patients. Arachnoscopy is a helpful adjunct to microsurgery and can be performed safely and easily. It allows the surgeon to detect further adhesions in the subarachnoid space, which would remain undetected by microscopy alone.

Spinal Cord Compression by Epidural Involvement Over 21 Vertebral Levels in Acute Lymphoblastic Leukemia

Spinal cord compression is a rare complication of acute lymphoblastic leukemia (ALL). We report a 13-year-old boy with B-precursor ALL, presenting with restriction of breathing and back pain. Cerebrospinal fluid examination showed extremely high protein levels. Radiologic examination indicated that leukemia extended from the thoracic to sacral epidural spaces over 21 vertebral lengths in a band-shaped form, threatening to induce compressive spinal cord neuropathy. Prompt initiation of systemic chemotherapy relieved the obstruction of cerebrospinal fluid flow without local irradiation or surgical intervention. To our knowledge, this patient has shown the most extensive epidural involvement among ALL patients previously reported.

Research advances on associated genes and pathogenesis of hydrocephalus

Hydrocephalus is a common medical condition characterized by abnormalities in the secretion,circulation or resorption of cerebrospinal fluid (CSF), resulting in ventricular dilatation. The pathogenetic mechanism for the hydrocephalus is attributed to: the overproduction of CSF by the choroid plexus; the defect in CSF absorption and obstruction of CSF flow in the cerebral ventricles. However, the underlying etiology is poorly understood. With the development of genetic engineering, a growing body of evidence indicates that genetic factors play an essential role in the pathogenesis of hydrocephalus. It is the aim of this review to summarize these findings.

Intraoperative ventriculo-stomographic evaluation of endoscopic cerebrospinal fluid diversion and flow restoration procedures

Purpose. This prospective study was designed for intra-operative demonstration of cerebrospinal fluid (CSF) flow in ventricles and cisternal spaces before and after neuroendoscopic procedure. The aim of this study was to evaluate site of obstruction of CSF flow and subsequent stomal or aqueductal patency after endoscopic third ventriculostomy (ETV) or aqueductoplasty in patients with hydrocephalus of diverse aetiology.Method. Seventeen patients with hydrocephalus due to diverse aetiology underwent ETV (n = 15) and aqueductoplasty (n = 2) or cysto-ventrticulostomy (n = 1) or transaqueductal removal of neurocysticercus cyst (NCC) (n = 1). Intra-operatively, radio-opaque contrast agent (iohexol) instillation into the third ventricle was used for qualitative evaluation of obstruction and post-procedure CSF flow across the stoma into cisternal spaces.Result: 11 male and 6 female patients ranging from 3 to 50 years of age were included in the study. Post-procedure intra-operative ventriculo-stomography (IOVSG) showed free flow of dye across the endoscopic stoma (n = 13) or aqueduct (n = 2) into cisternal spaces. Diagnosis of fourth ventricular NCC was made in one patient with panventriculomegaly. In two patients of tuberculous meningitis hydrocephalus, poor flow of contrast in the prepontine area and basal cisterns was seen on IOVSG. They were subjected to ventriculoperitoneal shunt insertion in the same sitting. Cine MRI confirmed the patency of stoma or aqueduct in follow-up period in all patients with successful endoscopic procedure.Conclusion. IOVSG is a simple and safe technique that helps in confirming the adequacy of endoscopic procedure during surgery and thereby facilitates intra-operative decision about further management.

An unusual cause of posterior fossa mass: Lhermitte-Duclos disease

Lhermitte-Duclos disease (LDD) (dysplastic cerebellar gangliocytoma) is a rare disorder of unknown pathogenesis, presenting with signs and symptoms resulting from obstruction of cerebrospinal fluid flow and mass effect in the posterior fossa. Magnetic resonance imaging is the diagnostic modality of choice allowing preoperative diagnosis with characteristic findings. Surgery is the choice of treatment. The typical histopathological findings of LDD are characterized by widening of the molecular layer, absence of the Purkinje cell layer and hypertrophy in the granule cell layer. Herein we report an adolescent girl with LDD diagnosed preoperatively by the conventional and advanced MR techniques.

Acute respiratory arrest following partial suboccipital cranioplasty for cerebellar ptosis from Chiari malformation decompression

Cerebellar ptosis is a rare complication following Chiari malformation decompression, and generally is the result of a very large suboccipital craniectomy. This can lead to the descent of the cerebellum through the craniectomy defect, which in turn may result in cerebellar herniation through the surgical defect as well as the reestablishment of contact between the cerebellar tonsils and the brainstem. In addition, dorsal adherence of the herniated cerebellum to the dura mater or dural patch and an associated obstruction of cerebrospinal fluid flow at the cervicomedullary junction may ensue. Such a result is not desirable, in that it reproduces or mimics the pathoanatomical relationships that existed prior to the surgical decompression.

Thecal shunt placement for treatment of obstructive primary syringomyelia

The most commonly reported treatment of primary syringomyelia has been laminectomy with duraplasty or direct shunting from the syrinx cavity. Diversion of cerebrospinal fluid (CSF) from the spinal subarachnoid space to peritoneal, atrial, or pleural cavities has been described previously in only a few case reports. Shunting of the CSF from the subarachnoid space rostral to the level of myelographic blockage may reduce the filling force of the syrinx cavity and avoids myelotomy and manipulation of the spinal cord parenchyma. The authors report on 7 patients who underwent thecal shunt placement for primary spinal syringomyelia. This study is a retrospective review of a consecutive series. The authors reviewed the medical records and neuroimaging studies of 7 adult patients with posttraumatic, postsurgical, or postinflammatory syringomyelia treated with thecoperitoneal, thecopleural, or thecoatrial shunt placement at the University of California Los Angeles Medical Center. Myelographic evidence of partial or complete CSF flow obstruction was confirmed in the majority of patients. The mean duration of follow-up was 33 months (range 6-104 months). Six (86%) of 7 patients showed signs of clinical improvement, whereas 1 remained with stable clinical symptoms. Of the 6 patients with available postoperative imaging, each demonstrated a reduction in syrinx size. Three patients (43%) had > or = 1 complication, including shunt-induced cerebellar tonsillar descent in 1 patient and infections in 2. If laminectomy with duraplasty is not possible for the treatment of primary syringomyelia, placement of a thecoperitoneal shunt (or thecal shunt to another extrathecal cavity) should be considered. Although complications occurred in 3 of 7 patients, the complication rate was outweighed by a relatively high symptomatic and imaging improvement rate.

Chiari I malformation without hydrocephalus: acute intracranial hypertension managed with endoscopic third ventriculostomy (ETV)

In a small subset of patients, a Chiari malformation can present with signs of raised intracranial pressure due to obstruction of cerebrospinal fluid flow or with the raised intracranial pressure as the primary pathological driving force resulting in tonsillar herniation. The authors report a unique case in a 14-year-old boy with a Chiari malformation type 1-syringomyelia complex with slit-like ventricles. We have successfully managed the acute presentation of raised intracranial pressure, mimicking idiopathic intracranial hypertension, utilizing a frameless stereotactic image-navigated endoscopic third ventriculostomy alone. We present the preoperative and postoperative radiological and ophthalmological findings and discuss the possible mechanisms related to the pathophysiology and treatment in this case. The patient's symptoms resolved immediately postoperatively with resolution of papilledema. At 18-month follow-up, the patient remains entirely asymptomatic and the need for craniovertebral decompression appears to have been obviated. We advocate that in the Chiari malformation type 1-syringomyelia complex with normal or small ventricles, patients presenting with isolated signs and symptoms of raised intracranial pressure alone can be safely and effectively managed with an electromagnetic-guided stereotactic endoscopic third ventriculostomy as a primary treatment option.

Migrating intraventricular cysticercosis: magnetic resonance imaging findings

Dr. Emerson L. Gasparetto – Rua Lopes Trovao 88 / 1702B 24110-071 Niteroi RJ Brasil. Neurocysticercosis (NCC) is the most common parasitic infestation affecting the central nervous system (CNS). It is frequent cause of seizures and hydrocephalus in adults from endemic regions, including Brazil. Brain parenchymal involvement occurs in 60 to 92% of patients with NCC, but intraventricular (IV) lesions are seen in only 7 to 20% of cases. Although NCC is usually self-limited by the life cycle of the parasite, intraventricular involvement is often more difficult to manage due to obstruction of cerebrospinal fluid (CSF) pathways and ependymal inflammation. Intraventricular neurocysticercosis (IVNCC) can produce mechanical obstruction of CSF flow anywhere in the ventricular system, resulting in hydrocephalus or focal neurological deficits. The symptoms can also result from ependymal inflammation associated with cyst degeneration, or from diffuse meningitis causing communicating hydrocephalus. The intraventricular cysts may circulate freely throughout the CSF pathways or become attached to the ependyma anywhere in the ventricles, but their predilection is for the occipital horn of the lateral and fourth ventricles. Although the obstruction of the CSF flow is a common cause of symptoms in patients with IVNCC, reports demonstrating the migrating cysts causing hydrocephalus are extremely rare. We report a case of intraventricular neurocysticercosis presenting with hydrocephalus due to third ventricle obstruction secondary to migrating cysticercus.

Regression of syringomyelia and tonsillar herniation after posterior fossa arachnoid cyst excision. Case report and literature review

Some reports have documented posterior fossa cysts resulting in syringomyelic obstruction of cerebrospinal fluid (CSF) flow caused by cyst displacement within the foramen magnum. Rarely the syringomyelia is caused by acquired Chiari malformation due to a retrocerebellar arachnoid cyst. To report the case of a 38-year-old man with hydrocephalus and syringomyelia, who was found to have a Chiari malformation secondary to a posterior fossa arachnoid cyst. After endoscopic third ventriculostomy, the patient was submitted to foramen magnum decompression and arachnoid cyst removal that were followed by resolution of both the Chiari malformation and the syringomyelia. In most published cases the syringomyelia has been attributed to obstruction of CSF flow at the foramen magnum by the arachnoid cyst itself. There is only one previous report of a posterior fossa arachnoid cyst producing tonsillar descent and syringomyelia. Posterior fossa arachnoid cysts can result in acquired Chiari malformation and syringomyelia. In our view, the management of these patients should be directed at decompressing the foramen magnum and include the removal of the walls of the coexistent arachnoid cyst as it seems to be the crucial factor that accounts for the development of the syringomyelia that these patients present.

Treatment of hydrocephalus with functionally isolated ventricles

Rapid therapeutic drainage of one lateral ventricle may lead to ipsilateral slit ventricle, and the resultant functional obstruction of cerebrospinal fluid flow through the foramen of Monro may cause dilatation of the contralateral ventricle. Drainage of the lateral ventricle with a low-pressure shunt led to functionally isolated contralateral ventriculomegaly in this report. The patient's condition was complicated by a Candida albicans shunt infection. Following effective treatment of the infection by chemotherapy and removal of the shunt system, the patient was treated by bridging two lateral ventricles with ventricular catheters connected to an Ommaya reservoir. An occipital ventricular catheter was then inserted and connected to a programmable valve to drain the bridged lateral ventricles. Modern centers, caring for patients with infantile hydrocephalus, should have endoscopic facilities available but in cases with extensive ventricular adhesions and in asymmetric hydrocephalus where endoscopic septostomy between the ventricles is impossible our described technique may be used.