4-dimensional local radial basis function interpolation of large, uniformly spaced datasets

BACKGROUND AND OBJECTIVE

Large, uniformly spaced, complex and time varying datasets derived from high resolution medical image velocimetry can provide a wealth of information regarding small-scale transient physiological flow phenomena and pulsation of anatomical boundaries. However, there remains a need for interpolation techniques to effectively reconstruct a fully 4-dimensional functional relationship from this data. This paper presents a preliminary evaluation of a 4-dimensional local radial basis function (RBF) algorithm as a means of addressing this problem for laminar flows.

METHODS

A 4D interpolation algorithm is proposed based on a Local Hermitian Interpolation (LHI) using a combination of multi-quadric RBF with a partition of unity scheme. The domain is divided into uniform sub-systems with size restricted to immediately neighbouring points. The validity of the algorithm is first established on a known 4D analytical dataset and a CFD based laminar flow phantom. Application is then demonstrated through characterisation of a large 4D laminar flow dataset obtained from magnetic resonance imaging (MRI) measurements of cerebrospinal fluid velocities in the brain.

RESULTS

Performance of the algorithm is compared to that of a quad-linear interpolation, demonstrating favourable improvement in accuracy. The technique is shown to be robust, computationally efficient and capable of refined interpolation in Euclidean space and time. Application to MR velocimetry data is shown to produce promising results for the 4D reconstruction of the transient flow field and movement of the fluid boundaries at spatial and temporal locations intermediate to the original data.

CONCLUSION

This study has demonstrated feasibility of an accurate, stable and efficient 4-dimensional local RBF interpolation method for large, transient laminar flow velocimetry datasets. The proposed approach does not suffer from ill-conditioning or high computational cost due to domain decomposition into local stencils where the RBF is only ever applied to a limited number of points. This work offers a potential tool to assist medical diagnoses and drug delivery through better understanding of physiological flow fields such as cerebrospinal fluid. Further work will evaluate the technique on a wider range of flow fields and against CFD simulation.

Virtual neurosurgery, training for the future

Virtual reality (VR) simulators have been created for various surgical specialties. The common theme is extensive use of graphics, confined spaces, limited functionality and limited tactile feedback. A development team at the University of Nottingham, UK, consisting of computer scientists, mechanical engineers, graphic designers and a neurosurgeon, set out to develop a haptic, e.g. tactile simulator for neurosurgery making use of boundary elements (BE). The relative homogeneity of the brain, allows boundary elements, e.g. 'surface only' rendering, to simulate the brain structure. A boundary element simplifies the computing equations saves computing time, by assuming the properties of the surface equal the properties of the body. A limited audit was done by neurosurgical users confirming the potential of the simulator as a training tool. This paper focuses on the application of the computational method and refers to the underlying mathematical structure. Full references are included regarding the mathematical methodology.

Intrathecal chemotherapy delivered by a lumbar-thecal catheter in metastatic medulloblastoma: a case illustration

BACKGROUND

Medulloblastoma is the most common malignant brain tumour in children. Despite recent advances, the prognosis in high risk patients remains poor. Further improvement in survival is dependent upon the development of strategies to attack the tumour more effectively, but with less toxicity. Intrathecal chemotherapy, is an ideal but currently underused method of directly targeting residual tumour within the area of resection and the leptomeningeal disease commonly associated with this tumour.

METHOD

We describe the case of a 12 yr old child with metastatic medulloblastoma, who received intrathecal topotecan via a spinal catheter.

CONCLUSION

This method represents a simple, safe and effective method of delivering an even and widespread distribution of drug within the cerebrospinal fluid (CSF) of the neuroaxis. With new agents being identified and others in the early stages of development, intrathecal chemotherapy may emerge as an important therapeutic option to consider when faced with such challenging cases.

Three-dimensional cerebrospinal fluid flow within the human ventricular system

Cerebrospinal fluid (CSF) is a Newtonian fluid and can, therefore, be modelled using computational fluid dynamics (CFD). Previous modelling of the CSF has been limited to simplified geometric models. This work describes a geometrically accurate three dimensional (3D) computational model of the human ventricular system (HVS) constructed from magnetic resonance images (MRI) of the human brain. It is an accurate and full representation of the HVS and includes appropriately positioned CSF production and drainage locations. It was used to investigate the pulsatile motion of CSF within the human brain. During this investigation CSF flow rate was set at a constant 500 ml/day, to mimic real life secretion of CSF into the system, and a pulsing velocity profile was added to the inlets to incorporate the effect of cardiac pulsations on the choroid plexus and their subsequent influence on CSF motion in the HVS. Boundary conditions for the CSF exits from the ventricles (foramina of Magendie and Lushka) were found using a "nesting" approach, in which a simplified model of the entire central nervous system (CNS) was used to examine the effects of the CSF surrounding the ventricular system (VS). This model provided time varying pressure data for the exits from the VS nested within it. The fastest flow was found in the cerebral aqueduct, where a maximum velocity of 11.38 mm/s was observed over five cycles. The maximum Reynolds number recorded during the simulation was 15 with an average Reynolds number of the order of 0.39, indicating that CSF motion is creeping flow in most of the computational domain and consequently will follow the geometry of the model. CSF pressure also varies with geometry with a maximum pressure drop of 1.14 Pa occurring through the cerebral aqueduct. CSF flow velocity is substantially slower in the areas that are furthest away from the inlets; in some areas flow is nearly stagnant.

A virtual reality surgery simulation of cutting and retraction in neurosurgery with force-feedback

A virtual-reality surgical simulator aimed at neurosurgery is presented. The simulator utilises boundary element (BE) technology to develop real-time realistic deformable models of the brain. The simulator incorporates the simulation of surgical prodding, pulling and cutting. Advanced features include the separation the cut surfaces by retractors and post-cutting deformations. The experience of virtual surgery is enhanced by implementing 3D stereo-vision and the use of two hand-held force-feedback devices.

Fetal hydrocephalus and intrauterine cerebral ventriculoscopy: an animal model

OBJECTIVE

The aim of this study was to create an animal model of obstructive ventriculomegaly in the fetal lamb at 78 days of gestation by injecting maternal blood into the lateral ventricles under ultrasound guidance.

METHODS

An endoscope of 1.2 mm housed in a 1.6-mm trocar was introduced into the dilated lateral ventricle. The lambs were sacrificed after delivery.

RESULTS

All fetuses diagnosed with ventriculomegaly on ultrasound showed dilatation on the anatomical sections. The ventricles had a dilated aspect when compared to the controls. In 1 fetus the septum between the two ventricles was completely ruptured. Microscopically the ependymal cells were flattened and the cellular lining was disruptured.

CONCLUSION

The model proved suitable for ventriculoscopic examination at 128 days of gestation. This should allow to elaborate further on therapeutic studies in this controversial area.

Rigid-body modelling of shaken baby syndrome

Recent reassessment of the literature on the shaken baby syndrome (SBS) has revealed a lack of scientific evidence and understanding of all aspects of the syndrome. In particular, studies have been unable to clarify the mechanisms of injury, indicating that impact, rather than shaking alone, is necessary to cause the type of brain damage observed. Rigid-body modelling (RBM) was used to investigate the effect of neck stiffness on head motion and head-torso impacts as a possible mechanism of injury. Realistic shaking data obtained from an anthropometric test dummy (ATD) was used to simulate shaking. In each study injury levels for concussion were exceeded, though impact-type characteristics were required to do so in the neck stiffness study. Levels for the type of injury associated with the syndrome were not exceeded. It is unlikely that further gross biomechanical investigation of the syndrome will be able to significantly contribute to the understanding of SBS. Current injury criteria are based on high-energy, single-impact studies. Since this is not the type of loading in SBS it is suggested that their application here is inappropriate and that future studies should focus on injury mechanisms in low-energy cyclic loading.

The role of neuroendoscopy in the management of brain tumours

Neuroendoscopy is increasingly used in the management of brain tumours and tumour related hydrocephalus and this study reviews the efficacy of neuroendoscopic interventions in this unit in patients with brain tumours. A series of 87 neuroendoscopic operations carried out in 77 patients with brain tumours over a 6-year period is reported. The age range of the patients was from 5 months to 70 years (median 13 years). In 56 cases (64%) presentation was with a newly-diagnosed tumour and hydrocephalus. The majority of the remaining patients had varying degrees of worsening hydrocephalus on the background of a previously diagnosed tumour. Neuroendoscopic third ventriculostomy (NTV) was successful in relieving hydrocephalus in the short term in 63/66 cases (95%) and in the longer term in 55/66 cases (83%). Neuroendoscopic tumour biopsies were successful in providing a tissue diagnosis in 17/28 cases (61%) and four extensive and three partial resections of tumour were carried out. There were two deaths within 30 days of the procedure with only one of these, secondary to intraventricular haemorrhage, directly related to neuroendoscopy. Few significant complications were noted otherwise. For selected intraventricular and paraventricular tumours neuroendoscopy offers the opportunity to combine relief of hydrocephalus with tumour biopsy and sampling of CSF in a single procedure.

Changes in third ventricular size with neuroendoscopic third ventriculostomy: a blinded study

The objective was to study the relation between changes in cerebral ventricular size and clinical outcome after neuroendoscopic third ventriculostomy (NTV) in both primary (no previous surgery) and secondary (previous CSF diversion for hydrocephalus) NTV. Changes in ventricular size were related to the need for further surgery for CSF diversion. A blinded retrospective study of the pre-NTV and post-NTV sizes of the ventricles in an unselected series of patients undergoing this procedure was done. A decrease in third ventricular size was seen in significantly more patients in the primary group than in the secondary group. Median change in third ventricle width for those who did not require further CSF diversion was significantly greater than those with no clinical benefit (p=0.01). Positive predictive power for successful outcome was highest for measures of the third ventricle; 73% and 68% for third ventricle width and height respectively, 88% for anterior to posterior commissure distance. In conclusion, third ventricular size reduces after NTV. The use of such a change as an arbiter of success in this procedure is questionable as clinically successful cases can have no change in ventricular size. It is considered that clinical outcome is the most important guide to success or failure as reduction in ventricular size is by no means guaranteed. Radiological outcomes alone may be misleading and reliance on them should be avoided.

The effectiveness of neuroendoscopic interventions in children with brain tumours

OBJECT

The purpose of this study was to review the efficacy of neuroendoscopic interventions in children with brain tumours and tumour-related hydrocephalus.

METHODS

In all, 61 consecutive neuroendoscopic operations carried out in 53 children with brain tumours over a 6-year period were reviewed. The patients ranged in age from 5 months to 18 years (median 9 years). Forty of 61 presentations were with a newly diagnosed tumour and hydrocephalus - the remainder predominantly had a known tumour and worsening hydrocephalus.

CONCLUSIONS

Neuroendoscopic third ventriculostomy (NTV) successfully relieved hydrocephalus in the short term in 45 of 47 cases and in the longer term in 39 of 47 cases. Neuroendoscopic biopsy provided definitive tissue diagnosis in 10 of 16 cases and 5 tumours were resected. There was 1 postoperative death, which not directly related to the neuroendoscopy and few significant complications otherwise. Neuroendoscopic methods allow effective immediate and longer term control of hydrocephalus as well as the opportunity for CSF sampling and tumour biopsy in selected cases.

Neuroendoscopic third ventriculostomy in dysmorphic brains

Neuroendoscopic third ventriculostomy (NTV) has superseded shunting as the treatment of choice in non-communicating hydrocephalus. Intracranial developmental anomalies have been considered to be relative contraindications for this procedure. We present one patient with a Dandy-Walker malformation and another with septo-optic dysplasia who presented with hydrocephalus. An NTV was performed successfully in both patients using a flexible neuroendoscope and utilising transendoscopic Doppler ultrasound to ensure a safe target area for ventriculostomy.

Neuroendoscopic third ventriculostomy for hydrocephalus in adults: report of a single unit's experience with 63 cases

BACKGROUND

Neuroendoscopic third ventriculostomy (NTV) is becoming a first line treatment for hydrocephalus in this center. Its use in a consecutive series of adults is reported.

METHOD

Initially a retrospective data collection after 7 months becoming prospective studying all patients who underwent NTV in this center. The adults (17 years or older) have been studied.

RESULTS

Sixty-three patients met the criteria for inclusion: 38 male, 25 female. Mean age at first NTV 37.5 years. There was an 80% success rate (i.e., no further therapy for the hydrocephalus required). Follow-up was for a mean of 3.1 years. The largest subgroup were patients with third ventricular tumours (35%), of whom 86% were successfully treated. Mean time to failure for the whole series was 8.5 months (range immediate--30 months). Complications occurred in 17.5%; those deemed serious in 11%. There were three deaths (4.7%) within 30 days of the procedure. There were six other deaths during follow-up, five because of tumour progression and one because of pneumonia.

CONCLUSIONS

This procedure lends itself to the treatment of hydrocephalus in adults and appears to be more successful than in young children. It is efficacious in both previously shunted and non shunted patients. It is now the first-line treatment for noncommunicating hydrocephalus in this center and also for patients with shunt failure who are anatomically suitable, having cerebrospinal fluid spaces large enough to admit the endoscope. The complication and mortality rates compare favorably with those for shunts.

The fate of the cerebrospinal fluid after neuroendoscopic third ventriculostomy

This paper describes the case of a 9-year-old girl with a posterior thalamic/pineal region lesion and secondary obstructive hydrocephalus. The hydrocephalus was treated by neuroendoscopic third ventriculostomy (NTV), and she underwent simultaneous transendoscopic biopsy. The tumour biopsy was haemorrhagic, but the bleeding settled with constant irrigation. The patient remained neurologically unchanged, but subsequent imaging revealed an asymptomatic thoracolumbar spinal subdural haematoma thought to be due to blood flowing out through the NTV into the subdural space. This demonstrates the subdural location of the cerebrospinal fluid after NTV.

Soft tissue rapid prototyping in neurosurgery

As part of our research into the fluid hydrodynamics of the human ventricular system, a fused deposition model of the human ventricular system was made using magnetic resonance imaging (MRI) data. This article describes the manufacturing of a positive cast of the ventricles as a first step in the construction of a hollow model. After decryption of the original MRI file (ACR-Nema format), the MRI slices were reassembled semiautomatically and a rapid prototyping station produced a resin model. Because of its ease and speed, this method harbors great potential for teaching purposes, research, and preoperative planning in complex three-dimensional soft tissue targets.

Liliequist's membrane in minimally invasive endoscopic neurosurgery

Liliequist's membrane, an arachnoid condensation extending from the upper border of the dorsum sellae to the anterior edge of the mammillary bodies and formerly a relatively insignificant structure, has been found to be extremely important in the neuroendoscopic management of hydrocephalus. Failure to open this membrane can lead to the failure of third ventriculostomies.

Flexible neuroendoscopic treatment of suprasellar arachnoid cysts

Endoscopic treatment of suprasellar arachnoid cysts is now the treatment of choice. By marsupializing the roof of the cyst the condition can be cured. The perceived necessity to open both the roof and the floor is called into question by this paper. Three cases of suprasellar arachnoid cyst are described all of which have had successful marsupialisation of the cysts by flexible neuroendoscopy Flexible neuroendoscopic marsupialization of the cyst by widely opening the cyst roof only is described. This is compared with the other techniques, and also the endoscopic technique involving opening both the roof and the floor of the cyst, a more difficult and potentially dangerous method. Successful treatment of this condition is achieved by marsupialization of only the roof of the cyst. This is a much safer procedure, and has resulted in a resolution of signs and symptoms in the cases described followed-up between 24 and 28 months from the procedure.

Sinus pericranii. Report of a case and review of the literature

Sinus pericranii is an unusual anomaly of venous drainage from intracranial to extracranial systems via the diploë of the skull. A case and its management are presented. The aetiology, various options regarding treatment and their indications are discussed, including various surgical techniques and interventional radiology.

Constructive interference in steady-state 3D Fourier-transform MRI in the management of hydrocephalus and third ventriculostomy

We describe the use of three-dimensional Fourier transform constructive imaging in the steady state (CISS) MRI in the assessment of patients with hydrocephalus. We have found it of value both as a diagnostic investigation and in the follow-up of patients treated by third ventriculostomy.

Neuroendoscopy in the premature population

The population born prematurely is particularly prone to hydrocephalus. Shunting techniques, whilst still the gold standard, have considerable failure rates and contribute significant morbidity and mortality. The role of neuroendoscopic techniques in the treatment of such patients is explored, and a series of 19 patients born prematurely and operated on neuroendoscopically before their 1st birthdays is described.

Ruptured fusiform cerebral aneurysm in a neonate

An 11-day-old male infant presented with subarachnoid and intraventricular haemorrhage caused by a ruptured intracranial aneurysm. Magnetic resonance (MR) angiogram and digital subtraction angiography (DSA) revealed a fusiform aneurysm 10 mm in diameter supplied by the proximal segment of the anterior cerebral artery (A1), with both distal segments (A2) arising from the aneurysm. The right A1 was aplastic. There have been 13 previous case reports of neonatal cerebral artery aneurysms, but only 1 of these has been fusiform. None of the earlier reports has mentioned dysplastic segments or other anomalies of the circle of Willis.

Neuroendoscopic third ventriculostomy in patients less than 1 year old

A series of neuroendoscopic third ventriculostomies in children less than 1 year old is reported. Twenty-seven patients underwent the procedure with 21 (77%) failing within a mean of 1.36 months of the procedure. Nineteen were subsequently shunted. The presence or absence of flow through the ventriculostomy and the size of the lateral ventricles on post-operative imaging were not an indicator of success or failure. Only 4 (15%) had a complication of the procedure. Although the majority fail, approximately 1/3 are spared the added morbidity and mortality of having a shunt. With such a low morbidity and zero mortality the procedure has many benefits over shunting. Consequently, neuroendoscopic third ventriculostomy is used in this institution, where possible, rather than a shunt.

Monstrous skull osteomas in a probable Gardner's syndrome: case report

BACKGROUND

Gardner's syndrome includes a clinical triad of familial polyposis coli, osteomas, and soft tissue tumors.

METHODS

We present a very unusual case of probable isolated Gardner's syndrome characterized by extremely voluminous osteomas in the occipital and frontal areas associated with diffuse subcutaneous lipomas and without colic abnormality.

RESULTS

The neurosurgical management included resection of the osteomas for cosmetic reasons. After a follow-up period of 5 years, the patient remains free of digestive complaints and the resected osteomas did not recur.

CONCLUSIONS

The special clinical presentation of our case of possible Gardner's syndrome is discussed.

Spinal arachnoiditis mimicking a spinal cord tumor: a case report and review of the literature

We report on an unusual case of idiopathic arachnoiditis mimicking a spinal cord tumor in a 50-year-old man with progressive paraparesis. The medical imaging work-up showed an enlarged terminal cone with adjacent cysts. Although there was no enhancement of the terminal cone or the surrounding structures, the diagnosis of spinal cord tumor was maintained and surgery was carried out. Exploration of the cauda equina and the tissue surrounding the terminal cone did not reveal a tumor. The patient improved dramatically after surgery but the symptoms recurred 1 year later. We review arachnoiditis, its pathology, and its treatment with special attention drawn to the primary form of spinal arachnoiditis.

Solitary dorsal intramedullary schwannoma. Case report

A case of solitary dorsal intramedullary schwannoma diagnosed by magnetic resonance imaging and treated surgically is reported. The authors review the previously published cases. The possible etiology of the tumor as well as some difficulties encountered in the diagnostic procedure and treatment are discussed.

A patient with two chronic posttraumatic aneurysms of the thoracic aorta

A case of successful replacement of two coexistent chronic post-traumatic aneurysms of the thoracic aorta is presented. Presumably, these aneurysms at the aortic isthmus and the descending thoracic aorta resulted from two different deceleration traumas.

Posttraumatic rupture of the thoracic aorta

Ten patients with traumatic lesions of the thoracic aorta were seen in a hospital. Most were victims of traffic accidents and presented severe associated lesions along with their vascular trauma. We found that the vascular injuries were clinically manifest in only a minority of patients. The remaining ruptures were discovered through CT-scanning of the mediastinum or angiography. We believe that in every major trauma victim aortic lesions should be actively sought for by complimentary examinations to guarantee maximum survival of the patients.