Review of theories into the pathogenesis of normal pressure hydrocephalus.

Normal pressure hydrocephalus (NPH) represents a unique form of hydrocephalus characterised by the paradox of ventriculomegaly without significant elevations in intracranial pressure, with the clinical triad of gait instability, cognitive impairment, and urinary incontinence. A myriad of neurobiological correlates have been implicated in its pathophysiology. We review the literature to provide an up-to-date, narrative review of the proposed mechanisms underlying the pathophysiology of NPH, proposing a holistic framework through which to understand the condition.

A quantitative model of the cerebral windkessel and its relevance to disorders of intracranial dynamics.

Objective: Traditional models of intracranial dynamics fail to capture several important features of the intracranial pressure (ICP) pulse. Experiments show that, at a local amplitude minimum, the ICP pulse normally precedes the arterial blood pressure (ABP) pulse, and the cranium is a band-stop filter centered at the heart rate for the ICP pulse with respect to the ABP pulse, which is the cerebral windkessel mechanism. These observations are inconsistent with existing pressure-volume models.

Brain Circuitry of Consciousness: A Review of Current Models and a Novel Synergistic Model With Clinical Application.

How consciousness arises in the brain has important implications for clinical decision-making. We summarize recent findings in consciousness studies to provide a toolkit for clinicians to assess deficits in consciousness and predict outcomes after brain injury. Commonly encountered disorders of consciousness are highlighted, followed by the clinical scales currently used to diagnose them.

Why don't ventricles dilate in pseudotumor cerebri? A circuit model of the cerebral windkessel.

Objective: Pseudotumor cerebri is a disorder of intracranial dynamics characterized by elevated intracranial pressure (ICP) and chronic cerebral venous hypertension without structural abnormalities. A perplexing feature of pseudotumor is the absence of the ventriculomegaly found in obstructive hydrocephalus, although both diseases are associated with increased resistance to cerebrospinal fluid (CSF) resorption. Traditionally, the pathophysiology of ventricular dilation and obstructive hydrocephalus has been attributed to the backup of CSF due to impaired absorption, and it is unclear why backup of CSF with resulting ventriculomegaly would not occur in pseudotumor.

Bifrontal Biparietal Cruciate Decompressive Craniectomy in Pediatric Traumatic Brain Injury.

Background: We investigated a novel surgical approach to decompressive craniectomy (DC), the bifrontal biparietal, or "cruciate," craniectomy, in severe pediatric traumatic brain injury (TBI). Cruciate DC was designed with a fundamentally different approach to intracranial pressure (ICP) control compared to traditional DC. Cruciate DC involves craniectomies in all 4 skull quadrants.

Ventricular peritoneal shunt malfunction after operative correction of scoliosis: report of three cases.

Background Context: Two of the most common disease processes associated with hydrocephalus in children are spina bifida and intraventricular hemorrhage of prematurity, both of which are known to be also associated with spinal deformity in later childhood. The occurrence of shunt malfunction after mechanical injury or stress to the hardware has been well documented. Newer techniques in the treatment of neuromuscular scoliosis, including anterior release with segmental fixation, have resulted in more powerful corrections of these large spinal deformities.

Resonant and notch behavior in intracranial pressure dynamics.

Object: The intracranial pulse pressure is often increased when neuropathology is present, particularly in cases of increased intracranial pressure (ICP) such as occurs in hydrocephalus. This pulse pressure is assumed to originate from arterial blood pressure oscillations entering the cranium; the fact that there is a coupling between the arterial blood pressure and the ICP is undisputed. In this study, the nature of this coupling and how it changes under conditions of increased ICP are investigated.

Ventricular dilation and elevated aqueductal pulsations in a new experimental model of communicating hydrocephalus.

In communicating hydrocephalus (CH), explanations for the symptoms and clear-cut effective treatments remain elusive. Pulsatile flow through the cerebral aqueduct is often significantly elevated, but a clear link between abnormal pulsations and ventriculomegaly has yet to be identified. We sought to demonstrate measurement of pulsatile aqueductal flow of CSF in the rat, and to characterize the temporal changes in CSF pulsations in a new model of CH.

Intracranial pressure waves: characterization of a pulsation absorber with notch filter properties using systems analysis: laboratory investigation.

Object: The relationship between the waveform of intracranial pressure (ICP) and arterial blood pressure can be quantitatively characterized using a newly developed technique in systems analysis, the time-varying transfer function. This technique considers the arterial blood pressure as an input signal composed of multiple frequencies represented in the output ICP according to the transfer function imposed by the intracranial system on the input signal. The transfer function can change with time and with physiological manipulations.

Communicating hydrocephalus in adult rats with kaolin obstruction of the basal cisterns or the cortical subarachnoid space.

Communicating hydrocephalus (CH) occurs frequently, but clinically-relevant animal models amenable to diagnostic imaging and cerebrospinal fluid shunting are not available. In order to develop and characterize models of subarachnoid space (SAS) obstruction at the basal cisterns (BC) or cerebral convexities (CX), 25% kaolin was injected in adult female Sprague-Dawley rats following halothane anesthesia; intact- or saline-injected animals served as controls. For BC animals (n=28 hydrocephalics, n=20 controls), an anterior approach to the C1-clivus interval was employed and 30 microl of kaolin or saline was injected.

Increased Phase Synchronization between Intracranial Pressure and Arterial Blood Pressure during Elevated Intracranial Pressure in Dogs.

We applied the concept of "phase synchronization" from nonlinear dynamics to the complex relationship between intracranial pressure (ICP) and arterial blood pressure (ABP) signals. This method is based on multiresolution wavelet transform (MRWT) in which the signals are divided into different frequency bands. We examined ICP and ABP signals from anaesthetized dogs, exploring normal ICP and elevated ICP by 1~3 ml injection of saline into the cerebral ventricles.

Improved cerebrospinal fluid flow measurements using phase contrast balanced steady-state free precession.

We present a demonstration of phase contrast balanced steady-state free precession (PC-bSSFP) for measuring cerebrospinal fluid (CSF) flow in the brain and spine, and a comparison of measurements obtained with this technique to conventional phase contrast using incoherent gradient echoes (PC-GRE). With PC-GRE sequences, CSF images suffer from low signal-to-noise ratio (SNR), due to short repetition times required for adequate temporal resolution, and the long relaxation time of CSF. Furthermore, CSF flow is often nonlaminar, causing phase dispersion and signal loss in PC-GRE images.

Amplitude and phase of cerebrospinal fluid pulsations: experimental studies and review of the literature.

Object: A recently developed model of communicating hydrocephalus suggests that ventricular dilation may be related to the redistribution of pulsations in the cranium from the subarachnoid spaces (SASs) into the ventricles. Based on this model, the authors have developed a method for analyzing flow pulsatility in the brain by using the ratio of aqueductal to cervical subarachnoid stroke volume and the phase of cerebrospinal fluid (CSF) flow, which is obtained at multiple locations throughout the cranium, relative to the phase of arterial flow.

Methods: Flow data were collected in a group of 15 healthy volunteers by using a series of images acquired with cardiac-gated, phase-contrast magnetic resonance imaging.

What we don't (but should) know about hydrocephalus.

In an effort to identify critical gaps in the prevailing knowledge of hydrocephalus, the authors formulated 10 key questions. 1) How do we define hydrocephalus? 2) How is cerebrosinal fluid (CSF) absorbed normally and what are the causes of CSF malabsorption in hydrocephalus? 3) Why do the ventricles dilate in communicating hydrocephalus? 4) What happens to the structure and function of the brain when it is compressed and stretched by the expanding ventricles? 5) What is the role of cerebrovenous pressure in hydrocephalus? 6) What causes normal-pressure hydrocephalus? 7) What causes low-pressure hydrocephalus? 8) What is the pathophysiology of slit ventricle syndrome? 9) What is the pathophysiological basis for neurological impairment in hydrocephalus, and to what extent is it reversible? 10) How is the brain of a child with hydrocephalus different from that of a young or elderly adult? Rigorous answers to these questions should lead to more effective and reliable treatments for this disorder.

Decompressive craniectomy in pediatric patients with traumatic brain injury with intractable elevated intracranial pressure.

Background: Care of pediatric traumatic brain injury (TBI) has placed emphasis on maximizing cerebral perfusion to prevent ischemia and reperfusion injury. A subset of patients with TBI will continue to have refractory intracranial pressure (ICP) elevation despite aggressive therapy including ventriculostomy, pentobarbital coma, hypertonic saline, and diuretics. Decompressive craniectomy (DC) is a controversial treatment of severe TBI.

A model of pulsations in communicating hydrocephalus.

The traditional theory of communicating hydrocephalus has implicated the bulk flow component of CSF motion; that is, hydrocephalus is generally understood as an imbalance between CSF formation and absorption. The theory that the cause of communicating hydrocephalus is malabsorption of CSF at the arachnoid villi is not substantiated by experimental evidence or by physical reasoning. Flow-sensitive MRI has shown that nearly all CSF motion is pulsatile, and there is substantial evidence that hyperdynamic choroid plexus pulsations are necessary and sufficient for ventricular dilation in communicating hydrocephalus.

Massive cystic heterotopic brain tissue.

The differential diagnosis of large cystic masses in the newborn should include heterotopic brain tissue. This lesion is attributed to early displacement of pluripotential cells and cyst formation may result from cerebrospinal fluid production by choroid plexus-like structures. Treatment consists of surgical excision.

Acute traumatic central cord syndrome: MRI-pathological correlations.

The acute traumatic central cord syndrome (ATCCS) is commonly stated to result from an injury which affects primarily the center of the spinal cord and is frequently hemorrhagic. To test the validity of this widely disseminated hypothesis, the magnetic resonance images [MRI] of 11 consecutive cases of ATCCS caused by closed injury to the spine were analyzed and correlated with the gross pathological and histological features of 3 cervical spinal cords obtained at post mortem from patients with ATCCS, including 2 of patients studied by MRI. The MRI studies were performed acutely (18 h to 2 days after injury) in 7 patients and subacutely (3-10 days after injury) in 4.

Intraoperative ultrasonography and cortical mapping for removal of deep cerebral tumors.

Stereotactic biopsies of brain tumors have recently become frequent, but prognosis may be improved by more aggressive surgery for primary and metastatic tumors. This report describes techniques for debulking and removal of deep cerebral tumors that are commonly subjected only to biopsy. With the use of intraoperative cranial ultrasonography and cortical mapping, five gliomas were debulked and three metastatic lesions were grossly totally removed.