Cerebrospinal Fluid

The total volume of cerebrospinal fluid (CSF) within the ventricles and subarachnoid space is about 150 mL. The absorption of CSF is directly linked to intracranial pressure. In steady states, the rate of CSF absorption equals CSF formation, and the normal resting pressure of CSF is typically between 150 and 180 mm H2O (reference range, 65-200 mm H2O [5-15 mm Hg]). The most common cause of error in measurement of CSF pressure is failure to position the patient properly (the correct position is lateral decubitus; the right atrial pressure serves as the reference [0 mm H2O]).

Umbilical hernia causing ventriculoperitoneal shunt dysfunction: illustrative cases

BACKGROUND When ventriculoperitoneal (VP) shunts and umbilical hernias coexist in the same patient, unique complications can occur. Typically, these are readily identified problems such as cerebrospinal fluid (CSF) fistulas or entrapment of the peritoneal catheter in the hernia. The authors present cases of two children whose VP shunt dysfunction resolved after repair of their umbilical hernias. OBSERVATIONS The authors present two cases of infant patients with shunted hydrocephalus and umbilical hernias. In both cases, the patients presented with distal shunt malfunctions not due to infection. Their shunt function improved once the umbilical hernia was repaired by pediatric surgery. Neither has required shunt revision since umbilical hernia repair. LESSONS Although there are case reports of VP shunts eroding through the umbilicus, developing CSF fistulas, or becoming trapped inside umbilical hernias, there is no case of VP shunt dysfunction caused by just the presence of an umbilical hernia. The authors suspect that the catheter may intermittently enter and exit the hernia. This may cause intermittent obstruction of the distal catheter, or inflammation in the hernia may occur that limits CSF absorption.

Secondary Chiari malformation due to enlarged spinal arachnoid villi–like structure: illustrative case

BACKGROUNDSecondary Chiari malformation can be caused by various disorders associated with cerebrospinal fluid (CSF) leakage at the spinal level. In this report, the authors describe a rare case of secondary Chiari malformation caused by excessive CSF absorption through the enlarged spinal arachnoid villi–like structure.OBSERVATIONSA 20-year-old woman presented with progressive severe headache and posterior neck pain. Magnetic resonance imaging showed tonsillar herniation and decreased subarachnoid space around the spinal cord. A hypointense signal area was observed in the ventral spinal canal on a T2-weighted image. An axial image revealed multiple small, arachnoid cyst–like structures at the right T1 nerve root sleeve. Direct surgery revealed that the cyst-like structures were continuous with the arachnoid membrane and protruded into the abnormally large epidural venous sinus. The cyst-like structures were resected, and the dural sleeve was repaired using fascia. The patient showed good improvement of symptoms after surgery.LESSONSExcessive CSF absorption through the enlarged spinal arachnoid villi–like structure can cause secondary Chiari malformation. Neurosurgeons should be aware of this unusual mechanism of CSF leakage. Simple posterior fossa decompression will be ineffective or even harmful.

Idiopathic Normal Pressure Hydrocephalus: Surgical Outcome of Endoscopic Third Ventriculostomy Comparing VP Shunt

Background: Normal-pressure hydrocephalus (NPH) affects the older people and the presentations are gait disturbance, incontinence and dementia. The reason is still unknown and there is increased CSF volume causing pressure to the periventricular brain causing the symptoms where there is no evidence of absorption failure or obstruction of the CSF pathway. Aims: The main objective of this study is to compare the surgical outcome of endoscopic third ventriculostomy (ETV) and VP shunt (VPS) in NPH. Methodology: A total of 24 patients were included in the study where 12 patients underwent ETV and 12 patients VPS. Patients having a definite cause of hydrocephalus and multiple co-morbid diseases were excluded from the study. Various Scoring systems were studied to see the efficiency of ETV. Results: About 60% of patients were successfully recovered. 40% needed to revision surgery either VP shunt or LP shunt. Some scales showed higher effieciency of ETV. Conclusion: ETV in NPH is a safe and effective procedure. Whether the CSF absorption is hampered at arachnoid granulation is doubtful for failure cases. ETV is a short procedure with a good success rate in selected patients.

The pathophysiology of chronic noncommunicating hydrocephalus: lessons from continuous intracranial pressure monitoring and ventricular infusion testing

OBJECTIVEThe pathophysiology of chronic noncommunicating hydrocephalus (ncHC) is poorly understood. This present study explored whether lessons about the pathophysiology of this clinical entity might be retrieved from results of overnight monitoring of pulsatile and static intracranial pressure (ICP) and ventricular infusion testing.METHODSThe study cohort included adult patients (> 20 years of age) with chronic ncHC due to aqueductal stenosis in whom symptoms had lasted a minimum of 6 months. A reference cohort consisted of age- and sex-matched patients managed for communicating HC (cHC). Information about symptoms and clinical improvement following surgery was retrieved from a quality register, and results of overnight ICP recordings and ventricular infusion testing were retrieved from the hospital ICP database.RESULTSThe cohort with ncHC consisted of 61 patients of whom 6 (10%) were managed conservatively, 34 (56%) by endoscopic third ventriculostomy (ETV), and 21 (34%) using ETV and subsequent shunt surgery. In patients responding to surgery, pulsatile ICP (mean ICP wave amplitude) was significantly increased to a similar magnitude in patients with ncHC and the reference cohort (cHC). Furthermore, intracranial compliance (ICC) was reduced in clinical responders. The results of ventricular infusion testing provided evidence that patients responding to ETV have impaired ventricular CSF absorption, while those requiring shunt placement after ETV present with impaired CSF absorption both in the intraventricular and extraventricular compartments.CONCLUSIONSThe study may provide some lessons about the pathophysiology of chronic ncHC. First, increased pulsatile ICP and impaired ICC characterize patients with chronic ncHC who respond clinically to CSF diversion surgery, even though static ICP is not increased. Second, in patients responding clinically to ETV, impaired ventricular CSF absorption may be a key factor. Patients requiring shunt placement for clinical response appear to have both intraventricular and extraventricular CSF absorption failure. A subgroup of patients with ncHC due to aqueductal stenosis has normal ventricular CSF absorption and normal ICC and may not be in need of surgical CSF diversion.

Pseudotumor Cerebri : A Rare Presentation of Systemic Lupus Erythematosus

Raised intracranial pressure in the absence of an intracranial mass or hydrocephalus (BIH or pseudotumor cerebri) has been described in association with many conditions including SLE. Several pathogenic pathways tie BIH with SLE as thrombotic obliteration of cerebral arteriolar and venous systems and immune complex deposition within the arachnoid villi that are responsible for cerebrospinal fluid (CSF) absorption. The diagnosis of BIH was confirmed by increased intracranial pressure in the absence of any abnormal radiological findings of the brain. We report a young woman with SLE complicated by BIH which resolved with corticosteroid therapy and osmotic diuretics.J Bangladesh Coll Phys Surg 2016; 34(2): 104-107

Finite element analysis of periventricular lucency in hydrocephalus: extravasation or transependymal CSF absorption?

OBJECT Periventricular lucency (PVL) is often observed in the hydrocephalic brain on CT or MRI. Earlier studies have proposed the extravasation of ventricular CSF into the periventricular white matter or transependymal CSF absorption as possible causes of PVL in hydrocephalus. However, there is insufficient evidence for either theory to be conclusive. METHODS A finite element (FE) model of the hydrocephalic brain with detailed anatomical geometry was constructed to investigate the possible mechanism of PVL in hydrocephalus. The initiation of hydrocephalus was modeled by applying a transmantle pressure gradient (TPG). The model was exposed to varying TPGs to investigate the effects of different geometrical characteristics on the distribution of PVL. The edema map was derived based on the interstitial pore pressure. RESULTS The model simulated the main radiological features of hydrocephalus, i.e., ventriculomegaly and PVL. The degree of PVL, assessed by the pore pressure, was prominent in mild to moderate ventriculomegaly. As the degree of ventriculomegaly exceeded certain values, the pore pressure across the cerebrum became positive, thus inducing the disappearance of PVL. CONCLUSIONS The results are in accordance with common clinical findings of PVL. The degree of ventriculomegaly significantly influences the development of PVL, but two factors were not linearly correlated. The results are indicative of the transependymal CSF absorption as a possible cause of PVL, but the extravasation theory cannot be formally rejected.

Postural effects on intracranial pressure: modeling and clinical evaluation

The physiological effect of posture on intracranial pressure (ICP) is not well described. This study defined and evaluated three mathematical models describing the postural effects on ICP, designed to predict ICP at different head-up tilt angles from the supine ICP value. Model I was based on a hydrostatic indifference point for the cerebrospinal fluid (CSF) system, i.e., the existence of a point in the system where pressure is independent of body position. Models II and III were based on Davson's equation for CSF absorption, which relates ICP to venous pressure, and postulated that gravitational effects within the venous system are transferred to the CSF system. Model II assumed a fully communicating venous system, and model III assumed that collapse of the jugular veins at higher tilt angles creates two separate hydrostatic compartments. Evaluation of the models was based on ICP measurements at seven tilt angles (0–71°) in 27 normal pressure hydrocephalus patients. ICP decreased with tilt angle (ANOVA: P < 0.01). The reduction was well predicted by model III (ANOVA lack-of-fit: P = 0.65), which showed excellent fit against measured ICP. Neither model I nor II adequately described the reduction in ICP (ANOVA lack-of-fit: P < 0.01). Postural changes in ICP could not be predicted based on the currently accepted theory of a hydrostatic indifference point for the CSF system, but a new model combining Davson's equation for CSF absorption and hydrostatic gradients in a collapsible venous system performed well and can be useful in future research on gravity and CSF physiology.

Realizations of Experimental Hydrocephalus Data Through the Analytical Model of Poroviscoelastic Brain Tissue

Despite recent advances in hydro-mechanical characterization of brain tissue [1], existing models remain inadequate due to complexities associated with the brain’s geometry and rheological properties [2] as well as limited knowledge on the mechanisms which control the CerebroSpinal Fluid (CSF) absorption or formation and their impact on the extracellular fluid content changes inside parenchyma [3].