Contralateral deafness following unilateral suboccipital brain tumor surgery in a patient with large vestibular aqueduct--case report. (1/123)

A 68-year-old female developed contralateral deafness following extirpation of a left cerebellopontine angle epidermoid cyst. Computed tomography showed that large vestibular aqueduct was present. This unusual complication may have been caused by an abrupt pressure change after cerebrospinal fluid release, which was transmitted through the large vestibular aqueduct and resulted in cochlear damage.  (+info)

Oxygenation of the cat primary visual cortex. (2/123)

Tissue PO2 was measured in the primary visual cortex of anesthetized, artificially ventilated normovolemic cats to examine tissue oxygenation with respect to depth. The method utilized 1) a chamber designed to maintain cerebrospinal fluid pressure and prevent ambient PO2 from influencing the brain, 2) a microelectrode capable of recording electrical activity as well as local PO2, and 3) recordings primarily during electrode withdrawal from the cortex rather than during penetrations. Local peaks in the PO2 profiles were consistent with the presence of numerous vessels. Excluding the superficial 200 microm of the cortex, in which the ambient PO2 may have influenced tissue PO2, there was a slight decrease (4.9 Torr/mm cortex) in PO2 as a function of depth. After all depths and cats were weighted equally, the average PO2 in six cats was 12.8 Torr, with approximately one-half of the values being +info)

The effect of spinal instrumentation on lumbar intradiscal pressure. (3/123)

The purpose of this study was to investigate the effect of spinal instrumentation on the intradiscal pressure (IDP) within the fixed motion segment. In vitro biomechanical testing was performed in six single functional spinal units of fresh calf lumbar spines using a pressure needle transducer. Various loads were applied by a materials testing system device. In addition to intact spine (control), anterior spinal instrumentation (ASI) and pedicle screw fixation (PS) constructs, as well as destabilized spine were tested. Relative to the control, the destabilized spine tended to have an increased IDP; by 15% in axial compression and by 9-36% in flexion-extension. Compared to the control, PS decreased the IDP by 23% in axial loading and 51% in extension loading and increased it by 60% in flexion for each loading. ASI decreased the IDP by 32% in flexion and 1% in extension. Lateral bending produced symmetrical changes of IDP in the control and destabilized spine, but no change in the PS construct. The IDP of the ASI construct was decreased by 77% in ipsilateral bending and increased by 22% in contralateral bending. These results demonstrated that eccentric loading from the spinal instruments increased IDP and significant disc pressure may still exist despite an increase in motion segment stiffness after lumbar stabilization.  (+info)

Spontaneous ventriculostomy: report of three cases revealed by flow-sensitive phase-contrast cine MR imaging. (4/123)

Spontaneous ventriculostomy is a rare condition that occurs with the spontaneous rupture of a ventricle, resulting in a communication between the ventricular system and the subarachnoid space. Three cases of spontaneous ventriculostomy through the floor of the third ventricle that occurred in cases of chronic obstructive hydrocephalus are presented. The communication was identified via flow-sensitive phase-contrast cine MR imaging. Spontaneous ventriculostomy is probably a result of a rupture of the normally thin membrane that forms the floor of the third ventricle and, with long-standing obstructive hydrocephalus, creates an internal drainage pathway that spontaneously compensates for the hydrocephalus.  (+info)

Effects of positive end-expiratory pressure ventilation on cerebral venous pressure with head elevation in dogs. (5/123)

Mechanical ventilation with positive end-expiratory pressure (PEEP) may prevent venous air embolism in the sitting position because cerebral venous pressure (Pcev) could be increased by the PEEP-induced increase in right atrial pressure (Pra). Whereas it is clear that there is a linear transmission of the PEEP-induced increase in Pra to Pcev while the dog is in the prone position, the mechanism of the transmission with the dog in the head-elevated position is unclear. We tested the hypothesis that a Starling resistor-type mechanism exists in the jugular veins when the head is elevated. In one group of dogs, increasing PEEP linearly increased Pcev with the dog in the prone position (head at heart level, slope = 0.851) but did not increase Pcev when the head was elevated. In another group of dogs, an external chest binder was used to produce a larger PEEP-induced increase in Pra. Further increasing Pra increased Pcev only after Pra exceeded a pressure of 19 mmHg (break pressure). This sharp inflection in the upstream (Pcev)-downstream (Pra) relationship suggests that this may be caused by a Starling resistor-type mechanism. We conclude that jugular venous collapse serves as a significant resistance in the transmission of Pra to Pcev in the head-elevated position.  (+info)

Isolated dilation of the trigono-inferior horn--four case reports. (6/123)

Four patients presented with isolated dilation of the trigono-inferior horn associated with either mass lesion at the trigone of the lateral ventricle or with shunt over-drainage. We investigated clinical symptoms, course, and neuroradiological findings of these cases. The pressure of the isolated ventricle was measured or estimated at surgery in all cases. The common symptoms were recent memory disturbance and contralateral homonymous hemianopia. Contralateral hemiparesis was observed occasionally. Rapid deterioration of the isolation caused uncal herniation in one case. Comma-shaped dilation of the inferior horn was observed in all cases. Midline shift was not conspicuous except in one case. Intraventricular pressure at surgery was 18 cmH2O, 35 cmH2O, 3 cmH2O, and within normal range. These cases had very similar clinical symptoms and neuroradiological findings. The pathophysiology of isolation suggested three types of isolation (high-, normal-, and low-pressure isolation), depending on the pressure of the isolated ventricle. The isolation of trigono-inferior horn is an important clinical entity as it may cause uncal herniation in patients with high-pressure lesions.  (+info)

How much work is required to puncture dura with Tuohy needles? (7/123)

The effects of needle bevel orientation and cerebrospinal fluid (CSF) pressure on dural displacement and force required to penetrate cadaveric dura were studied using 40 samples. A constant hydrostatic pressure was applied to the subdural surface, either high or low, simulating the sitting and lateral positions. A 17-gauge Tuohy needle was advanced through the dura with the bevel oriented parallel or perpendicular to dural fibres. Travel distance and peak force at which dural penetration occurred were measured under both pressure conditions. The work required to produce dural penetration was calculated. Greater force and work were required to penetrate dura in the perpendicular orientation (P < 0.05), regardless of the subdural pressure exerted. Dural displacement was similar under both pressure conditions.  (+info)

CSF flow measurement in syringomyelia. (8/123)

BACKGROUND AND PURPOSE: CSF circulation has been reported to represent a major factor in the pathophysiology of syringomyelia. Our purpose was to determine the CSF flow patterns in spinal cord cysts and in the subararachnoid space in patients with syringomyelia associated with Chiari I malformation and to evaluate the modifications of the flow resulting from surgery. METHODS: Eighteen patients with syringomyelia were examined with a 3D Fourier encoding velocity imaging technique. A prospectively gated 2D axial sequence with velocity encoding in the craniocaudal direction in the cervical region was set at a velocity of +/- 10 cm/s. Velocity measurements were performed in the larger portion of the cysts and, at the same cervical level, in the pericystic subarachnoid spaces. All patients underwent a surgical procedure involving dural opening followed by duroplasty. Pre- and postoperative velocity measurements of all patients were taken, with a mean follow-up of 10.2 months. We compared the velocity measurements with the morphology of the cysts and with the clinical data. Spinal subarachnoid spaces of 19 healthy subjects were also studied using the same technique. RESULTS: A pulsatile flow was observed in syrinx cavities and in the pericystic subarachnoid spaces (PCSS). Preoperative maximum systolic cyst velocities were higher than were diastolic velocities. A systolic velocity peak was well defined in all cases, first in the cyst and then in the PCSS. Higher systolic and diastolic cyst velocities are observed in large cysts and in patients with a poor clinical status. After surgery, a decrease in cyst volume (evaluated on the basis of the extension of the cyst and the compression of the PCSS) was observed in 13 patients. In the postoperative course, we noticed a decrease of systolic and diastolic cyst velocities and a parallel increase of systolic PCSS velocities. Diastolic cyst velocities correlated with the preoperative clinical status of the patients and, after surgery, in patients with a satisfactory foraminal enlargement evaluated on the basis of the visibility of the cisterna magna. CONCLUSION: CSF flow measurement constitutes a direct evaluation for the follow-up of patients with syringomyelic cysts. Diastolic and systolic cyst velocities can assist in the evaluation of the efficacy of surgery.  (+info)