CSF flow waveform analysis helps demonstrate abnormalities in CSF flow at the foramen magnum and the benefits of decompressive surgery in patients with the Chiari I malformation.

Application of road salts in regions with colder climates is leading to ground and surface water contamination. However, we know little about how modern stormwater management practices affect the movement of road salt through urban watersheds. We investigated groundwater contamination and transport of road salts at two stormwater ponds in Baltimore County, Maryland. In association with the ponds, we documented a plume of contaminated groundwater that resulted in Cl loadings to the adjacent stream of 6574 to 40 008 kg Cl per winter, depending on winter snowfall. We also monitored Na and Cl ion concentrations and the temporal dynamics of conductivity at a range of stream sites in watersheds with and without stormwater management ponds. Streams draining watersheds with stormwater ponds had consistently higher conductivities and Cl concentrations during base flow conditions and often exhibited greater peaks in Cl and conductivity associated with winter storms and subsequent melting events, despite the degree of watershed development. Our results indicate that modern stormwater management practices are not protecting surface waters from road salt contamination and suggest they create contaminated plumes of groundwater that deliver Cl and Na to streams throughout the year.

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The Llandeilo-Caradoc black shales of southwest Wales, U.K. record a paragenetic sequence that requires redistribution of rare earth elements (REE) on a mineralogic scale during diagenesis. The main evidence for this redistribution is formation and replacement of REE-rich apatite and monazite and variations in whole-rock REE patterns. The processes that produce these mineralogic changes create a diagenetic overprint on the Llandeilo-Caradoc black shales that obscures geochemical information related to both provenance and paleoenvironmental conditions of deposition. Periods of open-system conditions existed during the diagenetic alteration of the Llandeilo-Caradoc black shales, which allow an evaluation of the extent and timing of the REE redistribution inferred from petrography. The observed variations in La/Sm ratios in the whole-rock REE patterns are strong evidence that REE were redistributed on a scale greater than an individual hand sample. This change in the whole-rock REE pattern altered the Cerium anomaly by as much as 20% and produced a range in the Sm/Nd ratio from 0.14 to 0.20. This change in the whole-rock Sm/Nd ratio indicates a disturbance in the Sm-Nd isotopic system at about 460 Ma that can be directly linked to the formation and dissolution of diagenetic apatite and monazite during diagenesis. One effect of this disturbance is to alter the range in Nd model age for the Llandeilo-Caradoc black shales from 1.6 to 1.8 Ga to about 1.4 to 2.25 Ga, thus complicating any interpretation of provenance. The ability to link petrographic observations from a black shale to measurable wholerock geochemical changes provides us with one tool to evaluate the presence of a diagenetic overprint on trace elements commonly used in paleoenvironmental reconstruction.

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Our purpose was to explore the utility of cine phase-contrast MRI velocity measurements in determining the functional status of third ventriculostomies, and to correlate the quantitative velocity data with clinical follow-up. We examined six patients with third ventriculostomies and 12 normal subjects by phase-contrast MRI. The maximum craniocaudal to maximum caudocranial velocity range was measured at regions of interest near the third ventricular floor, and in cerebrospinal fluid anterior to the upper pons and spinal cord on midline sagittal images. Ratios of the velocities of both the third ventricle and prepontine space to the space anterior to the spinal cord were obtained. The velocities near the third ventricular floor and in the pontine cistern were significantly higher in patients than in normal subjects, but the velocity anterior to the spinal cord was similar between the groups. The velocity ratios, used to normalize individual differences, were also higher in patients than in controls. Two patients had lower velocity ratios than their fellows at the third ventricular floor and in the pontine cistern; one required a shunt 11 months later, while in the other, who had a third ventricular/thalamic tumor, the lower values probably reflect distortion of the third ventricular floor. We conclude that phase-contrast MR velocity measurements, specifically the velocity ratio between the high pontine cistern and the space anterior to the spinal cord, can help determine the functional status of third ventriculostomies.