Kernohan-Woltman notch phenomenon: an exceptional neurological picture?

INTRODUCTION: Ipsilateral hemiparesis (IH) can be defined as a paradoxical dysfunction of the first motor neuron involving the extremities on the opposite side to that expected, given the location of the triggering intracranial pathology. Compression of the corticospinal tract (CSt) along its course through the contralateral cerebral peduncle against the free edge of the tentorium, known as the Kernohan-Woltman notch phenomenon (KWNP), represents the main cause of IH. METHODS: This retrospective study analyses a series of 12 patients diagnosed with IH secondary to KWNP treated at our institution, including a descriptive study of epidemiological, clinical, radiological, neurophysiological, and prognostic variables. RESULTS: In 75% of the cases, symptoms had an acute or subacute onset. Initial imaging studies showed signs of significant mass effect in half of the patients, whereas magnetic resonance imaging (MRI) identified a structural lesion in the contralateral cerebral peduncle in two thirds of them. Impairment of the motor evoked potentials (MEP) was verified in 4 patients. During follow-up 7 patients experienced improvement in motor activity, and near half of the cases were classified in the first three categories of the modified Rankin scale. CONCLUSIONS: In contrast to prior historical series, most of our patients developed a KWNP secondary to a traumatic mechanism. MRI represents the optimal method to identify both the classic cerebral peduncle notch and the underlying structural lesion of the CSt. The use of MEP can help to establish the diagnosis, especially in those cases lacking definite radiological findings.

Topologically driven linear magnetoresistance in helimagnetic FeP.

The helimagnet FeP is part of a family of binary pnictide materials with the MnP-type structure, which share a nonsymmorphic crystal symmetry that preserves generic band structure characteristics through changes in elemental composition. It shows many similarities, including in its magnetic order, to isostructural CrAs and MnP, two compounds that are driven to superconductivity under applied pressure. Here we present a series of high magnetic field experiments on high-quality single crystals of FeP, showing that the resistance not only increases without saturation by up to several hundred times its zero-field value by 35 T, but that it also exhibits an anomalously linear field dependence over the entire range when the field is aligned precisely along the crystallographic c-axis. A close comparison of quantum oscillation frequencies to electronic structure calculations links this orientation to a semi-Dirac point in the band structure, which disperses linearly in a single direction in the plane perpendicular to field, a symmetry-protected feature of this entire material family. We show that the two striking features of magnetoresistance-large amplitude and linear field dependence-arise separately in this system, with the latter likely due to a combination of ordered magnetism and topological band structure.

Small-angle neutron polarimetry apparatus (SANPA): Development at the NIST Center for Neutron Research.

Spherical neutron polarimetry directly measures the rotation of the neutron polarization after scattering from materials with magnetic structure. It is an under utilized measurement technique that is capable of measuring all nine elements of the polarization tensor of a material. In this article, we describe our new cryogen-free small-angle neutron polarimetry apparatus and infrastructure at the NIST Center for Neutron Research. The resulting apparatus is capable of continuous operation and is designed for measurements at low temperatures (4-8 K) using niobium Meissner shielding and mu-metal shielding to produce a zero-field (≤1 µT) cooling sample environment.

Anharmonic Magnon Excitations in Noncollinear and Charge-Ordered RbFe

RbFe^{2+}Fe^{3+}F_{6} is an example of a charge ordered antiferromagnet where iron sites, with differing valences, are structurally separated into two interpenetrating sublattices. The low temperature magnetically ordered Fe^{2+} (S=2) and Fe^{3+} (S=5/2) moments form a noncollinear orthogonal structure with the Fe^{3+} site displaying a reduced static ordered moment. Neutron spectroscopy on single crystals finds two distinct spin wave branches with a dominant coupling along the Fe^{3+} chain axis (b axis). High resolution spectroscopic measurements find an intense energy and momentum broadened magnetic band of scattering bracketing a momentum-energy region where two magnon processes are kinematically allowed. These anharmonic excitations are enhanced in this noncollinear magnet owing to the orthogonal spin arrangement.

Orphan Spins in the S=5/2 Antiferromagnet CaFe_{2}O_{4}.

CaFe_{2}O_{4} is an anisotropic S=5/2 antiferromagnet with two competing A (↑↑↓↓) and B (↑↓↑↓) magnetic order parameters separated by static antiphase boundaries at low temperatures. Neutron diffraction and bulk susceptibility measurements, show that the spins near these boundaries are weakly correlated and a carry an uncompensated ferromagnetic moment that can be tuned with a magnetic field. Spectroscopic measurements find these spins are bound with excitation energies less than the bulk magnetic spin waves and resemble the spectra from isolated spin clusters. Localized bound orphaned spins separate the two competing magnetic order parameters in CaFe_{2}O_{4}.

Solitary Magnons in the S=5/2 Antiferromagnet CaFe_{2}O_{4}.

CaFe_{2}O_{4} is a S=5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c-axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ∼1 ns at the onset of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions ∼1-2 c-axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A+B orders as well as localization of spin excitations in a classical magnet.

Single to Multiquasiparticle Excitations in the Itinerant Helical Magnet CeRhIn(5).

CeRhIn(5) is an itinerant magnet where the Ce(3+) spins order in a simple helical phase. We investigate the spin excitations and observe sharp spin waves parameterized by a nearest-neighbor exchange, J(RKKY)=0.88±0.05 meV. At higher energies, the spin fluctuations are heavily damped, where single-quasiparticle excitations are replaced by a momentum- and energy-broadened continuum constrained by kinematics of energy and momentum conservation. The delicate energy balance between localized and itinerant characters results in the breakdown of the single-quasiparticle picture in CeRhIn(5).

(C4H12N2)[CoCl4]: tetrahedrally coordinated Co2+ without the orbital degeneracy.

We report on the synthesis, crystal structure and magnetic properties of a previously unreported Co(2+) S = 3/2 compound, (C4H12N2)[CoCl4], based upon a tetrahedral crystalline environment. The S = 3/2 magnetic ground state of Co(2+), measured with magnetization, implies an absence of spin-orbit coupling and orbital degeneracy. This contrasts with compounds based upon an octahedral and even known tetrahedral Co(2+) [Cotton et al. (1961). J. Am. Chem. Soc. 83, 4690] systems where a sizable spin-orbit coupling is measured. The compound is characterized with single-crystal X-ray diffraction, magnetic susceptibility, IR and UV-vis spectroscopy. Magnetic susceptibility measurements find no magnetic ordering above 2 K. The results are also compared with the previously known monoclinic hydrated analogue.

Mössbauer study of the '11' iron-based superconductors parent compound Fe(1+x)Te.

(57)Fe Mössbauer spectroscopy was applied to investigate the superconductor parent compound Fe(1+x)Te for x = 0.06, 0.10, 0.14, 0.18 within the temperature range 4.2-300 K. A spin density wave (SDW) within the iron atoms occupying regular tetrahedral sites was observed, with the square root of the mean square amplitude at 4.2 K varying between 9.7 and 15.7 T with increasing x. Three additional magnetic spectral components appeared due to the interstitial iron distributed over available sites between the Fe-Te layers. The excess iron showed hyperfine fields at approximately 16, 21 and 49 T for three respective components at 4.2 K. The component with a large field of 49 T indicated the presence of isolated iron atoms with large localized magnetic moments in interstitial positions. Magnetic ordering of the interstitial iron disappeared in accordance with the fallout of the SDW with increasing temperature.

A new feature extraction method for signal classification applied to cord dorsum potential detection.

In the spinal cord of the anesthetized cat, spontaneous cord dorsum potentials (CDPs) appear synchronously along the lumbo-sacral segments. These CDPs have different shapes and magnitudes. Previous work has indicated that some CDPs appear to be specially associated with the activation of spinal pathways that lead to primary afferent depolarization and presynaptic inhibition. Visual detection and classification of these CDPs provides relevant information on the functional organization of the neural networks involved in the control of sensory information and allows the characterization of the changes produced by acute nerve and spinal lesions. We now present a novel feature extraction approach for signal classification, applied to CDP detection. The method is based on an intuitive procedure. We first remove by convolution the noise from the CDPs recorded in each given spinal segment. Then, we assign a coefficient for each main local maximum of the signal using its amplitude and distance to the most important maximum of the signal. These coefficients will be the input for the subsequent classification algorithm. In particular, we employ gradient boosting classification trees. This combination of approaches allows a faster and more accurate discrimination of CDPs than is obtained by other methods.

Rhabdomyolysis-induced acute renal failure in Legionnaires' disease.

A 57-year-old man with legionnaires' disease had acute renal failure as a result of nontraumatic rhabdomyolysis. This report documents an association between legionnaires' disease and rhabdomyolysis, an association only rarely suggested previously. The mechanism of rhabdomyolysis is unknown. Rhabdomyolysis should be considered in patients with legionnaires' disease who have acute renal failure.

[Cardiac index, oxygen and serum lactate consumption in infants with hypovolemic and septic shock]. / Indice cardíaco, consumo de oxígeno y lactato sérico en lactantes con choque hipovolémico y séptico.

Determination was made of cardiac output (using the stain dilution technique), gases in blood and serum lactate levels in eight infants with hypovolemic shock and sixteen with septic shock. The data were carried to indexes (values per square meter of body surface). In children with hypovolemic shock the cardiac index was 1.88 +/- 0.031/min/m,2 while in septic patients it was 4.02 +/- 1.011/min/m2. The peripheral resistances were 3,079 din/min/cm.5 in hypovolemic cases and 907 din/min in the septic. In both groups serum lactante levels rised close to 4 mM 61. Oxigen consumption was found low in hypovolemic patients and slightly high in the septic. It is concluded that our data are similar to those reported in similar studies in adults and hypodynamic shock is shown in hypovolemic patients, while hyperdynamic shock appears in septic cases.