Hallazgos extrarraquídeos en la realización de informes de resonancia magnética de la columna / Frequent extraspinal findings in magnetic resonance imaging of the spine

Resumen Durante la realización de informes de resonancia magnética (RM) de columna, pueden encontrarse hallazgos extrarraquídeos, normales o patológicos, que no deben ser omitidos por el médico imagenólogo. Estas imágenes casuales, conocidas como “incidentalomas”, pueden ser la causa que originó la realización de la RM o bien ser totalmente asintomáticas. Se describen hallazgos extrarraquídeos habituales en las RM de columna.

Abstract When reading spinal MR examinations normal or abnormal extra spinal changes can be found but they should be described in the report.These findings, known as “incidentalomas”, can be related to the patient’s symptoms or can be asymptomatic. We describe frequent extraspinal findings found on MR of the spine.

Predicting the locations of force-generating dyneins in beating cilia and flagella.

Cilia and flagella are slender cylindrical organelles whose bending waves propel cells through fluids and drive fluids across epithelia. The bending waves are generated by dynein motor proteins, ATPases whose force-generating activity changes over time and with position along the axoneme, the motile structure within the cilium. A key question is: where, in an actively beating axoneme, are the force-generating dyneins located? Answering this question is crucial for determining which of the conformational states adopted by the dynein motors generate the forces that bend the axoneme. The question is difficult to answer because the flagellum contains a large number of dyneins in a complex three-dimensional architecture. To circumvent this complexity, we used a molecular-mechanics approach to show how the bending moments produced by single pairs of dynein motors work against elastic and hydrodynamic forces. By integrating the individual motor activities over the length of the axoneme, we predict the locations of the force-generating dyneins in a beating axoneme. The predicted location depends on the beat frequency, the wavelength, and the elastic and hydrodynamic properties of the axoneme. To test these predictions using cryogenic electron microscopy, cilia with shorter wavelengths, such as found in Chlamydomonas, are more suitable than sperm flagella with longer wavelengths because, in the former, the lag between force and curvature is less dependent on the specific mechanical properties and experimental preparation.

Lesiones oncológicas intracraneales de apariencia quística / Oncologic Intracranial Lesions with Cystic Appearance

Resumen La presencia de lesiones quísticas de etiología oncológica en el encéfalo es cada vez más frecuente. El rol del especialista en imágenes es describir sus características, morfología y comportamiento con el contraste endovenoso, para llegar a realizar un diagnóstico presuntivo y enumerar sus diagnósticos diferenciales, y así orientar al médico tratante. Haremos una revisión de las lesiones quísticas de etiología oncológica de presentación frecuente en el encéfalo.

Abstract The presence of an oncologic cystic formation in the brain is frequent. The imaging specialist's role is to describe its features, morphology, and image enhancement characteristics with endovenous contrast, to make a presumptive diagnosis, and enumerated differential diagnoses and thus orientate the practitioner. We will analyze the most common expansive cystic formations.

Contribution of increasing plasma membrane to the energetic cost of early zebrafish embryogenesis.

How do early embryos allocate the resources stored in the sperm and egg? Recently, we established isothermal calorimetry to measure heat dissipation by living zebra-fish embryos and to estimate the energetics of specific developmental events. During the reductive cleavage divisions, the rate of heat dissipation increases from ∼60 nJ · s-1 at the two-cell stage to ∼90 nJ · s-1 at the 1024-cell stage. Here we ask which cellular process(es) drive this increasing energetic cost. We present evidence that the cost is due to the increase in the total surface area of all the cells of the embryo. First, embryo volume stays constant during the cleavage stage, indicating that the increase is not due to growth. Second, the heat increase is blocked by nocodazole, which inhibits DNA replication, mitosis, and cell division; this suggests some aspect of cell proliferation contributes to these costs. Third, the heat increases in proportion to the total cell surface area rather than total cell number. Fourth, the heat increase falls within the range of the estimated costs of maintaining and assembling plasma membranes and associated proteins. Thus, the increase in total plasma membrane associated with cell proliferation is likely to contribute appreciably to the total energy budget of the embryo.

Mediciones frecuentes en el sistema nervioso central mediante tomografía computada e imágenes de resonancia magnética / Frequent measurements in the central nervous system by computed tomography and magnetic resonance imaging

Resumen En la práctica diaria, durante la realización de informes, suelen presentarse variantes anatómicas, lesiones y diversas patologías del sistema nervioso central (SNC) en las que es necesario realizar algún tipo de mediciones con la finalidad de formular un diagnóstico preciso. Esas mediciones permiten al médico derivante o tratante programar y realizar procedimientos terapéuticos mínimamente invasivos o que requieran una intervención quirúrgica de mayor relevancia. Realizamos una descripción de las mediciones más frecuentes en el SNC empleando tomografía computada (TC) e imágenes de resonancia magnética (RM).

Abstract On daily practice, during the making of reports, anatomical variants often appear, as well as injuries and different pathologies of the central nervous system (CNS) in which it is necessary to take some kind of measurements, to make an accurate diagnosis. These measurements allow the practicing physician to program and perform minimally invasive therapeutic methods or others that request a surgery of greater relevance. We describe the most frequent measurements in the NCS using Computed Tomography (CT) or Magnetic Resonance Imaging (MRI).

Lessons from equilibrium statistical physics regarding the assembly of protein complexes.

Cellular functions are established through biological evolution, but are constrained by the laws of physics. For instance, the physics of protein folding limits the lengths of cellular polypeptide chains. Consequently, many cellular functions are carried out not by long, isolated proteins, but rather by multiprotein complexes. Protein complexes themselves do not escape physical constraints, one of the most important being the difficulty of assembling reliably in the presence of cellular noise. In order to lay the foundation for a theory of reliable protein complex assembly, we study here an equilibrium thermodynamic model of self-assembly that exhibits 4 distinct assembly behaviors: diluted protein solution, liquid mixture, "chimeric assembly," and "multifarious assembly." In the latter regime, different protein complexes can coexist without forming erroneous chimeric structures. We show that 2 conditions have to be fulfilled to attain this regime: 1) The composition of the complexes needs to be sufficiently heterogeneous, and 2) the use of the set of components by the complexes has to be sparse. Our analysis of publicly available databases of protein complexes indicates that cellular protein systems might have indeed evolved so as to satisfy both of these conditions.

Espectro de lesiones en imágenes de tomografía computarizada y resonancia magnética, en deportistas que participaron en los Juegos Olímpicos de la Juventud Buenos Aires 2018: Nuestra experiencia / Spectrum of lesions observed by computed tomography and magnetic resonance imaging scans in young athletes that participated in the 2018 Youth Olympic Games in Buenos Aires

Objetivo: Describir las lesiones evaluadas por imágenes de los atletas que participaron en los Juegos Olímpicos de la Juventud Buenos Aires 2018. Materiales y Métodos: Se llevó a cabo un estudio descriptivo con una serie de 38 deportistas que participaron en los Juegos Olímpicos de la Juventud Buenos Aires 2018 y se sometieron a estudios por imágenes. Se analizaron los siguientes datos: distribución por sexo, edad, país, disciplina deportiva y hallazgos patológicos. Resultados: Se atendió a más deportistas mujeres (63,15%), la mayoría (31,57%) era de América del Sur. El atletismo fue la disciplina que más pacientes aportó (7 estudios). Predominaron las lesiones de los tejidos blandos de los miembros inferiores (51,51%). Conclusiones: Las atletas fueron quienes más se realizaron estudios por imágenes, y las lesiones más frecuentes fueron las de los tejidos blandos de los miembros inferiores. Nivel de Evidencia: IV

Objectives: To describe the sports-related injuries observed in young athletes that participated in the 2018 Youth Olympic Games in Buenos Aires. Materials and Methods: This was a descriptive study including 38 athletes that participated in the 2018 Youth Olympic Games in Buenos Aires and who were evaluated using imaging techniques. Athlete's distribution was analyzed by sex, age, sports activity and pathologic findings. Results: There were 4012 athletes that participated in the 2018 Youth Olympic Games in Buenos Aires, and, surprisingly, the number of male and female athletes was exactly the same. Injuries in female athletes were the most common (63.15%), most of them occurring in athletes of South American origin (31.57%). Athletics was the sport practiced by most patients (7 studies). Soft tissue injuries were most common in female athletes and mostly involved the lower limb (51.51%). Conclusions: The number of imaging studies carried out was higher in young female athletes, and the most common injuries were soft tissue injuries of the lower limb. Level of Evidence: IV

Environment-to-phenotype mapping and adaptation strategies in varying environments.

Biological organisms exhibit diverse strategies for adapting to varying environments. For example, a population of organisms may express the same phenotype in all environments ("unvarying strategy") or follow environmental cues and express alternative phenotypes to match the environment ("tracking strategy"), or diversify into coexisting phenotypes to cope with environmental uncertainty ("bet-hedging strategy"). We introduce a general framework for studying how organisms respond to environmental variations, which models an adaptation strategy by an abstract mapping from environmental cues to phenotypic traits. Depending on the accuracy of environmental cues and the strength of natural selection, we find different adaptation strategies represented by mappings that maximize the long-term growth rate of a population. The previously studied strategies emerge as special cases of our model: The tracking strategy is favorable when environmental cues are accurate, whereas when cues are noisy, organisms can either use an unvarying strategy or, remarkably, use the uninformative cue as a source of randomness to bet hedge. Our model of the environment-to-phenotype mapping is based on a network with hidden units; the performance of the strategies is shown to rely on having a high-dimensional internal representation, which can even be random.

Tomografía computada y resonancia magnética de variantes normales/congénitas de apariencia quística y presentación frecuente en el encéfalo / CT and MRI of Normal/Congenital Variables with Cystic Appearance and Frequent Presence in the Brain

La presentación de una imagen de apariencia quística durante el estudio del encéfalo constituye un hallazgo incidental cada vez más frecuente, pudiendo encontrarse en el espacio extra o intraaxial. Las mismas pueden ser de naturaleza congénita o adquirida, benigna o maligna, ocupantes de espacio con desplazamiento de la línea media o simplemente presentarse sin efecto compresivo alguno. De localización supra o infratentorial, esas imágenes constituyen un desafío diagnóstico, siendo imprescindible su reconocimiento para no solicitar estudios o tratamientos innecesarios. Valoraremos las imágenes de apariencia quística más frecuentes empleando tomografía computada o imágenes de resonancia magnética.

Presence of a cystic formation in brain examination is frequently an incidental finding. They can be intra or extra-axial in location, congenital or acquired, benign or malignant with or without mass effect. Intracranial cysts can be a diagnostic challenge and we should know them to avoid unnecessary exams or treatment. We will analyze the most common cystic formations seen in computed tomography and magnetic resonance.

Curvature regulation of the ciliary beat through axonemal twist.

Cilia and flagella are hairlike organelles that propel cells through fluid. The active motion of the axoneme, the motile structure inside cilia and flagella, is powered by molecular motors of the axonemal dynein family. These motors generate forces and torques that slide and bend the microtubule doublets within the axoneme. To create regular waveforms, the activities of the dyneins must be coordinated. It is thought that coordination is mediated by stresses due to radial, transverse, or sliding deformations, and which build up within the moving axoneme and feed back on dynein activity. However, which particular components of the stress regulate the motors to produce the observed waveforms of the many different types of flagella remains an open question. To address this question, we describe the axoneme as a three-dimensional bundle of filaments and characterize its mechanics. We show that regulation of the motors by radial and transverse stresses can lead to a coordinated flagellar motion only in the presence of twist. We show that twist, which could arise from torque produced by the dyneins, couples curvature to transverse and radial stresses. We calculate emergent beating patterns in twisted axonemes resulting from regulation by transverse stresses. The resulting waveforms are similar to those observed in flagella of Chlamydomonas and sperm. Due to the twist, the waveform has nonplanar components, which result in swimming trajectories such as twisted ribbons and helices, which agree with observations.

Dynamic curvature regulation accounts for the symmetric and asymmetric beats of Chlamydomonas flagella.

Cilia and flagella are model systems for studying how mechanical forces control morphology. The periodic bending motion of cilia and flagella is thought to arise from mechanical feedback: dynein motors generate sliding forces that bend the flagellum, and bending leads to deformations and stresses, which feed back and regulate the motors. Three alternative feedback mechanisms have been proposed: regulation by the sliding forces, regulation by the curvature of the flagellum, and regulation by the normal forces that deform the cross-section of the flagellum. In this work, we combined theoretical and experimental approaches to show that the curvature control mechanism is the one that accords best with the bending waveforms of Chlamydomonas flagella. We make the surprising prediction that the motors respond to the time derivative of curvature, rather than curvature itself, hinting at an adaptation mechanism controlling the flagellar beat.

Independent Control of the Static and Dynamic Components of the Chlamydomonas Flagellar Beat.

When the green alga Chlamydomonas reinhardtii swims, it uses the breaststroke beat of its two flagella to pull itself forward [1]. The flagellar waveform can be decomposed into a static component, corresponding to an asymmetric time-averaged shape, and a dynamic component, corresponding to the time-varying wave [2]. Extreme lightening conditions photoshock the cell, converting the breaststroke beat into a symmetric sperm-like beat, which causes a reversal of the direction of swimming [3]. Waveform conversion is achieved by a reduction in magnitude of the static component, whereas the dynamic component remains unchanged [2]. The coupling between static and dynamic components, however, is poorly understood, and it is not known whether the static component requires the dynamic component or whether it can exist independently. We used isolated and reactivated axonemes [4] to investigate the relation between the two beat components. We discovered that, when reactivated in the presence of low ATP concentrations, axonemes displayed the static beat component in absence of the dynamic component. Furthermore, we found that the amplitudes of the two components depend on ATP in qualitatively different ways. These results show that the decomposition into static and dynamic components is not just a mathematical concept but that the two components can independently control different aspects of cell motility: the static component controls swimming direction, whereas the dynamic component provides propulsion.

Free energy cost of reducing noise while maintaining a high sensitivity.

Living systems need to be highly responsive, and also to keep fluctuations low. These goals are incompatible in equilibrium systems due to the fluctuation dissipation theorem (FDT). Here, we show that biological sensory systems, driven far from equilibrium by free energy consumption, can reduce their intrinsic fluctuations while maintaining high responsiveness. By developing a continuum theory of the E. coli chemotaxis pathway, we demonstrate that adaptation can be understood as a nonequilibrium phase transition controlled by free energy dissipation, and it is characterized by a breaking of the FDT. We show that the maximum response at short time is enhanced by free energy dissipation. At the same time, the low frequency fluctuations and the adaptation error decrease with the free energy dissipation algebraically and exponentially, respectively.

Thermodynamic costs of information processing in sensory adaptation.

Biological sensory systems react to changes in their surroundings. They are characterized by fast response and slow adaptation to varying environmental cues. Insofar as sensory adaptive systems map environmental changes to changes of their internal degrees of freedom, they can be regarded as computational devices manipulating information. Landauer established that information is ultimately physical, and its manipulation subject to the entropic and energetic bounds of thermodynamics. Thus the fundamental costs of biological sensory adaptation can be elucidated by tracking how the information the system has about its environment is altered. These bounds are particularly relevant for small organisms, which unlike everyday computers, operate at very low energies. In this paper, we establish a general framework for the thermodynamics of information processing in sensing. With it, we quantify how during sensory adaptation information about the past is erased, while information about the present is gathered. This process produces entropy larger than the amount of old information erased and has an energetic cost bounded by the amount of new information written to memory. We apply these principles to the E. coli's chemotaxis pathway during binary ligand concentration changes. In this regime, we quantify the amount of information stored by each methyl group and show that receptors consume energy in the range of the information-theoretic minimum. Our work provides a basis for further inquiries into more complex phenomena, such as gradient sensing and frequency response.

Meningioma intraventricular. Un reporte de caso / Intraventricular meningioma. A case report

Los meningiomas intraventriculares representan los tumores más frecuentes de la región del atrio (trígono) en adultos. Pueden ser asintomáticos, cursar con cefalea o hidrocefalia por obstrucción u ocasionar déficit neurológico focal. Se presentan como masas globulares intraventriculares con realce homogéneo luego de la administración de contraste endovenoso y también pueden acompañarse de un edema en el parénquima adyacente. El diagnóstico se presume por sus características imagenológicas y se confirma por anatomía patológica. Se presenta un caso de meningioma intraventricular de forma típica en el trígono derecho, que se manifestó con cefalea. Esta entidad debería incluirse entre los diagnósticos diferenciales ante la presencia de una masa en el atrio ventricular con realce homogéneo, tras la administración de gadolinio...

Meningioma intraventricular. Un reporte de caso / Intraventricular meningioma. A case report

Los meningiomas intraventriculares representan los tumores más frecuentes de la región del atrio (trígono) en adultos. Pueden ser asintomáticos, cursar con cefalea o hidrocefalia por obstrucción u ocasionar déficit neurológico focal. Se presentan como masas globulares intraventriculares con realce homogéneo luego de la administración de contraste endovenoso y también pueden acompañarse de un edema en el parénquima adyacente. El diagnóstico se presume por sus características imagenológicas y se confirma por anatomía patológica. Se presenta un caso de meningioma intraventricular de forma típica en el trígono derecho, que se manifestó con cefalea. Esta entidad debería incluirse entre los diagnósticos diferenciales ante la presencia de una masa en el atrio ventricular con realce homogéneo, tras la administración de gadolinio...(AU)

Kinetic versus energetic discrimination in biological copying.

We study stochastic copying schemes in which discrimination between a right and a wrong match is achieved via different kinetic barriers or different binding energies of the two matches. We demonstrate that, in single-step reactions, the two discrimination mechanisms are strictly alternative and cannot be mixed to further reduce the error fraction. Close to the lowest error limit, kinetic discrimination results in a diverging copying velocity and dissipation per copied bit. On the other hand, energetic discrimination reaches its lowest error limit in an adiabatic regime where dissipation and velocity vanish. By analyzing experimentally measured kinetic rates of two DNA polymerases, T7 and Polγ, we argue that one of them operates in the kinetic and the other in the energetic regime. Finally, we show how the two mechanisms can be combined in copying schemes implementing error correction through a proofreading pathway.

Medios de contraste en imágenes / Media contrasts in imaging

En el presente trabajo realizamos una revisión y actualización de las acciones, indicaciones, reacciones adversas y sus tratamientos, interacciones y contraindicaciones de los distintos medios de contrastes.

In this review, we revised and updated the actions, indications, interactions and contraindications of the different contrast media, as well as their adverse reactions and how to treat them.