A case of benign periosteal chondroma seeding into humeral medullary bone via percutaneous needle biopsy tract.

We report an occurrence of periosteal chondroma seeding into the medulla of humerus via percutaneous needle biopsy tract. To our knowledge, this is the first described case of benign cartilage tumour biopsy tract seeding in the literature. We discuss the clinical, radiological and histological features of periosteal chondroma, as well as the diagnostic challenges associated with distinguishing this entity from periosteal chondrosarcoma. Finally, we briefly discuss the safety of imaging-guided percutaneous needle biopsy and methods to minimize the risk of iatrogenic tumour seeding.

Neuronal and glial cell expression of angiotensin II type 1 (AT1) and type 2 (AT2) receptors in the rat retina.

The bio-active peptide, angiotensin II (Ang II), has been suggested to exert a neuromodulatory effect on inner retinal neurons. In this study, we examined the distribution of angiotensin receptors (ATRs) in the developing and mature rat retina and optic nerve using immunofluorescence immunocytochemistry. Double-labeling experiments were performed with established markers to identify different retinal cell populations. In adult retinae, ATRs were observed on neurons involved in "ON" pathways of neurotransmission. Angiotensin II type 1 receptors (AT(1)Rs) were expressed by a sub-population of "ON" cone bipolar cells that also labeled for G alpha(0) and islet-1. Extra-neuronal expression of AT(1)Rs was evident on retinal astrocytes, Müller cells and blood vessels. Immunoreactivity for the angiotensin II type 2 receptor (AT(2)R) was observed on conventional and displaced GABAergic amacrine cells. Co-localization studies showed that AT(2)R-expressing amacrine cells constituted at least two separate sub-populations. Cell counts revealed that all wide-field amacrine cells expressing protein kinase C-alpha were also AT(2)R-positive; a further subset of amacrine cells expressing AT(2)Rs and stratifying in sublamina "b" of the inner plexiform layer (IPL) was identified. Developmental expression of AT(1)Rs was dynamic, involving multiple inner neuronal classes. At postnatal day 8 (P8), AT(1)R immunoreactivity was observed on putative ganglion cells. The characteristic bipolar cell labeling observed in adults was not evident until P13. In contrast, AT(2)Rs were detected as early as P2 and localized specifically to amacrine cells from this age onward. These data provide further evidence for the potential role of angiotensin II in the modulation of retinal neurons and glia. The differential pattern of expression of these receptors across these cell types is similar to that observed in the brain and suggests that a similar functional role for Ang II may also exist within the retina.

Dark adaptation recovery of human rod bipolar cell response kinetics estimated from scotopic b-wave measurements.

We recorded ganzfeld scotopic ERGs to examine the responses of human rod bipolar cells in vivo, during dark adaptation recovery following bleaching exposures, as well as during adaptation to steady background lights. In order to be able to record responses at relatively early times in recovery, we utilized a 'criterion response amplitude' protocol in which the test flash strength was adjusted to elicit responses of nearly constant amplitude. In order to provide accurate and unbiased measures of response kinetics, we utilized a curve-fitting procedure to fit a smooth function to the measured responses in the vicinity of the peak, thereby extracting both the time-to-peak and the amplitude of the responses. Following bleaching exposures, the responses exhibited both desensitization and accelerated kinetics. During early post-bleach recovery, the flash sensitivity and time-to-peak varied according to a power-law expression (with an exponent of 6), as found in the presence of steady background light. This light-like phenomenon, however, appeared to be set against the backdrop of a second, more slowly recovering 'pure' desensitization, most clearly evident at late post-bleach times. The post-bleach 'equivalent background intensity' derived from measurements of flash sensitivity faded initially with an S2 slope of approximately 0.24 decades min(-1), and later as a gentle S3 tail. When calculated from kinetics, the results displayed only the S2 slope. While the recovery of rod bipolar cell response kinetics can be described accurately by a declining level of opsin in the rods, the sensitivity of these cells is reduced further than expected by this mechanism alone.

Direct percutaneous portocaval shunt creation for haematemesis: case report.

Creating a direct intrahepatic portocaval shunt (DIPS) is a procedure similar to a transjugular intrahepatic portosystemic shunt (TIPS) in patients for whom the latter is not appropriate due to unsuitable hepato-venous and porto-venous anatomy. We present a patient for whom TIPS was not possible, and DIPS successful.

Bilateral spontaneous adrenal haemorrhage complicating acute pancreatitis.

Bilateral adrenal haemorrhage is an event that mandates prompt diagnosis and treatment to prevent primary adrenocortical insufficiency and potential death. Presentation can be non-specific and incidentally diagnosed with imaging alone, primarily CT. We present a case of acute pancreatitis with spontaneous bilateral adrenal haemorrhage and briefly discuss imaging and treatment implications.

Localization of amino acid neurotransmitters following in vitro ischemia and anoxia in the rat retina.

Glutamate and gamma-aminobutyric acid (GABA) are two of the dominant neurotransmitters in the retina and brain. The production/degradation of glutamate and GABA involves an intricate interrelationship between neurons and glia, as well as aerobic and anaerobic metabolic pathways. The aim of this work was to develop an in vitro model of retinal ischemia/anoxia and determine the changes in cellular localization of glutamate and GABA and the time course for such changes. After anoxic/ischemic insult, glutamate and GABA rapidly accumulate within glia with GABA showing a quicker time course and larger magnitude change. The accumulation time constant for both glutamate and GABA under anoxic conditions was dependent upon glucose concentration: high glucose levels resulted in delayed glial amino acid loading. The differences in time constants between GABA and glutamate glial loading most likely reflect the multitude of glutamate degradation pathways compared to the single aerobically dependent GABA pathway. Oxygen availability and reduced glucose (hypoglycemia) lead to an almost immediate increase (within 1 min) of glutamate and GABA labelling within glia. In addition, altered labelling patterns were found under anoxic/ischemic conditions for amino acids involved in glutamate transamination reactions: aspartate, leucine, alanine. and ornithine. These changes are consistent with alterations of equilibria of enzymatic reactions involved in glutamate metabolism, and thus support a role for all four amino acids in glutamate metabolism within a variety of retinal neurons.

Characterisation of dark adaptation in human cone pathways: an application of the equivalent background hypothesis.

It is well accepted that in rod photoreceptors the photoproducts generated by a bleach cause desensitisation during dark adaptation. We examine whether this notion holds for cones. A model of cone dark adaptation is developed based on the equivalent background concept. The underlying theory of the model relies on a series of assumptions that link psychophysically determined detection thresholds to cone phototransduction. Correction of thresholds for the reduced quantum-catching ability of the cones (due to the depletion of photopigment caused by a bleaching light) is an important aspect of the model. Foveal detection thresholds were measured for a small test flash presented on a large steady background field or presented alone after adapting to the background field. Test and background fields were monochromatic, with wavelengths closely matched to promote detection by the luminance mechanism. The model provided a good description of the data collected under these conditions. Parameters of the model were similar for all wavelengths and each observer, as were the derived equivalent background relationships. Analysis of previously published data for Stiles' pi5 mechanism gave analogous results. The model is made up of two components. The early (fast) component is likely to be due to the direct action of the cone equivalent of inactivated Rh* on the G-protein cascade and/or the reverse reaction of the cone equivalent of inactivated Rh* to Rh*. The later (slow) component may be due to the direct action of cone opsin on the G-protein cascade.

A new look at threshold estimation algorithms for automated static perimetry.

Automated perimetry is often associated with lengthy test times when a staircase algorithm is applied. This arises because the fixed step sizes used during threshold estimation (e.g.,4/2 dB) yield reduced test efficiency, with test times being dependent on the relative positioning of the start and endpoints, as well as the step size. Neighborhood logic may speed up the process, although several presentations are still required for normal threshold values and many more presentations are required for abnormal values. We consider whether there is any justification for using a fixed step size during the threshold procedure. We show how empirical data can be applied, within a Bayesian framework, to reduce test time with little or no loss of accuracy. Finally, we demonstrate the effect that the starting probability density function can have on test efficiency by implementing an empirically determined and bimodal probability density function that provides fast outcomes.

Reduced glutamate uptake by retinal glial cells under ischemic/hypoxic conditions.

The high-affinity uptake of glutamate by glial cells and neurons of the central nervous system, including the retina, serves to inactivate synaptically released glutamate and maintains glutamate at low concentrations in the extracellular space. This uptake prevents accumulation of glutamate extracellularly and thus minimizes the possibility of glutamate neurotoxicity secondary to ischemic insult. One mechanism whereby glutamate neurotoxicity may occur in ischemic/hypoxic insult is through increased extracellular K+ reversing the electrogenic glutamate uptake into retinal glial (Müller) cells. We investigated glial uptake of the amino acids glutamate, GABA, and D-aspartate in the intact isolated rat retina under high extracellular K+ conditions and under conditions simulating ischemia. Immunocytochemical findings showed that uptake of glutamate and GABA by MIller cells in the intact isolated rat retina continues under conditions simulating ischemia and high extracellular K+ conditions, and uptake of D-aspartate also continues under high K+ conditions. However, under high K+ conditions, the glutamate uptake system saturates at a lower concentration of exogenous glutamate than in the normal K+ condition. These findings provide evidence that disruption of glutamate uptake by Müller cells is likely to be a significant contributing factor to excess glutamate accumulation in the extracellular space which can lead to neurotoxicity.

Developing a clinical probability density function for automated perimetry.

BACKGROUND: Automated perimetry is associated with lengthy test times, but Baysean predictions can be applied to speed up testing. A critical component of such methods is the starting probability density function (PDF). METHODS/RESULTS: In the present study we show that a unimodal PDF, suggested n the literature as adequate for clinical data, fails to describe the thresholds of diseased eyes and we develop a bi-modal PDF representative of a clinical population. CONCLUSION: We suggest that the implementation of a bi-modal PDF will save test time and retain test accuracy.

Characteristics of anisometropic suppression: simple reaction time measurements.

The characteristics of artificially induced anisometropic suppression were investigated in observers with normal and abnormal binocular vision (anisometropic amblyopia) by using a simple reaction time paradigm. Reaction time was measured as a function of stimulus intensity for various stimulus durations. For all conditions, the reaction time increased as stimulus intensity decreased toward threshold. We found that traditional techniques for modeling this trend were inadequate, so we developed a simple visuogram method for comparing these functions. Using this technique, reaction time versus intensity functions are shown to be shape-invariant for all conditions examined. This means that, although reaction times are longer during induced anisometropic suppression or in anisometropic amblyopia, they are the same if contrast is normalized to equate threshold. The shape-invariant nature of these functions is also consistent with the notion that a single mechanism mediates detection under these conditions. Temporal summation was investigated at both threshold (method of limits) and suprathreshold (criterion reaction time) levels. Again, because of shape invariance, the suprathreshold results mirror the threshold results. The critical duration (the duration at the intersection of the complete summation and zero summation regions) is not affected by any of the conditions. However, the critical intensity (the intensity for the zero summation region) is higher for the amblyopic eyes, as compared with the normal or nonamblyopic eyes. Induced anisometropic suppression always increases the critical intensity, with a smaller increase occurring for the amblyopic eyes. This suggests that amblyopic eyes do not have a need for strong suppression.

L and M cone input into spectral sensitivity functions: a reanalysis.

In order to better understand the nature of long-wavelength (L) and middle-wavelength (M) cone input into spectral sensitivity functions and determine the reliability with which it is possible to predict L:M cone inputs, we developed analytical methods to determine confidence intervals for L:M cone input for spectral sensitivity functions or data transformed to cone-contrast space. Spectral sensitivity functions measured by direct heterochromatic brightness matches are dominated by the L/M opponent channel over most of the spectral range. For detection of large/ long test stimuli, spectral sensitivity functions show a characteristic "notch" at the adapting wavelength, with the L/M opponent channel dominating most of the spectral range. Flicker increment threshold (FIT) spectral sensitivity functions display many of the characteristics of the luminance flicker mechanism described by Stromeyer et al. (1987). [Vision Research, 27, 1113-1137]. Previous modelling of FIT spectral sensitivity functions proposed a 2:1 L:M cone input for most of testing conditions. We show that FIT spectral sensitivity functions are dominated by L cones but show L cone suppression under bright red adapting fields. For the fitted spectral sensitivity functions or simulated data sets, we found small confidence intervals for L:M cone input into the L/M opponent channel and conclude that it is possible to reliably predict L:M cone input ratios. However, for similar data sets of additive spectral sensitivity functions, we found large confidence intervals for L:M cone input ratios and conclude that it is not possible reliably predict L:M cone input into the L/M non-opponent channel using available spectral sensitivity functions.