Dural infiltration of metastatic Hodgkin's lymphoma.

Hodgkin's disease is a neoplasm of clonal Reed-Sternberg cells. Intracranial Hodgkin's lymphoma is rare. We present a unique case of a 57-year-old woman with secondary intracranial lymphoma infiltrating the dura. Her past medical history included Hodgkin's lymphoma from which she was deemed to be in remission at the time of presentation. Following an acute onset of seizures, she underwent radiological investigations that demonstrated an enhancing right-sided temporal dural-based space occupying lesion. Histopathological findings revealed nodular sclerosing Hodgkin's lymphoma with pathognomonic Reed-Sternberg cells. In cases of intracranial lesions with dural infiltration, Hodgkin's lymphoma should be considered in the diagnosis.

A colorectal cancer patient focus group develops an information package.

INTRODUCTION: In order to deliver high quality care and empower cancer patients in decision-making, good quality information and communication are essential. We describe the development of an information booklet. PATIENTS AND METHODS: A total of 22 colorectal cancer patients (12 male; median age, 72 years, range, 40-86 years) met on 3 occasions. Patients were asked to define their information needs and score them (1-4) according to importance. The information document was written. The second meeting involved feedback on the booklet. The modified booklet was reviewed/approved by the group before submission for local ethics committee approval prior to its distribution to other patients. RESULTS: All participants felt the project a good idea. Essential information included the surgeon's individual morbidity, mortality, survival, recurrence data and details of adjuvant therapies (score = 4). Also important were type of surgery, complications and postoperative recovery (score = 3). Simple anatomical drawings were also considered important. CONCLUSIONS: The booklet is now used to personalise information for all our patients and serves, in part, as a record of the key issues discussed during the consultation. The booklet has been evaluated in a randomised trial.

Jass staging is a predictor of outcome following "curative" resection of Dukes' B colorectal carcinoma.

BACKGROUND AND AIMS: We have sought to determine if the addition of the Jass pathological classification to Dukes' staging would provide improved prognostic information for patients undergoing curative surgery for Dukes' B colorectal carcinoma. PATIENTS AND METHODS: One hundred and eighty three patients who underwent curative surgery for Dukes' B colorectal cancers between December 1988 and January 1998 were identified. An assessment of Jass scoring was made at the time of initial histological staging. All patients entered a comprehensive follow-up system. RESULTS: Jass grouping was found to correlate significantly with cancer specific mortality rates; group III having a worse prognosis than groups I and II (p<0.005). There was no significant difference between either local recurrence or systemic recurrence and the Jass group. CONCLUSION: The Jass classification provides additional prognostic information in patients following curative resection of Dukes' B colorectal carcinoma and may therefore facilitate the selection of patients who will benefit most from adjuvant treatment

Management of recurrent anastomotic stricture and iatrogenic stenosis by circular stapler.

Anastomotic stricture is an increasingly common clinical finding. It is thought to arise because of ischemia, disruption, or leakage at an anastomosis site. Its management can be difficult and strictures often are resistant to standard dilation therapy. Major corrective surgery is possible; however, it is technically challenging and not without risk. We have used a circular stapler to excise colorectal strictures, introducing the anvil of the stapler via a proximal stoma or colotomy, drawing the anvil through the stricture with a snare via a colonoscope and affixing it to the body of a circular staple gun and excising the stricture. We have with found this to be an effective treatment in appropriately selected patients.

Laparoscopic inguinal hernia repair: a NICE operation.

Published evidence comparing laparoscopic and open herniorraphy is controversial. NICE recommends that open techniques are used for first time repairs and that TEP be considered for bilateral/recurrent repairs undertaken in specialist units. We report a consecutive series of 224 patients undergoing 268 TEP repairs between 1996 and 2001. Operating time, complications, return to normal activity/full time employment and recurrence were examined. The median operating time was 30 minutes. There was one conversion. Ninety four percent of patients drove on the third post-operative day. The median time to normal activity was 4 days (1-10 days). The median time to return to professional employment in 82 patients was 3 days (range 2-9 days). Four patients (1.7%) had self-limiting minor groin pain. There were 3 recurrences (1.4%) and none since altering the surgical technique to use a larger anchored mesh. We have demonstrated TEP to be an easily learnt, safe, effective technique with low morbidity, and with sufficient experience, takes no longer than an open repair. It can be performed at little increased cost and restores selected patients to an early return to full-time employment. We believe that the choice between open and laparoscopic repair is a subjective decision for patient and surgeon

Rate and timing cues associated with the cochlear amplifier: level discrimination based on monaural cross-frequency coincidence detection.

The perceptual significance of the cochlear amplifier was evaluated by predicting level-discrimination performance based on stochastic auditory-nerve (AN) activity. Performance was calculated for three models of processing: the optimal all-information processor (based on discharge times), the optimal rate-place processor (based on discharge counts), and a monaural coincidence-based processor that uses a non-optimal combination of rate and temporal information. An analytical AN model included compressive magnitude and level-dependent-phase responses associated with the cochlear amplifier, and high-, medium-, and low-spontaneous-rate (SR) fibers with characteristic frequencies (CFs) spanning the AN population. The relative contributions of nonlinear magnitude and nonlinear phase responses to level encoding were compared by using four versions of the model, which included and excluded the nonlinear gain and phase responses in all possible combinations. Nonlinear basilar-membrane (BM) phase responses are robustly encoded in near-CF AN fibers at low frequencies. Strongly compressive BM responses at high frequencies near CF interact with the high thresholds of low-SR AN fibers to produce large dynamic ranges. Coincidence performance based on a narrow range of AN CFs was robust across a wide dynamic range at both low and high frequencies, and matched human performance levels. Coincidence performance based on all CFs demonstrated the "near-miss" to Weber's law at low frequencies and the high-frequency "mid-level bump." Monaural coincidence detection is a physiologically realistic mechanism that is extremely general in that it can utilize AN information (average-rate, synchrony, and nonlinear-phase cues) from all SR groups.

Evaluating auditory performance limits: i. one-parameter discrimination using a computational model for the auditory nerve.

A method for calculating psychophysical performance limits based on stochastic neural responses is introduced and compared to previous analytical methods for evaluating auditory discrimination of tone frequency and level. The method uses signal detection theory and a computational model for a population of auditory nerve (AN) fiber responses. The use of computational models allows predictions to be made over a wider parameter range and with more complete descriptions of AN responses than in analytical models. Performance based on AN discharge times (all-information) is compared to performance based only on discharge counts (rate-place). After the method is verified over the range of parameters for which previous analytical models are applicable, the parameter space is then extended. For example, a computational model of AN activity that extends to high frequencies is used to explore the common belief that rate-place information is responsible for frequency encoding at high frequencies due to the rolloff in AN phase locking above 2 kHz. This rolloff is thought to eliminate temporal information at high frequencies. Contrary to this belief, results of this analysis show that rate-place predictions for frequency discrimination are inconsistent with human performance in the dependence on frequency for high frequencies and that there is significant temporal information in the AN up to at least 10 kHz. In fact, the all-information predictions match the functional dependence of human performance on frequency, although optimal performance is much better than human performance. The use of computational AN models in this study provides new constraints on hypotheses of neural encoding of frequency in the auditory system; however, the method is limited to simple tasks with deterministic stimuli. A companion article in this issue ("Evaluating Auditory Performance Limits: II") describes an extension of this approach to more complex tasks that include random variation of one parameter, for example, random-level variation, which is often used in psychophysics to test neural encoding hypotheses.

Evaluating auditory performance limits: II. One-parameter discrimination with random-level variation.

Previous studies have combined analytical models of stochastic neural responses with signal detection theory (SDT) to predict psychophysical performance limits; however, these studies have typically been limited to simple models and simple psychophysical tasks. A companion article in this issue ("Evaluating Auditory Performance Limits: I") describes an extension of the SDT approach to allow the use of computational models that provide more accurate descriptions of neural responses. This article describes an extension to more complex psychophysical tasks. A general method is presented for evaluating psychophysical performance limits for discrimination tasks in which one stimulus parameter is randomly varied. Psychophysical experiments often randomly vary a single parameter in order to restrict the cues that are available to the subject. The method is demonstrated for the auditory task of random-level frequency discrimination using a computational auditory nerve (AN) model. Performance limits based on AN discharge times (all-information) are compared to performance limits based only on discharge counts (rate place). Both decision models are successful in predicting that random-level variation has no effect on performance in quiet, which is the typical result in psychophysical tasks with random-level variation. The distribution of information across the AN population provides insight into how different types of AN information can be used to avoid the influence of random-level variation. The rate-place model relies on comparisons between fibers above and below the tone frequency (i.e., the population response), while the all-information model does not require such across-fiber comparisons. Frequency discrimination with random-level variation in the presence of high-frequency noise is also simulated. No effect is predicted for all-information, consistent with the small effect in human performance; however, a large effect is predicted for rate-place in noise with random-level variation.

Studies of binaural detection in the rabbit (Oryctolagus cuniculus) with Pavlovian conditioning.

A Pavlovian conditioned eyeblink response in rabbits (Oryctolagus cuniculus) was used to study psychoacoustical phenomena previously demonstrated in human listeners and other animals. This article contains the results of a tone-in-noise detection study to examine 2 psychoacoustical phenomena in rabbit and in human listeners: (a) the binaural masking level difference (BMLD) and (b) differential performance across reproducible noise masker waveforms. The rabbits demonstrated a BMLD comparable in size to other species. Significant differences in performance across reproducible noise masker waveforms were seen in the rabbits. This performance was compared with the performance of human listeners using the same set of waveforms.

A phenomenological model for the responses of auditory-nerve fibers: I. Nonlinear tuning with compression and suppression.

A phenomenological model was developed to describe responses of high-spontaneous-rate auditory-nerve (AN) fibers, including several nonlinear response properties. Level-dependent gain (compression), bandwidth, and phase properties were implemented with a control path that varied the gain and bandwidth of tuning in the signal-path filter. By making the bandwidth of the control path broad with respect to the signal path, the wide frequency range of two-tone suppression was included. By making the control-path filter level dependent and tuned to a frequency slightly higher than the signal-path filter, other properties of two-tone suppression were also included. These properties included the asymmetrical growth of suppression above and below the characteristic frequency and the frequency offset of the suppression tuning curve with respect to the excitatory tuning curve. The implementation of this model represents a relatively simple phenomenological description of a single mechanism that underlies several important nonlinear response properties of AN fibers. The model provides a tool for studying the roles of these nonlinearities in the encoding of simple and complex sounds in the responses of populations of AN fibers.

Evidence for two distinct mechanisms of neurogenesis and cellular pattern formation in regenerated goldfish retinas.

After its destruction by intraocular injection of ouabain, the goldfish retina regenerates, but little is known about the histogenesis of the new tissue, including the structure and formation of regenerated cell mosaic patterns. In an effort to determine how retinal cells are generated and spatially organized within retina regenerated after ouabain injection, in situ hybridization and immunocytochemical techniques were combined with computational analyses of two-dimensional spatial patterns of identified neurons. Labeling with specific opsin riboprobes revealed two distinct cone patterns in the ouabain-injected eyes, each of which was different from the relatively orderly cone patterns of native retina. Central, regenerated regions had sparse aggregates of cones, and a relatively lower density of each cone type. Peripheral regions of experimental retina, likely derived from the circumferential germinal zone, had high densities of all cone types, each of which tended to be distributed randomly. The spatial patterns of inner retinal neurons in experimental eyes were also disorganized with respect to native retina. These results indicate that although some aspects of retinal regeneration resemble normal retinal development and growth, ouabain-induced regeneration does not produce well-organized mosaics of neurons, indicating a failure of the developmental interactions needed for proper pattern formation, which in turn could compromise visual recovery. Furthermore, the distinct cone patterns in different regions of experimental retina support the hypothesis that new goldfish retina arises via two spatially and cellularly distinct mechanisms after exposure to ouabain.

Flexure of thin rigid contact lenses.

The flexure of spherical rigid contact lenses was measured on the eyes of 10 young subjects using a videokeratoscope. Five subjects had little or no with-the-rule astigmatism (<0.75 D) andfive had moderate levels of with-the-rule astigmatism (1.00-2.00 D). Two lens materials (polymethylmethacrylate [PMMA] and Boston XO) in three centre thicknesses (0.05, 0.10 and 0.15 mm) were used in the study. No significant difference in the amount of flexure was found between the two materials tested. The degree of regular astigmatism on the lens front surface was found to increase as the centre thickness of the contact lens decreased. For the astigmatic group, the lenses with centre thicknesses of 0.05 mm had levels of front surface astigmatism similar to those of the underlying cornea. On spherical corneas the level of regular astigmatism can exceed that of the cornea for thinner lenses. When sphero-cylinder variations are accounted for, residual higher order aberration (root mean square) levels were found to approach those of the cornea when the lens thickness was reduced to 0.05 mm.

The accuracy and precision performance of four videokeratoscopes in measuring test surfaces.

In this study we evaluated the accuracy and precision of three placido-disk videokeratoscopes (the Keratron, Medmont and TMS) and one videokeratoscope that uses the raster-stereogrammetry technique (PAR-CTS) in elevation topography with six test surfaces. The test surfaces were a sphere, an asphere, a multicurve, and three bicurve surfaces. Each instrument performed well on certain test surfaces, but none of the instruments excelled on all of the surfaces. The results showed high accuracy of the Keratron and Medmont instruments in measuring the sphere, asphere, and multicurve surfaces, but not the bicurve surfaces. The precision of the Keratron and Medmont instruments were high. The TMS and PAR-CTS instruments showed poorer accuracy than the Keratron and Medmont instruments for the multicurve test surface but showed better performance for the bicurve surfaces. The PAR-CTS had the poorest performance in precision of the four instruments. The use of the Noryl spherical test surface instead of polymethyl methacrylate (PMMA) resulted in small differences in the accuracy performance of the placido-disk videokeratoscopes only.

Cell mosaic patterns in the native and regenerated inner retina of zebrafish: implications for retinal assembly.

In part because of its laminar organization and morphologically distinct cell populations, the vertebrate retina has often been used as a system for investigating the assembly of neural structures. The retinas of adult teleost fish, because they grow throughout life and can regenerate following an injury, provide an especially attractive model system for such investigations. In an effort to provide a quantitative foundation for testing hypotheses regarding the mechanisms of pattern formation during growth and regeneration of the vertebrate retina, nearest neighbor and auto-correlation analyses were used to examine the mosaic patterns of eight inner retinal cell groups in the native and regenerated retina of adult zebrafish. In both native and regenerated retina, the mosaic patterns of most inner retinal cells are non-random. However, regenerated mosaics tend toward significantly lower nearest neighbor distances, less orderly patterns, and more variable radial locations than their native retina counterparts. The individual cell groups in both native and regenerated inner retina are likely to be spatially distributed independently. The results support the hypotheses that, in the adult zebrafish: 1) distinct inner retinal cell groups of native retina are also present in regenerated retina; 2) the assembly of inner retinal cell mosaics is controlled by non-random spatial organizing mechanisms during development, growth, and regeneration; and 3) the spatial organization of cell mosaics is disrupted during regeneration. The results suggest that retinal regeneration may represent a spatially disrupted recapitulation of retinal developmental mechanisms.

Temporal response properties of neurons in the auditory pathway.

A number of laboratories have recently refined descriptions of temporal response properties, from the auditory periphery to the midbrain. At many levels of the auditory pathway, the role of inhibition in temporal coding of complex sounds is being explored. In addition, quantitative relationships between physiology and psychophysics are being investigated.

Frequency glides in the impulse responses of auditory-nerve fibers.

Previous reports of frequency modulations, or glides, in the impulse responses of the auditory periphery have been limited to analyses of basilar-membrane measurements and responses of auditory-nerve (AN) fibers with best frequencies (BFs) greater than 1.7 kHz. These glides increased in frequency as a function of time. In this study, the instantaneous frequency as a function of time was measured for impulse responses of AN fibers in the cat with a range of BFs (250-4500 Hz). Impulse responses were estimated from responses to wideband noise using the reverse-correlation technique. The impulse responses had increasing frequency glides for fibers with BFs greater than 1500 Hz, nearly constant frequency as a function of time of BFs between 750 and 1500 Hz, and decreasing frequency glides for BFs below 750 Hz. Over the levels tested, the glides for fibers at all BFs were nearly independent of stimulus level, consistent with previous reports of impulse responses of the basilar membrane and AN fibers. Implications of the different glide directions observed for different BFs are discussed, specifically in relation to models for the auditory periphery as well as for the derivation of impulse responses for the human auditory periphery based on psychophysical measurements.

Masking of irregular corneal topography with contact lenses.

PURPOSE: We examined the effectiveness of various types of contact lenses in masking irregular corneal topography using videokeratoscopy, residual aberrations, and measurement of visual acuity. METHODS: Thirteen subjects with differing degrees of keratoconus were recruited. Four types of soft lenses were used that varied in both thickness and water content, along with a rigid gas permeable (RGP) and a flexible gas permeable contact lens. RESULTS: RGP contact lenses provided the best visual acuity and the least residual aberrations. Flexible gas permeable lenses showed a reasonable masking of corneal distortion but did not provide the expected improvement in visual acuity. Soft contact lenses provided marginally better visual acuity than spectacle correction, but the level of residual aberrations was still high, even for relatively thick soft lenses (up to 0.2 mm). A significant correlation existed between the regularity of the front surface of the contact lenses on the eye and visual acuity in low illumination. CONCLUSIONS: Among the currently available contact lens materials, RGP lenses provide the best visual performance for subjects with keratoconus.