Understanding dynamic state changes in temporal lobe epilepsy.

The authors review their work in applying nonlinear dynamics to predict onset of seizures in patients with medically refractory temporal lobe epilepsy. The underlying mathematical methodology is presented in some detail. To illustrate their approach, they present an extensive discussion of the analysis of preictal data from two seizures of one patient, and from one disease-free subject. They find similar behavior in some nonlinear measures across seizures, which suggests the possibility of forming a robust method of seizure prediction. However, despite clinical and electrographic preictal and ictal similarity, they have also found marked heterogeneity in other nonlinear measures of preictal activity across seizures arising out of stage 2 nonrapid eye movement sleep. The underlying basis for this variation remains uncertain and needs to be the subject of further intense study to gain a better understanding of the dynamic basis of epilepsy. The origin of these heterogeneities may or may not be related to the much larger differences in nonlinear measures between patients and disease-free subjects. To understand these differences, the authors think it is crucial to pay close attention to potentially confounding factors such as behavioral and other state changes, and to study and report in detail the ways in which relevant nonlinear measures behave in the presence of such changes, independent of seizure onset.

Nonstationarity in epileptic EEG and implications for neural dynamics.

In this paper, we use a recently developed method to analyze the nonstationarity in time series from intracranial depth and subdural recordings of patients with temporal lobe epilepsy. We show that the nonstationarity in the signal can be accounted for by the variation of a single parameter. We then show that the various dominant nonlinear waveforms observed in different electrodes can be explained by a simple stochastic model in which the mesoscopic collection of neurons, whose potential the electrodes measure, can be on one of two states. The nonstationarity observed in our analysis is a consequence of a time-dependent transition probability between these two states. In general, this transition probability increases as a seizure is approached. The model that we propose incorporates this bistability. We find good agreement between real data and simulated data generated by our model. We understand that this mesoscopic bistability may be associated with the existence of excitation waves traversing the brain in these patients.

Non-linearity in invasive EEG recordings from patients with temporal lobe epilepsy.

Electrographic recordings from depth and subdural electrodes, performed in two patients with seizures of mesial temporal origin, were analyzed for the presence of non-linearities in the signal. The correlation integral, a measure sensitive to a wide variety of non-linearities, was used for detection. Statistical significance was determined by comparison of the original signal to surrogate datasets. Statistically significant non-linearities were present in signals generated by the epileptogenic hippocampus and interictal spike foci in the temporal neocortex. Less prominent non-linearities were found in EEG signals generated by more normal areas of the brain. These results indicate that techniques developed for the study of non-linear systems can be used to characterize the epileptogenic regions of the brain during the interictal period and can elucidate the dynamical mechanisms of the epileptic transition.

Contracted gallbladder: a cause of false-positive hepatobiliary scan in patients with cystic fibrosis.

Gallbladder nonvisualization on hepatobiliary scintigraphy in cystic fibrosis is generally secondary to cystic duct obstruction from inspissated bile, mucus, or gallstones. We report gallbladder nonvisualization on hepatobiliary imaging in two patients with cystic fibrosis who had contracted gallbladders on ultrasonography. Repeat ultrasonography at 6 months revealed persistent gallbladder contraction. A contracted gallbladder therefore is a potential cause of a false-positive hepatobiliary scan which can be treated with conservative management.

Adenocarcinoma of the ovary with fat-fluid level: CT appearance.

A fat-fluid level on CT is reported for biopsy proven undifferentiated adenocarcinoma of the ovary. This uncommon radiographic finding has been described in association with germ cell tumors of the ovary, such as cystic teratomas and immature teratomas, but not in other ovarian histologies. The finding of a fat-fluid level on CT is, therefore, suggestive but not exclusive to cystic teratomas.

Tufted angioma of the thigh.

Tufted angioma or angioblastoma of Nakagawa is a rare vascular tumor that usually appears in early childhood. It frequently is seen as an erythematous to red-brown, frequently indurated plaque that usually occurs on the trunk or neck. Typically tufted angiomas enlarge for a few years and then cease growing and remain stable. Histopathologic findings are pathognomonic. We describe a patient with a tufted angioma of the thigh who sought treatment for paroxysmal episodes of pain. Treatment with topical clobetasol propionate resulted in a decreased frequency of painful episodes.

Time dependencies in the occurrences of epileptic seizures.

A new method of analysis, developed within the framework of nonlinear dynamics, is applied to patient recorded time series of the occurrence of epileptic seizures. These data exhibit broad band spectra and generally have no obvious structure. The goal is to detect hidden internal dependencies in the data without making any restrictive assumptions, such as linearity, about the structure of the underlying system. The basis of our approach is a conditional probabilistic analysis in a phase space reconstructed from the original data. The data, recorded from patients with intractable epilepsy over a period of 1-3 years, consist of the times of occurrences of hundreds of partial complex seizures. Although the epileptic events appear to occur independently, we show that the epileptic process is not consistent with the rules of a homogeneous Poisson process or generally with a random (IID) process. More specifically, our analysis reveals dependencies of the occurrence of seizures on the occurrence of preceding seizures. These dependencies can be detected in the interseizure interval data sets as well as in the rate of seizures per time period. We modeled patient's inaccuracy in recording seizure events by the addition of uniform white noise and found that the detected dependencies are persistent after addition of noise with standard deviation as great as 1/3 of the standard deviation of the original data set. A linear autoregressive analysis fails to capture these dependencies or produces spurious ones in most of the cases.

"Upside-down" contrast-urine level in glycosuria: CT features.

Contrast-urine levels are often encountered in CT of the urinary bladder. Opacified urine occupies the dependent portion of the bladder, while unopacified urine layers above it. We report a case in which this relationship was reversed. An explanation of this phenomenon is proposed.