Mariak Z

Intracranial pressure processing with artificial neural networks: prediction of ICP trends.

Summary¶ It is well known that intracranial pressure (ICP) is influenced by an array of predictable and unpredictable factors, which gives rise to a signal heavily loaded with stochastic, i.e. random components. Hence, statistical modelling of this signal has proved to be of limited utility, in spite of the very sophisticated mathematical methods applied. In recent years, neural network algorithms (ANN), which are an alternative to statistical methods, have proved their effectiveness in the prediction of trends, as applied in a variety of medical and non-medical tasks. We therefore attempted to test the efficiency of neural models in the on-line prediction of ICP values, compare their effectiveness to statistically oriented algorithms and combine ANN methods with some newer signal processing algorithms, like wavelet decomposition. Prediction horizons of up to 5 minutes have been tested with various architectures of the neural predictor. For a 3 minute prediction horizon, a satisfactory accuracy of forecasting has been achieved with “plain” ANN, as expressed by the “average relative variance coefficient”. This was measured by the ratio of the prediction error obtained, in relation to the error which would occur if a current value were taken as the forecasted one. The prediction quality with statistical autoregressive models has proved unsatisfactory, whilst the result obtained using the ANN model with the wavelet transform incorporated, performed significantly better than the ANN models alone. The prediction quality obtained with the ANN methodology seems to be satisfactory over a short time horizon, though no conclusion can be derived at this stage of the study, as to the clinical utility of this method. In particular, even with this methodology, it is not possible to forecast any sudden dehiscencies of the ICP signal with any practical reliability. From the point of view of modelling theory, such sharp deviations of the signal may be regarded as a “catastrophe”. This implies the necessity for a different approach to the ICP signal analysis with the artificial intelligence methodology; one, that is more oriented towards the global properties of the signal.

No Specific Brain Protection Against Thermal Stress in Fever

Summary Knowledge about human brain temperature is still very limited, despite evidence demonstrating the critical influence of mild increases in temperature on the ischaemic brain. It has been suggested that in passive and exercise hyperthermia the brain may be protected against thermal damage by a mechanism of selective brain cooling (SBC). It is said to bring about suppression of the temperature of the brain, rendering it significantly lower than trunk and arterial blood temperature. Yet very little is known about the possible role of this mechanism in fever, a condition fundamentally different from “physiological” hyperthermia, especially when it occurs in brain – damaged patients. In our investigation we retrospectively analysed the results of direct recordings of cerebral temperature within the subdural space (Tsd) and within the brain parenchyma (Tbr−16 cases) in 63 unanaesthetized patients following neurosurgical procedures, including 23 with fever >38 °C. The differences between trunk temperature, measured in the rectum (Tre) or in the oesophagus (Tes), and the intracranial temperature, were calculated in all subjects. A statistically significant reduction of these differences, in step with increasing fever, would be compatible with demonstrating a process of selective brain cooling. The offsets Tre−Tsd, Tre−Tbr, and Tes−Tsd were plotted against Tre over a wide range of body temperature and near zero correlation was found. This finding suggests that brain temperature in fever was not selectively suppressed by any specific thermolytic mechanism and that dissipation of the main bulk of cerebral metabolic heat both in normothermia and in fever depends on heat uptake by arterial blood. The results suggest that the brain in fever can be seriously jeopardized by heat stress and no specific cooling mechanism exists, to reduce it below body temperature in feverish neurosurgical patients. Tbr and/or Tsd remained the highest body temperature in 14 out of the 23 patients during fever.

Twinkling artifact in color Doppler imaging of the orbit.

Objective. To show an artifact related to color Doppler flow imaging of the orbit. Methods. Three patients with strongly reflective structures in the orbit were selected from those routinely referred by clinicians for color Doppler ultrasonography of the orbit. Gray scale and color flow images were obtained with a 7.5‐MHz linear array probe for a region with strongly reflective structures. A spectral display was acquired to confirm the presence of blood flow. Results. One patient had a metallic foreign body just behind the bulb; another had calcification within the irregular mass of phthisis bulbi; and the third had hyperechoic drusen in the periphery of the intraocular melanoma. The color mosaic, suggesting the presence of blood flow, was detected beyond all hyperechoic structures. Close vertical bands with no outer wrapping were detected in the spectrum display, obtained by placing the sample volume on the region of color flow. The artificial color flow was recognized as a color Doppler twinkling artifact. Conclusions. The color flow beyond the strongly reflecting structures in the orbit might be mistakenly interpreted as real blood flow if an examiner is not familiar with the artifact. It should prompt further imaging with spectral Doppler ultrasonography.

Intracranial Pressure Processing with Artificial Neural Networks: Classification of Signal Properties

Summary¶ Intracranial pressure (ICP) is commonly used by neurosurgeons as a source of valuable information about the current condition of the neurosurgical patient. Nevertheless, despite years of effort, extracting clinically valuable information from the ICP signal is still problematical. Approaches, using current values of ICP, may fail to disclose imminent risk, because unpredictable factors can rapidly change the properties of the signal. An alternative approach is to determine some global characteristics of the signal within a longer time interval and such statistical analyses have been proposed by several authors. A further, rarely considered, problem is assessment of the results obtained from the point of view of their practical utility and/or such classification of the obtained properties of the signal that they correspond to certain clinical states of the patient. While this might be a typical task for discriminant analysis, we approached the analysis using an alternative methodology, that of computational intelligence, implemented in artificial neural networks (ANN). We tested two variants of the ANN algorithms for classification and discrimination of global properties of the ICP signal. In a “dynamic pattern classification” the network was presented with several sections of ICP records together with information from the expert-neurosurgeon, classifying 4 risk groups. In this mode no data pre-processing was carried out, in contrast to our second approach, in which the signal had been pre-processed using published statistical analyses and only these intermediate coefficients were fed into the ANN classifier. The results obtained with both classification methods at their current stage of training were similar and approximated to a 70% rate of judgements consistent with the expert scoring. Nevertheless, the method based on the assessment of global parameters from the ICP record looks more promising, because it leaves the possibility for modification of the set of parameters analysed. The new parameters may include information extracted not only from the ICP signal, but also from other diagnostic modalities, like colour coded Doppler ultrasonography. The ultimate goal of this work is to build up a pseudo-intelligent computer expert system, which would be able to reason from a reduced set of input information, available from a standard monitoring modality, because it had been taught salient links between these data and higher-order data, upon which expert scoring was based.

Can optical coherence tomography replace fluorescein angiography in detection of ischemic diabetic maculopathy

BackgroundWe studied the association between (1) the retinal thickness, volume and structure assessed by optical coherence tomography (OCT), and (2) vascular changes around the fovea in FA to define the role of these methods in the detection of ischemic diabetic maculopathy.MethodsThis retrospective observational study included 51 eyes of 51 patients with severe non-proliferative and proliferative diabetic retinopathy, considering that they present advanced ischemic retinal changes. Based on the clinical examination and presence of leakage on FA, patients with clinically significant macular edema were excluded.On FA, foveal avascular zone (FAZ) corresponds to capillary loss and reflects ischemic processes. Its outline and size were assessed according to the ETDRS standards. Patients were divided in two groups according to the severity of damage of the FAZ outline: ≤ grade 2 (n = 28) and ≥ grade 3 (n = 23).As we expected ischemia-related damage, SD-OCT images were evaluated for retinal structure, volume, total thickness with division into the outer and inner retina (to assess the influence of two, non-overlapping blood sources) and ganglion cell layer thickness.ResultsThe comparisons revealed that at least currently with described methods:1. There is no significant association between FAZ outline and retinal volume, total thickness, and thickness of the outer and inner retina and ganglion cell layer.2. There is no significant association between FAZ outline and following retinal structure characteristics: continuity of the external limiting membrane and inner segment/outer segment junction, and identification of the inner/outer retina boundary.3. The identification of ganglion cell layer boundaries was significantly more difficult in more advanced FAZ outline grades.4. FAZ size is not correlated with the retinal thickness and volume.ConclusionsIn patients with severe non-proliferative and proliferative diabetic retinopathy, it is not possible to predict FAZ outline/size based solely on the measurements assessing volume and thickness or retinal structure evaluation on OCT. Consequently, at present OCT cannot replace FA in the detection of ischemic diabetic maculopathy.

Endoscopic trans-nasal approach for biopsy of orbital tumours using image-guided neuro-navigation system

SummaryBackground. Histopathological diagnosis of intraorbital tumours is of crucial value for planning further therapy. The aim of the study was to explore clinical utility of image-guided endoscopy for biopsy of orbital tumours. Method. Trans-nasal endoscopic biopsy of intraorbital mass lesions was performed in 6 patients using a neuro-navigation system (Medtronic Stealth Station Treon plus). The CT and MRI 1 mm slice images were fused by the system in order to visualise both bony and soft tissue structures. The anatomic fiducial registration protocol was used during the procedure. Results. All lesions were precisely localised and the biopsies could be taken from the representative part of the pathological mass. None of the patients developed aggravation of ocular symptoms after the procedure. The operative corridor as well as the size of orbital wall fenestration could be limited to a minimum. The accuracy of neuro-navigation remained high and stable during the entire procedure. Conclusions. The image-guided neuro-navigation system facilitated endoscopic localisation and biopsy of intraorbital tumours and contributed to the reduction of surgical trauma during the procedure. The technique was particularly useful in small, medially located, retrobulbar tumours and in unclear situations when the structure of the lesion resembled surrounding intraorbital tissue.

Evaluation of the Endothelial Cell Density and the Central Corneal Thickness in Pseudoexfoliation Syndrome and Pseudoexfoliation Glaucoma

Purpose. Evaluation of central corneal thickness (CCT) and endothelial cell density (ECD) in patients with senile cataract and coexisting pseudoexfoliation (PEX) syndrome with glaucoma (PEXG) and without glaucoma using specular microscopy. Participants and Methods. The study included 122 patients (217 eyes). In this group of patients we identified 133 eyes with PEX syndrome (65 with glaucoma, 68 without glaucoma) and 84 eyes without PEX syndrome. ECD and CCT were measured in each eye by specular microscopy. Results. ECD in eyes with PEX syndrome without glaucoma (2297 ± 359 cell/mm2) and in eyes with PEXG (2241 ± 363 cell/mm2) was lower than in the control group (2503 ± 262 cell/mm2) (P < 0.001). CCT in eyes with PEXG (508.2 ± 32.6 μm) was thinner than in eyes with PEX syndrome without glaucoma (529.7 ± 30.3 μm) and control group (527.7 ± 29.4 μm) (P < 0.001). Conclusions. This research shows that in eyes with PEX syndrome, both with and without glaucoma, ECD was statistically significantly lower than in the control group. In patients with PEXG, CCT was statistically significantly thinner than in the PEX syndrome and control group.

Ophthalmic manifestation of skull base metastasis from breast cancer

Summary Background There is a vast discrepancy between the incidence of skull base metastases reported in vivo and at autopsy. Asymptomatic character or unspecific symptoms make the diagnosis difficult, particularly in patients with no history of cancer. Our case illustrates a skull base metastasis from breast cancer, detected in a diagnostic process initiated by ophthalmologic examination. Case Report We report the case of a 53-year-old woman complaining of ptosis and diplopia, with concomitant loss of skin sensation within the right half of the forehead, and without any other worrisome symptoms or signs. Ophthalmic examination revealed impairment in eye movements, slight proptosis and corneal hypoesthesia on the right side, with normal pupillary light reflexes. The anterior and posterior segments of the eye were normal. Based on CT and MRI, an extensive tumor was detected, infiltrating the right orbit and the frontotemporal region of the skull base, and producing edema of the adjacent aspects of the brain. Aside from partial palsy of the oculomotor nerve and the ophthalmic division of the trigeminal nerve, no abnormalities were found on neurological examination. Explorative craniotomy and histopathological findings revealed a skull base metastasis from breast cancer. Conclusions Diplopia, ptosis, proptosis, and ophthalmic nerve sensory loss may be the only manifestation of a skull base metastasis. Careful ophthalmologic examination is crucial in early detection of this life-threatening condition.

Endoscopic Repair of CSF Leaks in the Postero-Superior Wall of the Frontal Sinus – Report of 2 Cases

BACKGROUND Bony defects extending laterally or superiorly within the posterior wall of the frontal sinus are generally deemed too difficult for endoscopic repair in spite of significant progress in surgical endoscopic techniques. PATIENTS AND METHODS We describe a technique of endoscopic repair of posttraumatic cerebrospinal fluid (CSF) leak from the postero-superior aspect of the frontal sinus in a 40- and a 29-year-old male. In both cases after careful assessment of the surgical anatomy the sinus was widely opened transnasally (Draf IIB and Draf III approach, respectively). Angled (45 and 70°) optics and malleable, individually profiled instruments were used to fit specific anatomic variations encountered during the procedure. RESULTS Endoscopic manipulation near the dome of the sinus proved to be very limited in spite of a wide surgical opening. In our cases the site of the leak could be identified and successfully sealed with gentle pressure on the dura mater. The bony defects were repaired with a 2-layer reconstruction technique. There were no signs of recurrence during 6 months follow-up. CONCLUSION With contemporary endoscopic instrumentation, endoscopic closure of CSF leaks in the supero-posterior wall of the frontal sinus is feasible, especially in patients with favourable anatomy of the frontal sinus.

LC-MS-Based Metabolic Fingerprinting of Aqueous Humor

Aqueous humor (AH) is a transparent fluid which fills the anterior and posterior chambers of the eye. It supplies nutrients and removes metabolic waste from avascular tissues in the eye. Proper homeostasis of AH is required to maintain adequate intraocular pressure as well as optical and refractive properties of the eye. Application of metabolomics to study human AH may improve knowledge about the molecular mechanisms of eye diseases. Until now, global analysis of metabolites in AH has been mainly performed using NMR. Among the analytical platforms used in metabolomics, LC-MS allows for the highest metabolome coverage. The aim of this study was to develop a method for extraction and analysis of AH metabolites by LC-QTOF-MS. Different protocols for AH preparation were tested. The best results were obtained when one volume of AH was mixed with one volume of methanol : ethanol (1 : 1). In the final method, 2 µL of extracted sample was analyzed by LC-QTOF-MS. The method allowed for reproducible measurement of over 1000 metabolic features. Almost 250 metabolites were identified in AH and assigned to 47 metabolic pathways. This method is suitable to study the potential role of amino acids, lipids, oxidative stress, or microbial metabolites in development of ocular diseases.