Focal cortical dysplasia and hemimegalencephaly: histological and neuroimaging correlations

BACKGROUND: The classification of cerebral cortical dysplasia is difficult and there are histological similarities between focal cortical dysplasia (FCD) and hemimegalencephaly. Objectives. To correlate the MR features and histological data of cortical dysplasias. MATERIALS AND METHODS: The MR appearances of 17 brains were examined. According to the signal intensity within the pathological area on T2-weighted (T2-W) sequences we selected two groups. RESULTS: Group 1 comprised ten patients with high signal in the dysplastic area on T2-W images. This group included five hemimegalencephalies, three frontal quadramegalencephalies, and one gyral dysplasia. The pathological hemisphere was reduced in size in one case. The cortex was thickened in all cases on T1-weighted (T1-W) images. There was loss of delineation between white matter (WM) and grey matter (GM) in all cases on both T1-W and T2-W sequences. The differential diagnosis with tumour, neoplastic-like malformation or polymicrogyria was questionable. Group 2 comprised seven patients presenting without increased signal within the dysplastic area on T2-W images. WM and GM were of similar signal intensity in six cases, and delineation between white and grey matter was absent in all cases. There were mild abnormalities on T1-W sequences in all cases. The dysplasias were limited to a lobe in five cases and a gyrus in two cases. In all cases, depiction of the malformation was a greater diagnostic problem than the differential diagnosis. CONCLUSIONS: A constant MR sign in our series was the loss of delineation between WM and GM in the dysplastic area. This correlated well with the observed histological disorganisation. Markedly high signal within the dysplastic area seems to be related to myelin abnormalities rather than glial cell abnormalities.     

Primitive cerebral neuroectodermal tumors excluding medulloblastomas: a retrospective study of 30 cases

We present a retrospective study of 30 cases of primitive cerebral neuroectodermal tumors (PNET), excluding medulloblastomas, referred to us postoperatively for additional therapy to evaluate prognostic factors and treatment efficiency. The histologic types were: pinealoblastomas (n = 7); ependymoblastomas (n = 2); medulloepitheliomas (n = 4), and other PNET (n = 17). The tumor was located in the supratentorial area in 24 patients and in the posterior fossa in 6 patients. Among the supratentorial tumors, 8 were metastatic. Maximal surgical resection was performed. Sixteen of 30 patients had no measurable disease after surgery and were considered as standard-risk (SR) cases, and 14 with a local residue or metastasis as high-risk (HR) cases. The objective of postsurgical treatment was to avoid radiotherapy in children below 4 years of age. It consisted of radiotherapy alone in 6 patients, chemotherapy alone in 17, and radiotherapy with chemotherapy in 7. Furthermore, high-dose chemotherapy (busulfan, thiotepa) and autologous bone marrow transplantation, performed in 6 patients, yielded a response rate of 3/6. Event-free survival (EFS) of SR patients was 37% at 3 years (95% confidence interval (CI) 14-60%) and overall survival 44% (95% CI 26-62%). Only 1 of the HR patients achieved a complete remission and all of them died early. The critical prognostic factors appear to be the completeness of initial surgical resection and absence of metastasis. These tumors have a poor prognosis. Novel strategies (high-dose chemotherapy) are needed to improve their outcome because the children concerned are very young and the effects of radiotherapy are particularly deleterious when tumors are situated in the supratentorial area.     

Une étude ethnomathématique au Burkina Faso: L'arithmétique au quotidien

Abstract

This study is based on the observation of a divide between mathematics taught in school and the social and cultural context in which they apply. These mathematics, which present significant difficulties for students, appear to be far-removed from the needs and concerns of society. However, many social practices require daily recourse to mathematical concepts. To better understand how these concepts—the nature of which is not fully understood in schools—are used in context, an ethnographic study was carried out to examine various practices of daily life. Here we address practices involving the sale and purchase of agricultural products.     

Spalling and pore pressure in HPC at high temperatures

High-performance concrete (HPC) are subject to spalling under certain thermal and mechanical conditions. Spalling results mainly from two processes: a “thermo-mechanical” process in which the stress originates in the gradients of thermal deformation within the material, and a thermo-hydral process where spalling is due to the build-up of gas pressure fields in the porous network. This paper deals with the thermo-hydral process. An original device was designed in order to make simultaneous measurements of pressure and temperature at various positions in a concrete specimen (30×30×12 cm³) heated on one face up to 800°C. The specimen was also continuously weighed during the tests, thus, the mass loss, resulting mainly from water transport and loss, was recorded. This campaign was carried out on an ordinary concrete (OC) and a HPC (90 MPa). As expected, the pressure peaks were much higher than in HPC (40 bars) than in OC (20 bars). In HPC, these pressures exceeded the saturated vapor pressure. It is demonstrated that the thermal expansion of liquid water and the transport of water towards the inner part of the specimen play a significant role on the build-up of gas pressure. The experimental correlation between the pressure peaks and the plateau in the temperature curves confirmed the hypothesis that the drying front is preceded by a quasi-saturated layer that acts as a moisture clog.     

Regularization in tomographic reconstruction using thresholding estimators

In tomographic medical devices such as single photon emission computed tomography or positron emission tomography cameras, image reconstruction is an unstable inverse problem, due to the presence of additive noise. A new family of regularization methods for reconstruction, based on a thresholding procedure in wavelet and wavelet packet (WP) decompositions, is studied. This approach is based on the fact that the decompositions provide a near-diagonalization of the inverse Radon transform and of prior information in medical images. A WP decomposition is adaptively chosen for the specific image to be restored. Corresponding algorithms have been developed for both two-dimensional and full three-dimensional reconstruction. These procedures are fast, noniterative, and flexible. Numerical results suggest that they outperform filtered back-projection and iterative procedures such as ordered-subset-expectation-maximization.