[Infratentorial ischemic stroke in children: Three case reports]. / Accidents vasculaires cérébraux de la fosse postérieure chez l'enfant : à propos de trois cas.

Ischemic stroke is rare in children, most of which occur in the supratentorial brain, and infratentorial infarcts are very rare. Some clinical manifestations may be similar but others such as ataxia and cranial nerve palsy are more specific. Vertebral artery dissection is the most frequent cause of stroke in the vertebrobasilar territory, but the cause most often remains unknown in children. We report three cases of infratentorial stroke in children. The first observation concerns a 4-year-old boy brought to medical attention because left hemicorporal motor deficit associated with ataxia following a minor cranial traumatism. While computed tomography (CT) of the brain was normal, magnetic resonance imaging (MRI) revealed an area of signal alteration on the diffusion-weighted image within the right protuberance. The second observation is a 15-year-old girl who developed sudden-onset ataxia. The CT scan and MRI of the brain revealed an acute bilateral cerebellar stroke. MRI angiography showed an anatomical variant of the left vertebral artery that did not participate in the Willis polygon. In these two observations, no other abnormalities were detected except they were homozygotous for MTHFR mutation in the first observation and minor alpha-thalassemia for the second one. The outcome in these two children was good without sequelae after a 6-month follow-up. The third observation is a 6-year-old girl who suddenly exhibited cephalalgia, ataxia, and left visual impairment. The brain MRI revealed left occipital and cerebellar strokes due to vertebral artery dissection. The authors recommend the systematic search for vertebral artery dissection in cases of infratentorial stroke.

An isocenter position verification device for electronic portal imaging: physical and dosimetrical characteristics.

The physical and dosimetrical characteristics of a device, designed to visualize the isocenter position on electronic portal images, were examined. The device, to be mounted on the gantry head of the accelerator, containing five spheric lead markers, was designed in order to visualize the isocenter position on portal images. A quality control device was designed to check the reliability of this technique. The disturbance of the dose distribution by the markers was studied with gel dosimetry. The use of markers resulted in a precise and accurate method to visualize the isocenter on portal images. A maximum underdosage of 11%, due to attenuation by the markers, was observed. The use of markers to visualize the isocenter position on portal images, is a fast and reliable method when analyzing patient setup errors with online electronic portal imaging.