Spontaneous dissection of the anterior inferior cerebellar artery.

A patient presented with the clinical features of a brain stem infarct. MRI confirmed changes of infarction but also revealed an unusual lesion in the left cerebellopontine angle cistern. The evolution of this lesion on MRI, together with angiographic changes, indicated a dissecting aneurysm of the left anterior inferior cerebellar artery, a previously unreported phenomenon. The presentation, causes and diagnosis of intracranial dissection are discussed.

Accuracy of colonoscopy in localisation of colorectal cancer.

An audit was performed of 77 patients with a single colorectal cancer visualised and sited before surgery by colonoscopic examination. The site of the cancer described at colonoscopy was compared with the actual site found at laparotomy. Six significant errors in preoperative localisation were encountered, when a change from the preoperatively planned resection to an alternative resection was found necessary. In two of these cases, extra morbidity was encountered as a result of these siting errors. Inaccurate localisation is a potential hazard of colonoscopy, especially when the examination is incomplete.

Light propagation through a moving gas.

A light beam sufficiently intense to appreciably heat a gas it traverses will be deflected on account of the heat-induced gradients in the index of refraction. We compute these effects (bending into the wind, and self-defocusing due to nonuniformities in the beam) for a nonzero wind velocity in the framework of geometrical optics. For each of the initial intensity distributions considered, a bending into the wind occurs, with accumulation of intensity in those regions in which the intensity gradient is negative. The beam becomes very sharp at a definite range, resulting in sharp bending and much detailed structure there; beyond, bending gives way to near-rectilinear propagation with uniform continuing beam spread.