Air embolism may cause unrecognized ischemia of the gray-white junction

The border between the gray and white matter is defined by an abrupt change in average blood flow. This difference allows one to distinguish structure with [14C]iodoantipyrine autoradiography. The angioarchitecture of the cortical gray-white junction suggests that an air embolism might preferentially lodge in this border zone, and thus ischemia of the border might go unrecognized if one depended only on the difference in average blood flow to define the gray-white junction. Accordingly, a computerized image processing technique was applied to compare the area of the cortex measured on an autoradiogram to the area measured on a histologic section after staining for myelin. In dogs that had received air embolism, the autoradiogram underestimated the thickness of the cortical mantle even in sections that did not seem to have an obvious focal zone of low blood flow. This suggests that the deep cortical layers are especially vulnerable to air embolism.