Quantitative analysis of cerebral vessels in the newborn puppy: the structure of germinal matrix vessels may predispose to hemorrhage.
Intracerebral hemorrhage in premature infants commonly originates in the germinal matrix (GM). We performed a quantitative analysis of cerebral microvasculature from newborn puppies, a model for neonatal periventricular and intraventricular hemorrhage, at the light and electron microscopic level. GM vessels were compared with those of other brain regions in an effort to delineate pathogenetically significant structural features that might predispose to hemorrhage. Light microscopic examination revealed that GM vessel density (103.0 vessels/mm2) was similar to that in white matter (98.3 vessels/mm2), but lower than that of cortex (155.6 vessels/mm2) or caudate (259.9 vessels/mm2). Mean blood vessel diameter was slightly larger in GM (9.0 mu) than cortex (6.9 mu), caudate (7.9 mu), and white matter (8.9 mu). Ultrastructurally, GM vessels were thinner along greater portions of their circumferences than vessels from other brain regions, as shown by their smaller ratio of vessel wall area/vessel lumen area and their greater fraction of vessel wall with thickness less than 0.25 mu. In addition, a significantly larger fraction of GM capillary wall lacked direct contact with perivascular structures. We postulate that the larger size, thinner walls, and diminished support from surrounding neuropil, which characterize GM vessels, may render them more susceptible to both physical (e.g. hypertension) and metabolic (e.g. hypoxia) insults than vessels from other brain regions.