Pathophysiology.—Oligemia is a reduction in pulmonary blood volume. Most frequently, this reduction is regional, but occasionally it is generalized. Regional oligemia is usually associated with reduced blood flow in the oligemic area.
Radiographs and CT scans.—Oligemia appears as a regional or widespread decrease in the size and number of identifiable pulmonary vessels (Fig 44), which is indicative of less than normal blood flow. (See also mosaic attenuation pattern, pulmonary blood flow redistribution.) [Fleischner Society]