Patients with markedly decreased PBF (e.g., severe tetralogy of Fallot) tend to show numerous small and tortuous bronchial arterial collaterals in the upper medial lung zones near their origin from the descending aorta. The native pulmonary arteries are extremely small, although smooth and gracefully branching (seeB+;Si Fig. 12-3E).
In reality, an abnormal pulmonary vascularity is often a mixed type. There is a great variety of possible combinations-e.g., cephalization plus decreased flow in severe mitral stenosis (see B+;B; Fig. 12-3^4) or centralization with increased PBF in Eisenmenger's atrial septal defect (B-hB; Fig. 12-22).
Roentgen analysis of the pulmonary vasculature is accomplished in two steps. First, the volume of the pulmonary flow can be estimated by the degree of pulmonary arterial enlargement as long as the PBF pattern remains normal. Second, the distribution of the pulmonary flow is assessed by the presence of an abnormal flow pattern. The volume and the distribution of pulmonary blood flow may change singly or in combination de pending on the nature and severity of the underlying heart disease.
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