What is a classical sign of congestive heart failure on a radiograph?

A classical sign of congestive heart failure on a radiograph is the presence of Kerley B lines. These lines are indicative of interstitial edema due to increased pulmonary venous pressure, which occurs in heart failure. Kerley B lines appear as thin, horizontal lines at the periphery of the lungs, commonly seen in the lower lobes, and they result from the expansion of interlobular septa due to fluid accumulation.

In congestive heart failure, the heart's inability to effectively pump blood leads to fluid overload, which can manifest as pulmonary congestion on imaging. The identification of Kerley B lines is therefore critical in diagnosing heart failure and assessing its severity.

While cardiomegaly, interlobar pulmonary edema, and pleural effusion can also be associated with congestive heart failure, Kerley B lines are specifically regarded as a classical radiographic feature that highlights the interstitial fluid overload characteristic of this condition.