Kerley-B lines are seen when pulmonary venous pressure is:
**Core Concept**
Kerley-B lines are interstitial edema lines seen on chest radiographs, indicating increased hydrostatic pressure in the pulmonary interstitium. They are a sign of pulmonary venous hypertension, which can be due to various conditions such as left-sided heart failure or mitral valve disease.
**Why the Correct Answer is Right**
Kerley-B lines are short, horizontal lines at the lung periphery, representing fluid accumulation in the interstitial spaces. They are caused by increased hydrostatic pressure in the pulmonary veins, which leads to fluid leakage into the interstitial tissue. This is due to the increased pressure exerted on the pulmonary capillaries, causing them to rupture and release fluid into the surrounding tissue.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Kerley-B lines are not a sign of primary pulmonary hypertension. While pulmonary hypertension can cause interstitial edema, Kerley-B lines are specifically associated with increased pulmonary venous pressure.
**Option B:** This option is incorrect because Kerley-A lines are a different radiographic finding, representing larger, more irregular lines at the lung periphery. They are also a sign of interstitial edema, but are more indicative of pulmonary venous hypertension than Kerley-B lines.
**Option C:** This option is incorrect because Kerley-B lines are not a sign of pulmonary edema caused by high altitude. While high altitude can cause pulmonary edema, Kerley-B lines are specifically associated with increased pulmonary venous pressure, which is not directly related to high altitude.
**Clinical Pearl / High-Yield Fact**
Kerley-B lines are a classic radiographic finding in pulmonary venous hypertension, and can be seen in conditions such as left-sided heart failure, mitral valve disease, and pulmonary embolism. They are an important clinical clue to the presence of increased pulmonary venous pressure.
**Correct Answer:** C.