On lateral chest X-ray, which of the following findings MOST reliably localizes an opacity to the posterior basal segment of the right lower lobe?

• A Obscuration of the right hemidiaphragm on the PA view
• B Opacity behind the heart with loss of the descending thoracic aorta outline on lateral view ✓
• C Loss of right heart border on PA view
• D Obscuration of the left hemidiaphragm on PA view

Explanation

Left lower lobe (LLL) or posterior basal segment lesions are located in the retrocardiac region and cause loss of the descending thoracic aortic outline on the lateral view. Right lower lobe consolidation obscures the right hemidiaphragm on PA (since RLL is adjacent to the right hemidiaphragm). Loss of right heart border indicates right middle lobe (RML) pathology (silhouette sign). Obscuration of the left hemidiaphragm points to left lower lobe disease. The lateral view with posterior opacity and loss of aortic contour specifically identifies posterior basal segment LLL.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.