On a frontal chest X-ray, the right lower lobe fissure is displaced superiorly and medially. What is the most likely diagnosis?

Explanation

## Fissural Displacement and Lobe Collapse **Key Point:** Superior and medial displacement of a fissure indicates volume loss in the lobe bounded by that fissure. The right lower lobe is bounded by the oblique (major) fissure; its upward shift means the lower lobe has shrunk (collapsed). ### Anatomy of Fissural Displacement ```mermaid flowchart TD A[Fissure displacement on CXR]:::outcome --> B{Direction of shift?}:::decision B -->|Superior/medial| C[Volume loss in lobe]:::outcome C --> D[Lobe collapse]:::action B -->|Inferior/lateral| E[Volume increase or effusion]:::outcome E --> F[Consolidation or effusion]:::action D --> G[Right lower lobe collapse]:::outcome ``` **High-Yield:** Fissural displacement ALWAYS indicates volume change. Superior displacement = loss of volume = collapse. Inferior displacement = gain of volume = consolidation or effusion. ### Collapse Patterns by Lobe | Lobe | Fissure Displaced | Direction | Associated Signs | |------|---|---|---| | **Right upper** | Horizontal fissure | Superiorly | Elevated hilum, mediastinal shift | | **Right middle** | Horizontal + oblique | Medially | Silhouette of right heart border | | **Right lower** | Oblique fissure | Superiorly & medially | Silhouette of right hemidiaphragm | | **Left upper** | Oblique fissure | Superiorly & anteriorly | Elevated left hilum | | **Left lower** | Oblique fissure | Posteriorly & superiorly | Silhouette of left hemidiaphragm | **Clinical Pearl:** When you see fissural displacement, always ask: "Is the fissure moving TOWARD or AWAY FROM the hilum?" Toward = collapse. Away = consolidation or effusion. **Mnemonic — FISSURE SHIFT:** - **F**issure moves toward hilum = collapse (volume loss) - **I**ncrease in opacity = consolidation - **S**ilhouette sign = both possible - **S**uperior shift = upper/middle lobe collapse - **U**pward = loss of volume - **R**adial displacement away = consolidation - **E**ffusion = fissure bows outward [cite:Chest Radiology: The Essentials, 3e]