Introduction

Pleural effusions demonstrated with chest radiography are nothing if not commonplace. For the radiographer there can be more to imaging a pleural effision than you might think. This page is dedicated to the radiographic appearances of pleural effusions, appearances that mimic pleural effusions and the radiographic techniques for demonstrating pleural effusions.

Definition of terms

A pleural effusion is a collection of fluid in the pleural space.

Pleural Effusion on Erect Chest Images

Pleural Effusion on Supine Chest Images


False Effusions

	This 68 year old male presented to the Emergency Department with a history of presyncopal episodes after exertion. He was referred for chest radiography. There are sternal wires associated with a previous thoracotomy.
	There are prominent serratus muscle opacities (white arrows) producing a false impression of pleural effusion on the left (black arrow). There is right sided pleural opacity- possibly pleural thickening.
	The lateral projection image demonstrates loss of clarity of the right hemidiaphragm (silhouette sign). The arrowed opacity is not an interlobar effusion- it is a combination shadow produced by the combined opacity f the cardiac shadow and the right hemidiaphragm
	Note that the combination shadow is produced by the combined opacity of the right hemidiaphragm and the posterior cardiac shadow which is within the left hemithorax.

Subpulmonic Effusion

A subpulmonic effusion refers to a plural effusion which is loculated/contained between the diaphragm and the lung within the pleural space.

Subpulmonic effusion	Normal Chest
Note the flat looking "hemidiaphragm", particularly medially. When you compare this appearance with the normal chest, the differences may appear subtle. The raised right hemidiaphragm, the flattened look of the diaphragm and the concave horizontal fissure suggest a possible subpulmonic effusion http://www.med.yale.edu/intmed/cardio/imaging/cases/pleural_effusion_subpulmonic/index.html	Compare this normal right hemidiaphragm shape to that of the patient with the right sided subpulmonic effusion.

A subpulmonic effusion can be mimicked by "subdiaphragmatic abscess, enlarged liver, paralysis and eventration of the diaphragm, and ascites

Case 1

This is a PA chest image. The radiographer has positioned the patient with the shoulders rolled well forward affording a good view of the lungfields. The linear opacity above the right hemidiaphragm is subsegmental atelectasis (lower white arrow). There are multiple pleural plaques associated with previous asbestos exposure (black arrow). Conveniently for this case study, there is a diaphragmatic plaque on the left (white arrow). The grey arrows identify the normal space between the fundus of the stomach and the diaphragm.

This is a PA chest image on the same patient taken after cardiac surgery. Note the increased distance between the fundus of the stomach (black arrow) and what appears to be the diaphragm (white arrow). The diaphragmatic plaque is marked by the grey arrow. Question: If the diaphragmatic plaque identifies the position of the left hemidiaphragm.... what is the structure marked by the white arrow? Answer: The white arrow identifies the visceral pleural surface of the left lung base (so called pseudodiaphragm). The appearance is complicated somewhat by the apparent air fluid level (not marked), suggesting that there is air as well as fluid in the pleural space. Where it is clinically indicated, the presence of a subpulmonic effusion can be proven with the aid of a lateral decubitus projection.

Decubitus Chest Technique for Pleural Effision

This is a PA chest image. The patient is post cardiac surgery. Note the increased distance between the air-filled fundus of the stomach and the left "hemidiaphragm" (arrowed). The radiographer noted this finding and suspected a subpulmonic effusion. He/she performed a left lateral decubitus view to see if the pleural fluid would track along the left chest wall within the pleural space.

The left lateral decubitus chest image demonstrates fluid in the pleural space (arrow). Note that this is termed a left lateral decubitus view even though it is marked "R decubitus".

Artifacts and Normal Variants Simulating Pleural Effusion

This patient has prominent serratus muscles bilaterally. This apparance can be mistaken for pleural effusion or pleural thickening (single white arrow). The Serratus anterior muscle can produce an opacity that may resemble pleural tickening. This is sometimes referred to as a "bowling-pin" silhouette. "When the muscle is well developed, the medial edge of this silhouette may be superimposed upon the air shadow of the lung in a variety of ways. When it overlies the apex of the lung, it gives rise to the companion shadow; when overlying the midlateral lung edge and costophrenic angle it may mimic pleural and/or extrapleural disease. Recognition of the various possible patterns is important to prevent overdiagnosis of disease, particularly asbestosis." Gilmartin D.The serratus anterior muscle on chest radiographs. Radiology. 1979 Jun;131(3):629-35. http://en.academic.ru/pictures/enwiki/83/Serratus_anterior.png

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