Massive Unilateral Pleural Effusion - Hepatic Hydrothorax

This article is an answer to the Case – Liver Failure, Ascites, and Absent Right-Sided Breath Sounds

Radiologic Findings

PA chest radiograph show complete “white-out” of the right hemithorax. No air bronchograms are seen and only the left diaphragm is perceptible on the lateral exam. Note the contralateral displacement of the tracheal air column and mediastinum “away” from the white-out on the PA exam.

Diagnosis

Massive Unilateral Pleural Effusion; Hepatic Hydrothorax

Differential Diagnosis

Unilateral Opaque Thorax (“White-out”) is quite broad (see table bellow)
Differential can be narrowed based on location of trachea (see table bellow)
Other Causes of Unilateral Pleural Effusion (see table bellow)

Differential Diagnosis of Unilateral Opaque Thorax (“White-out”) Based on Trachea Location

Unilateral Pleural Effusion Differential Diagnosis

Etiology of Pleural Effusion

Thoracentesis is usually performed to evaluate pleural effusions of unknown etiology. Fluid is examined grossly and submitted for biochemical analysis, red and white blood cell counts, Gram and acid-fast stains, and cytology. More invasive procedures, including closed, open, or thoracoscopic biopsy, are sometimes necessary to establish a diagnosis.

Most effusions are categorized as transudates or exudates using criteria established by Light. Such categorization is useful in narrowing the differential diagnosis (see tables bellow) and dictating patient management.

Exudates exhibit one or more of the following characteristics:

pleural fluid protein/serum protein ratio >0.5;
pleural fluid lactic acid dehydrogenase (LDH)/serum LDH ratio >0.6;
pleural fluid LDH ratio greater than two-thirds the normal serum LDH.

Transudates are characteristically clear, straw-colored, have a low protein concentration, and have few cells. Most transudates result from systemic factors that alter pleural fluid formation or absorption.

Exudative effusions result from diseases that alter the pleural surface and its permeability to protein. Bilateral pleural effusions sometimes have different etiologies (Contarini condition)—for example, an exudative pleural effusion (empyema) in one thorax and a transudative pleural effusion (heart failure) on the other side.

Pleural effusions may also be characterized by their composition (e.g., hydrothorax, hemothorax, pyothorax, chylothorax, bilothorax, urinothorax, pyohemochylothorax).

Differential Diagnosis of Transudative and Exudative Pleural Effusion

Clinical Findings

The clinical presentation varies depending on the underlying cause of the effusion and how rapidly the pleural fluid accumulated. Some patients are asymptomatic (15%), whereas others present with dull aching chest pain, cough, fever, and dyspnea. Large effusions may displace the mediastinum and cause respiratory distress. Physical exam findings may include decreased or absent breath sounds over the affected thorax and dullness to percussion.

Imaging Findings

Chest Radiography

Hazy increase in radio-opacity (i.e., ground glass veil) that does not obscure underlying bronchovascular markings on supine chest radiography
Radio-opacity involving posterior or lateral costophrenic sulcus with meniscus-shaped upper border (i.e., blunting) on upright radiography
Smooth meniscus-shaped opacity, the upper border of which curves gently downward from its lateral aspect to the mid-cardiac region in small to moderate pleural effusions

Predicting Volume of Pleural Fluid

Lateral decubitus exam: may demonstrate as little as 5 mL of pleural fluid; also useful in differentiating loculated from mobile pleural fluid collections
Posterior costodiaphragmatic sulcus blunting on lateral chest radiography: 20–30 mL
Lateral costodiaphragmatic sulcus blunting on frontal chest radiography: 200–300 mL
Obscuration of ipsilateral hemidiaphragm on frontal radiography: >500 mL

Subpulmonic Pleural Effusion

Bilateral subpulmonic effusions unlikely to be recognized; mimics hypoventilation
Lateral displacement of apex of apparent diaphragm (i.e., pseudodiaphragm) on frontal exams
Convex margin of fluid flattens as it contacts oblique fissure and descends abruptly to anterior costophrenic sulcus on lateral radiography; Rock of Gibraltar sign
± Small amount of fluid in inferior aspect of oblique fissure on lateral radiography
Left-sided effusion may be characterized by downward displacement of gastric air bubble from pseudodiaphragm by ≥2.0 cm on upright chest exams

Interlobar Fluid Collections (Pseudotumor; Vanishing Tumor)

Most often associated with heart failure; renal failure and hepatic hydrothorax less often
Invariably radiographic evidence of concomitant or resolving heart failure
Homogeneous ovoid opacity oriented along long axis of fissure
Evidence of ipsilateral pleural fluid
Absence of air bronchograms
Morphology changes from one orthogonal view to the next
Mobile with decubitus positioning

MDCT

Sensitive in detection of free pleural fluid
Layers posteriorly with characteristic meniscoid appearance
Attenuation coefficients: 0–20 HU; higher with hemothorax
Small effusions may be difficult to differentiate from pleural thickening; fibrosis; dependent atelectasis; decubitus CT imaging aids in differentiation
Dependent lung may appear to “float” in the fluid of large effusions
Loculated effusion: sharply marginated lenticular fluid attenuation mass; conforms to concavity of chest wall; forms obtuse margins at its edges; compresses adjacent lung
Septations indicative of complicated, organizing effusion
Pleural fluid and ascites may occur concurrently; relationship to diaphragm, bare area of liver, and interface with liver and spleen aid in differentiation

Ultrasound

Effusions displace lung away from chest wall; allows visualization of pleural cavity
Most pleural fluid is anechoic or hypoechoic (e.g., transudate, exudate); may see floating particulate matter
Septations not apparent on CT are often evident; septations, floating particles or layering debris, increased echogenicity more suggestive of exudate
Collapsed/consolidated lung moves within the effusion during respiration

MRI

Signal intensity of pleural fluid depends on its biochemical characteristics
Most cases of non-hemorrhagic or non-chylous effusion:
- High signal intensity: T2WI
- Low signal intensity: T1WI

Management

Transudative Effusion

Systemic disorder is treated; no further investigation is necessary

Exudative Effusion

Further investigation is warranted to determine its etiology and is then directed toward that disease process

Prognosis

Dependent upon the underlying disease process

Pearls

Heart failure is the most common cause of transudative pleural effusion encountered in clinical practice.
Parapneumonic effusion is the most common cause of exudative pleural effusion; neoplasia is the second most common cause.
Interlobar pseudotumor: interlobar accumulation of interfissural fluid that can mimic but should be differentiated from a true lung mass. Although this may occur in any standard or accessory fissure, there is a predilection for it to occur in the horizontal fissure. Remember that these fluid collections are “localized” and not “loculated” within the fissure and will easily layer out on decubitus exams.
The majority of massive unilateral pleural effusions are malignant (e.g., primary lung cancer, metastatic disease, lymphoma).