Can you have a pleural effusion in the lower middle area without involving the costophrenic angle?

Pleural Effusion Distribution and Costophrenic Angle Involvement

Yes, a pleural effusion can occur in the lower middle area of the chest without involving the costophrenic angle, particularly in cases of loculated effusions or when fluid accumulates in a subpulmonic location.

Radiographic Appearance of Pleural Effusions

• The typical radiographic appearance of pleural effusion involves blunting of the costophrenic angle, which is usually the earliest sign of fluid accumulation 1
• A minimum of approximately 200 ml of pleural fluid is required to be visible on a PA chest radiograph, while only 50 ml can produce detectable posterior costophrenic angle blunting on a lateral chest radiograph 1
• Lateral decubitus films are useful for detecting free fluid as it gravitates to the most dependent part of the chest wall 1

Atypical Presentations of Pleural Effusions

Subpulmonic Effusions

• Subpulmonic effusions occur when pleural fluid accumulates in a subpulmonic location without involving the costophrenic angle 1
• These effusions are often transudates and can be difficult to diagnose on PA radiographs 1
• The PA radiograph typically shows lateral peaking of an apparently raised hemidiaphragm with a steep lateral slope and gradual medial slope 1
• Lateral radiographs may show a flat appearance of the posterior aspect of the hemidiaphragm with a steep downward slope at the major fissure 1

Loculated Effusions

• Pleural effusions can become loculated due to fibrinous septations, which compartmentalize the fluid 1
• These loculations can occur in various locations within the pleural space, including the lower middle area, without extending to the costophrenic angle 2
• Ultrasound is particularly useful for detecting loculated effusions and can visualize fibrinous septations better than CT scans 1

Supine Patient Considerations

• In supine patients (e.g., in intensive care settings), free pleural fluid layers out posteriorly 1
• Pleural fluid in supine patients often appears as a hazy opacity of one hemithorax with preserved vascular shadows 1
• Other signs include loss of the sharp silhouette of the ipsilateral hemidiaphragm and thickening of the minor fissure 1
• Supine radiographs often underestimate the volume of pleural fluid and have only moderate sensitivity (67%) and specificity (70%) for detecting pleural effusions 3

Diagnostic Approach for Atypical Effusions

• Ultrasound is more accurate than plain chest radiography for estimating pleural fluid volume and should be used when standard radiographs are inconclusive 1, 2
• Ultrasound-guided aspiration yields fluid in 97% of cases of loculated pleural effusion 1
• CT scans with contrast enhancement should be performed when the diagnosis remains uncertain after ultrasound 1, 2
• In cases of difficult drainage, CT scanning should be used to delineate the size and position of loculated effusions 1

Clinical Implications

• The presence of a pleural effusion in an atypical location should prompt consideration of specific etiologies 2
• Right-sided predominance is notable in certain conditions like benign asbestos pleural effusion (BAPE), occurring in 69-76% of cases 1, 2
• Complete pleural symphysis (adhesions) can be predicted by a blunted costophrenic angle with high specificity (96.1%) and accuracy (95.3%) 4
• For small effusions not visible on standard radiographs, lateral decubitus views or ultrasound examination should be considered 1, 2

Management Considerations

• Thoracentesis should be performed for new and unexplained pleural effusions, regardless of their location 2, 5
• Ultrasound guidance is particularly important for accessing small or loculated effusions that don't involve the costophrenic angle 1, 2
• Laboratory analysis of pleural fluid helps distinguish between transudates and exudates, guiding further management 2, 5
• If dyspnea persists after thoracentesis, other causes should be investigated, including atelectasis, lymphangitic carcinomatosis, or pulmonary embolism 2