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Year : 2021  |  Volume : 9  |  Issue : 1  |  Page : 58-61

Pleural effusion - A radiological review

Department of Internal Medicine, RAK Medical and Health Sciences University, Ras Al Khaimah, United Arab Emirates

Date of Submission16-Aug-2020
Date of Decision23-Oct-2020
Date of Acceptance27-Oct-2020
Date of Web Publication03-Feb-2021

Correspondence Address:
Dr. Raghavendra Bhat
Department of Internal Medicine, RAK Medical and Health Sciences University, Ras Al Khaimah, P.O. Box 11172
United Arab Emirates
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ajim.ajim_60_20

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Pleural effusion is a collection of fluid in the pleural cavity. Various types of pleural effusions are discussed with illustrations (8 images).

Keywords: Apical cap, empyema, fibrothorax, lamellar effusion, loculated effusion

How to cite this article:
Bhat R. Pleural effusion - A radiological review. APIK J Int Med 2021;9:58-61

How to cite this URL:
Bhat R. Pleural effusion - A radiological review. APIK J Int Med [serial online] 2021 [cited 2022 Sep 25];9:58-61. Available from: https://www.ajim.in/text.asp?2021/9/1/58/308651

Normally, 5 ml of the fluid is present within the layers of the pleura.

Parietal pleura is never visualized.

Pleural effusion (PE) is the accumulation of excess fluid in the pleural space, which may be transudate/exudate/blood/chyle/pus (all radiologically identical).

  • Right-sided PE – Ascites, congestive heart failure (CHF), and amebic liver abscess
  • Left-sided PE – Acute pancreatitis, esophageal rupture (Boerhaave's syndrome), aortic dissection, pericarditis, and ovarian malignancy
  • Bilateral PE – Hypothyroidism, lymphoma, metabolic syndrome, connective tissue disease, and pulmonary embolism.

Tuberculosis, parapneumonic, pulmonary embolism, and malignancy can mimic any of these radiological features of PE:

  1. Homogenous opacification with blunting of costophrenic/cardiophrenic angle – 200–500 ml of pleural fluid
  2. Obliteration of Cardiophrenic and Costophrenic angles (CP) angle with obliteration of hemidiaphragm. Superior margin concave to the lung + higher laterally than medially – due to capillary action
  3. Massive PE – Dense opacification with contralateral shift of the mediastinum
  4. Subpulmonic effusion mimics elevated hemidiaphragm with a change of contour of the hemidiaphragm shift of the apex of the hemidiaphragm laterally with or without blunting of CP angles
  5. Loculated PE – It is localized between visceral and parietal pleural layers in the fissures between the lobes of the lung (interlobar) or between visceral and parietal layers usually against the chest wall. It can be seen in hypothyroidism, lymphoma (wherein solid lesions also may be seen), connective tissue diseases such as rheumatoid arthritis, and systemic lupus erythematosus.
  6. Lamellar PE – Shallow collections between lung surface and visceral pleura – CP angles may or may not be spared. It represents the interstitial pulmonary fluid
  7. Empyema-pus – Lenticular/biconvex shape as against transudate sterile effusions which are crescent-shaped – concave toward the lung
  8. Pleural thickening-organized, end-stage result of various processes – usually localized – though it can be extensive enough to incarceration of the lung, preventing its normal functioning. It could be due to a benign (empyema, asbestosis, and hemothorax) or a malignant process
  9. Fibrothorax – This process of pleural thickening is gross and generalized and may involve parenchymal fibrosis and lung damage. This could be a result of infection (tuberculosis) or a noninfectious process (asbestosis). Pleural plaques are more often seen in asbestosis than fibrothorax
  10. Apical cap – Fibrosis at the apex of the lung hiding the morphology of the hidden lung – could be bilateral or unilateral
  11. Pleural calcification may be irregular (tubercular empyema, hemothorax) or more regular (asbestosis wherein like the plaques, it can also be bilateral)
  12. Mesothelioma (tumor of the pleura), benign or malignant, can mimic any one of these processes at various stages
  13. Metastasis, particularly from adenocarcinomas, can involve pleura. Tumors from lung, ovary, and lymphomas can also metastasize to pleura. A skin tumor (aggressive malignant tumor of primitive neuroectodermal origin) can also involve the pleura
  14. Phantom tumor/pseudotumor – Lenticular/biconvex opacity most often seen in minor fissure due to CHF, renal insufficiency, and cirrhosis. It resolves with diuretic therapy.

  Image A: Massive Pleural Effusion Top

  1. Opacity on the left side with obliteration of costophrenic and cardiophrenic angles
  2. The trachea and mediastinum are shifted to the right (opposite side)

  3. These observations suggest the presence of a massive pleural effusion

  4. In addition, one can see the opacity rising up in the axilla with an S shape – the so-called “Ellis S curve” due to capillary effect
  5. A linear shadow can be seen on the top of the opacity emanating from and partly obliterated by the opacity – localized collection in the oblique fissure on the left side
  6. The gastric bubble normally visualized below the left hemidiaphragm and the left hemidiaphragm both are obliterated. This suggests the presence of fluid below the left lung – between the lung and diaphragm - known as subpulmonic effusion [Figure 1].
Figure 1: Massive pleural effusion

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  Image B: Pleural Effusion Associated with Elevated Right Hemidiaphragm Top

  1. Opacity with costophrenic and cardiophrenic angles' obliteration on the right side
  2. The opacity seen on the right costophrenic angle seems to ascend up in the axilla

  3. These two observations strongly support the possibility of pleural effusion

  4. Elevation of the right hemidiaphragm – This is an important observation. In the presence of unilateral pathology and in the absence of any lesion above the diaphragm, it can be safely assumed that the elevation of the right hemidiaphragm is due to pathology below the diaphragm, most likely causing an upward enlargement of the liver. The most common cause in India is amebic liver abscess. An abscess in the right lobe of the liver (most common location) results in upward enlargement of the liver and perihepatitis restricting the diaphragmatic movement and a “sympathetic” pleural effusion (a reaction to inflammation).

  5. Screening of the chest done routinely on the days of admission would easily help diagnose this condition. This is now replaced by an ultrasound examination.

    Clinical examination of this febrile patient may reveal tender hepatomegaly with intercostal tenderness. The patient may complain of (referred) pain in the right shoulder clinching the diagnosis.

  6. The contour of the dome shape of the apex of the right hemidiaphragm is shifted laterally, suggesting the presence of a subpulmonic effusion [Figure 2].
Figure 2: Pleural effusion associated with elevated right hemidiaphragm

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  Image C: Bilateral Localized Interlobar Effusions Top

[Figure 3] shows the presence of localized effusions in the interlobar fissures - interlobar effusions
Figure 3: Bilateral localized interlobar effusions

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  1. Spindle-shaped opacity is observed in the oblique fissure on the right side, suggesting an interlobar effusion on the right oblique fissure
  2. A similar spindle-shaped opacity is also seen in the oblique fissure on the left side, suggesting an interlobar effusion in the left interlobar fissure too
  3. The cardiac shadow suggests a borderline cardiomegaly. A possibility of pericardial effusion has to be considered. This patient has bilateral interlobar effusions with pericardial effusion. The etiology was hypothyroidism.

Other conditions to be considered which can cause similar picture are lymphoma, connective tissue disease, and tuberculosis (primary complex).

  Image D: Opacity Showing Varying Densities – “Layering Effect” Top

There is opacity on the right side with the following observations [Figure 4]:
Figure 4: Opacity showing varying densities – “layering effect”

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  1. Obliteration of cardiophrenic and costophrenic angles
  2. Highest level of opacity in the axilla
  3. Trachea and mediastinum are shifted to the opposite side

  4. All these suggest a right-sided pleural effusion.

  5. There is a “layering effect” on the right side with multiple layers of different density being seen on the right side. This suggests a high protein content in the pleural fluid, which has a tendency to stick to the pleura in layers. This exudate could be an empyema. The “layering effect” suggests that this exudative pleural effusion has been there for days to weeks and the patient has been mobile.

  Image E: Areas of Pleural Thickening and Calcification Top

[Figure 5] shows the following observations:
Figure 5: Areas of pleural thickening and calcification

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  1. Opacity on the right side
  2. Varying density of the opacity – suggesting calcification of the pleura in the costophrenic angle and the lower part on the right side. There is another area of pleural calcification near the right hilum.

These observations suggest that this exudative pleural effusion/empyema has been there for weeks to months, resulting in pleural thickening and later calcification.

  Image F: Volume Loss on the Left Side with Tracheal and Mediastinal Shift to the Left Side with Pleural Calcification and Fibrothorax Top

[Figure 6] has interesting observations:
Figure 6: Volume loss on the left side with tracheal and mediastinal shift to the left side with pleural calcification and fibrothorax

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  1. Left hemithorax is much smaller than the right. There are dense pleural calcification and fibrosis incarcerating the heart, with loss of volume on the left side and shifting of trachea and mediastinum on the left side, suggesting fibrothorax which greatly restricts the work of the left lung. Over a period of time, the other lung tries to compensate, resulting in compensatory emphysema on the right side
  2. This suggests a possibility of empyema (most likely tubercular) – the sequelae are seen here.

  Image G: Hydropneumothorax Top

[Figure 7] shows the following observations:
Figure 7: Hydropneumothorax

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  1. Dense opacity with obliteration of costophrenic and cardiophrenic angles and the diaphragm on the right side
  2. Presence of free air in the pleural cavity seen as hyperlucency
  3. A fluid level at the junction of fluid and air seen across the hemothorax outside the lung – hydropneumothorax.

  Image H: Apical Cap Right Side Top

The observations are as follows [Figure 8]:
Figure 8: Apical cap right side

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  1. Tracheal and mediastinal shift to the right side, with volume loss on the right side
  2. Opacification of the right upper zone including apex of the right lung with a concave border below suggesting apical cap
  3. Blunting of costophrenic and cardiophrenic angles on the right side
  4. Possibly due to involvement of lung parenchyma and pleura over apex of the right lung.

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]


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Image C: Bilater...
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