HomeHealth articleslateral decubitus chest x-rayWhat Is Lateral Decubitus Chest X-Ray?

Lateral Decubitus Chest X-Ray - Indications, Procedure, and Evaluation Criteria

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A lateral decubitus chest X-ray is a specialized chest X-ray technique that is now majorly used in the pediatric population. Read the article for more details.

Medically reviewed by

Dr. Muhammad Shoyab

Published At October 20, 2022
Reviewed AtJuly 26, 2023


X-rays are diagnostic procedures that use a certain form of radiation to create images of the structures within the body. They are non-invasive, painless, and the preferred technique for examining most body parts. Chest X-rays are vital to assess the lungs, heart, spine, rib cage, and other associated structures. They can be used to diagnose various conditions and also monitor treatment planning. Chest X-rays are crucial in emergency diagnoses as they are quick and easy to obtain.

What Are the Different Types of Chest X-Rays?

Chest X-rays are categorized based on the viewing direction:

  • Posteroanterior View: X-ray goes through the back and exits the front. Most common, shows front of the chest, including lungs and heart.

  • Anteroposterior View: Less common, shows the heart less clearly. X-ray enters through the front and exits the back.

  • Decubitus: Patient lies down, X-ray shows the front side of the chest.

  • Lateral: Complementary to frontal view, patient stands sideways with hands raised above their head.

Why Is a Lateral Decubitus Chest X-Ray Important?

The lateral decubitus chest X-ray is a specialized position X-ray of the chest. Considering the omnipresent usage of imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI), a lateral decubitus chest X-ray is rarely used. However, they are still vital diagnostic tools in the pediatric population and in certain lung conditions. The lateral decubitus chest X-ray is primarily used to diagnose the presence of fluid or air in the lungs. It is extremely sensitive as it can detect even 50 ml of fluid in the lungs.

Where Is Lateral Decubitus Chest X-Ray Indicated?

The primary indications of lateral decubitus chest X-ray are as mentioned below:

  • Accumulation of excessive fluid surrounding the lungs is known as pleural effusion. Since pleural effusion cannot be distinctly seen on any other views of chest X-rays, a lateral decubitus chest X-ray is considered the gold standard in diagnosing pleural effusion.

  • To determine if the pleural effusion is free-flowing or loculated (pooled up in an area of pleural scarring).

  • If the fluid is freely movable, a lateral decubitus chest X-ray can be used to check if the quantity is enough for thoracentesis. Thoracentesis is an invasive medical procedure that helps in removing fluid or air trapped in the lungs.

  • It is also used to diagnose pneumothorax. Pneumothorax is air entrapment in the lungs.

What Are the Types of Lateral Decubitus Chest X-Ray?

Based on the position of the patient, the lateral decubitus chest X-ray can be of two types. It is known as a right lateral decubitus X-ray if the patient is lying down on the right-hand side. If the patient is reclining on the left side, it is known as a left lateral decubitus X-ray.

What Are the Patient Preparations Required Before a Lateral Decubitus Chest X-Ray?

  • The patient is advised to wear a hospital gown.

  • They should remove jewelry such as necklaces, chains, and earrings.

  • Female patients should tie their hair on top of their heads.

  • Ladies who are pregnant or who might be pregnant should inform the doctor.

How Is the Patient Positioned for a Lateral Decubitus Chest X-Ray?

  • The doctor should determine the affected site and ask the patient to lie on that side.

  • It is ideal for laying on the affected side for pleural effusion and the unaffected side for pneumothorax.

  • Mostly the lateral decubitus chest X-ray is taken in the anteroposterior view, though the posteroanterior view may also be considered.

  • Place the patient in the same position for a minimum of five minutes before taking the X-ray so that the fluid, if present, can settle or the air can rise and be visible clearly.

What Is the Working Principle of X-Ray?

X-rays are nothing but a type of radiation. The X-ray procedure uses this form of radiation to produce images within the body. An X-ray unit comprises a tube-like device through which the X-ray is produced. A detector is a photographic plate or a film on which the image is recorded. When emitted into the body, the X-rays are absorbed by different body parts in varying degrees. Structures such as bones which are dense, absorb more of the radiation and hence appear white on the image, whereas radiation can pass through the soft tissue such as organs and muscles. Hence they appear in gray shades. The air looks black.

How Is a Lateral Decubitus Chest X-Ray Taken?

  • Once the patient is made to lie down, the detector is placed behind the patient, parallel to the long axis of the patient.

  • The film should be marked appropriately with an indication on the upper side as a decubitus X-ray. This is also known as a decubitus marker.

  • The patients should be advised to extend their neck and chin so that the lung fields are not obstructed by the image.

  • They should be instructed to raise their arm above their head.

  • The chest should be placed in a perfect lateral position, and it should be ensured that the patient does not lean forward or backward, or sideways.

  • The technician can place a lead shield in front of the pelvis to protect the gonads against radiation.

  • Ensure that the pelvis and shoulders of the patient are not rotated.

  • The patient will be advised to take two deep breaths before aiming the X-ray.

  • The X-ray is taken on the second full breath so that the lung is in maximum expansion.

Since an X-ray is a non-invasive and painless procedure, no special instructions are required after the procedure is complete.

What Are the Evaluation Criteria for a Perfect Image?

  • A decubitus marker should always be present.

  • The image should clearly show the lung fields, the heart, the apices of the lungs, and the costophrenic angles (the place where the diaphragm and rib cage meet).

  • No superimposition of the image by any anatomical structures.

  • The sternoclavicular joints (joint of the shoulder) should be equidistant.

  • The clavicle (bone connecting the arm to the body) should be in the same plane horizontally.

  • Above the diaphragm, at least ten ribs should be visible posteriorly.

  • The vessels of the lungs should be demarcated clearly.

How Is Pleural Effusion Seen on a Lateral Decubitus Chest X-Ray?

  • The lateral decubitus chest X-ray is the preferred imaging modality for diagnosing pleural effusion.

  • It can detect even a tiny amount of fluid if present.

  • The fluid layering can be seen as a well-defined linear opacity.

  • The layering of the fluid indicates free-flowing effusion, whereas a loculated fluid appears without any layers.

  • If the layering opacity is around 1 cm in thickness, it is indicative of a pleural effusion of more than 200 ml.

What Are The Alternative Techniques To A Lateral Decubitus Chest X-Rays?

Frontal Chest X-ray:

  • Visualization of the lungs, heart, and surrounding structures.

  • Not as sensitive as a lateral decubitus X-ray for detecting small amounts of fluid.

CT Scan (Computed Tomography):

  • Detailed cross-sectional images of the chest.

  • Better visualization of lung structures and abnormalities, including fluid accumulation.


  • Evaluation for pleural effusion (fluid in the chest cavity).

  • Performed in various positions, including lateral decubitus.

MRI (Magnetic Resonance Imaging):

  • Not commonly used for routine evaluation of pleural effusion.

  • Detailed images of the chest and suggested in certain situations.


Lung diseases such as pneumonia, tuberculosis, fibrosis, and lung cancer are extremely common, and their incidence is rising day to day. Early diagnosis and timely management of lung disease are essential for a good prognosis for the patient. Chest ultrasound, computed tomography (CT), and thoracoscopy are considered the gold standard for assessing lung diseases. However, certain practical limitations, such as their availability, technical considerations, and high price, restrict their usage. Therefore, chest X-rays, being rapid, cost-effective, and simple, are still the preferred first-line diagnostic tool for lung disorders.

Frequently Asked Questions


What Is the Purpose of the Decubitus Position in Chest Radiography?

A decubitus chest X-ray is a specialized technique that has found increasing application in the pediatric population. Decubitus means lying down and hence a lateral decubitus chest X-ray suggests an X-ray that is taken with the patient lying down. Lateral decubitus chest X-ray is primarily indicated in diagnosing pleural effusion and pneumothorax.


What Are the Indications of Lateral Position?

Lateral decubitus chest X-rays are indicated in the following condition:
- It is a gold standard tool in diagnosing pleural effusion.
- To detect if the pleural effusion is free flowing or pooled up in an area of scarring.
- If the pleural effusion is free flowing, a lateral decubitus chest X-ray can help determine if the fluid can be removed via thoracentesis (surgical removal of the fluid from the lungs).
- To diagnose pneumothorax (air entrapment).


What Is Another Name for the Lateral Decubitus View?

The lateral view is also known as a decubitus X-ray or a lateral decubitus X-ray. It is a specialized X-ray that is taken with the patient in a recumbent position.


Why Do You Do a Left Lateral Chest X-Ray?

The lateral chest X-ray can be of two types based on the positioning of the patient. It is known as right lateral if the patient is lying down on the right-hand side and left lateral if lying on the left side. A left lateral chest X-ray is mostly preferred as the cardiac structures are closer to the film and thus less chance of magnification. A left lateral view is primarily indicated for better visualization of the cardiac structures.


What Is Lateral Chest Position?

A lateral chest radiograph requires the patient to lie on the affected lateral side. The affected side is positioned against the image receptor or the film while capturing the image. A lateral chest X-ray clearly shows the lungs, mediastinum, major blood vessels, and thoracic cavity.


Why Is Left Lateral Decubitus Preferred Over Right?

A left lateral decubitus X-ray is usually preferred over the right as the cardiac structures would be closer to the X-ray film and hence less chances for magnification. It is increasingly preferred to image the cardiac organs and associated structures.


How Do You Mark a Lateral Decub?

At first, the patient is asked to lie down on the affected side, which is determined clinically. The detector is placed on the rear side of the patient parallel to the long axis. A marking annotating decubitus chest X-ray should be clearly signed on the upper side of the film. This is known as a decubitus marker.


How Do You Do Lateral Decubitus?

The patient is made to lie down in a lateral position, preferably on the affected side. The detector is placed parallel to the long axis behind the patient. The film is marked with the decubitus marker. The patient is advised to extend their neck and chin and raise their arm above their head. The technician should ensure that the chest is placed in a perfect lateral position. The patients are advised to take two deep breaths before the image is captured.


Can You Do a Chest X-ray Laying Down?

Yes, a chest X-ray can be taken in a recumbent position with the patient lying down on their side. It is known as a lateral decubitus chest X-ray. Based on the position, either left or right, it is termed as left lateral decubitus chest X-ray or right lateral decubitus chest X-ray.
Dr. Muhammad Shoyab
Dr. Muhammad Shoyab



lateral decubitus chest x-ray
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