Chest (lateral decubitus view)

The lateral decubitus view of the chest is a specialized projection that is now rarely used due to the ubiquity of CT.  It is chiefly used in the pediatric population.

Indication

Undertaken to demonstrate small pleural effusions, or for the investigation of pneumothorax and air trapping due to inhaled foreign bodies.

Patient position

• the patient is lying either left lateral or right lateral on a trolley on top of a radiolucent sponge
  • note: when investigating pneumothorax the side of interest should be up; when investigating pleural effusions the side of interest should be down
• the detector is placed landscape posterior to the patient running parallel with the long axis of the thorax 
• patient's hands should be raised to avoid superimposing on the region of interest, legs may be flexed for balance
• rotation of shoulders or pelvis should be minimized
• patients should be changed into a hospital gown, with radiopaque items (e.g. belts, zippers) removed
• x-ray is taken in full inspiration

Technical factors

• lateral decubitus
• centering point
  • midsagittal place (xiphisternum) at the level of T7
• collimation
  • laterally to include both lungs 
  • superior to the apex
  • inferior to the costodiaphragmatic recess
• orientation
  • portrait (relative to the patient)
• detector size
  • 35 cm x 43 cm
• exposure
  • 100 - 125 kVp
  • 3 - 10 mAs
• SID
  • 100 cm
• grid
  • yes

Image technical evaluation

A marker annotating 'horizontal beam decubitus" should always be present, with the side of interest clearly labeled.

The entire lungs should be visible from the apices down to the lateral costophrenic angles. 

• the chin should not be superimposing any structures
• minimal to no superimposition of the scapulae borders on the lung fields
• sternoclavicular joints are equal distant apart
• the clavicle is in the same horizontal plane
• a minimum of ten posterior ribs is visualized above the diaphragm
• the ribs and thoracic cage are seen only faintly over the heart
• clear vascular markings of the lungs should be visible

Practical points

• in the context of inhaled foreign bodies, bilateral decubitus lateral views should be performed, allowing for adequate assessment of any air trapping
  • patients with obstructive foreign bodies will not have a collapsed lung, however, will manifest hyperlucency of the dependent lung
• ensure the patient is carefully rested against the wall detector and at no risk of falling 
• rotation of a chest radiograph can simulate common pathology processes and make it hard to produce an appropriate diagnosis
  • the sternoclavicular joints are a sound indicator for positional rotation, if one sternoclavicular joint is notably wider than the other, that respected side needs to be rotated toward the image receptor to correct rotation  
• patients with a longstanding history of emphysema or COPD will have abnormally long lungs compared to the general population, remember this when collimating superior to inferior
• side marker placement is imperative; patients can have congenital conditions that mimic a mirrored image
• remember to explain to your patient what you are about to do; that is ask them to take a breath in and hold it; many times this gives the patient time to prepare and results in a better breath hold and therefore a higher quality radiograph
  • always remember to tell your patient to breathe again