Chest x-ray anatomy
Bones
Bones are the densest tissue visible on a normal chest x-ray. Despite this it is easy to overlook important abnormalities of a single bone, or diffuse bone disease, which may be very subtle.
The bones visible on a chest x-ray include the clavicles, the ribs, the scapulae, part of the spine, and the proximal humera (upper arms). Of these only the clavicle is seen in entirety. The sternum is also included on a frontal view, but overlies other midline structures and so is obscured.
The bones are used as useful markers of chest radiograph quality. They are used to assess patient rotation, adequacy of inspiration and x-ray penetration.
Key points
- Assess the bones on every chest x-ray
- Check for abnormalities of single bones and for diffuse bone disease
- The bones are helpful in assessing the quality of the chest x-ray
Hover over image to show findings
Clavicles, spinous processes and ribs
The clavicles are clearly seen on a chest x-ray. The spinous processes of the vertebrae (posterior structures) should lie midway between the medial ends of the clavicles (anterior structures). If the spinous processes are not central, the patient is rotated, that is, positioned obliquely to the x-ray beam.
The anterior and posterior ends ot the 5th rib are also shown.
Click image to align with the top of the page
Hover over image to show findings
Clavicle, scapula, and humerus
The clavicle, scapula and humerus are often clearly seen on a chest x-ray. Occasionally you will see evidence of important disease such as metastases in these bones.
Key
- 1 - Clavicle
- 2 - Acromioclavicular joint
- 3 - Acromion process of scapula
- 4 - Body of scapula
- 5 - Glenoid fossa of scapula
- 6 - Head of left humerus
- 7 - Glenohumeral joint
- 8 - Coracoid process of scapula
Click image to align with the top of the page
Hover over image to show findings
Ribs
The ribs play a role in assessing the adequacy of inspiration taken by the patient. The anterior end of approximately 5-7 ribs should be visible above the diaphragm in the mid-clavicular line. Less than this indicates an incomplete breath in, and more than 7 ribs or flattening of the diaphragm, suggests lung hyper-expansion. On this normal x-ray the anterior end of the 7th rib (*) intersects the diaphragm at the mid-clavicular line.
This chest x-ray also demonstrates the subcostal grooves (red) on the underside of the ribs. These grooves contain the neurovascular bundles that accompany each rib. To avoid damaging the nerves or vessels, the superior edge of a rib is used as the landmark for needle insertion during procedures such as chest drain insertion or lung biopsy.
Also note the spine can be seen through the heart, indicating adequate x-ray penetration.
Click image to align with the top of the page
Assessing the bones
Bones are useful for the initial assessment of image quality, and offer useful information regarding rotation, inspiration and penetration.
Chest x-rays are not helpful if there is thought to be an isolated rib injury as rib fractures are often invisible. Occasionally you will see an important abnormality of the bones on a chest x-ray such as a metastatic deposit. These may be seen in the bones at the edge of the image such as the scapula or proximal humerus, and so you should always have a careful look at all the bones whenever looking at a chest x-ray.