X-RAYS Flashcards
Causes of true and apparent tracheal deviation
True tracheal deviation:
Pushing of the trachea: large pleural effusion or tension pneumothorax.
Pulling of the trachea: consolidation with associated lobar collapse.
Apparent tracheal deviation:
Rotation of the patient can give the appearance of apparent tracheal deviation, so as mentioned above, inspect the clavicles to rule out the presence of rotation.
Carina and bronchi
The carina is cartilage situated at the point at which the trachea divides into the left and right main bronchus.
On appropriately exposed chest X-ray, this division should be clearly visible. The carina is an important landmark when assessing nasogastric (NG) tube placement, as the NG tube should bisect the carina if it is correctly placed in the gastrointestinal tract.
The right main bronchus is generally wider, shorter and more vertical than the left main bronchus. As a result of this difference in size and orientation, it is more common for inhaled foreign objects to become lodged in the right main bronchus.
Depending on the quality of the chest X-ray you may be able to see the main bronchi branching into further subdivisions of bronchi.
Hilar structures
The hilar consist of the main pulmonary vasculature and the major bronchi.
Each hilar also has a collection of lymph nodes which aren’t usually visible in healthy individuals.
The left hilum is often positioned slightly higher than the right, but there is a wide degree of variability between individuals.
The hilar are usually the same size, so asymmetry should raise suspicion of pathology.
The hilar point is also a very important landmark; anatomically it is where the descending pulmonary artery intersects the superior pulmonary vein. When this is lost, consider the possibility of a lesion here (e.g. lung tumour or enlarged lymph nodes).
Causes of hilar enlargement or abnormal position
Hilar enlargement can be caused by a number of different pathologies:
Bilateral symmetrical enlargement is typically associated with sarcoidosis.
Unilateral/asymmetrical enlargement may be due to underlying malignancy.
Abnormal hilar position can also be due to a range of different pathologies. You should inspect for evidence of the hilar being pushed (e.g. by an enlarging soft tissue mass) or pulled (e.g. lobar collapse).
Lungs
When interpreting a chest X-ray you should divide each of the lungs into three zones, each occupying one-third of the height of the lung.
These zones do not equate to lung lobes (e.g. the left lung has three zones but only two lobes).
Inspect the lung zones ensuring that lung markings are present throughout.
Compare each zone between lungs, noting any asymmetry (some asymmetry is normal and caused by the presence of various anatomical structures e.g. the heart).
Some lung pathology causes symmetrical changes in the lung fields, which can make it more difficult to recognise, so it’s important to keep this in mind (e.g. pulmonary oedema).
Increased airspace shadowing in a given area of a lung field may indicate pathology (e.g. consolidation/malignant lesion).
The complete absence of lung markings should raise suspicion of a pneumothorax.
Pleura
Inspect the pleura for abnormalities:
The pleura are not usually visible in healthy individuals. If the pleura are visible it indicates the presence of pleural thickening which is typically associated with mesothelioma.
Inspect the borders of each lung to ensure lung markings extend all the way to the edges of the lung fields (the absence of lung markings is suggestive of pneumothorax).
Fluid (hydrothorax) or blood (haemothorax) can accumulate in the pleural space, resulting in an area of increased opacity on a chest X-ray. In some cases, a combination of air and fluid can accumulate in the pleural space (hydropneumothorax), resulting in a mixed pattern of both increased and decreased opacity within the pleural cavity.
Heart size
Cardiac
Assess heart size
In a healthy individual, the heart should occupy no more than 50% of the thoracic width (e.g. a cardiothoracic ratio of less than 0.5).
This rule only applies to PA chest X-rays (as AP films exaggerate heart size), so you should not draw any conclusions about heart size from an AP film.
Cardiomegaly is said to be present if the heart occupies more than 50% of the thoracic width on a PA chest X-ray. Cardiomegaly can develop for a wide variety of reasons including valvular heart disease, cardiomyopathy, pulmonary hypertension and pericardial effusion.
Heart borders
Inspect the borders of the heart which should be well defined in healthy individuals:
The right atrium makes up most of the right heart border.
The left ventricle makes up most of the left heart border.
The heart borders may become difficult to distinguish from the lung fields as a result of pathology which increases the opacity of overlying lung tissue:
Reduced definition of the right heart border is typically associated with right middle lobe consolidation.
Reduced definition of the left heart border is typically associated with lingular consolidation.
Diaphragm
The right hemidiaphragm is, in most cases, higher than the left in healthy individuals (due to the presence of the liver). The stomach underlies the left hemidiaphragm and is best identified by the gastric bubble located within it.
The diaphragm should be indistinguishable from the underlying liver in healthy individuals on an erect chest X-ray, however, if free gas is present (often as a result of bowel perforation), air accumulates under the diaphragm causing it to lift and become visibly separate from the liver. If you see free gas under the diaphragm you should seek urgent senior review, as further imaging (e.g. CT abdomen) will likely be required to identify the source of free gas.
There are some conditions which can result in the false impression of free gas under the diaphragm, known as pseudo-pneumoperitoneum, including Chilaiditi syndrome. Chilaiditi syndrome involves the abnormal position of the colon between the liver and the diaphragm resulting in the appearance of free gas under the diaphragm (because the bowel wall and diaphragm become indistinguishable due to their proximity). As a junior doctor, you should always discuss a scan that appears to show free gas with a senior colleague immediately.
costophrenic angles
The costophrenic angles are formed from the dome of each hemidiaphragm and the lateral chest wall.
In a healthy individual, the costophrenic angles should be clearly visible on a normal chest X-ray as a well defined acute angle.
Loss of this acute angle, sometimes referred to as costophrenic blunting, can indicate the presence of fluid or consolidation in the area. Costophrenic blunting can also develop secondary to lung hyperinflation as a result of diaphragmatic flattening and subsequent loss of the acute angle (e.g. chronic obstructive pulmonary disease).
Mediastinal contours
The mediastinum contains the heart, great vessels, lymphoid tissue and a number of potential spaces where pathology can develop. The exact boundaries of the mediastinum aren’t particularly visible on a chest X-ray, however, there are some important structures that you should assess.
Aortic knucle
The aortic knuckle is located at the left lateral edge of the aorta as it arches back over the left main bronchus. Reduced definition of the aortic knuckle contours can occur in the context of an aneurysm.
Aortopulmonary window
The aortopulmonary window is a space located between the arch of the aorta and the pulmonary arteries. This space can be lost as a result of mediastinal lymphadenopathy (e.g. malignancy).
Bones
Inspect the visible skeletal structures looking for abnormalities (e.g. fractures, lytic lesions).
Soft tissues
Inspect the soft tissues for obvious abnormalities (e.g. large haematoma).
Tubes
Nasogastric tube placement is something you’ll often be asked to assess on a chest X-ray to confirm safe placement for feeding. See our NG tube placement guide for more details.
