Chest X-ray:

• Normal Anatomy
• Types of Projection
• Assessing the Film
• Technical Qualities
• Heart and Vessels
• Lungs
• Mediastinum
• Bones
• Soft Tissues
• Presenting the Film ('30 second presentation')

Abdominal X-ray:

• Normal Anatomy
• Assessing the Film
• Technical Qualities
• Gas containing structures
• Solid Organs
• Bones
• Soft Tissues
• Presenting the Film ('30 second presentation')

KEY TIPS:

• Always view with clinical information in mind.
   
• Be systematic in approach.
   
• Think of the anatomical structures on the image.
   
• Compare with other x-rays if available.
   
• Don't stop looking if an abnormality is seen - there may be more!

The chest x-ray (CXR) is the single most requested imaging investigation and is also the most likely film to feature in an exam.  It is the perfect prompt for questioning other aspects of a patient's condition and management.

To be able to comment confidently on the film's findings, an appreciation of normality is required. Don't forget a CXR is a two-dimensional representation of three-dimensional structures.

One may think of a CXR as a picture which contains 5 'shades'.  These shades represent 5 different 'tissues':

The big two are:

• 1. Bone is WHITE
• 2. Gas is BLACK

• 3. Soft tissue is GREY
• 4. Fat is DARKER GREY
• 5. Anything Man-Made (eg. a pace-maker), is BRIGHT WHITE

These descriptions can be combined. For example an acutely unwell patient who has a CXR taken on a ward may have a MOBILE, SEMI-ERECT AP film.

You might think of this part of the interpretation like the safety announcement on an airplane one has heard many times: necessary to acknowledge, but boring and nothing will make any difference anyway. However, this could not be further from the truth. Changes in these parameters can give the impression of abnormalities in the structures seen and lead to a whole path of misguidance. Take some time to give it attention.

It is good practice to mention a clear-cut abnormality at the outset. A reasonable way to say this would be, 'The technical quality of the film is satisfactory. The most striking abnormality on initial assessment is .....'

The examiner will then expect the candidate to demonstrate an organized approach to looking at the rest of the film. Do not stop when one abnormality has been noted - there may be more to see.

The structures below need to be considered in the interpretation of the film. As long as all aspects are covered one cannot be faulted over the order in which they are reviewed. It is fair to assume however if one major abnormality is clearly seen from the beginning that this structure or system be commented on first.

Review of Structures to Assess on CXR:

• Heart and Major Vessels
• Lungs & Pleura
• Mediastinum (including hila)
• Bones and soft tissues

Be particularly careful not to miss the following review areas. They should be specifically checked as abnormalities in these areas may be easily overlooked.

Review Areas:

• Costophrenic angles
• Apices
• Behind the Heart
• Below the diaphragms
• Breast Shadows (in females)

• Size of heart
• Size of individual chambers of heart
• Size of pulmonary vessels
• Evidence of stents, clips, wires and valves
• Outline of aorta and IVC and SVC

• Size
• Intrapulmonary pathology
• Vascular lung markings

• Thickness
• Opposition against chest wall (i.e. is there a pneumothorax?)

• Width of mediastinum
• Contour of mediastinum
• Size of hila
• Level of hila

• Generalized bone disease, fractures and bony deposits
• Surgical emphysema
• Breast presence/absence and symmetry

The radiation exposure of an AXR compared to a CXR is also considerably higher. One AXR is equivalent to 35 CXRs.

The AXR is of most use in the patient with an acute abdomen. As with a CXR, an appreciation of normal structures is vital.

'BLACK BITS'

Intra-luminal gas can be normal. Extra-luminal gas is abnormal. However, intra-luminal gas can be abnormal if it is in the wrong place or if too much is seen.

The maximum normal diameter of the large bowel is 55mm. Small bowel should be no more than 35mm in diameter. The natural presence of gas within the bowel allows assessment of caliber - although the amount varies between individuals. The caecum is not said to be dilated unless wider than 80mm.

Large and small bowel may be distinguished by looking at bowel wall markings, as shown in the box below.

It is usual to see small volumes of gas throughout the GI tract and the absence in one region may in itself represent pathology. For example, if gas is seen to the level of the splenic flexure and nothing is seen beyond this, a site of the obstruction at this site - a 'cut off' point is noted.

An erect CXR (not AXR) is the best projection to diagnose a pneumoperitoneum (gas in the peritoneal cavity)

'WHITE BITS'

Calcified structures ('WHITE BITS') are often seen on AXR. The main question is - does its presence have any important implications. Calcification can be broadly divided into 3 types.

1. Calcium that is an abnormal structure
eg. gallstones and renal calculi

2. Calcium that is within a normal structure, but represents pathology
eg. nephrocalcinosis, splenic artery aneurysm

3. Calcium that is within a normal structure, but is harmless
eg. lymph node calcification

Bones are normal 'white' structures. On the AXR they comprise mainly those of the thoraco-lumbar spine and pelvis. Findings are largely incidental as direct bone pathology would be investigated with specific views.

'GREY BITS'

Soft tissues represent most of the contents of the abdomen and feature heavily in the AXR. However, these tissues are poorly seen when compared to other imaging techniques such as ultrasound or CT.

The kidneys, spleen, liver and bladder (if filled) can be seen in addition to psoas muscle shadows and abdominal fat. Rarely would action be taken on the basis of this imaging alone.

'BRIGHT WHITE BITS'

Foreign Bodies represent an interesting final observation. Objects that may be seen include ingested and rectal foreign bodies, items in the path of the x-ray beam such as belt buckles, dress buttons and jewelry. Other objects may have been deliberately placed for example an aortic stent, an inferior vena cava filter or a suprapubic urinary catheter. Sterilization clips and an intra-uterine device are common findings in women.