The chest radiograph is the most requested examination in medicine and the one most often read quickly. Most missed findings on a chest film are not subtle. They are missed because the eye stopped at the first abnormality, or never reached the area at all.
What follows is the systematic approach we teach, the review areas that catch what a casual look does not, and the appearances worth knowing cold. Our CXR Interpretation course covers the same ground with cases and a certificate, and it is free.
Before you interpret: assess the film
Three questions, every time, before any pathology.
Projection. PA or AP? On an AP film the heart is magnified and the mediastinum looks wider. Calling cardiomegaly on a supine AP film in a sick patient is one of the commonest errors in reporting.
Rotation. Compare the medial ends of the clavicles against the spinous processes. A rotated film shifts the mediastinum, alters apparent lung density and creates asymmetry that is not there.
Inspiration and penetration. Five to six anterior ribs or around ten posterior ribs above the diaphragm. A poorly inspired film crowds the lung bases and manufactures basal shadowing. On a correctly penetrated film you should just see the lower thoracic vertebrae through the cardiac shadow.
A systematic approach
Any fixed sequence works provided you never vary it. The one below moves from outside in.
Airway. Trachea central, or deviated? Deviation towards a pathology suggests volume loss; deviation away suggests a mass or a large effusion. Check the carina and the main bronchi.
Breathing. Compare the lungs zone by zone, left against right at the same level, rather than reading one lung then the other. Asymmetry is easier to see than absolute density. Follow the pleural edge all the way round.
Circulation. Heart size on a PA film, under half the thoracic diameter. Then the mediastinal contours, the aortic knuckle, and the pulmonary arteries at the hila. Hilar position matters as much as hilar size.
Diaphragm. Right usually sits slightly higher than left. Check both costophrenic angles, and look under the diaphragm for free gas on an erect film.
Everything else. Bones, soft tissues, lines, tubes and the edges of the film.
The review areas
These are where findings hide, and where a deliberate second pass pays for itself.
The apices. Obscured by clavicles and ribs. A Pancoast tumour sits here and is routinely missed.
Behind the heart. A retrocardiac mass, a left lower lobe collapse or a hiatus hernia all live in this blind spot. Look for a double contour through the cardiac shadow and check you can trace the left hemidiaphragm all the way to the spine.
Below the diaphragm. Free gas, abnormal bowel gas, and the upper abdominal structures included on the film.
The bones. Ribs, clavicles, shoulders and the visible spine. Lytic lesions and healing fractures are often the incidental finding that matters most.
The soft tissues and film edges. Surgical emphysema, breast shadows and absent breast shadows, and whatever is sitting at the very margin of the image.
Consolidation and pneumonia
Consolidation is alveolar filling. It appears as ill-defined opacification that does not displace fissures or structures, frequently containing air bronchograms. The silhouette sign localises it: loss of the right heart border places disease in the right middle lobe, loss of the left heart border in the lingula, and loss of a hemidiaphragm contour in a lower lobe.
Lobar consolidation with air bronchograms in a febrile patient is straightforward. The harder calls are the early or patchy changes, consolidation against collapse, and distinguishing pneumonia from pulmonary oedema or haemorrhage, where distribution and the clinical context carry more weight than appearance alone.
Collapse
Collapse is volume loss, and volume loss has signs: displaced fissures, a raised hemidiaphragm, mediastinal shift towards the abnormality and crowded ribs. Each lobe collapses in a characteristic direction, and recognising the pattern is usually quicker than reasoning it out. Left lower lobe collapse behind the heart is the one most often overlooked.
Pneumothorax
Look for a visible visceral pleural line with no lung markings beyond it. On a supine film, where air collects anteriorly and basally rather than apically, look instead for a deep sulcus, an unusually sharp hemidiaphragm or cardiac border, and a relatively lucent upper abdomen.
Tension pneumothorax is a clinical diagnosis, not a radiological one. If the signs are there, treat rather than image.
Pleural effusion
On an erect film, blunting of the costophrenic angle with a meniscus. Several hundred millilitres are needed before this is visible, and considerably more on a supine film, where fluid layers posteriorly and produces a general veil-like increase in density across the hemithorax with preserved vascular markings.
Masses and nodules
Note size, margin, location and whether it is truly intrapulmonary. Check for rib destruction, and always compare with any previous film before describing something as new. A stable nodule over two years behaves very differently from the same nodule seen once.
Lines, tubes and devices
On any film with hardware, state the position of each device explicitly. Endotracheal tube tip a few centimetres above the carina, central line tip at the cavoatrial junction, nasogastric tube clearly below the diaphragm and ideally seen within the stomach. A misplaced nasogastric tube is a never event, and the chest film is where it is caught.
Taking it further
Our CXR Interpretation course is free and works through this material with cases and a certificate on completion. For trauma radiographs and preliminary clinical evaluation, see our red dot page. For a wider case set, the case review series covers chest and body, emergency and bone and joint imaging.
Radicon Institute of Radiology has taught radiology since 2017, with over ninety filmed tutorials and delegates across the UK, the Gulf and South Asia.
