🔬 Chest X-ray

A Chest X-ray (CXR) is a projectional radiograph of the chest used to diagnose conditions affecting the thoracic cavity, its contents, and nearby structures. It is one of the most commonly performed medical tests due to its utility in assessing the lungs, heart, and great vessels. A standard CXR consists of a Postero-Anterior (PA) view, though Anteroposterior (AP) and lateral views are also utilised.

Productive cough, chest pain, or dyspnoea. Suspected pneumonia or heart failure. Assessment of thoracic trauma or suspected rib fractures. Screening for lung cancer or tuberculosis. Post-procedural check for placement of NG tubes, central lines, or pacemakers. Pre-operative assessment in patients with significant respiratory or cardiac history. Monitoring of known conditions like COPD exacerbations or pleural effusions.

The standard view is Postero-Anterior (PA), where the patient stands with the chest against the plate and the X-ray beam passes from back to front. This minimises magnification of the heart. An Anteroposterior (AP) view is used for unwell or immobile patients in bed, though this often causes the heart to appear larger. The patient is asked to take a deep breath and hold it during the exposure to ensure maximum lung expansion. Protective lead shields may be used for patients of childbearing age if appropriate.

Clear lung fields with no opacities or masses. Trachea is central. Normal cardiothoracic ratio (<0.5 on PA film). Both hemidiaphragms are smooth and sharply defined costophrenic angles are visible. Gastric bubble present under the left hemidiaphragm. No free air under the diaphragm. Hilar regions should be of normal size and density. Bony structures (ribs, clavicles) and soft tissues are intact.

Systematic approach (ABCDE): Airway (trachea central?); Breathing (lung fields clear, symmetry, pleura?); Circulation (heart size <50% of thoracic width, mediastinal contours?); Diaphragm (height, costophrenic angles, air underneath?); Everything else (bones, soft tissues, tubes, and lines). Assess technical quality using 'RIPE': Rotation (medial ends of clavicles), Inspiration (5-7 anterior ribs), Picture (ensure the whole thorax is included), and Exposure (vertebrae visible behind the heart).

Consolidation (patchy or lobar opacification) indicates pneumonia. Pulmonary oedema presents with 'Bat’s wing' shadows, Kerley B lines, and cardiomegaly. Pneumothorax is identified by a visible lung edge with an absence of peripheral lung markings. Pleural effusions show blunting of the costophrenic angles or a meniscus sign. A 'sail sign' may indicate lobar collapse. Subdiaphragmatic free air (pneumoperitoneum) indicates a perforated viscus and is a surgical emergency. Hilar lymphadenopathy may signify sarcoidosis or malignancy.

The CXR is the most frequent imaging modality used in hospital medicine. It is a rapid, relatively low-radiation tool for diagnosing life-threatening conditions like tension pneumothorax (though this is a clinical diagnosis) and acute heart failure. It is also used to confirm the correct positioning of invasive lines and tubes, such as central venous catheters, nasogastric tubes, and endotracheal tubes. It serves as a baseline for monitoring chronic lung diseases.

Misinterpreting skin folds or clothing as a pneumothorax. Failing to recognise that 'normal' heart size cannot be accurately assessed on an AP film. Misidentifying the gastric bubble as free air or vice versa. Forgetting to look at 'hidden areas' like the apices, behind the heart, and below the diaphragm. Confusing nipple shadows or external artifacts (ECG leads) with lung nodules.

A standard PA film has low sensitivity for early pneumonia or small nodules. It is a 2D representation of 3D structures, necessitating lateral views if clinical suspicion remains high. Technical factors like poor inspiration or patient rotation can mimic pathology (e.g., pseudo-cardiomegaly on an AP film). It may be normal in significant pathology like early pulmonary embolism or interstitial lung disease. Radiation exposure, though low, must be justified.

Students must be able to identify a pneumothorax and differentiate it from a large bulla. Recognition of pneumoperitoneum under the diaphragm is a critical 'must-spot' finding. Understanding the difference between PA and AP films is vital for assessing heart size (cardiothoracic ratio). Always check the side marker and patient details before interpreting. Reference the 'Golden Rules' for NG tube confirmation.