Commonly Missed Areas on Chest Radiographs

1. Lung Apices

The lung apices are often obscured by overlying structures such as the clavicles and ribs. They are best assessed in the PA view, as there is less overlay with other structures compared to the lateral view.

Studies have shown that the majority of missed lung cancers on chest radiographs have an upper lobe predominance [1, 2].

A careful comparison of both lung apices may reveal subtle difference in opacities, which may be the only clue to pathology. Apical lung tumors (e.g., Pancoast tumors) can be easily overlooked, and small pneumothoraces can be subtle and missed.

Apical pleural capping may be present in normal individuals when it measures less than 5 mm, and may represent apical scarring or prominent fatty tissue. However, when it is thickened or irregular it may suggest other diagnoses, such as superior sulcus tumors, masses or hemorrhage [3].

2. Inferior Lung Bases and Costophrenic Angles

The inferior lung bases extend caudally beyond the dome of the diaphragm, making them a frequent “blind spot” in the evaluation of a chest X-ray. On the lateral view, the density of the vertebral bodies should gradually decrease along the cranial-caudal plane. An increase in density projected over the inferior third of the vertebral bodies on this view is known as the “spine sign” and should raise suspicion for pathology.

The evaluation of the costophrenic angles is critical for detecting pleural effusions, pleural thickening, or subpulmonic effusions. A blunted costophrenic angle is compatible with fluid accumulation, which is best appreciated on the lateral view. 

3. Retrosternal and Retrocardiac Spaces

The retrosternal space, visible on the lateral radiograph as a lucent area, should be evaluated for anterior mediastinal masses (e.g., thymomas, teratomas, lymphadenopathy). Masses in this location may compress adjacent structures and can present as increased density in this area, causing obliteration of this space.

Hiatal hernias are one of the most common abnormalities found in the retrocardiac space, and may be recognized by the presence of retrocardiac air-fluid levels, best appreciated on the lateral view. This area may harbor other pathologies, such as lung nodules, lower lobe consolidation, or left lower lobe collapse, which may be inconspicuous on the PA view.

4. Hilum

The hila are composed of pulmonary arteries, veins, bronchi, and lymph nodes, making them a critical area for detecting pathology such as lymphadenopathy, vascular abnormalities, or masses.

The hila are regions that can have varied appearances, making it difficult and subjective to assess pathology. The normal hilum should have a concave angle formed by the superior pulmonary vein and the interlobar pulmonary artery.

Asymmetry between the right and left hilum should raise suspicion for pathology. A unilaterally enlarged or elevated hilum may indicate malignancy, infection, or vascular conditions such as pulmonary hypertension (PH). In cases of known PH, it may be challenging to differentiate between vascular and non-vascular causes of hilar abnormalities. The “hilar convergence” sign may be helpful in these cases, if present the vessels converge into the hilar abnormality, indicating a vascular cause. However, if the vessels are seen coursing through the hilum, a secondary cause must be suspected [4].

5. Mediastinum

The mediastinum contains critical structures such as the heart, great vessels, trachea, esophagus, and lymph nodes. The most common pathologies in this region include lymphadenopathy, mediastinal masses and vascular anomalies.

It is important to evaluate the position of the trachea, along with the width of paratracheal stripes, which should measure less than 4 mm. The aortopulmonary (AP) window should be concave while the paraspinal lines should have smooth contours. Loss of the normal concavity of the AP window or lateral displacement or thickening of the paratracheal and paraspinal lines may suggest an abnormality and follow up imaging should be performed [5].

6. Bones

Bony lesions in chest X-rays are often subtle and can be easily overlooked and may appear as small, irregular opacities or localized changes in bone density. Commonly affected areas include the ribs, clavicles, and vertebrae. The vertebrae should have the same height and the cortices of all the bones should be assessed for normal contours and continuity.

Systematic Approach to Chest Radiograph Interpretation

Reviewing previous studies can help identify subtle changes and confirm new findings. Subtle changes in lung nodule size, mediastinal contours, or pleural thickness should be noted. The interpretation of both PA and lateral views is recommended to detect abnormalities that may not be apparent on a single view.

To minimize the risk of missing abnormalities, a structured and systematic approach should be employed:

ABCDE Method:

• Airway: Tracheal deviation, narrowing and splayed carina.
• Breathing: Lungs, pulmonary vessels and pleural spaces.
• Circulation: Cardiac enlargement and mediastinal contour abnormalities.
• Diaphragm and below: diaphragmatic paresis, pneumoperitoneum, gaseous distension, splenomegaly and calculi.
• External: Chest wall (look for fractures or bony lesions in the ribs, shoulder girdles and vertebral bodies), soft tissues.