General X-ray signs
When analyzing a radiograph, it is important to consider individual characteristics and normal variants. For example, the nipple shadow should not be confused with adenopathy (lymphadenopathy).
The border between the left lung and the aortic wall is normally traceable down to the diaphragm. However, contact with the proximal portion of the left pulmonary artery may partially obscure this border. Its shape varies depending on the unfolding of the aorta. Additionally, the lung may invaginate between the heart and the aorta; if gas is present in the esophagus, the contact between the lung and the left wall of the esophagus will be visible as a thin line.
Paraspinal and retrosternal lines
Normally, lymph nodes and intercostal veins in the paraspinal region are not differentiated. Paraspinal lines follow the contours of the lateral ligaments of the spine, especially in lean individuals; in obese patients, these contours are smoothed out. The left paravertebral space is usually thicker than the right (in obese individuals — more than 10 mm). When the aorta unfolds, the pleura is displaced away from the spine, which alters the thickness of the left paraspinal line.
The retrosternal line is visible on a lateral view as an opacity along the lower third of the anterior chest wall. This is a complete variant of the norm, formed by mediastinal fat and varying degrees of anterior lung apposition, which is often mistaken for pleural pathology.
X-ray anatomy of the diaphragm
The diaphragm consists of a muscular part and a central tendon, attaching to the lower ribs and the xiphoid process.
- Shape: Usually dome-shaped, but a scalloped contour is a common normal variant.
- Costophrenic angle: Normally sharp and distinct. In athletes during deep inspiration, the diaphragm can flatten significantly, leading to blunting of the angle — this is also a normal variant.
- Location: The right dome projects at the level of the anterior segment of the 6th rib (with possible variation of one intercostal space). It is usually 1.5–2.5 cm higher than the left. However, in 9% of people, the domes are at the same level, and in some, the left may even be slightly higher than the right (up to 1 cm).
Class and exam questions
Why is the right hemidiaphragm usually higher than the left?
Normally, the right dome is located 1.5–2.5 cm higher than the left due to the presence of the liver on the right and the pressure of the heart on the left.
What is the retrosternal line and is it always pathological?
The retrosternal line on a lateral radiograph is a normal variant. It is formed by mediastinal adipose tissue and cardiac structures, rather than pleural pathology.
Can paraspinal lymph nodes be seen normally?
No, lymph nodes and intercostal veins between the spine and the lung are not individually visualized under normal conditions.
What else to study on this topic
- Radiological signs of pneumothorax
- Differential diagnosis of round pneumonia
- Pleural ultrasound in health and disease
- Signs of tension in pneumothorax
- Pediatric chest skeletal radiology
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