Findings: chest radiographs show emphysematous lungs with chronic fibrotic changes in the RUL (A, arrow) and left middle lung. The most important finding is an irregular opacity projected over the descending aorta, visible only in the lateral view (B, arrow).

Comparison with a previous lateral film shows that the opacity was not present five years earlier (C and D, circles). Axial CT confirms an irregular mass hidden in the azygoesophageal recess (insert, arrow).

Final diagnosis: Carcinoma of the lung, hidden in the PA view

In the second chapter of The Wisdom of Dr. Pepe I intend to discuss the lateral view (lv), the second component of the equation:

D = (bc + lv + ps + chl) e

My purpose is to emphasise the importance of the lateral view in the detection of chest abnormalities. When examining other organs (skeleton, breast, etc.), it is mandatory to take two right-angle projections (Fig. 1). I see no reason why this practice should not also be applied to chest imaging.

Fig. 1. Traumatic lunate dislocation. The PA view shows that the lunate has a triangular shape, a sign of possible dislocation (A and B, arrows). Lateral projection confirms the lunate dislocation (C and D, arrows).

The main reasons to obtain a lateral view of the chest are:

To visualise blind areas in the PA view
To clarify lesions that are poorly depicted in the PA view

As I’ve already mentioned, around 25% of the lung surface is hidden in the PA radiograph by other structures (blind areas). These areas may be better visualised in the lateral film, which serves as an aid to detect abnormalities that might be missed otherwise. The blind areas are sketched in Fig. 2, including the thoracic spine, which is poorly seen in the PA view.

Fig. 2. The shaded area (A) depicts the blind areas in the PA view. They are visible in the lateral view (B) as the anterior clear space (acs), middle zone (mz), and posterior clear space (pcs). The dorsal spine (ds) is also included.

Blind areas were discussed in Diploma cases 100 and 101 and I don’t think it is necessary to review the subject again. As a reminder, I’m showing an example of disease detected in the lateral radiograph, not visible in the PA view (Fig. 3).

Fig. 3. 54-year-old man with colon carcinoma. Lateral view shows a nodule in the anterior clear space (B, arrow), hidden behind the right hilum in the PA view (A). CT confirms the nodule (insert, arrow). Surgically proven metastasis.

Aside from depicting the blind areas, the lateral view also contributes to interpreting abnormalities that may have a confusing appearance in the PA view and are more clearly seen in the lateral radiograph. To confirm this, examine the images below (Fig. 4, A and B) and try to determine what objects they represent.

Fig. 4. Radiographs (A and B) of two familiar objects.

The right-angle view shows that the first image corresponds to a banana (C) and the second to a bottle (D). This is an example of the usefulness of the right-angle view (ie, lateral view) to clarify inconclusive images seen in a single projection.

It is difficult to determine which abnormalities may be better visualized in the lateral view, but I’ll do my best. In my opinion, the conditions that most benefit from a lateral view are:

1. Hilar abnormalities
2. Some types of lobar collapse
3. Abnormalities in the major fissures
4. Abnormalities of the pleura/chest wall

Hilar abnormalities are important because more often than not they are related to malignant disease. The lateral view helps to differentiate true hilar pathology from lesions in front of or behind the hilum that simulate hilar pathology in the PA view (Figs. 5 and 6).

Fig. 5: 28-year-old man with cough and fever. PA radiograph shows an apparently abnormal left hilum (A, arrow). Lateral view depicts a posterior pulmonary infiltrate (B, circle), simulating an abnormal left hilum in the PA view.

Follow-up films two weeks later show that the hilum has a normal appearance (C and D, arrows) and the infiltrate has disappeared (E and F, circle). Diagnosis: acute pneumonia.

Fig. 6. Neurogenic tumour projected over the right hilum in the PA view, simulating a hilar mass (A, arrow). Lateral radiograph shows that the right hilum is normal (B, white arrow). The tumour is visible as an extrapulmonary lesion in the posterior mediastinum (B, red arrow).

It is important not to overlook lobar collapse because it is a common presentation of lung carcinoma. Collapse of three of the lobes (RUL, RLL, and LLL) is easily diagnosed in the PA view. However, the last two (RML and LUL) may offer a confusing appearance in the PA radiograph and are better identified in the lateral view (Figs. 7 and 8)

Fig. 7. Chronic RML collapse. The only indication in the PA view is slight blurring of the right heart border (A, arrow). The lateral view clearly identifies RML collapse (B, arrow).

Fig. 8. LUL collapse in a patient with endobronchial carcinoma. PA radiograph shows haziness of the left lung, with blurring of the left heart border (A, arrows). Lateral view shows the typical sharply-defined retrosternal opacity, which corresponds to the collapsed lobe limited by the left major fissure (B, arrows). Axial CT confirms the endobronchial obstruction and the collapsed lobe (insert, arrow).

Fluid and tumours within a fissure have a typical ovoid shape with tapering ends. When located in the major fissure, they have a deceiving appearance in the PA view because the fissure offers an oblique face to the X-ray beam. The lateral view clearly depicts the typical appearance (Figs. 9 and 10).

Fig. 9. 59-year-old man with loculated fluid in the left major fissure. PA film shows a nondescript opacity in the left middle lung (A, arrow). Lateral view depicts the typical appearance of an intrafissural lesion (B, arrow). Sagittal CT confirms the findings (C, arrow). The most common etiology of a fissure mass is heart failure, in which pleural fluid may collect within the fissures.

Fig. 10. 35-year-old woman with a fibrous tumour in the left major fissure. PA radiograph shows a poorly defined peripheral opacity (A, arrow) that simulates a lung tumour. Lateral view demonstrates the typical ovoid shape and tapering edges, better seen in the cone-down view (B and C, arrows).

Disease of the pleura/chest wall may offer a blurred appearance in the PA view when seen en face. The extrapulmonary location is easily recognizable in the lateral projection (Figs. 11 and 12).

Fig. 11. 47-year-old woman with chest pain. PA radiograph depicts a poorly defined opacity, apparently located in the left lung (A, arrow). Lateral view shows that the lesion is clearly extrapulmonary (B, arrow), confirmed with CT (insert, arrow). Fibrous tumour of pleura.

Fig. 12. 39-year-old woman with breast carcinoma. PA radiographs depict a poorly defined opacity in the left lung (A, arrow). Lateral view shows an extrepulmonary anterior lesion (B, arrow). CT confirms the location of the lesion (insert, arrow). Diagnosis: fibrous tumour of pleura.

In single calcified pleural plaques, high KV techniques tend to “burn” the calcium. When seen en face, they may simulate a pulmonary infiltrate. Seen in profile they appear as a calcified line (Fig. 14) and the diagnosis is then apparent.

Fig. 14. 52-year-old woman with two pleural plaques. The PA radiograph shows the plaques en face, simulating a pulmonary infiltrate (A, arrows). In the lateral view, the posterior plaque is depicted as a calcified line (B, white arrow), whereas the anterior one is more oblique and simulates a rounded opacity (B, red arrows).

Sagittal CT clearly shows the anterior (C, arrow) and posterior (D, arrow) plaques .

Dr. Pepe’s second commandment:

Thou shalt always take a lateral view:

• To examine the blind areas in the PA view
• To clarify findings in the PA radiograph