by Tommaso Gregori

In this short article, I would like to briefly discuss the benefits and importance of obtaining orthogonal views when performing radiographs in practice. As x-ray images are a two-dimensional representation of the anatomy of a patient, at least two views are required to localise a certain abnormality or a lesion in the three-dimensional plane. This is useful to assess its relationship with anatomical structures and helps to provide a meaningful differential diagnosis.

An example of anatomical localisation of a lesion identified on radiographs is provided in Figure 1. On the lateral projections (Figure 1, A and B), there is a large soft tissue opaque mass, partially surrounded by gas, located within the caudodorsal aspect of the thorax. At a first look, this could appear associated with one of the caudal lug lobes, possibly the right, due to its slightly better visibility on the left lateral view. However, the mass is difficult to localise with certainty based on lateral projections only. Based on the lateral views, primary pulmonary neoplasia, such as a bronchogenic carcinoma, was a primary consideration. A large intrapulmonary granuloma or an abscess would be other differential diagnosis. However, on the dorsoventral view provided, the mass was identified in the midline (Figure 1 C) and therefore it is more likely that this lesion is located within the caudodorsal aspect of the mediastinum rather than within the pulmonary parenchyma.

Due to its location, an oesophageal or paraoesophagheal lesion (including of diaphragmatic origin), such as of neoplastic or inflammatory origin was considered most likely. This was a challenging case and the patient underwent computed tomography of the thorax to further investigate the origin and location of this mass. A large pyogranuloma, possibly due to a previously migrated foreign body (not clearly seen on the scan), was found within the caudodorsal mediastinum.

There are situations where obtaining orthogonal views is still insufficient to rule out a certain condition. The classical example is radiographic evaluation of pulmonary metastatic disease. Case 2 is a good example of how important it is to obtain three different projections of the thorax when searching for pulmonary lesions.

On the initial two views of the thorax, a dorsoventral and a right lateral projection (Figure 2 A and B), you could interpret this study as negative for pulmonary lesions. If you have a close look at the left lateral projection, which was acquired following a recommendation by the radiologist, you can identify a solitary pulmonary lesion superimposed to the ventral aspect of the 4th intercostal space (Figure 2 C). This lesion could have been missed by obtaining only two views.

There are obviously other factors that could lead to miss a lesion, such as the degree of inflation of the lungs, for which reason thoracic radiographs should be obtained during the inspiratory phase. Still, obtaining 3 views of the thorax helps to increase the chances of identifying a lesion, which could be invisible on certain projections due to effacement by the cardiac silhouette or by the collapsed pulmonary parenchyma on the recumbent side of the patient. The same principles as explained above, also apply to radiography of other anatomical regions such as the head, abdomen or musculoskeletal structures, where lesions could be misinterpreted or missed due to an incomplete study.

Published: 25-05-2016

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