Written by: Elliott R. Carthy BMedSc (Hons)
School of Medicine, Imperial College London, UK
Chest radiographs (CXR) are one of the most commonly requested investigations by clinicans in both primary and secondary care settings. In particular, CXR’s can be used to diagnose or exclude the presence of space occupying lesions including malignancies, infections or granulomas. This article will endeavour to outline these pathologies, and the associated diagnostic features that distinguish them on a CXR.
Basic CXR sequence for interpretation
My particular chosen method of CXR interpretation follows an ABCDEF approach, after confirming the patient’s name, D.O.B. orientation, exposure, inspiration and rotation. Remember to compare one side to the other.
A: airway (including hilar enlargement)
B: bones and soft tissues (including breast shadows)
C: cardiac (with great vessels and retrocardiac space)
D: diaphragm (including costophrenic and costocardiac angles and under the diaphragm)
E: Edges and extrathoracic tissues (e.g. for pneumothorax and pleural disease)
F: Fields (lung parenchyma, including the apices)
Types of Masses
Single nodules may be referred to as space-occupying lesions within the lung. However, if >3cm across, the term ‘pulmonary mass’ is used instead of ‘nodule’. When evaluating a solitary pulmonary nodule, the first aspect that needs to be determined is whether the nodule is most likely benign or malignant, which will in turn direct patient follow-up and treatment. When answering this question, it is important to firstly establish the stability of the lesion over time, often requiring any previous imaging.
The differential diagnosis of a solitary mass includes a carcinoma, solitary metastasis, a focal area of necrosis or infarction, and abscesses or a benign tumour.
Lesions >5mm have a 95% chance of malignancy, and tend to increase in size more gradually that a nodule of inflammatory aetiology (changes within weeks) but quicker than that of a benign lesion (no change for over a year). Adenocarcinomas tend to grow more slowly than small cell or squamous cell carcinomas, with large cell carcinomas growing the most rapidly.
Solitary pulmonary nodules
Lung cancer is one of the most common cancers worldwide, with primary lung cancer usually presenting as a solitary pulmonary nodule, compared to metastatic disease presenting with multiple nodules known as “cannonball mets”. It is not possible to accurately differentiate between malignant lesions merely from a chest radiograph. Heightened suspicion for various subtypes can occur based on the rate of growth (if previous imaging is available) and location, however further cytological testing would be needed for diagnosis.
Figure 1: solitary pulmonary nodule. Image courtesy of www.learningradiology.com.
Benign causes of solitary pulmonary nodules include:
Squamous cell carcinoma
Small cell carcinoma
Large cell carcinoma
Cavitating lung lesions
Some lesions may cavitate, i.e. they may develop an area of necrosis, appearing as darkness within the lesion and an air-fluid level (fluid is white with a black air above).
Figure 2: Cavitating lung lesions. A: bronchogenic carcinoma; B: tuberculous lesion; C: lung abscess caused by Staphylococcus. Images courtesy of www.learningradology.com.
Figure 3: Pancoast tumour. Image obtained from Jmarchn, Wikipedia.
Metastatic cancer in the lung
Metastatic disease most often presents with multiple nodules, usually of slightly differing sizes and sharply marginated, ranging from micronodular to cannonball masses. The most common sites of primary neoplasia causing metastatic spread to the lungs include colorectal carcinoma (most common in males), breast cancer (most common in females), renal cell carcinoma, and malignant melanoma.
Fig. 4: Cannonball metastatic lesions from breast cancer (Hsu et al., Radiopaedia.org).
Lymphatic spread of cancer
Tumours can grow and obstruct the pulmonary lymphatics, causing interstitial oedema similar to that caused by congestive cardiac failure. Unilateral oedema should raise suspicion of lymphatic spread of cancer to the lung. The most common primary sources of such cancers include breast, lung, and pancreatic carcinoma.
Information obtained from: Herring, W. Learning Radiology: recognising the basics. 2007. Mosby Inc., USA.
Images obtained with permission from www.learningradiology.com
Hsu et al., Pulmonary metastases, Radiopaedia.org.
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