Nodule
A nodule is a discrete opacity in the lung which may be caused by:* Neoplasm: benign or malignant
* Granuloma: tuberculosis
* Infection: round pneumonia
* Vascular: infarct, varix, Wegener's granulomatosis, rheumatoid arthritis
There are a number of features that are helpful in suggesting the diagnosis:
* rate of growth
** Doubling time of less than one month: sarcoma/infection/infarction/vascular
** Doubling time of six to 18 months: benign tumour/malignant granuloma
** Doubling time of more than 24 months: benign nodule malignancy
* calcification
* margin
** smooth
** lobulated
** presence of a corona radiata
* shape
* site
If the nodules are multiple, the differential is then smaller:
*infection: tuberculosis, fungal infection, septic emboli
*neoplasm: e.g., metastases, lymphoma, hamartoma
*sarcoidosis
*alveolitis
*auto-immune disease: e.g., Wegener's granulomatosis, rheumatoid arthritis
*inhalation (e.g., pneumoconiosis)
Cavities
A cavity is a walled hollow structure within the lungs. Diagnosis is aided by noting:*wall thickness
*wall outline
*changes in the surrounding lung
The causes include:
*cancer (usually malignant)
*infarct (usually from a pulmonary embolus)
*infection: e.g., ''Staphylococcus aureus'', tuberculosis, Gram negative bacteria (especially ''Klebsiella pneumoniae''),anaerobic bacteria, and fungal
*Wegener's granulomatosis
Pleural abnormalities
Fluid in space between the lung and the chest wall is termed a pleural effusion. There needs to be at least 75ml of pleural fluid in order to blunt the costophrenic angle on the lateral chest radiograph, and 200ml on the posteroanterior chest radiograph. On a lateral decubitus, amounts as small as 5ml of fluid are possible. Pleural effusions typically have a meniscus visible on an erect chest radiograph, but loculated effusions (as occur with an empyema) may have a lenticular shape (the fluid making an obtuse angle with the chest wall).Pleural thickening may cause blunting of the costophrenic angle, but is distinguished from pleural fluid by the fact that it occurs as a linear shadow ascending vertically and clinging to the ribs.
Diffuse shadowing
The differential for diffuse shadowing is very broad and can defeat even the most experienced radiologist. It is seldom possible to reach a diagnosis on the basis of the chest radiograph alone: high-resolution CT of the chest is usually required and sometimes a lung biopsy. The following features should be noted:*type of shadowing (lines, dots or rings)
**reticular (crisscrossing lines)
**companion shadow (lines paralleling bony landmarks)
**nodular (lots of small dots)
**rings or cysts
**ground glass
**consolidation (diffuse opacity with air bronchograms)
*location (where is the lesion worst?)
**upper (e.g., sarcoid, tuberculosis, silicosis/pneumoconiosis, ankylosing spondylitis, Langerhans cell histiocytosis)
**lower (e.g., cryptogenic fibrosing alveolitis, connective tissue disease, asbestosis, drug reactions)
**central (e.g., pulmonary oedema, alveolar proteinosis, lymphoma, Kaposi's sarcoma, PCP)
**peripheral (e.g., cryptogenic fibrosing alveolitis, connective tissue disease, chronic eosinophilic pneumonia, bronchiolitis obliterans organising pneumonia)
*lung volume
**increased (e.g., Langerhans cell histiocytosis, lymphangioleiomyomatosis, cystic fibrosis, allergic bronchopulmonary aspergillosis)
**decreased (e.g., fibrotic lung disease, chronic sarcoidosis, chronic extrinsic allergic alveolitis)
Pleural effusions may occur with cancer, sarcoid, connective tissue diseases and lymphangioleiomyomatosis. The presence of a pleural effusion argues against pneumocystis pneumonia.
;Reticular (linear) pattern
:(sometimes called "reticulonodular" because of the appearance of nodules at the intersection of the lines, even though there are no true nodules present)
:*cryptogenic fibrosing alveolitis
:*connective tissue disease
:*sarcoidosis
:*radiation fibrosis
:*asbestosis
:*lymphangitis carcinomatosis
:*PCP
;Nodular pattern
:*sarcoidosis
:*silicosis/pneumoconiosis
:*extrinsic allergic alveolitis
;*Langerhans cell histiocytosis
;*lymphangitis carcinomatosis
;*miliary tuberculosis
;*metastases
;Cystic
:*cryptogenic fibrosing alveolitis (late stage "honeycomb lung")
:*cystic bronchiectasis
:*Langerhans cell histocytosis
:*lymphangioleiomyomatosis
;Ground glass
:*Extrinsic allergic alveolitis
:*Diffuse interstitial pneumonitis
:*Alveolar proteinosis
:*Infant respiratory distress syndrome (RDS)
;Consolidation
:*Alveolar haemorrhage
:*Alveolar cell carcinoma
:*vasculitis
:*chronic eosinophilic pneumonia
Signs
:*The silhouette sign is especially helpful in localizing lung lesions. (e.g., loss of right heart border in right middle lobe pneumonia),:*The air bronchogram sign, where branching radiolucent columns of air corresponding to bronchi is seen, usually indicates air-space (alveolar) disease, as from blood, pus, mucous, cells, protein surrounding the air bronchograms.
Adapted from the Wikipedia article Chest radiograph, under the G. N. U. Free Documentation License. Please also see http://en.wikipedia.org/wiki
