Chest x rays made easy
In the final part of the series, Elizabeth Dick looks at lung nodules and masses.
The basics of looking at a chest x ray (recap):
- First look at the mediastinal contours - run
your eye down the left side of the patient
and then up the right.
- The trachea should be central. The aortic
arch is the first structure on the left,
followed by the left pulmonary artery;
notice how you can trace the pulmonary
artery branches fanning out through the
lung (see figure 1).
- Two thirds of the heart lies on the left side
of the chest, with one third on the right.
The heart should take up no more than
half of the thoracic cavity. The left border
of the heart is made up by the left atrium
and left ventricle.
- The right border is made up by the right
atrium alone. Above the right heart border
lies the edge of the superior vena cava.
- The pulmonary arteries and main bronchi
arise at the left and right hila. Enlarged
lymph nodes can also occur here, as can
primary tumours. These make the hilum
seem bulky - note the normal size of the
hila on this film.
- Now look at the lungs. Apart from the
pulmonary vessels (arteries and veins), they
should be black (because they are full of
air). Scan both lungs, starting at the apices
and working down, comparing left with
right at the same level, just as you would
when listening to the chest with your
stethoscope. The lungs extend behind the
heart, so look here too. Force your eye to
look at the periphery of the lungs - you
should not see many lung markings here; if
you do then there may be disease of the air
spaces or interstitium. Don't forget to look
for a pneumothorax.
- Make sure you can see the surface of the
hemidiaphragms curving downwards, and
that the costophrenic and cardiophrenic
angles are not blunted - suggesting an
effusion. Check there is no free air under
the hemidiaphragm.
- Finally, look at the soft tissues and bones.
Are both breast shadows present? Is there
a rib fracture? This would make you look
even harder for a pneumothorax. Are the
bones destroyed or sclerotic?
Abnormality: multiple discrete nodules in the lungs
Discrete nodules do not have a reticular
or linear component. They can be small
(up to 5 mm) or large. The differential
diagnosis is shown in box 1 and some
of them are illustrated in figures 1, 2,
and 3.
Fig 1 - Miliary tuberculosis. There are multiple small discrete nodules throughout both lungs
Box 1- Differential diagnosis of small and large lung nodules Small nodules (<5 mm)
- Miliary tuberculosis (so called because they look like tiny seeds "milia"), due to haematogenous spread
- Sarcoid (which can also cause reticulo-nodular shadowing)
- Metastases (although they are usually bigger)
- Pneumoconiosis - for example, due to inhaling coal dust. This is rare nowadays
- Chickenpox pneumonia Larger nodules/masses (>5 mm)
- Common: Metastases (especially breast, testis, gastrointestinal tract, kidney, and thyroid)
- Rare: Inflammatory nodules - for example, due to vasculitis of rheumatoid arthritis or Wegener's granulomatosis
Abnormality: single nodule or mass in the lung
The two main causes of a single mass
in the lung are: infection/ - for example,
tuberculosis and neoplasm - for
example, primary bronchial tumour or
single metastasis. In both cavitation may
occur.
Other causes of single or multiple masses in the lung are rare. Only mention them
if pressed by an examiner. They include
hydatid cyst and pulmonary arteriovenous
malformation.
Tuberculosis (TB)
Turberculosis has various manifestations
in the lung. In primary tuberculosis there
is a peripheral lung mass (Ghon focus)
with enlarged hilar lymph nodes (fig 4).
Fig 2 - Multiple miliary lung metastases (arrowed). These were caused by a thyroid carcinoma
Fig 3 - Multiple small calcified lung nodules (arrowed), most are less than 5mm in diameter. These are caused by previous chickenpox pneumonia which has calcified. The patient is usually asymptomatic
Fig 4 - Previous primary tuberculosis. Both the peripheral lung nodule (Ghon focus, arrow 1) and the hilar lymph nodes (arrow 2), which have been infected with tuberculosis, have calcified.
Fig 5 - Secondary tuberculosis. Some consolidation in the right upper lobe with a cavity (arrowed), typical of secondary tuberculosis
Fig 6 - Pneumocystis carinii pneumonia in a patient with AIDs. PCP has varied appearances. Here there is an air space shadowing in the lower zones plus a cyst in the right upper zone (arrow)
Consolidation can also occur. In secondary
tuberculosis there is patchy consolidation
especially in the upper lobes (fig 5). This
can cavitate. Other manifestations include
pleural effusions and miliary tuberculosis.
Mediastinal lymphadenopathy does not
occur in secondary TB.
Other infections can cavitate, including
pneumonias due to Staphylococcus, Klebsiella, and Cryptococcus. Pneumocystis carinii, as
the name suggests, can form cysts which
are airfilled and have a similar appearance
on an x ray film to cavities (fig 6).
Lung carcinomas can also cavitate, squamous cell carcinomas are the typical histological subtype to do so (fig. 7).
Apart from cavitation, other features
of lung carcinomas are listed in box 2:
they can occur in the periphery of the
lung or centrally (in or near the mediastinum). The outline of the tumour may be spiculated. Look for associated pleural effusion or hilar lymphadenopathy.
Box 2 - Primary lung carcinoma - features to look for
- l Any site (from central to peripheral lung)
- May cavitate
- Spiculated, irregular outline
- Distal consolidation or collapse
- Pleural effusion
- Hilar lymphadenopathy
- Local bony destruction
- Multiple bony metastases
Proximal tumours can cause distal consolidation or collapse. Local rib destruction or multiple bony metastases can also occur so look for these.
I would like to thank Dr Anju Sahdev, Dr Brian Holloway, and Dr Robert Dick for contributing some of the films which are illustrated.
Elizabeth Dick, specialist registrar in radiology, North Thames Deanery
studentBMJ 2001;09:1-42 February ISSN 0966-6494
