How to read a chest X-ray

How to read a chest X-ray

Reading a chest X-ray requires a methodical approach that can be appliedto all films so that abnormalities are not overlooked.

Clinicians and
radiologists develop an individual approach but there are certain core areas
that should be looked at on all films.

These may be inspected in any order –
this is largely down to personal preference.

Listed below is the outline of a
method which can be applied to read chest X-rays.

Initial quick review of film
To identify any obvious abnormality.

Systematic analysis
Label
Verify the patient’s identity. In examination situations look at the name,
if present, as this can give a clue to sex and ethnic background.
The date and hospital where the film was taken give further clues. If a film
has been taken at a centre for oncology or chest medicine, for instance,
this may help with interpretation.

Projection and patient position
Postero-anterior (PA) is the preferred projection as this does not produce
as much radiographic magnification of the heart and mediastinum as
an antero-posterior (AP) projection. A PA film is taken with the film
cassette in front of the patient and the beam delivered from behind
with the patient in an upright position. Portable films and those taken on
intensive care are all AP projection. Patient position causes important
although sometimes subtle variations in appearance. The supine position
causes distension of the upper lobe blood vessels which may be confused
with elevated left atrial pressure. Imaging of a pleural effusion in a
supine position appears as faint increased density over a hemithorax – this
is due to fluid collecting in the dependent part of the chest, i.e. as a thin
layer posteriorly.
All films taken in the AP projection are usually labelled as such but to
avoid difficulties when describing films in examinations the use of the term
frontal projection is often helpful.
A lateral radiograph is used to localise lesions in the AP dimension;
locate lesions behind the left side of the heart or in the posterior recesses
of the lungs. A left lateral (with the left side of the chest against the film
and the beam projected from the right) is the standard projection.
The heart is magnified less with a left lateral as it is closer to the film.
To visualise lesions in the left thorax obtain a left lateral film and for
right-sided lesions a right lateral.
Lordotic views are taken to examine the lung apices if potential lesions
are partially obscured by overlying ribs or the clavicles. This view was
formerly taken in an AP position with the patient leaning backwards by
30 degrees. Now they are obtained in a PA position with the beam angled
downward by 45 degrees – a less awkward position for patients.
Expiratory films are used to assess air trapping in bronchial obstruction
such as a foreign body. A pneumothorax always appears larger on
an expiratory film and occasionally a small pneumothorax may only be
visible on expiration

Side marker

Dextrocardia is easily missed if the side marker is not identified.

Quality of film

Penetration – the vertebral bodies should just be visible through the
cardiac silhouette.

Rotation – the medial aspect of the clavicles should be symmetrically
positioned on either side of the spine.

Inspiration – the diaphragm should lie at the level of the sixth or seventh
rib anteriorly.
Large airways, lungs and pleura
The ‘lung shadows’ are composed of the pulmonary arteries and veins.
Apart from the pulmonary vessels, the lungs should appear black because
they contain air. Examine the lungs for density variation. Compare the
interspaces on the right with those on the left. Compare the right side with
the left just as you would, if auscultating the chest. Look all the way out
to the periphery of the lungs. Look at the overall lung vascularity and
compare one side with the other. It is important to look at the main
airways – the trachea and the main bronchi. Check the position of the
trachea, that it is central and not deviated.
Look at the pleural surfaces and the fissures, if visible. Check for
masses, calcifications fluid or pneumothorax.

Heart and mediastinum
Examine the cardiac outline identifying all the heart borders and the
outline of the great vessels (see Figs 1.1 and 1.2). Check that there are not
any abnormal densities projected through the cardiac silhouette. Look at
the aortic and pulmonary artery outlines. The heart and mediastinal outline
are made up of a series of ‘bumps’ (see Fig. 1.3). On the right side, there
are right braciocephalic vessels, the ascending aorta and superior vena cava,
the right atrium, and the inferior vena cava. On the left side, there are four
‘moguls’ in addition to the left brachiocephalic vessels: these are the aortic
arch, the pulmonary trunk, the left atrial appendage and the left ventricle.
The size and shape of each of these structures need to be looked at for
signs of enlargement or reduction in size. The right heart border is created
by the right atrium alone (the right ventricle is an anterior structure,
therefore does not contribute to any heart borders) – this is a question
examiners love to ask

Heart size can be estimated using the cardiothoracic ratio. The cardiac
measurement is taken as the greatest transverse heart diameter and is
compared to the greatest internal width of the thorax. A ratio of greater
than 0.5 is often used in clinical practice to indicate cardiomegaly.

Look at the position of the hila and their density – compare the
left with the right side. Tumours and enlarged lymph nodes can occur
here making the hila appear bulky.

Diaphragm

Check the shape, position and clarity/sharpness of both hemidiaphragms.
Both costophrenic angles should be clear and sharp. The cardiophrenic
angles should be fairly clear – cardiophrenic fat pads can cause added
density. The right hemidiaphragm is usually slightly higher than the left –
up to 1.5 cm. On the lateral film, the right hemidiaphragm is seen in its
entirety but the anterior aspect of the left hemidiaphragm merges with the
heart, so is not seen (see Fig. 1.6).

Bones

This is an area which is frequently overlooked.

Ribs: The ribs are a common site for fracture or metastatic deposits
but the remainder of the skeleton must also be carefully examined.
Identify the first rib and carefully trace its contour from the spine to its
junction with the manubrium. Each rib must be carefully and
individually traced in this manner, initially for one hemithorax and
then the contralateral side. A useful trick is to turn the film on its side,
rib fractures may then appear more obvious.

Thoracic spine: Look at the thoracic spine alignment – is it straight or
is there a scoliosis? Take particular care to exclude pathology from the
thoracic spine in trauma patients when even moderate malalignment can
be overlooked when projected through the heart or mediastinal shadows.

Clavicles scapulae and humeri: Fractures and dislocation of the humerus
are often obvious when looked for. Look for fractures, metastatic deposits,
abnormal calcifications or evidence of arthritis around the shoulders.

Soft tissues

A visual examination should be routinely performed on the chest wall,
the neck and both the breast shadows. Look for surgical emphysema and
abnormal calcification. With reference to the breast shadows be sure to
check whether there are two breast shadows and whether there is
symmetry of size, shape and position. The lung field missing a breast will
appear a little darker than the other side.

Review areas

These review areas are sites where pathology is commonly missed and
warrant a second look before any chest X-ray is reported as normal:

Breasts (symmetry/mastectomy).

Below the diaphragm, do not forget that the lungs extend below
the diaphragms, also look at the upper abdomen for surgical clips/
calcification/pneumoperitoneum.
Imaging the chest

Behind the heart (hiatus hernia/lung nodules/left lower lobe
collapse).

Thoracic spine and paraspinal lines (trauma).

Clavicle (nodule behind medial end and eroded lateral end).

Shoulder (dislocation).

Apices (pancoast tumour).

Hila (assess position, size and density).

Lung parenchyma.

Bones, especially ribs (look for metastases or fractures

Spinal Anaesthesia for medical students

Introduction
Spinal anaesthesia is induced by injecting small amounts of local anaesthetic into the cerebro-spinal fluid (CSF).
The injection is usually made in the lumbar spine below the level at which the spinal cord ends (L2).
Spinal anaesthesia is easy to perform and has the potential to provide excellent operating conditions for surgery below the umbilicus.
If the anaesthetist has an adequate knowledge of the relevant anatomy, physiology and pharmacology; safe and satisfactory anaesthesia can easily be obtained to the mutual satisfaction of the patient, surgeon and anaesthetist.
The Advantages of Spinal Anaesthesia
Cost. Anaesthetic drugs and gases are costly and the latter often difficult to transport. The costs associated with spinal anaesthesia are minimal.
Patient satisfaction. If a spinal anaesthetic and the ensuing surgery are performed skilfully, the majority of patients are very happy with the technique and appreciate the rapid recovery and absence of side effects.
Respiratory disease. Spinal anaesthesia produces few adverse effects on the respiratory system as long as unduly high blocks are avoided.
Patent airway. As control of the airway is not compromised, there is a reduced risk of airway obstruction or the aspiration of gastric contents. This advantage may be lost if too much sedation is given.
Diabetic patients. There is little risk of unrecognised hypoglycaemia in an awake patient. Diabetic patients can usually return to their normal food and insulin regime soon after surgery as they experience less sedation, nausea and vomiting.
Muscle relaxation. Spinal anaesthesia provides excellent muscle relaxation for lower abdominal and lower limb surgery.
Bleeding. Blood loss during operation is less than when the same operation is done under general anaesthesia. This is because of a fall in blood pressure and heart rate and improved venous drainage with a resultant decrease in oozing.
Splanchnic blood flow. Because it increases blood flow to the gut, spinal anaesthesia may reduce the incidence of anastomotic dehiscence.
Visceral tone. The bowel is contracted during spinal anaesthesia and sphincters are relaxed although peristalsis continues. Normal gut function rapidly returns following surgery.
Coagulation. Post-operative deep vein thromboses and pulmonary emboli are less common following spinal anaesthesia.
Disadvantages of Spinal Anaesthesia
Sometimes it can be difficult to find the dural space and occasionally, it may be impossible to obtain CSF and the technique has to be abandoned. Rarely, despite an apparently faultless technique, anaesthesia is not obtained.
Hypotension may occur with higher blocks and the anaesthetist must know how to manage this situation with the necessary resuscitation drugs and equipment immediately to hand. As with general anaesthesia, continuous, close monitoring of the patient is mandatory.
Some patients are not psychologically suited to be awake, even if sedated, during an operation. They should be identified during the preoperative assessment. Likewise, some surgeons find it very stressful to operate on conscious patients.
Even if a long-acting local anaesthetic is used, a spinal is not suitable for surgery lasting longer than approximately 2 hours. Patients find lying on an operating table for long periods uncomfortable. If an operation unexpectedly lasts longer than this, it may be necessary to convert to a general anaesthetic or supplement the anaesthetic with intravenous ketamine or with a propofol infusion if that drug is available.
When an anaesthetist is learning a new technique, it will take longer to perform than when one is more practised. When one is familiar with the technique, spinal anaesthesia can be very swiftly performed.
There is a theoretical risk of introducing infection into the sub-arachnoid space and causing meningitis. This should never happen if equipment is sterilised properly and an aseptic technique is used. A postural headache may occur postoperatively. This should be rare (see later).
Indications for Spinal Anaesthesia
Spinal anaesthesia is best reserved for operations below the umbilicus e.g. hernia repairs, gynaecological and urological operations and any operation on the perineum or genitalia. All operations on the leg are possible, but an amputation, though painless, may be an unpleasant experience for an awake patient. In this situation it may be appropriate to combine the spinal with a light general anaesthetic.
Spinal anaesthesia is particularly suitable for older patients and those with systemic disease such as chronic respiratory disease, hepatic, renal and endocrine disorders such as diabetes. Many patients with mild cardiac disease benefit from the vasodilation that accompanies spinal anaesthesia except those with stenotic valvular disease or uncontrolled hypertension (see later). It is suitable for managing patients with trauma if they have been adequately resuscitated and are not hypovolaemic. In obstetrics, it is ideal for manual removal of a retained placenta (again, provided there is no hypovolaemia). There are definite advantages for both mother and baby in using spinal anaesthesia for caesarean section. However, special considerations apply to managing spinal anaesthesia in pregnant patients (see later) and it is best to become experienced in its use in the non-pregnant patient before using it for obstetrics.
Contra-indications to Spinal Anaesthesia
Most of the contra-indications to spinal anaesthesia apply equally to other forms of regional anaesthesia.
These include:
Inadequate resuscitation drugs and equipment. No regional anaesthetic technique should be attempted if drugs and equipment for resuscitation are not immediately to hand.
Clotting disorders. If bleeding occurs into the epidural space because the spinal needle has punctured an epidural vein, a haematoma could form and compress the spinal cord. Patients with a low platelet count or receiving anticoagulant drugs such as heparin or warfarin are at risk. Remember that patients with liver disease may have abnormal clotting profiles whilst low platelet counts as well as abnormal clotting can occur in pre-eclampsia.
Hypovolaemia from whatever cause e.g. bleeding, dehydration due to vomiting, diarrhoea or bowel obstruction. Patients must be adequately rehydrated or resuscitated before spinal anaesthesia or they will become very hypotensive.
Patient refusal. Patients may be understandably apprehensive and initially state a preference for general anaesthesia, but if the advantages of spinal anaesthesia are explained they may then agree to the procedure and be pleasantly surprised at the outcome. If, despite adequate explanation, the patient still refuses spinal anaesthesia, their wishes should be respected. Likewise, mentally handicapped patients and those with psychiatric problems need careful pre-operative assessment.
Children. Although spinal anaesthesia has been successfully performed on children, this is a highly specialised technique best left to experienced paediatric anaesthetists.
Sepsis on the back near the site of lumbar puncture lest infection be introduced into the epidural or intrathecal space.
Septicaemia. If a patient is septicaemic, they are at increased risk of developing a spinal abscess. Epidural abscesses can, however, appear spontaneously in patients who have not had spinal/epidural injections especially if they are immuno-deficient: e.g., patients with AIDS, tuberculosis, and diabetes.
Anatomical deformities of the patient's back. This is a relative contraindication, as it will probably only serve to make the dural puncture more difficult.
Neurological disease. The advantages and disadvantages of spinal anaesthesia in the presence of neurological disease need careful assessment. Any worsening of the disease post-operatively may be blamed erroneously on the spinal anaesthetic. Raised intracranial pressure, however, is an absolute contra-indication as a dural puncture may precipitate coning of the brain stem.




Dr NAZIM MOHAMMAD
CONSULTANT ANAESTHESIOLOGIST
K . V . G MEDICAL COLLEGE ., SLUUIA