CXR & AXR Flashcards
Quantify the radiation dose of a CXR
Equivalent to 3 days of standard background radiation
Why does the heart appear larger in the AP view
X-ray beam diverges as it travels - similar to a light beam - any object further from the film will cast a larger ‘shadow’
What is adequate penetration
Ideally one should see the upper vertebral bodies down to approximately the fifth thoracic vertebral body through the mediastinum.
What is normal CTR
< 50%
What is the correct position of the ETT on CXR
4 cm above the carina
Describe the normal movement of the ETT inside the trachea
Chin up = tip up ± 2 cm
Chin down = tip down ± 2 cm
Therefore correct placement 4cm above the carina will prevent extubation/vocal cord damage and endobronchial intubation
Describe the correct placement of a tracheostomy tube
The tracheostomy tube should occupy 1/2 to 2/3 of the tracheal diameter
The tip of the tracheostomy tube should be centrally located within the trachea at the level of the 3rd thoracic vertebra
What level is the carina
T4/T5 = same level as the sternal angle
What is the ideal position for the tip of a central venous line
Ideal: mid SVC = tip should be just above the right main bronchus on CXR
Acceptable: brachiocephalic vein
Where are the venous valves located relevant to subclavian and internal jugular central venous access. Why are these valves relevant
Near the first rib
Relevance: Should the tip of the catheter abut one of these valves –> impaired flow
Why should the tip of a central venous catheter not lie within the right atrium
Risk of cardiac arrhythmia or perforation
Describe the CXR appearance of a correctly positioned pulmonary artery balloon tipped catheter (Swan-Ganz)
Middle third of CXR about 5 cm from the midline
Describe some of the risks related to a pulmonary artery ballon tipped catheter
- Pulmonary infarction/thrombosis (tip left inflated)
- Pulmonary thromboembolism (stasis from inflated tip)
- Arterial rupture
- Pseudoaneurysm formation (Pseudoaneurysm = only adventitia of vessel encloses the dilatation - intima and media excluded)
Where should chest drain be placed in pneumothoraces
Anterosuperiorly (air collects in the least dependent part of the chest)
Where should the chest drain be positioned in pleural effusion
Posteroinferiorly –> fluid collects in the most dependent parts of the thoracic cavity
What is the definition of a widened mediastinum
Widened mediastinum: Definition: A mediastinum measurement of ≥8 cm or >1/3rd the transthoracic distance at the level of the aortic knob on a supine AP film.
How can the radiological signs of pulmonary collapse be classified
DIRECT SIGNS - Displacement of fissures - Increased density of lobe (outline of adjacent structures may be obscured) - Crowded vessels of bronchi
INDIRECT SIGNS
- Elevated hemidiaphragm
- Mediastinum shift (trachea upper lobe collapse | heart in lower lobe collapse)
- Hilar displacement
- Compensatory hyperinflation of other lobes (more lucent)
What are the causes of pulmonary consolidation
INFLAMMATORY INFILTRATE IN ALVEOLI
- Infection
Pulmonary infection (TB/bacterial)
- Non-infectious Extrinsic allergic pneumonia Eosinophilic pneumonia Aspiration Sarcoidosis
FLUID IN ALVEOLI
Pulmonary oedema
Trauma (contusion)
Pulmonary haemorrhage
TUMOUR IN ALVEOLI
Lyphoma
Bronchoalveolar cell carcinoma
Distinguish the clinical and radiological appearance of:
- lobar pneumonia
- bronchopneumonia
- aspiration pneumonia
LOBAR
Consolidation confined to a single lobe of the lung
- Previous healthy patient
- Streptococcus pneumoniae
BRONCHO and ASPIRATION
Consiolidation is patchy and often perihilar with bronchial wall thickening
- Elderly/debilitated patients
- Gram negative organisms
What type of organism causes cavitation on CXR
- Staphylococcus aureus,
- Gram negative organisms (especially Klebsiella),
- anaerobes and
- Mycobacterium tuberculosis
How to distinguish between right middle and right lower lobe pneumonia
Right lower lobe pneumonia causes loss of clarity of the right hemidiaphragm
How is left lingula lobar pneumonia distinguished from left lower lobe pneumonia
Distorted left heart border
How is the mediastinum divided and what does each section contain
Anterior - thymus and fat
Middle - heart, GVs and hila
Posterior - Oesophagus, azygous vein, descending aorta
What is extramedullary haematopeisis
Extramedullary hematopoiesis is when blood precursor cells typically found in bone marrow (erythroblasts, megakaryocytes, myeloid precursors) accumulate outside of the bone marrow.
How can one tell if the mass is in the middle mediastinum versus anterior or posterior
The heart border will be distorted by a mass originating in the middle mediastinal compartment.
What are the most common causes of pulmonary hypertension
Chronic lung disease
Multiple pulmonary emboli
Primary pulmonary hypertension
Left to right shunt (Septal defect)
Classify the CXR and signs and symptoms related to severity of left ventricular failure
PCWP < 15 mmHg
No symptoms
Normal CXR
PCWP 15 -20
Exertional dyspnoea | PND | Basal crackles
CXR: Upper lobe diversion
PCWP 20 - 25
Dyspnoea at rest | Orthopnoea | Crackles and wheezes
CXR: Interstitial oedema (Septal lines, perihilar haze, Peri-bronchial cuffing | Reticular opacities | Small pleural effusions)
PCWP > 25
Severe dyspnoea | Pink frothy sputum | CRT > 2 s
CXR: Alveolar oedema (Air-space opacities in a perihilar ‘batwing’ distribution)
List common causes of dilated bowel on AXR
Mechanical obstruction (Adhesions/Cancer) Pseudo-obstruction Paralytic ileus Air swallowing (pain/asthma/BVM)
What is the difference between pseudo-obstruction and paralytic ileus
Pseudo-obstruction is clearly limited to the colon alone, whereas ileus involves both the small bowel and colon. The right colon is involved in classic pseudo-obstruction, which typically occurs in elderly bedridden patients with serious extraintestinal illness or in trauma patients.
What causes paralytic ileus
Postoperatively
Local inflammatory processes, e.g. pancreatitis or appendicitis
Trauma Congestive cardiac failure Renal failure Debility Infection
How can small and large bowel dilatation be distinguished
Variable
Small Bowel
Colon
Distribution of dilated bowel
Central
Peripheral
Number of loops of dilated bowel
Many
Few
Diameter of dilated bowel
3-5 cm
5 cm +
Haustra
Absent
Present
Valvulae conniventes
Present in jejunum
Absent
Radius of curvature of dilated loops
Small
Large
Solid faeces
Absent
Present
List the causes of mechanical bowel obstruction
Adhesions (75%) Strangulated hernia (8%) Small bowel volvulus Strictures (inflammatory/radiation) Extrinsic compression Intrinsic lesions - Gallstones - Small bowel tumours
