24 2020 University of Cape Town Paper III Session ...

Part II Anaesthesia Refresher Course – 2020 University of Cape Town 24

Paper III Session: Radiology Interpreting imaging of the chest and mediastinum

Prof. Sally Candy

Associate Professor (Emeritus) Division of Diagnostic Radiology

University of Cape Town

An imprecise tool! Only five different densities are detectable on plain films: (if you exclude the odd bullet / knife /stent etc)

• Air, fat, soft tissue, calcium and contrast (barium, iodine).

An optimistic claim! Is has been said (no doubt by a radiologist), “Expert radiologists not only perceive abnormalities that non-experts do not, but they also better understand what to attend to and what to ignore” (Gunderman and Patel, 2019).

An interesting statistic! So in that case…

…why did 83% of radiologists not notice the gorilla in the top right of this image when scrolling through five chest CT scans looking for lung nodules?!

A poor excuse! This is explained by a phenomenon known as ‘inattention blindness’: “….when engaged in a demanding task, we may fail to perceive an unexpected stimulus that is in plain

sight….” The error rate in reading radiological images has not improved in the last seven decades!

The implications of getting it wrong! It goes without saying that false negatives and false positives may be equally disastrous for the patient and that you cannot see what you do not know.

Paper III: Radiology – interpreting imaging of the chest and mediastinum Prof. S Candy

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So how should we approach the interpretation of a CXR? Armed with:

• a knowledge of the clinical scenario

• a little knowledge of 3D anatomy

• a very good idea of what is normal

• an educated guess as to what you might expect to see

• extreme caution! Compare these CXR’s with similar features: Can you make the diagnosis in each?

Back to basics – the normal chest radiograph /plain film:

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And here is the artist’s rendition (with a little help from the computer)

Case courtesy of Dr Vincent Tatco, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/46331">rID: 46331</a>

Sadly, most of our radiographs do not come with “augmented reality” but in a few shades of black and white. They are often technically suboptimal – a challenge to even the most experienced viewer. An anatomic distance of roughly 20 cm is collapsed into one dimension, incorporating all anatomy, pathology and any incidental overlying foreign body e.g. sheet fold, hair braid, buttons, catheters and tubing etc. This applies equally to both the PA and Lateral; having both views adds significantly to the interpretation. Outlines and edges seen on plain radiographs depend on differential density. Two structures of similar density will be distinguishable only if they are separated by air (the silhouette). This applies both to normal anatomical structures (e.g. the right and left ventricles) and to an abnormal structure or process lying adjacent to a normal bit of the anatomy (e.g. left lower lobe consolidation and the left hemidiaphragm).

Assessing the image

1. Does this radiograph belong to the patient you want to review? Correct name, age, sex

2. How was the film taken? Erect /supine /semi-erect /PA /AP/inspiration/expiration? NB mobiles are AP - easy to miss pleural effusions and pneumothoraces

3. Is the left /right marker correct?

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4. Is the film rotated? Beware the rotated film – over-call pulmonary artery prominence/ adenopathy. Distorts or obscures mediastinal pathology False impression of differential translucency between the lungs

5. Is the image adequately penetrated? The intervertebral disc spaces should be more visible than the outlines of the vertebral bodies. Penetration is less of a problem with digital imaging (answer to a radiographer’s prayer), salvage possible.

6. Is the entire chest visible? Apices and CP angles fully visible?

7. Are the radiographic silhouettes maintained? Beware the right middle lobe and lingual

8. Develop a routine and stick to it. Start centrally and move peripherally scanning and re-scanning continually. This is particularly important when there is one glaring abnormality that will detract from others.

ABC: AIRWAY / BONES / CARDIAC / DIAPHRAGM (PLEURA) / EFFUSIONS / GIZMOS

REVIEW SITES: APICES / BEHIND THE HEART / BENEATH THE DIAPHRAGM / BONES

AIRWAY Is there an endotracheal tube in situ? Is the position adequate? Between the clavicular head and the carina (3-4cm above carina) Is the trachea central? Are both main bronchi visible? Is the angle of the carina normal? (60 to 100 degrees) Is there any foreign body? e.g. tooth often dislodged during intubation?

MEDIASTINUM Measure at the arch Is it widened (max allowed on a supine film 8cm, erect film, 6cm)? Is the aortic knuckle normally positioned? Is the aortic knuckle crisp? NB most sensitive sign of mediastinal haematoma on CXR Beware the right-sided arch Beware the small aortic knuckle Beware the big arch Beware the ‘Figure 3’ arch Aortic arch calcification (interrupted – dissection with imminent arch rupture)

Diagnoses A B C and D?

A B

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C D Describe the abnormalities visible on the following CXR:

• widened mediastinum >8 cm when supine>6 cm when erect

• indistinct or abnormal aortic contour

• deviation of trachea or NGT to the right

• depression of left main bronchus

• loss of the aorto-pulmonary window

• widened paraspinal stripe

• widened paratracheal stripe

• left apical pleural cap

• large left haemothorax (note difference in radiolucency)

• Features of traumatic aortic rupture

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CT Angiography takes away the guesswork:

Stanford Type A dissection Type B dissection

• Traumatic aortic rupture mediastinal haematoma and dissection flap shown on axial and oblique cor recons

THE HEART Size: Adults PA heart <50% Paediatric AP heart < 60% transverse diameter of the chest wall

Shape: Remarkably constant in normal adults. Thymus messes with the mediastinal contour in young children. If the heart is enlarged, then which chamber(s) are affected? Use your PA and Lateral for clues. Shapes: You know the common ones.

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Match the pairs: Tetralogy of Fallot Transposition of the great vessels Coarctation of the aorta Epstein Anomaly Normal thymus

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Reference: Department of Radiology Dankst University Poland. The tell-tale heart. Chest x-ray revisited in children with congenital heart disease. Pictorial essay. ECR 2018

RESOLVING THE MADDENING MYSTERY OF THE MEDIASTINUM – ITMIG based on multi-detector CT with multi-planar reformatting Old Classification of compartments based on lateral radiograph: (Reference: Swanevelder CME 2007!)

• Middle: Heart and pericardium, tracheal bifurcation and main bronchi, the lung hila, phrenic nerve, thoracic duct, lymphatics and lymph nodes.

• Anterior: Between anterior pericardial reflection and the sternum

• Posterior: Between the posterior pericardial reflection and the vertebral column. Descending aorta, oesophagus, vagus nerve, sympathetic chain.

• Anterosuperior: Thymus, aortic arch and its branches, SVC, nodes. thoracic duct, azygos and hemiazygos veins and paravertebral lymph nodes.

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So, let’s see how far our approach takes us on this CXR: Is the cardiac silhouette maintained? In which compartment is the lesion NOT located? What is the location and likely diagnosis?

ITMIG (INTERNATIONAL THYMIC MALIGNANCY INTEREST GROUP) IS BASED ON CT (AXIAL IMAGING) Axial CECT Chest

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ITMIG mediastinal compartments on corresponding axial CT levels: a) aortic arch b) left pulmonary artery c) heart

The pre-vascular compartment is anterior or peripheral to the pericardium The paravertebral compartment is separated from the visceral compartment by a line 1 cm posterior to the anterior vertebral body border 1. ANTERIOR / PREVASCULAR SPACE: BORDERS

• Superiorly: Thoracic inlet.

• Inferiorly: Diaphragm.

• Anteriorly: Posterior border of sternum.

• Laterally: Parietal mediastinal pleura.

• Posteriorly: Anterior aspect of the pericardium as it wraps around the heart.

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PATHOLOGY

• The four ‘T’s : Thymus / / Teratoma ( Germ Cell Tumor)/Terrible Lymphoma / +_Thyroid

• Morgagni Hernia / Ectopic parathyroid adenoma (rare)

Most masses are thymic in origin (even lymphoma and teratoma) Look for displacement of trachea (especially on lateral CXR) Check for fat (black / HU -80) (Teratoma/ thymolipoma/ anterior fat pad/ fat in Morgagni) Check for fluid/cysts (grey / HU 0-5) (Teratoma/ Pericardial cyst/ cystic thymoma) Check for soft tissue enhancement (NB vascular! More likely in malignant lesions) Check for calcification (white HU >100) (aneurysm/ thymoma/ teratoma) NOT lymphoma unless DXRT 2.MIDDLE / VISCERAL SPACE:

BORDERS

• Superiorly: Thoracic inlet.

• Inferiorly: Diaphragm.

• Anteriorly: Posterior boundaries of the prevascular compartment.

• Laterally: Parietal mediastinal pleura.

• Posteriorly: Vertical line 1 cm posterior to the anterior margin of the spine. PATHOLOGY Lymphadenopathy / Duplication cysts (bronchogenic and oesophageal) / Vascular eg aneurysms / Cardiac cardiac chamber enlargement /oesophageal /retrosternal thyroid goitre 3.PARAVERTEBRAL SPACE:

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BORDERS

• Superiorly: Thoracic inlet.

• Inferiorly: Diaphragm.

• Anteriorly: Posterior boundaries of the visceral compartment.

• Laterally: Parietal mediastinal pleura.

• Posteriorly: Vertical line along the posterior margins of the chest wall at the lateral aspect of the transverse processes.

PATHOLOGY Neurogenic neoplasm /discitis / osteomyelitis / bone tumours / haematoma / extramedullary haematopoiesis

PEARLS

• Cysts may bleed (HU> water /CSF but should NEVER enhance.

• Necrotic nodes may appear cystic but will have peripheral enhancement.

• Calcification in nodes in old TB, sarcoidosis or silicosis and some nodal mets.

• NB Papillary thyroid CA may be largely cystic.

• Hyper-enhancing lesions may be nodes, retrosternal goitre or vascular e.g. enlarged azygous vein / arch anomaly.

• MRI offers better contrast resolution and assessment of water motion within tissue (DWI!!)

• CT offers better spatial resolution

• CECT distinguishes vascular from non-vascular (e.g. nodes from hilar vesssels)

• In imaging as in life, timing is everything (CTPA, systemic arterial, porto-venous phases)

• ‘Windowing’ important – know what tissue you want to look at e.g. lung vs vessel vs bone vs soft tissue

• PET/CT offers combined anatomical & functional aspects of tissue (sensitive but not specific) So if we do a CECT we should be able to answer the following questions:

1. Is the lesion as dense as the vessels on CT? 2. Does it have fat or calcification? 3. Is it a simple or complex cyst or is it solid?

If we then superimpose PET on the CT, what further information do we get? Diagnosis?

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In the following example: What structure is displaced? Is the aortic arch silhouette lost? In which space is the mass? Is it calcified? Does it contain fat? Is it cystic or solid? CT enables us to answer these questions more precisely:

Multiplanar reformatting now possible on CT. Compare this coronal recon with the original CXR:

Using the above approach to the chest radiograph and CT, we will spend the last 30 minutes of the session working through a number of examples of relatively common conditions that the anaesthetist / intensivist is likely to encounter. References

1. Tapia et al [ITMIG classification of medistinal anatomy:exposure through augmented reality. ECR 2018]. http://dx.doi.org/10.1594/ecr2018/C-1392

2. Radiopaedia, Various Images. Editor: Frank Gaillard 3. Acute traumatic aortic injury. Radiology. State of the Art, Steenburg et al.2008 4. Interpreting the normal CXR : https://www.youtube.com/watch?v=L6bnD2wOEmg