Answer: Right upper lobe bronchus

This case shows us a zoomed up image of a post contrast axial CT of the chest. Here, going from top to bottom, we have just passed the carina and can see the right and left main bronchus.

The arrow however points at the first branch of the right main bronchus – this is the bronchus going to the right upper lobe. On an axial CT slice we can recognise this by the appearance of a ‘whale’!

On the coronal slice we can see the right upper lobe bronchus coming off the right main bronchus. After this comes off the airway is no longer the right main bronchus but the bronchus intermedius. This then splits into the right lower lobe bronchus and right middle lobe bronchus. We can see the upper lobe bronchus coming off on the coronal image below.

Knowing each of the airways on a CT scan can be really tricky especially when you first start looking at these scans. Having a good grasp of bronchial anatomy is fundamental when it comes to reviewing chest CT. Taking each airway in turn is important as subtle findings can lurk such as small endobronchial tumours (for example carcinoid tumours of the lung are classically endobronchial).

Although it can be daunting to learn each and every airway, recognising the ‘whale’ of the right upper lobe airway is a good start and something to build on!

Learning point

Remember when you see the ‘whale’ – remember you’re seeing the right upper lobe bronchus!

Answer: Posterior cruciate ligament

This is a sagittal image of a knee MRI which is T1 weighted. The image shows us the typical appearance of the posterior cruciate ligament on a sagittal view which I like to think of as ‘rainbow’ shaped, peering over the ‘hill’ (tibia) although maybe that’s just me.

If we go slightly lateral to this we’ll find its brother the anterior cruciate ligament.

Remember the cruciate ligaments are so called as they are ‘cross shaped’ and cross over one another. Whilst the PCL heads anteriorly the ACL heads posteriorly from its attachment on the tibia. In terms of where they attach remember:

• The posterior cruciate ligament arises from the posterior intercondylar area of the tibia and heads anteriorly to insert into the lateral surface of the medial femoral condyle.
• The anterior cruciate ligament arises from the anteromedial intercondylar area of the tibia and heads posteriorly to insert into the posteromedial aspect of the lateral femoral condyle.

Learning point

When you see the rainbow peering over the tibia on a sagittal view of the knee, remember you’re seeing the posterior cruciate ligament!

Answer: Right vertebral artery

This is an axial image of a cervical spine MRI. The arrow points at the right vertebral artery which can be seen within the right sided foramen transversarium.

The foramen transversarium lie either side of the vertebrae within the transverse processes and give passage to the vertebral artery, vein and a plexus of sympathetic nerves.

What is the course of the vertebral artery?

The right and left vertebral arteries arise from the subclavian arteries then pass up the neck before uniting to form the basilar artery at the level of the pons. The course can be split into four sections:

• Prevertebral (V1)  – Passes up between the longus colli and the scalenus anterior muscles
• Cervical (V2) – Passes vertically up through the transverse processes of the C2-6 vertebrae as can be seen in the image in this question
• Atlantic (V3) – Passes laterally from the C2 transverse process through the transverse process of the atlas. It then passes around the lateral mass of C1 before piercing the dura.
• Intracranial (V4) – Passes vertically to unite with the contralateral side and form the basilar artery at the lower border of the pons.

Learning point

When it comes to acute imaging, knowing the course of the vertebral arteries is important when assessing for a vertebral artery dissection. These happen most commonly within the V2 or V3 segments but can extend to involve the intracranial segment (V4). CT angiogram is usually the first line investigation given it is more readily available than MR. Non contrast CT can show a hyperdense vessel (due to clot). The post contrast phase typically shows an irregular lumen with a thickened vessel wall due to mural thrombus.

The most sensitive modality is MRI. T1 fat saturated images can highlight haemorrhage within the wall of the vessel, the so called ‘crescent sign’ where you see a high signal crescent at the periphery of the vessel on axial images. This can also look like a fried egg.

Answer: Left precentral gyrus

This is an axial image of a T2 weighted brain MRI. How can we tell this is T2 weighted? Look at the CSF spaces ie the sulci – these are bright. Some of the other common sequences used in brain MRI are T1 weighted and FLAIR (fluid attenuated inversion recovery) – in both of these fluid will be dark.

Now remember the gyri are the ridges on the brain surface whilst the sulci are the fissures in between these, think of these as the ‘cracks in the road’.

This question is all about knowing how to identify the central sulcus. There are a few ways to do this but one way I find helpful is to first identify the superior frontal gyrus – this is the most medial gyrus of the frontal lobe’s superior surface so is usually pretty easy to find.

Now once you’ve found this follow it down and you should find the precentral gyrus which it meets in an ‘L shape’.

Once you’ve found the precentral gyrus you are on the home straight. The central sulcus is just behind this – behind the central sulcus you’ll find the imaginatively named postcentral gyrus. Take a look at the annotated diagram below as a recap.

Learning point

In stroke imaging, the precentral gyrus is key: it’s the brain’s main motor strip. Damage here can explain contralateral weakness, with different vessels affecting different parts of the precentral gyrus and causing different clinical signs. Have a look at the table below for a recap:

Answer: Left lateral rectus

Here we have a coronal image from an MRI of the orbits. The scan is again T2 weighted – note how the CSF is bright in signal. We have a good view of the muscle cone which surrounds the optic nerve. The rectus muscles are relatively easy to identify here in north, south, east and west positions; they’re handily named superior, inferior, medial and lateral.

The other muscles that we can see here are the superior oblique (just medial to the superior rectus) and the levator palpebrae superioris (LPS on the diagram below) which sits just above the superior rectus and lifts the eyelid.

Learning point

When we see an orbital lesion on imaging, knowing the anatomy of the muscle cone is really important when it comes to producing an accurate differential diagnosis.
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We can differentiate lesions as being predominantly:⁣

Extraconal (outside the muscle cone)⁣: Infection is one of the most important causes – don’t miss a periosteal abscess! In these situtations you’ll likely see a peripherally enhacing collection and there may be underlying paranasal sinusitis. Other causes of an extraconal lesion include lymphoma, metastases (from breast and lung cancer) and sarcoid ⁣
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Conal (originate within the muscle cone)⁣: The most common culprits are pseudotumour and thyroid ophthalmopathy – the latter usually is bilateral and spares the tendinous insertion (known as the Coca Cola sign as the muscle looks like a bottle)⁣
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Intraconal (within the muscle cone)⁣: Examples include cavernous haemangiomas (may see small foci of calcification), metastases and sarcoidosis ⁣
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Intracanalicular (within the optic nerve)⁣: Such as optic glioma or meningioma

Answer: Right hepatic vein

This is an image of an ultrasound of the liver. We are near the top end (superior) of the liver. How do we know this? We can see the hepatic veins – these drain into the inferior vena cava at the superior end of the liver.

This image is a nice depiction of the hepatic veins and an image I try and see every time I do a liver ultrasound. I get the picture by placing the probe under the right costal margin (below the ribs anteriorly) and asking the patient to take a gentle but deep breath in before holding. I then fan through looking to find this picture. Don’t forget to let your patient breathe again or you’ll need to set off the crash alarm.

The three hepatic veins look a bit like ‘crow’s feet’ and can be easily distinguished as right, middle and left.

On ultrasound we can measure the blood flow within the hepatic vein by measuring the Doppler signal, which isn’t too difficult when you know the basics of your ultrasound machine. The hepatic vein Doppler waveform is a bit complicated but let’s try and break it down here.

Warning: this gets a bit complicated! Only read on if you are undertaking radiology/ultrasound exams or perform hepatic vein Dopplers in your normal practice – otherwise move on to the next question.

Changes of pressure within the right atrium feed their way through the inferior vena cava and have an impact on the hepatic vein Doppler waveform which we can see here:

Anything that increases right atrial pressure  such as atrial contraction or filling of the atrium against a closed tricuspid valve will cause the waveform to slope upward. In contrast, anything that decreases right atrial pressure (right ventricular filling) will cause the waveform to slope downward.

So let’s take each of the parts of the waveform in turn. We start with the ‘A’ wave which represents contraction of the right atrium (atrial systole). At this point blood gets propelled both into the right ventricle but also into the inferior vena cava and hepatic veins.

The ‘s’ wave represents ventricular systole. The right ventricle contracts sending blood into the right ventricular outflow tract and then pulmonary trunk. At this point the tricuspid valve annulus is ‘sucked’ down towards the cardiac apex and blood is pulled from the liver. towards the heart. Note if there was tricuspid regurgitation less blood would be pulled from the liver leading to a decreased or even reversed ‘s’ wave.

Next we have the ‘v’ wave which is considered a ‘transitional’ phase. The right atrium continues to fill whilst the valve is closed leading the wave to slope upwards before the valve opens, the ventricle fills and the wave slopes downwards.

The ‘d’ wave is formed during ventricular diastole – here the ventricle relaxes and fills with blood whilst blood travels passively from the liver to the heart (antegrade direction).

This represents the normal waveform however in some circumstances we will find an abnormal waveform, summarised in the table below.

Learning point

Knowing the pattern of a hepatic vein waveform is important for anyone performing liver ultrasound. One might want to specifically request a hepatic vein Doppler when suspecting Budd Chiari syndrome, obstruction of the hepatic veins usually caused by thrombosis.

A third of cases are idiopathic but otherwise any thrombotic risk factor (eg immobility, thrombophilia) can predispose to Budd Chiari syndrome. Note that it can co-exist with portal vein thrombosis and so the portal vein needs to be assessed as on any liver ultrasound.

Budd Chiari syndrome classically presents with the triad of abdominal pain, ascites and liver enlargement.

Answer: Inferior vena cava

This is an axial image of a lumbar spine MRI. When trying to decide what kind of sequence it is have a look at a couple of things:

1) Fluid – look for any regions of normal fluid on the slice, eg bladder, renal calyx or in this case the spinal canal. T2 weighted images will show fluid as bright whilst on T1 weighted images fluid will be dark. FLAIR sequences used in brain imaging will also show fluid as dark.

2) Fat – Find any normal fat on the image. Both T1 and T2 weighted images will show fat as bright signal whilst STIR sequences and fat saturated sequences will show fat as dark. The latter two are commonly used in MSK imaging to show regions of inflammation and oedema which is easier to do when the signal from fat is lower.

On this sequence then we can find fluid within the spinal canal – here it is dark. In normal circumstances there will be epidural fat behind the spinal canal, here it is bright. So we know this is a T1 weighted image.

This is an image of the lumbar spine and in the centre we are seeing the intervertebral disc in cross section. When looking at these MRI scans, the focus of the test is usually the spine, looking for any prolapse that may be causing stenosis of the spinal canal or impingement of the nerve roots.

However it is important to review everything that you can see on the scan, including the psoas muscles either side of the disc, looking in particular for expansion that may represent haematoma or abscess. Also look at the vessels in front of the disc, looking for the aorta on the left and inferior vena cava (IVC) on the right (remember we are looking up ‘through’ the patient so the right side is actually the patient’s left).

Looking in this region is important as you may find an incidental aortic aneurysm – spotting this can potentially save the patient’s life but getting them enrolled into a screening programme before it unexpectedly ruptures. It’s also not unheard of for enlarged retroperitoneal lymph nodes to be picked up on a lumbar spine MRI so look between the aorta and IVC and on either side of the vessels.

You may also be able to identify the ureters in front of the psoas muscles so check that these aren’t dilated – if they are you may want to go back to your localiser images (pictures that are taken to plan out the MRI scan). Here you may get to see the kidney and check if there is hydronephrosis.

Learning point

Don’t forget to check the structures outside of the spine on a lumbar spine MRI!

In front of the lumbar spine the you will find the aorta on the left and inferior vena cava on the right.

Answer: Oesophagus

This is a sagittal image of a cervical spine MRI. Going back to our rules we can see both fluid and fat is bright meaning this is a T2 weighted image.

We know we are likely to be in the midline here as we get a good view of the spinal cord surrounded by bright cerebrospinal fluid (CSF).

The arrow is pointing at a structure in front of the cervical spine – this is the typical place where we would find the oesophagus. Note how we can just make out different mucosal layers which differentiates it from the trachea which is more anterior.

Assessing this region is important when it comes to cervical spine MRI – an epidural metastasis in this region may be the only abnormality on the scan. In cases of trauma this region is important to review to exclude an epidural haematoma. For these reasons I always try to point out the oesophagus which gives me the reassurance that I haven’t missed anything in front of the vertebral bodies.

Learning point

The oesophagus lies anterior to the spine within the posterior mediastinum – assess this region on cervical spine MRI as you may pick up epidural metastases or haematoma.

Answer: Left precentral gyrus

This is a coronal image from an MR angiogram looking at the abdominal aorta and its branches.

When reading one of these scans it’s important to try and follow all of the major branches in turn including:

▫️T12 – the coeliac axis – this branches into the left gastric, splenic and common hepatic arteries ⁣(mnemonic GoSH)
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▫️L1 – the superior mesenteric artery (SMA) – supplies bowel from the ampulla of Vater at D2 (duodenum) to the distal third of the transverse colon⁣
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▫️L1-2 – the main renal arteries ⁣– usually one on each side but can be more than one
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▫️L3 – the inferior mesenteric artery (IMA) – supplies colon from the distal third of the transverse colon to the upper anal canal⁣
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At L4 we can see the bifurcation of the aorta into the common iliac arteries . The common iliac arteries then bifurcate into the external and internal iliac arteries with the internal more medial – making this the answer in this case.

Well done on making it this far, just one more question to go…

Answer: Dens

This is a coronal image from a cervical spine CT scan. Here we can see the upper cervical spine. There are a few different terms used to describe the different structures of the upper cervical spine so let’s take a moment to go through them:

The arrow points to the projection from the C2 vertebral body – this is the ‘dens’ or ‘odontoid peg’. Fractures of the peg like any fracture of C1 or C2 should be taken very seriously as they have the potential to cause life changing spinal cord injury. The risk changes depending on which part of the peg is fractured.

The Anderson and D’Alonzo classification is the most commonly used classification of peg fractures. Let’s take a look at this:

Learning point

Don’t miss a peg fracture! 

CT is now advocated as first line in many parts of the world as it is now clear that X-ray can miss important fractures. My advice would be to follow your local guidelines but always have a low threshold for CT in these patients if it is available to you.⁣