Answer: Right lower zone air space opacity

Have a look at both sides and you’ll hopefully spot there is an opacity within the right lower zone. 

Take a closer look at the opacity and you will hopefully spot some small circular lucencies. This is an important finding – these are termed ‘air bronchograms’ and reflect gas within airways within consolidated lung. The term ‘air space opacity’ can be used synonymously with the term ‘consolidation’.

Note that the presence of air bronchograms –  confirms the presence of consolidation.

The term ‘consolidation’ is commonly used interchangeably with pneumonia but this isn’t technically true as consolidation simply reflects anything that causes filling of the airspaces of the lung, ie the alveoli. This happens in a range of aetiology including:

• Infection
• Haemorrhage
• Heart failure
• Lung cancer (a subtype formally known as bronchoalveolar carcinoma)

The fact that consolidation can be caused by lung cancer is the reason that you will commonly see X-ray reports recommending a follow up film in 6 weeks to make sure that consolidation has cleared.

Why are we describing this as ‘right lower zone’ rather than ‘right lower lobe’ consolidation?

Answer: Colitis

Here we have an abdominal X-Ray. Now this is an old film – currently depending on where you are in the world you may be less likely to see an abdominal film done for this indication. With the rise of CT the justification of giving what can be a considerable radiation dose for a test that is not always specific is getting more dubious.

The clinical history is suggestive of a colitis with the indication for imaging here only really changing things if we think there to be a complication such as:

• Perforation
• Severe colonic dilatation (toxic megacolon – here there is loss of neurogenic tone of the colon, most commonly seen with ulcerative colitis but can be associated with colitis of any cause)
• Abdominal collection

In these instances, CT is far more sensitive and so rather than irradiating twice, as long as there is availability it makes sense to either do nothing if suspicion is low or go straight to CT.

However CT is not readily available everywhere and so we need to be able to recognise signs of colitis on an abdominal X-Ray. Taking a look at this X-Ray the bowel looks abnormal.

We can see semicircular indentations of the bowel wall – this is sometimes called ‘thumb printing’ given this has the shape of a thumb.

This happens because of thickening of the colonic haustrae, and can be seen classically in inflammatory bowel disease but can occur in any form of colitis.

In this case there was an underlying diagnosis of Crohn’s disease. If we have a look at the CT we will see signs of a colitis with diffuse mural thickening.

Learning point

Seeing ‘thumbprinting’ on an abdominal X-Ray can reflect a colitis. If the cause is known, CT not always indicated unless there is a suspicion of complications such as perforation or an abdominal collection.

Answer: Acute appendicitis

Here we have a non contrast CT KUB looking for renal tract calculi. However in this case the kidneys both look normal with no hydronephrosis and no bright renal calculi. If we follow the ureters down there are no definite ureteric calculi. Although there are some right sided pelvic foci of calcification these do not definitely run in the line of the ureter and are more likely phleboliths rather than ureteric calculi.

Make sure you have a look at the bladder as well for calculi – however there are none in this case. There is however an abnormality within the right iliac fossa – always make sure to look for alternative causes of pain.

When you suspect a right iliac fossa abnormality, first start by identifying the caecum. I do this by tracing the colon all the way from the rectum back to the origin. Once you find this, in normal circumstances you will find two things communicating with it. Firstly the terminal ileum and then the appendix.

You should be able to recognise the terminal ileum as communicating with the rest of the small bowel but also look out for some fat density which you will normally find with a normal ileocaecal valve as we can see below.

Now we have identified the terminal ileum we can look for the appendix. This should be a blind ending structure arising from the caecum measuring no more than 7 mm in diameter. You can also measure the wall thickness – more than 3 mm is usually abnormal.

In this case we can see a blind ending structure arising from the caecum – this is the appendix.

When we follow the appendix in this case we can see it is enlarged with surrounding fat stranding – this is acute appendicitis. It can sometimes be difficult on CT to make the call. I usually use the diameter of the appendix and the presence of surrounding fat stranding to help me make the call. A high density appendicolith within the appendix also adds weight to the diagnosis.

One you find appendicitis look for complications:

• Free gas: put on lung windows and make sure there is no perforation
• Collection

Other things to think about when it comes to appendicitis:

• Mucinous neoplasms of the appendix can be asymptomatic and are usually an incidental finding on CT which is why I try and identify the appendix on every abdominal CT I look at. In later stages these can lead to pseudomyxoma peritoneii which will show on CT as ascites with classic scalloping of the liver.
• Neuroendocrine appendiceal tumours can present with features of acute appendicitis although again can be asymptomatic.
• Dropped appendicolith: look out for a retained appendicolith in patients who re-present with abdominal pain after surgery for appendicitis. You may see this away from the surgical site.
• Stump appendicitis: consider when there are features of appendicitis after an appendectomy. Here there is recurrent appendicitis affecting residual appendiceal tissue.

Did you spot the other incidental findings? Firstly there are gallstones within the gallbladder.

There is an umbilical hernia but most importantly there is a soft tissue lesion within the subcutaneous tissues which was worked up after the scan, resected and proven to be a soft tissue sarcoma.

In normal circumstances you should find two structures communicating with the caecum: the terminal ileum heading to the ileocaecal valve with its characteristic fat density as well as the appendix.

Answer: Acute renal and splenic infarcts

Let’s start by having a look at the spleen. When assessing the spleen on a post contrast CT it is important to firstly assess which phase of contrast we are currently in. That is because on an arterial phase CT the spleen can appear very heterogeneous due to variable contrast flow rates through the open and closed circulation. This can easily be confused for pathology but is in fact normal!

In this case we are in what is called a ‘portal venous phase’: we can see from the images below that both the main portal vein and the hepatic veins are well opacified. This means we are not in an arterial phase and we can reliably assess the spleen.

Now the spleen does not appear normal – there are wedge shaped regions of low density seen throughout the spleen. With anything ‘wedge shaped’ the first thing to think about is a vascular cause and infarction.

Don’t stop there – have a look at the kidneys and in amongst some simple cysts and renal cortical scarring you will find a similar pattern of wedge shaped low density. With wedge shaped regions within the kidneys, it can be tricky to assess the cause as infarction and pyelonephritis can have similar appearances both causing wedge shaped regions of low density.

The ‘cortical rim sign’ can sometimes be seen in infarction where at the periphery of the wedge of low density there is a shallow rim of normal appearing renal cortex. This region is supplied by perforating branches of the renal capsular artery. If this sign is present you can say the cause is infarction but unfortunately if it is not present you are no further forward as it is not always present in infarction.

In our case there is no cortical rim sign – we can see low density extending all the way out to the periphery. In radiology there are often times where two things can have identical appearances but it is about putting the whole picture together be it the clinical picture or the other features of the scan. In this case the fact you have splenic infarcts makes it most likely that the pathology affecting the kidneys is also infarction rather than pyelonephritis.

Atrial fibrillation and subsequent thromboembolism is a common cause of acute renal and splenic infarction and should be investigated for even in the presence of a normal ECG. Other potential causes include septic emboli and a prothombotic state related to malignancy. An Echo is usually good idea to assess for a cardioembolic source and check the valves for endocarditis.

Learning point

When assessing the spleen on a post contrast CT it is important to check the phase of imaging as the spleen can appear spuriously abnormal on arterial phase CT.

Answer: Acute pancreatitis

There is significant fat stranding within the upper abdomen – we can see this is centred on the pancreas suggesting there is acute pancreatitis.

Once you see there is pancreatitis firstly think about the cause. The two big causes are alcohol use and gallstones. CT is not fully sensitive for picking up gallstones but can see gallstones about 75% of the time so it is worth checking for. In our case we can clearly see calcified stones within the gallbladder suggesting this is acute pancreatitis secondary to gallstones.

Once you see the stones also check for biliary dilatation however here the bile ducts have a normal calibre.

Now we know the cause look for complications of pancreatitis:

• Look to see if all of the pancreas enhances. If it doesn’t there could be necrosis. This usually starts at least 3 days after the onset of symptoms and in the very early stages oedema can also cause reduced enhancement which is why CT may not always be helpful in the very early stage of pancreatitis.
• Look for discrete peripancreatic fluid collections.
• Assess the splenic vein, main portal vein and superior mesenteric vein looking for filling defects that could represent thrombosis.
• Assess the splenic artery looking for focal dilatation which could represent a pseudoaneurysm. This is better done on an arterial phase scan (the one we have is a portal venous although it is worth checking on this).

In this case there are no clear complications. There is however an incidental finding of a small soft tissue lesion relating to the left kidney. Notice this does not show the normal density of a simple cyst (0-20 HU). The differential on this single phase CT includes a benign cyst with proteinaceous/haemorrhagic content or a soft tissue lesion such as an RCC.

The options in the first instance for further characterisation include ultrasound and a dual phase renal protocol CT. The lesion in this instance turned out to be a benign renal oncocytoma which can mimic renal cell carcinoma.

Learning point

Once you see signs of acute pancreatitis perform a focused review assessing for complications of necrosis, collection formation, venous thrombosis and pseudoaneurysm.

Answer: Small bowel obstructing due to adhesions

In the UK at least, abdominal X-Rays are being performed less and less. That is because of their relative insensitivity, their radiation dose and the rise of CT to make a more accurate diagnosis. Nonetheless we have an abdominal film in this case and it is important to still know the basics.

We can see some prominent bowel loops in the centre of this film suggesting there may be bowel obstruction. How can we tell the difference between small and large bowel obstruction?

Firstly if you see very dilated bowel loops it is unlikely you are dealing with small bowel as this would perforate before it gets to a diameter of 5 cm. The easiest way to tell if you are dealing with small or large bowel dilatation is to look at the indentations on the bowel wall. With small bowel you have valvulae conniventes which traverse the whole bowel. In comparison with large bowel you have haustrae only seen at the periphery

Also look at the location – small bowel loops will more likely live centrally whilst large bowel has a more peripheral location.

Now let’s look at the CT scan. I like to follow the large bowel from the rectum and follow it up. If you do so in this case you will find the whole of the large bowel is not dilated and normal in calibre, essentially excluding large bowel obstruction.

Now looking elsewhere we can see fluid filled dilated bowel loops – these are small bowel loops. There are however other loops of small bowel which are not dilated. This implies mechanical small bowel obstruction – here we are looking for dilated small bowel proximal to collapsed small bowel with a sharp transition point between the two.

It is now a case of following the small bowel and looking for a transition point between dilated and collapsed small bowel. I like to start from the stomach and follow the small bowel round. If you do so eventually you will come across a transition point within the right side of the abdomen from dilated small bowel to collapsed small bowel.

The two most common causes of small bowel obstruction are:

1. Adhesional small bowel obstruction (with a history of previous abdominal surgery)
2. Hernias

The former is the most likely scenario here. This can usually be treated conservatively in the first instance, unlike a hernia which will usually need reduction and surgical repair to relieve the small bowel obstruction. In bowel ischaemia you may find dilated bowel loops only as an early sign but there won’t usually be a sharp transition point to dilated bowel loops like you have here.

Learning point

It can be tedious but once you see dilated bowel loops on a CT you need to follow the bowel round. In mechanical bowel obstruction you are looking for dilated bowel loops with a sharp transition to collapsed bowel loops.

Answer: Gallstones within the CBD

Here we have coronal views of an MRCP study. The name of this sequence is a ‘TrueFISP’ (the name given by Siemens in this case), a type of gradient echo sequence performed to highlight blood vessels and fluid. It is also used in cardiac MRI, MR urography and MRI of the small bowel.

Here it is used to show the biliary tree which we can see as bright. Note that the blood vessels within the liver will also show as bright.

It is first important to orientate yourself with some anatomy. In the animated clip below we can see the gallbladder. This is thin walled and does not contain any gallstones. If you follow this through you’ll find a curly structure, this is the cystic duct.

Normally this connects to the common hepatic duct coming from the liver to form the common bile duct. In this case the insertion location is normal but it can insert inferiorly or medially. In these cases it is worth reporting on, especially if the patient is to have surgery.

We can see in the image above the common bile duct heading to its insertion at the ampulla which it shares in normal circumstances with the main pancreatic duct. The common bile duct here is dilated. A normal cut off value for this is difficult given this varies so much, especially with age, but when I see a CBD of over 7 mm I usually mention it.

Here we have a cause for the common bile duct dilatation with several stones throughout its course.

Learning point

An MRCP is the best imaging test to evaluate the whole course of the common bile duct although this can sometimes be identified on ultrasound.

Answer: Acute SAH due to anterior circulation aneurysm

I often start at looking at brain CT by looking at the lowest slice. Check to see if you can see the cerebellar tonsils at the foramen magnum – if you do, take a look at the sagittal view and see if there is cerebellar tonsil descent. This could represent an Arnold Chiari malformation or in the acute setting cerebellar tonsil herniation in the context of mass effect.

Secondly see if you can see high density CSF in this region. If you do you could be dealing with a subarachnoid haemorrhage and that’s what we have here.

With subarachnoid haemorrhage you have bleeding within the subarachnoid space which lies below the middle layer of the meninges, the arachnoid, and above the pia which is a thin structure that overlies the brain.

There are many different causes of subarachnoid haemorrhage but the most common by far is a ruptured berry aneurysm. So how do we look for subarachnoid haemorrhage on a non contrast CT head?

One key review area is the suprasellar cistern. We should see this as a pentagon shaped CSF filled structure but in our case we can’t see it clearly as it is filled with blood. This is subarachnoid haemorrhage.

Subarachnoid haemorrhage can also extend into the sulci like we can see here.

There is a subset of subarachnoid haemorrhage termed perimesencephalic haemorrhage. This is a venous bleed and there won’t be an abnormality on angiography. The epicentre of the bleed is seen anterior to the midbrain: so I always check in between the ‘Mickey Mouse ears’ of the midbrain for blood. This can be the only finding on the scan and can be very subtle and can be missed.

In our case you can see there is blood here anterior to the midbrain as well as within the sulci, the basal cisterns. There is even blood extending into the lateral ventricles and 4th ventricle.

A CT angiogram can be performed to look for an underlying aneurysm. These saccular or berry aneurysms tend to occur at sites of branching and happen at predictable places so it is worth scrutinising a few review areas:

1. Basilar tip
2. MCA bifurcation
3. Junction of anterior communicating artery (ACOM) and anterior cerebral artery (ACA)

In our case we will find a small aneurysm at the junction of ACOM and the ACA. This was successfully coiled and the patient made a good recovery.

Learning point

Don’t miss a subtle subarachnoid haemorrhage. My tips would be to change the window to a ‘blood window’ (eg centre 80-100 HU, width 150-300 HU), make the image small and look for asymmetry as well as interrogating the basal cisterns.

Answer: Psoas abscess

With any abdominal or back pain, remember to assess the psoas major muscles which originate from the T12 to L5 vertebrae and transverse processes. These then join up with muscle fibres from the iliacus muscle and insert into the lesser trochanter of the femur.

If we look at the psoas muscles on this scan below we can see there is some asymmetry. The right psoas is larger than the left and we’ve lost some of the fat planes within the muscle.

Also as we scroll down we can see there is fat stranding surrounding the psoas muscle extending into the pelvis.

What are the considerations when we see unilateral psoas enlargement on a CT scan?

1. Psoas Abscess: A psoas abscess can develop either primarily (typically in immunosuppressed patients or diabetics) or secondarily from infections in nearby areas like the abdomen or vertebral spine (spondylodiscitis). On CT, a psoas abscess might show peripheral enhancement and fluid density, although these signs aren’t always easy to detect.
2. Psoas Haematoma: Hematomas may occur in patients on anticoagulants or with blood disorders, and can also develop due to trauma or a ruptured abdominal aortic aneurysm (AAA). Differentiating a haematoma from an abscess can be challenging on CT, but high density within the psoas muscle often suggests a haematoma.
3. Tumour Invasion: While tumuors can invade the psoas muscle, this is more common as an extension from retroperitoneal cancers. Metastatic disease rather than primary tumuors usually accounts for psoas invasion.

In this case, the asymmetry and inflammation around the psoas muscle hinted strongly at a psoas abscess. The reporting radiologist picked this up and recommended an MRI to assess the psoas in more detail whilst also looking for a spondylodiscitis.

Due to pain the patient could only tolerate a few STIR sequences so we don’t have a complete scan but have a look at this axial STIR sequence below. We have high STIR signal within the right psoas with locules suggesting abscess formation.

If we look at a lateral STIR sequence of the lumbar spine, we can see high signal in the lateral aspect of the L3-4 disc which is continuous with the abscess formation within the right psoas. This highly suggests a spondylodiscitis as the primary pathology leading to secondary psoas abscess.

These usually present with back pain and typically occur over the age of 50. There may be a history of infection elsewhere whilst things like imunosuppresion, steroid use, diabetes and intravenous drug use can increase the risk. It usually involves a single level but several levels can be involved typically in tuberculous discitis.

The infection usually involves both the vertebral endplate and disc and in adults is thought to arise in the endplate first (hence why ‘spondylodiscitis’ is a preferred term over ‘discitis’).

Although we couldn’t see this on our CT case, irregularity of the endplates can be seen after a few weeks on X-Ray and CT as well as loss of disc space. MRI is more sensitive and we are looking for high T2 or STIR signal within the endplates, disc and paraspinal tissues and psoas muscles. Gadolinium contrast can help as we may see enhancement of the endplates, disc and peripheral enhancement of any abscesses. It’s important on MRI to ensure there is no significant central canal stenosis secondary to abscess formation or vertebral collapse.

The patient was treated with a long course of antibiotics and we saw a good response on imaging with improvement in the right psoas abnormality at 2 months.

Learning point

Remember to assess the psoas muscles on CT! Unilateral enlargement with surrounding fat stranding could mean a psoas abscess which may not show well on a CT alone and may need an MRI to confirm the diagnosis. MRI can also help assess for an underlying spondylodiscitis as it did in this case.

Answer: Large bowel obstruction due to sigmoid colon tumour

First let’s have a look at the abdominal film. It’s a difficult film to assess as it is split into two but we can see dilated bowel loops again like in the previous small bowel obstruction case. Let’s have another look at the table which helps us differentiate between large and small bowel obstruction.

In this case instead of valvulae conniventes traversing the whole wall of the bowel we can see haustrae which we can just see at the periphery of the bowel lumen.

This along with the degree of distension points us towards mechanical large bowel obstruction. When we look at the CT we will see diffusely dilated large bowel loops. The key here is to see whether we can find a transition point. Ie is there a point where the dilated large bowel becomes collapsed.

If we follow the colon round from the caecum we will find a transition from dilated colon to collapsed sigmoid colon. At this point there is some mural thickening. Now what are the causes of large bowel obstruction? The list is long but the most common and the most serious cause is colonic carcinoma (compare with this with small bowel obstruction where the majority of the time the aetiology is non-malignant). Other more common causes of large bowel obstruction include diverticular disease and sigmoid volvulus.

So with this mural thickening here we have to flag that this is a possible colon cancer. What makes us more certain is the presence of low density ill defined liver lesions which represent liver metastases. Note how these do not show fluid density and are not well defined as you would expect with simple liver cysts.

The patient went on to have a colonic stent before resection of the obstructing lesion for symptom control and then chemotherapy.

Learning point

Colon cancer is the most common cause of large bowel obstruction with other common causes including diverticular disease and sigmoid volvulus. Conversely most cases of small bowel obstruction are non-malignant in aetiology.