In this section,
we use cases from our tertiary referral centre in London (UK) to discuss the use of various imaging modalities for inflammatory bowel disease in paediatric patients. We detail from our experience the imaging appearances as well as advantages and disadvantages of each.
Modalities discussed include:
- Fluoroscopy.
- Ultrasound.
- MR.
At diagnosis:
As previously mentioned,
imaging of the small bowel is an important part of the investigation of inflammatory bowel disease,
partly because this region is poorly accessible by endoscopy and also because small bowel involvement suggests Crohn’s rather than ulcerative colitis.
Disease of the terminal ileum is the most common site of involvement.
Historically imaging of the small bowel was with fluoroscopy.
This process involves oral administration of barium with spot radiographs to track progress through the small bowel.
Once contrast has reached the caecum,
compression of the abdomen is performed to separate bowel loops,
often with a wooden spoon placed over the patient’s abdomen (Fig. 5).
Under compression further images,
both static and dynamic,
are taken.
Fig. 5: Patient A, Crohn’s, 8y male. Fluoroscopic image of the terminal ileum performed under compression using a wooden spoon (asterix). The visualised terminal ileum has long abnormal segment with a ‘cobblestone appearance’ and evidence of ‘rose-thorn’ ulceration (white arrows).
The example fluoroscopy image from patient A (Fig. 5),
an 8-year-old male patient with Crohn’s disease,
demonstrates disease of the terminal ileum with ‘rose-thorn’ ulceration and a ‘cobblestone’ appearance due to sections of thickened bowel wall being interrupted by deep ulcers.
Fluoroscopy images from patient B (Fig. 6),
an 11-year-old male patient presenting with Crohn’s disease,
also show ulceration as well as demonstrating multiple areas of stricture and separation of bowel loops by mesenteric fat hypertrophy.
Fig. 6: Patient B, Crohn’s, 11y male. Fluoroscopic image of the terminal ileum demonstrating active inflammation with multiple areas of stricture (white arrows), ’rose-thorn’ ulceration (black arrow) and mesenteric fat hypertrophy (asterix).
Advantages of barium fluoroscopy:
- Good visualisation of early mucosal lesions e.g.
ulceration
- Dynamic,
therefore functional evaluation of peristalsis
Disadvantages of barium fluoroscopy:
- Extra-luminal manifestations not well seen
- Ionising radiation
- Poor toleration of barium and compression
Fluoroscopy has now been largely replaced by cross-sectional imaging,
in particular MR,
however it should be noted that in our centre ultrasound may also be used in suitable patients to assess small bowel involvement as well as severity and extent of disease at diagnosis.
In MR imaging of inflammatory bowel disease,
the small bowel is usually distended with an oral contrast agent; this also displaces intraluminal air which would otherwise cause susceptibility artefact.
The sequences then obtained include:
- Coronal and axial T2 weighted sequences
- Axial T2 fat suppressed sequences
- Coronal and axial balanced FFE sequences
- Coronal and axial T1 fat suppressed images with and without IV gadolinium contrast
Increasingly diffusion weighted sequences are also obtained as these are highly sensitive for oedema and therefore inflammation.
Advantages of MRI:
- No ionizing radiation
- Multi-planar
- Good soft tissue contrast
- High sensitivity for fluid
- Ability to assess for extra-luminal manifestations of disease
- Particularly good for assessing fistulas
Disadvantages of MRI:
- Limited accessibility out of hours
- Long examination time
- Nausea from anti-peristaltic agents
- Poor tolerance ingesting large volumes of fluid
- Cannulation required for IV contrast
- Unsuitable for some patients e.g.
claustrophobic,
metalwork
- Low spatial resolution compared to CT therefore collapsed bowel lumen difficult to assess
Images from patient C (Fig. 7),
a 12-year-old male patient at initial presentation,
demonstrate bowel wall thickening at the terminal ileum with oedema.
Appearances are in keeping with Crohn’s disease.
Fig. 7: Patient C, Crohn’s, 12y male. Initial MR study: coronal T2 (FAR LEFT), axial T2 (MIDDLE LEFT), axial T1 fat saturated post gadolinium (MIDDLE RIGHT) and axial DWI b600 (FAR RIGHT). Images show mural thickening, hyper-vascularity and restricted diffusion of the terminal ileum (white arrows).
Acute features are also demonstrated well in MR images from patient D (Fig. 8),
a 15-year-old male patient who presented with a 3 year history of abdominal pain,
weight loss and raised inflammatory markers.
The post contrast T1 fat saturated and T2 weighted coronal images show multiple areas of inflamed small bowel with areas of sparing in between (‘skip lesions’) as well as pseudo-sacculation due to asymmetric bowel wall thickening where bowel adjacent to the mesenteric border is preferentially affected.
There is also mesenteric fat hypertrophy with hyperaemia of the mesentery post contrast (often described as the ‘comb sign’) in addition to multiple surrounding prominent lymph nodes.
The patient was subsequently diagnosed with Crohn’s disease.
Fig. 8: Patient D, Crohn’s, 15y male. Initial MR study: progressive anterior to posterior coronal sections from post gadolinium T1 fat saturated (TOP) and T2 weighted (BOTTOM) sequences. Images show multiple segments of thickened hyper-vascular small bowel, pseudo-sacculation (grey arrows), mesenteric fat hypertrophy (asterix) with hyperaemia on post gadolinium images (comb sign) (white arrow) and prominent lymph nodes (blue arrows).
Although the terminal ileum is most commonly affected in Crohn’s disease,
some patients do present with colonic disease.
Patient E,
a 13-year-old male patient,
presented with poor growth and high inflammatory markers.
On MR,
wall thickening in the ascending and transverse colon is demonstrated (Fig. 9).
Fig. 9: Patient E, Crohn’s, 13y male. Initial MR study: coronal sections from T2 weighted sequences. Images show a long segment of thickened ascending and transverse colon with submucosal increased T2 signal in keeping with active disease.
Another example is patient F,
a 12-year-old male patient presenting with acute proctitis (Fig. 10).
Fig. 10: Patient F, Crohn’s, 12y male. Coronal section from T2 weighted MR sequence. Image shows thickening and oedema of the rectum with multiple surrounding enlarged lymph nodes and free fluid in keeping with acute proctitis.
During disease flare:
In the case of a paediatric patient with known inflammatory bowel disease having a flare of symptoms,
MR imaging may not be available straight away.
In these cases,
again ultrasound is a useful first line imaging modality,
particularly if the previous distribution of disease is known.
A high frequency probe is used with graded compression to visualize bowel loops.
Five months after patient C had the scan above for his initial presentation,
he presented again with worsening symptoms.
An ultrasound scan was done (Fig. 11) which showed classic features in keeping with active Crohn’s disease including wall thickening of the terminal ileum with mesenteric fat hypertrophy and increased vascularity as well as ulceration.
During the scan reduced peristalsis was also seen.
Fig. 11: Patient C, Crohn’s, 12y male. Ultrasound during symptom flare. Longitudinal scan of the terminal ileum (LEFT) demonstrating wall thickening; transverse colour doppler scan of the terminal ileum (MIDDLE) demonstrating mural and mesenteric hypervascularity as well as mesenteric fat hypertrophy (asterix); and transverse scan of the terminal ileum (RIGHT) demonstrating ulceration.
Advantages of ultrasound:
- No ionizing radiation
- Accessible
- Non-invasive
- Low cost
- Dynamic
- Easy to see terminal ileum
Disadvantages of ultrasound include:
- Limited visualisation of some parts of bowel
- Lower sensitivity and specificity than MR
- Operator dependent
- Difficult in some patients e.g.
obesity,
intestinal gas
- Difficult to reproduce images and compare with prior studies
18 months later patient C had a repeat flare.
This time on ultrasound an inflammatory mass was seen in the right iliac fossa between two loops of bowel with surrounding disorganised hyper-echogenicity (Fig. 12).
This was an inflammatory phlegmon with surrounding fat hypertrophy.
Appearances were correlated with MR subsequently (Fig. 12) and the patient went on to have a right hemicolectomy.
Fig. 12: Patient C, Crohn’s, 14y male. Ultrasound during repeat symptom flare (LEFT) demonstrating an inflammatory phlegmon (labelled). Axial (MIDDLE) and coronal (RIGHT) T2 weighted MR images also demonstrate this inflammatory phlegmon (white arrows).
Patient B also had a right hemicolectomy.
Unfortunately,
5 years later he presented with a flare in symptoms.
Ultrasound and MR imaging showed that he had disease recurrence in the neo-terminal ileum (Fig. 13).
Recurrence post-surgery in this region proximal to the ileo-colic anastomosis is characteristic in the natural history of Crohn’s disease.
Fig. 13: Patient B, Crohn’s, 16y male. Ultrasound (LEFT) and colour doppler ultrasound (MIDDLE) images demonstrating wall thickening and hyper-vascularity of the neo terminal ileum 5 years post right hemicolectomy for active disease initially demonstrated in Fig. 6. Extent of disease confirmed on MR; coronal T2 weighted image (RIGHT) shows neo-terminal ileum wall thickening in the right iliac fossa (white arrow).
Imaging disease complications:
Due to the transmural nature of Crohn’s disease compared to ulcerative colitis,
complications such as strictures and fistulae are encountered as the full thickness of the bowel wall is affected by inflammation.
Strictures can be inflammatory or fibrotic.
In the acute phase,
luminal narrowing is likely due to bowel wall thickening; these inflammatory strictures improve once the acute inflammation is treated.
Chronic mural inflammation however leads to the deposition of fibrotic scar tissue; these strictures are irreversible and can cause bowel obstruction.
Surgery is often the necessary treatment option for symptomatic fibrotic strictures.
Patient G,
a 14-year-old patient with known Crohn’s disease,
presented acutely unwell.
On ultrasound, the terminal ileum lumen was narrow with proximal small bowel dilation up to 3cm (Fig. 14).
On subsequent MR imaging,
small bowel obstruction secondary to this stricture was demonstrated (Fig. 14).
Fig. 14: Patient G, Crohn’s, 14y male. Ultrasound of the terminal ileum (TOP) demonstrates dilatation proximal to strictured terminal ileum. On subsequent MR, anterior to posterior T2 weighted coronal sections (BOTTOM) show distension of upstream ileal loops in keeping with small bowel obstruction.
Bowel obstruction is also an important complication post-surgery as these patients are prone to adhesion formation.
An example is patient H,
a 17-year-old patient who presented with small bowel obstruction after bowel resection (Fig. 15).
The decision was made to use CT as the patient was older and acutely unwell.
In this situation CT is rapid,
more accessible than MR,
has high resolution and also has high sensitivity for extra luminal gas in the case of bowel perforation.
Fig. 15: Patient H, Crohn’s, 17y male. Coronal image from portal venous phase CT post bowel resection surgery; there are multiple dilated fluid filled loops of small bowel in keeping with small bowel obstruction, in this case secondary to adhesions.
Fistulae are abnormal connections between one lumen and another or between one lumen and the body surface.
Commonly in Crohn’s disease these are in a perianal location and can by classified using the Parks classification system [6] into inter-sphincteric,
trans-sphincteric,
supra-sphincteric and extra-sphincteric (Fig. 16).
Specific pelvic MR protocols are the gold standard for imaging with multi-planar T2 and STIR sequences.
Fig. 16: Schematic of Parks classification [6] of peri-anal fistulae showing inter-sphincteric (A), trans-sphincteric (B), supra-sphincteric (C) and extra-sphincteric (D) positions of fistulae (blue lines) relative to the external sphincter (ES). Drawn by V. Dattani.
Patient H,
discussed above with small bowel obstruction,
had been initially diagnosed 2 years prior to that episode.
Initial pelvic MR at the time demonstrated a trans-sphincteric fistula with its internal origin at the level of the dentate line and extension inferiorly and posteriorly to join a collection in the right ischio-anal fossa (Fig. 17).
Fig. 17: Patient H, Crohn’s, 15y male. Progressive posterior to anterior coronal STIR MR images (TOP) with axial image from the same sequence (BOTTOM). Images demonstrate a trans-sphincteric fistula with its internal origin at the level of the dentate line and extension inferiorly and posteriorly to join a collection in the right ischio-anal fossa.
Supra-sphincteric fistulas by comparison extend above the level of the levator ani as shown in images obtained from patient I,
a 17-year-old male patient with Crohn’s (Fig. 18).
Fig. 18: Patient I, Crohn’s, 17y male. Progressive inferior to superior axial STIR MR images demonstrating a horseshoe shaped collection in the inter-sphincteric space below the level of the ano-rectal junction which on the left tracks superiorly above the level of the levator ani muscle to terminate in the rectal wall.
Fistulae can be complex with multiple tracts and associated abscesses.
The scan from patient J,
a 16-year-old male Crohn’s patient with severe perianal disease,
demonstrates this (Fig. 19).
Fig. 19: Patient J, Crohn’s, 16y male. Successive superior to inferior axial STIR MR images demonstrating a complex branching inter-sphincteric fistula with a seton in situ. One inter-sphincteric tract communicates with an abscess within the left buttock.
As well as perianal fistulae,
patients can develop fistulae between bowel and other loops of bowel (Fig. 20) and bowel and skin (Fig. 21).
Fig. 20: Patient H, Crohn’s, 17y male. Ultrasound image demonstrating an entero-enteric fistula (white arrow).
Fig. 21: Patient H, Crohn’s, 17y male. Progressive superior to inferior axial T1 post gadolinium MR images demonstrating a fluid collection (white arrow) adjacent to and in continuity with an inflamed neo terminal ileum extending infero-medially deep to the anterior abdominal wall to connect with a central defect in the abdominal wall where small gas locules are seen (asterix); appearances are consistent with an entero-cutaneous fistula. Note the left iliac fossa ileostomy (grey arrow).
Assessing treatment response:
Imaging to assess for treatment response is usually with MR as this gives multi-planar images of the whole gastrointestinal tract and allows comparison with previous imaging.
Also at this stage patients are not acutely unwell and radiation is preferably avoided due to the need for multiple studies over time.
MR images from patient K (Fig. 22) show resolution in a fistula tract over 9 months after treatment with a seton.
Fig. 22: Patient K, Crohn’s, 16y male. Coronal T2 weighted MR image (LEFT) demonstrating a fistula tract containing a low signal line (white arrow); this is a seton with surrounding inflammation. Coronal T2 weighted image (RIGHT) from scan 9 months later shows resolution.
MR images from patient L (Fig. 23) show dramatic improvement in perianal disease after 6 months treatment with infliximab.
Fig. 23: Patient L, Crohn’s, 12y female. Coronal T2 weighted (TOP LEFT) and axial STIR (BOTTOM LEFT) MR images demonstrate large collections around the anal canal extending posteriorly and laterally into both ischio-anal fossae. Coronal T2 weighted (TOP RIGHT) and axial STIR (BOTTOM RIGHT) images 6 months later after treatment with Infliximab show resolution.
Extra-intestinal manifestations of disease:
As well as involvement of the gastrointestinal tract,
patients with ulcerative colitis and Crohn’s can present with a number of extra-intestinal manifestations of disease which can range from musculoskeletal and cutaneous in nature to hepato-biliary,
ocular and renal [7].
Imaging may also be required to aid the diagnosis and follow up of these,
for example,
patient M,
a 16-year-old male patient with ulcerative colitis presented with abnormal liver function tests.
An MRCP was performed (Fig. 24) which showed irregularity and stricture of the right hepatic ducts in keeping with primary sclerosing cholangitis; a condition known to be associated with ulcerative colitis.
Fig. 24: Patient M, ulcerative colitis, 16y male. Oblique coronal thick slab MRCP image demonstrating irregularity and stricture of the right hepatic ducts (white arrows) which did not open on any sequences of the study; note pruning of the peripheral ducts. Appearances are in keeping with primary sclerosing cholangitis.