The Role of Radiology/Radiologist in Colorectal Disease
Judy Holt - Consultant Radiologist
The range and sophistication of bowel imaging techniques has increased since multidetector CT and MRI have become universally available.
Whilst the tendency of modern medicine is to require a CT there is still a place for sequential imaging and radiology techniques are often complimentary.
The role of the Radiologist is to advise and to arrange for the most appropriate test to be performed.
The following will be discussed:
2. Plain Film
AXR, erect CXR, decubitus AXR
A combination of the above techniques is indicated in the initial assessment of patients presenting with clinically significant abdominal pain, an acute abdomen or possible intestinal obstruction.
The diagnosis of pneumoperitoneum or pneumatosis intestinalis may obviate the need for further imaging.
The demonstration of possible small or large bowel obstruction is an indication for further imaging particularly if the patient does not respond to conservative management.
Plain film findings will also help in deciding the next appropriate investigation, U/S will be unhelpful in the presence of a pneumoperitoneum and a prepared barium enema is contraindicated in intestinal obstruction.
Portable AXRs are rarely indicated because of the difficulty in obtaining an image of diagnostic quality (limitation of the power of the portable machine).
3. Contrast Studies
Double contrast barium enemas (DCBE) are performed following thoroughbowel cleansing with picolax (preferable) or Kleen prep.
Therefore the fitness of the patient must be assessed prior to requesting the investigation (the patient must be continent and sufficiently mobile to roll 360 supine/prone with minimal assistance).
Barium and air are introduced per rectum in order to coat the colonic mucosa.
Either the terminal ileum or theappendix should be demonstrated to ensure a complete examination.
Common indications include;
change in bowel habit
iron deficiency anaemia
Common findings include
Because of the relatively high radiation dose, consideration should begiven as to the appropriateness of this test in the young patient
A prepared enema is contraindicated if the patient is obstructed or if bowel wall integrity is in doubt
It can take up to 1 week for the barium to clear sufficiently for a subsequent CT examination of the abdomen +/- pelvis to be possible
Although both false positive and false negative tests are possible, DCBE is the first line radiological investigation in the detection of colonic carcinoma
Unprepared enemas are performed using either very dilute barium or water soluble contrast.
differentiating mechanical obstruction from pseudo obstruction
identifying the level of obstruction
assessing the integrity of the bowel wall or an anastomosis
assessing luminal patency distal to a defunctioning colostomy.
4. Ultrasound (U/S)
U/S is a very useful modality and because it does not utilise ionising radiation, it is safe to use in patients of all ages
Its effectiveness can be limited when used in very large patients and in the hands of inexperienced operators
The skin surface needs to be clean and clear of dressings and bags so that good acoustic contact is possible.
Its role in staging malignancy has largely been replaced by CT but it remains an excellent problem solving tool.
It complements CT in the characterisation of focal liver lesions and is superior to CT in differentiating solid/fluid lesions, demonstrating perfusion and in detecting gall stones.
It is the preferred modality for biopsy guidance because of the real time multiplanar imaging capability.
It is relatively quick, cheap, available and well tolerated by patients.
5. Computed Tomography (CT)
The sophistication of CT imaging has increased dramatically since the introduction of multidetector systems (4 and 16 slice (detector or row) is now standard whilst 64 and even 256 slice systems are available).
A staging CT of the chest, abdomen and pelvis is a high dose examination.
The risk to the patient is further increased by the routine use of intravenous contrast which is contraindicated in patients with a true history of contrast reaction and is relatively contraindicated in patients with atopy, poorly controlled asthma and renal impairment.
A properly performed CT is an extremely useful imaging technique but accurate clinical information is crucial so that the examination can be optimised to answer the clinical question - clinically important diagnoses can be missed as a result of inadequate technique.
CT is the staging modality of choice for most malignancies.
However routine CT is NOT the first line examination for the detection of mucosal lesions such as polyps and carcinoma.
It is also the imaging modality of choice for follow up.
Scanning parameters and protocols are standardised so that serial examinations can be directly compared (reduced inter operator variability).
CT is widely available and versatile.
Multiplanar reconstructions are possible from a single acquisition.
It is quick and generally well tolerated.
6. CT Colonography
This technique is gaining popularity because it is perceived by patients and clinicians to be less invasive than colonoscopy or DCBE.
Whilst elderly and less mobile patients will tolerate the examination, it still requires through bowel cleansing, and patients must to be continent and cooperative.
It is contraindicated in patients who are obstructed or who have a blind stump or end colostomy.
It involves two CT acquisitions, supine and prone and is therefore a high dose technique.
I.V. contrast is routinely used and it can double as a staging examination.
It is a lengthy technique in terms of machine time and post processing and specialist interpretation is required.
Colonic pathology is exquisitely demonstrated, but colonoscopy may still be required in order to obtain a pathological diagnosis.
In some centres it has been adopted as the first line radiological investigation for the detection of colonic carcinoma, more commonly it is used for problem solving in symptomatic patients.
Click here to watch a fly through video
MRI is the modality of choice for local staging of pelvic malignancy.
Where available it should be used for accurate pre surgical staging of pelvic tumours
It is also used in preference to CT in the imaging of benign pelvic surgical and gynaecological disease.
It does not utilise ionising radiation and can therefore be used safely in patients of all ages, however it is exquisitely sensitive to patient movement and is poorly tolerated in young, ill and claustrophobic patients.
It is contraindicated in patients with pacemakers and indwelling valves, clips, coils and devices must be cleared for MRI compatibility prior to scanning.
MRI has superior soft tissue contrast resolution compared to CT but the two modalities are complimentary, local disease stage is assessed with MRI, distant metastases are staged with CT. MRI is more sensitive and specific in the detection of liver metastases and is used for tissue characterisation and problem solving, but it is a time consuming and expensive technique and because there is competition for machine space, CT is usually performed first. MRI is superior to CT in the imaging of peri anal sepsis/ fistula and is used in surgical panning.
8. Colonic Stenting
This is generally a combined procedure involving an experienced Endoscopist and a Radiologist.
Stents are placed across suitable stenosing tumours under fluoroscopic guidance in order to palliate symptoms or as definitive treatment to decompress inoperable obstructing lesions
Stenting may buy time and avoid the need for a colostomy
Click here to see the procedure of colonic stenting
The Radiologist is a core member of the Lower GI MDT
The discussion of patients at the MDT involves review of the relevant imaging and advice on appropriate further investigation
This involves preparation before the meeting and although imaging and reports are reviewed, they are not re reported; any additional findings are discussed and documented
The imaging findings are correlated with surgical and pathological findings and any discrepancies are audited
The Radiologist reports back to the radiology department with any requests or changes in practice that arise at the MDT.
At any point in a patient's journey it might be necessary to seek Radiological advice.
Radiologists are usually less resistant to fitting in emergencies or extra cases once they are in possession of relevant clinical information and good clinico-radiological communication and cooperation are essential for patient welfare.
In short - if in doubt, ask, but know your patient!