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The Abdominal Plain Film in Clinical Context
The Jigsaw Puzzle Analogy
The Thermometer Analogy
Case Study 1
Abdominal plain film image interpretation is one of those areas of medical imaging that is widely considered by radiographers to be confusing and unmasterable. There are many reasons for this perception
- It is confusing
- Abdominal plain film interpretation has an accuracy of between 55 and 80%
- Images often don't have meaning without a clinical context (but not always)
- Radiographers are not trained in image interpretation to the same level as radiologists
- It requires sustained effort to master
- You need a radiologist mentor
Despite these formidable difficulties, radiographers can master abdominal plain film image interpretation to a very high level. This page looks at one of these obstacles- the importance of a clinical context.
The Jigsaw Puzzle Analogy
A significant aid to understanding the role of the abdominal plain film is to consider it in its clinical context. Looking at an abdominal plain film with no clinical information is often like looking at the abdominal plain film image below.It would be brave person who would offer a firm diagnosis on the abdominal plain film above!
The Thermometer Analogy
I have a colleague who suggests that an abdominal plain film is a bit like taking a patient's temperature. A patient with a significantly high temperature indicates that the patient is unwell, but is highly unlikely to throw up a diagnosis in isolation.The Importance of Clinical Context- Putting the Pieces together
Some abdominal plain films are only able to be given meaning in the context of all of what the clinician knows about the patient. Whilst each of the four sources of information shown below may suggest a diagnosis, the likelihood of correct diagnosis will require a consideration of all four findings.
The Abdominal Plain Film Spectrum
Abdominal plain films are not necessarily either normal or abnormal; this is not a dichotomy- it's a continuum. If you are one of those people that prefer to categorise things, you could think of them as being;
normal -------------> probably normal ----------> suspect ------->probably abnormal-----> definitely abnormal
An abdominal plain film will not always provide a diagnosis. Often you can only describe what you see e.g. "there are a few prominent air-filled loops of small bowel".
Case Study 1
Case Study 2
No Clinical ContextIn the absence of any other information, all you can say about this patient's abdominal image is that there are several prominent central loops of gas-filled small bowel. These loops of small bowel happen to look quite odd in that they appear concentric. This is probably just a chance event. They do not have the randomness of normal small bowel but equally are not dilated.Clinical ContextPatient has renal colic
Other ImagingThe patient proceeded to have a CT abdomen where a 5.4cm left renal stone was found with left upper renal tract obstruction with moderate left hydronephrosis.CommentIn the absence of any other patient information, this image suggests nothing specific. Knowing that the patient has renal colic raises the possibility that the patient has a reflex ileus which is causing the prominent small bowel loops. The renal stone and hydronephrosis found on CT support this finding.
- There is a paucity of bowel gas. This could be normal but might also be caused by a variety of pathologies including obstruction
- The colon is not clearly visualised. This may be normal or may be caused by an obstruction or previous colectomy . It is also possible that the patient has diarrhoea and the colon is fluid-filled, although this is not clearly seen.
- There is no gas in the rectum
- ? stoma in left iliac fossa
- ?sacral spina bifida occulta
- The appearances are not specifically abnormal but are suspicious of an early or low grade small bowel obstruction.
- There are a few air/fluid levels
- There are a few gas bubbles that may be caught in small bowel valvulae suggesting SBO
- There is no gastric fundus air bubble.
- The erect image is possibly slightly more suggestive of a SBO but is not conclusive.
•Crohn's Disease (quiescent at time of presentation)•Colectomy / ileostomy 1994•Multiple laparotomies for SBO secondary to adhesions
•Soft abdomen•Increased bowel sounds (indicative of obstruction)Blood Test Results
WBC count is the number of white blood cells in a volume of blood. Normal range varies generally between 4,300 and 10,800 cells per cubic millimeter (cmm). This can also be referred to as the leukocyte count and can be expressed in international units as 4.3 - 10.8 x 109 cells per litreWhite blood cell count (WBC) •WBC = 15.9 (4.3 - 10.8)CRP is a plasma protein which increases in patients who have inflammation or infection. CRP is not specific. A high result serves as a general indication of acute inflammation. In a healthy person, CRP is usually less than 10 mg/L. Most infections and inflammations result in CRP levels above 100 mg/L.
C-Reactive Protein (CRP) •CRP = 2 (normal < 10)
The patient's temperature is 35.2 An oral temperature between 36.1°C and 37.8°C is considered ‘normal'.
The clinical picture places a completely different perspective on the two abdominal plain film images. This patient has a history of Crohn's disease which is presently quiescent. Patients with Crohn's disease who present with an acute abdomen will commonly have either active Crohn's disease or SBO from adhesions secondary to previous surgery. The patient has a C-reactive protein (CRP) of 2 which does not indicate infection or inflammation. This suggests low grade SBO caused by adhesions as a more likely diagnosis. The failure to demonstrate the large bowel reflects the history of colectomy.
The patient history and blood results suggest the patient may have a SBO. The plain film appearance is consistent with a low grade or early SBO.
The abdominal plain film is a commonly performed radiographic examination despite its diagnostic limitations. It is not normally a challenging radiographic procedure, except in moribund and/or morbidly obese patients. Mastering abdominal plain film image interpretation can turn a relatively mundane radiographic procedure into a much more interesting and satisfying procedure. You are also more likely to perform appropriate supplementary views if you are able to identify pathology on the routine views.
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, Feb 8 2010, 2:53 AM EST
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Keyword tags: abdominal plain film c reactive protein clinical context crohn's disease jigsaw puzzle analogy small bowel thermometer analogy valvulae
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