December, 2016
Author: Dr. Paul Gagliardi
Basic approach to using Imaging exams:
Do: Establish what you need to know. Make a presumptive diagnosis or ask a specific question.
Do: Consider what is likely vs. what is possible. Establish a ball-park pre-test probability.
Do: Choose an exam that can answer your question.
Do: Think about what you will do with the results; expected, unexpected, or incidental.
Don’t: Embark on an elaborate sightseeing tour of the patient’s internal anatomy.
Be Aware: Diagnostic wild goose chases can lead to bad clinical decisions that may harm patients!
Example #1: Patient dropped crock pot on toes last week. Today has pain, swelling, redness, minimal skin wound. You could order MRI or CT but the best choice would be X-Ray. If you are moderately sure that only a toe or toes are involved, order a toe X-Ray. If your concern is wider, order a foot X-Ray. X-Ray detects most clinically important fractures. MRI and CT detect fractures but use more time, technical resources and money.
Example #2: 45 y/o describes “food sticking” after swallowing. You think it more likely to be something benign (peptic stricture, spasm from esophagitis, hiatal hernia) rather than neoplasm but are not certain. Diagnostic options are Upper Endoscopy or Barium Swallow (Esophagram). Wrong choices are Modified Barium Swallow (video of oral-pharyngeal phase of swallowing with different food consistencies) and Upper GI Series (looks at esophagus, stomach, duodenum with equal attention). Upper Endoscopy is better than Barium Swallow at detecting esophageal neoplasm, Barrett’s esophagus, and other mucosal processes.
Common pitfalls in using Imaging tests:
Answer to question is already known but you don’t know it. Check and double check if the patient has had recent, relevant, Imaging exams. A patient might come to you worried about post-traumatic foot pain and neglect to mention that they went to the Skowhegan ER two days ago with post-traumatic foot pain and had negative X-ray for fracture as well as negative CT and MRI for occult fracture.
Your exam choice is not anatomically focused enough: If a patient has thumb symptoms a thumb X-ray is better than a hand X-ray. For reasons of physics, X-rays have more diagnostic detail if they can be centered over an abnormality. Common areas where more focused X-rays are useful include fingers, toes, other small bones, calcaneus, mandible, and temporomandibular joints. X-rays to evaluate for arthritis only can be 2-view rather than 3-view or 4-view. Ultrasound can be regional or more focal based on what you need to see. CT Abdomen/Pelvis is sometimes ordered when CT Abdomen or CT Pelvis alone would be adequate.
You choose an exam that is out-of-date or almost obsolete: Barium studies of the esophagus, stomach, and duodenum have been largely replaced by Upper Endoscopy (EGD) for the evaluation of most serious upper GI tract symptoms. Barium Enema has been largely replaced by Colonoscopy. There are some special cases where barium study is useful (follow-up benign stricture, evaluation of pre-surgery or postsurgery anatomy, some bowel obstructions and some pediatric exams). Barium Small Bowel Series, Capsule Endoscopy, and CT Enterography are all used to evaluate the small intestine; which exam to choose probably requires the input of a Gastroenterologist. In general, Endoscopy is superior to barium study in the detection of mucosal abnormalities including neoplasm, ulceration, inflammation and other changes in color and texture. If you order barium studies, be aware that early, treatable neoplasms may go undetected. Other near-obsolete tests in the Primary Care realm are IVP, Myelogram, and skull Xray.
You need to order a follow-up exam but don’t know the type of exam or the follow-up interval: There are no general rules about follow-up. Mammography and CT screening for Lung Cancer require that abnormal reports include follow-up recommendations. For other exams, the Radiologist who interprets an exam needing follow-up should make specific recommendations. If not, please call one of the Radiologists on duty for a recommendation.
Two Commonly Imaged areas that generate confusion and questions:
Uncomplicated Low Back Pain: Many study groups have come to the same conclusion; uncomplicated low-back pain is usually self-limited and does not require imaging. However, you need to know what “uncomplicated” means and you need to know the “Red Flags” that make further evaluation necessary. I recommend “Evaluation of low back pain in adults: Limited utility of imaging” at https://www.uptodate.com. (Requires subscription but available free through MGMC Library). A Google search will find many similar sites.
Abdominal/Pelvic Pain: Multiple organs, complicated anatomy, and a wide variety of pathologic processes make it impossible to recommend one Imaging test for all situations. This is a good situation to ask for Radiologist input or to do some quick on-line reading. Here is an over-simplified but useful algorithm. The first choice for disease of the gallbladder, bile ducts, liver, scrotum, and female pelvis is ultrasound. Use non-contrast CT Abdomen/Pelvis for urinary tract stone disease. If you use CT Abdomen/Pelvis with oral and IV contrast (if tolerated) for all else you won’t be too far wrong.
Use on-line references; the books on your shelf may be way out-of-date!
Useful Websites
https://www.uptodate.com This covers virtually all of Medicine, has multispecialty input, and is continuously updated. In my experience the recommendations for imaging tests are concise and correct.
http://www.radiologyinfo.org Information about Imaging tests directed at patients but useful for practitioners also. This is an excellent resource to use for answering questions about radiation risk.
https://acsearch.acr.org/list American College of Radiology Appropriateness Criteria project describes the value of different Imaging Studies in specific clinical situations. These are consensus criteria based on both expert panel review and evidence-based data. Covered are Diagnostic Imaging studies, Interventional Radiology procedures, and Therapeutic Radiology/Radiation Oncology. This site is probably too cumbersome for routine patient care use but it can help in complex situations when you can’t get specialist input. Medicare has mandated that these Criteria be embedded in the EMR as the Imaging part of Clinical Decision Support (maybe by 2018).