Post#11 The 'Key to the Castle' for Abdominal and Pelvis Pain-ultrasound or CT

During the time I served as medical director, performing many peer-to-peer calls, providers would often confided in me by saying they were often uncertain as to which imaging study is the best one for abdominal pain.  They were not sure whether to order an ultrasound (US) or a CT or an MRI. Decisions about contrast were still a mystery, so often they would request a dual study (non-contrast AND contrast) without knowing whether that was the right call. Other times providers were uncertain as to whether an imaging study should include the abdomen, the pelvis, or both. The next few posts will address abdominal pain imaging, and clarify much of this uncertainty.  This first one will cover the value of ultrasound, the importance of pain location, and the presence of red flag signs.  

The decision which imaging study to request in the evaluation of abdominal pain depends heavily upon a history and physical exam, lab tests and any prior imaging studies.  Some providers automatically request a CT scan of the abdomen and pelvis with contrast (74177) hoping that this study will provide the diagnosis in all cases.  Unfortunately, CT is associated with significant radiation, which can be avoided by using a more targeted approach, starting with an ultrasound. The formulae for selecting a CT scan over an ultrasound are relatively clear, and are spelled out in most RBM’s Guidelines. 

Ultrasound and abdominal pain  

Unlike CT scan, ultrasound can be performed even if the patient has eaten recently.  Ultrasounds are performed in real time, so the technician is able to move the ultrasound transducer around to obtain the best picture.  Some ultrasonographers will compress organs in order to obtain a better view of cysts or mass lesions.  Free fluid and ascites may also be readily identified and aspirated for tissue diagnosis. On the other hand, some circumstances limit US efficacy. For example, morbid obesity may make performing US difficult or non-diagnostic, so CT would be preferred in these cases. Communicating to the radiology benefits manager that your request for a CT (rather than an US) is due to your patient’s BMI may make a more convincing argument for approval.   

During P2P calls, providers have occasionally voiced their opinion that an abdominal ultrasound is useless in patients with abdominal pain who have had a cholecystectomy.  In fact, ultrasound is still a very useful tool even in the absence of the gall bladder.   Occasionally the findings of an abdominal or pelvic US will demonstrate polycystic kidneys or small ovarian cysts, neither of which require follow-up imaging.  Other times a small abdominal aortic aneurysm (AAA) less than 5.4 cm is discovered, for which periodic follow-up should be performed with ultrasounds, not CT scans. 

Often an US may not provide the diagnosis, but instead may re-direct you to perform an MRI or MRCP or a different type of CT scan than originally considered. For example:

  • MRCP is preferred if US demonstrates dilated common bile duct
  • CT abdomen without and with contrast (74170) are preferred if US shows a liver nodule
  • CT abdomen without contrast, with contrast, and delayed views (triple study) are preferred if US suggests a liver hemangioma

Location of the Pain

The location of the pain in the abdomen or pelvis may determine which imaging study is best:  ultrasound or CT scan.   Right or left upper quadrant pain is usually evaluated initially with an ultrasound.  Right lower quadrant pain (suspected appendicitis) or left lower quadrant pain (with a prior history of diverticulitis) supports a CT abdomen and pelvis with contrast (74177). For lower quadrant pain, US is not useful as an initial imaging study unless primary disease in the pelvis is suspected. For pain in the pelvis in women, ultrasound is the best initial study. 

Red flags and abdominal pain

Red Flags are traditional danger signs, and patients who present with a red flag sign are candidates for more advanced diagnostic imaging.  Abdominal red flags may be identified after performing a history, physical exam or simple lab tests: 

  1. Fever (>101 °) d. Guarding
  2. Severe abdominal pain
  3. a palpable mass
  4. GI bleeding     
  5. Moderate to severe tenderness
  6. Guarding or rebound tenderness
  7. Elevated WBC
  8. Cancer history
  9. Persistent pain with failure of 4 weeks of conservative treatment 

All it takes is one red flag, communicated clearly to the nurse specialist to result in a prompt authorization number for a CT scan. When a red flag sign is present, a prior US is not required. 

Lesson #11:  Ultrasound in the evaluation of abdominal pain may provide the diagnosis or may direct providers to a different advanced imaging study than was initially considered.  Ultrasound is performed without radiation, at lower cost, requires no prep and will not cause delay for follow-up studies.  CT is preferred over US when patients have right or left lower quadrant pain or any red flag signs.