Utility of Pelvic US After Negative CT

Background

Women presenting to the Emergency Department (ED) with abdominal pain present a diagnostic dilemma when it comes to selection of imaging modality.  Differentiating pain originating from pelvic organs vs. intra-abdominal organs is difficult to do with history and physical alone, and many women ultimately end up undergoing both CT of the abdomen and pelvis (CTAP) and pelvic US in the ED. This increases length of stay, and subjecting women to both radiation and an invasive diagnostic test.  CT as a modality has the limitation of ionizing radiation but the advantage of being able to survey both intraabdominal and pelvic origins. Traditionally, though, it has been thought that US is better at evaluating patients for pelvic pathology. However, there are studies suggesting that CT is rarely normal when pelvic pathology is present.

Primary Results

Primary Results

• 962 women underwent CTAP and pelvic ultrasound during one ED visit
• 132 women underwent Pelvic ultrasound after negative CT. 6 excluded for lack of IV contrast
  • 126 women in final study cohort
  • 126 age matched controls who only underwent CTAP

Critical Results

• Primary Endpoint (findings on Pelvic US not seen on CTAP)
  • Overall: 97% of Pelvic ultrasounds were normal (122/126)
  • 3% (4/126) had findings on US. All were endometrial abnormalities.
  • None of the findings were indicative of acute pathology, nor did they definitively reveal the source of pain
• Secondary Endpoint (length of stay)
  • Study group 22h 13min
  • Control Group 16h 8min
  • P = 0.29

Strengths

• Enrollment was consecutive
• Minimal exclusion criteria increasing applicability of study results
• Raises an important question regarding the utility of diagnostic studies

Limitations

• This is a relatively small single center study limiting the generalizability. Emergent pelvic pathology, such as torsion, is rare with an incidence of 9 per 100,000.  This study may not be powered to detect real differences.
• Retrospective study with inherent limitations of this methodology
• This study is un-blinded.  The radiologists who read the ultrasounds were not blinded to the results of the CT introducing bias.
• The initial indications for CT did not include any pelvic pathology.  This is not a study that demonstrates sensitivity of CT for suspected pelvic pathology. It can only describe the utility of CT when the pretest probability is already low.
• This study followed up the charts of patients for up to a year after the initial visit. However, the study was done in Boston.  If patients with persistent pain went to another hospital, that information would not have necessarily been available to the authors.
• The images were not reviewed by an external reviewer unless an abnormal finding was noted. In one case that was reviewed the author found that an endometrial lesion seen on US, was in fact present on the prior CT that was read as normal.  This raises the issue of whether other pathology may have been missed on the initial read.

Author's Conclusions

“Immediate ultrasound re-imaging of the pelvis following negative CT in women with acute abdominal/pelvic pain yields no additional diagnostic information and does not alter acute care.”

Our Conclusions

Due to the numerous limitations of the methodology of this study, it should not be used to guide current clinical decision making. However, it raises an important issue about the necessity of dual imaging modalities to rule out acute pathology in women with abdominal and pelvic pain. This issue deserves more attention and future study.

Potential Impact To Current Practice

This study is too limited in its methodology to impact current practice. Future studies are needed to evaluate the true sensitivity and specificity of CT for pelvic pathology.

Bottom Line

Women may spend hours in the ED undergoing two imaging studies for acute abdominal pain. We need to consider whether this actually provides clinically relevant information.