The images show a large cecal mass (red arrow) with secondary intussusception of the distal small bowel and cecum into the proximal transverse colon (yellow arrow), resulting in small bowel obstruction. The majority of cases of intussusception in adults is secondary to benign and malignant lesions including metastases, inflammatory bowel disease, postoperative adhesions, Meckel's diverticulum, and intestinal tubes such as percutaneous gastrostomy and jejunostomy feeding tubes.
The radiologist was right about the small bowel obstruction. How did he miss the cecal mass and intussusception?
There are several reasons why this "obvious" finding is missed:
- Satisfaction of search (SOS): there are many findings in this study, including a left lower quadrant renal transplant, numerous kidney lesions, and small bowel obstruction. The identification of small bowel obstruction, which accounts for the patients abdominal pain, can lead to premature termination of the search pattern. Even if the radiologist continues along with his or her search pattern, they may not be looking carefully for any additional findings. Here's a tip, when you make a finding that accounts for the patients signs/symptoms, remember SOS and ask yourself what subtle but important finding will you make next because you are careful and thorough. This approach is called metacognition, which is described more fully in the lectures.
- Not developing and adhering to a comprehensive and reliable search pattern. Run the colon in every case. It doesn't matter if it's a 19 year old with appendicitis or 79 year old with a ruptured aortic aneurysm. I've seen incidental colon cancer in both, and I've seen it missed more times that I care to admit.
- Interruptions: when I see a miss like this, I wonder if the radiologist had been interrupted by a phone call or modified barium swallow in the middle of interpreting this case. We often cannot ignore the phone ringing or a gaggle of physicians standing behind us in the reading room waiting to review some cases. Expect interruptions and develop a workflow that addresses unexpected interruptions. I prefer using a standardized template based on body parts with each field empty. When I am interrupted, I can go back and see exactly where I left off. You lose many benefits of structured templates when they are prefilled.
Follow-up MRI
The images below are from a follow-up MRI performed a few weeks after the CT exam. Remember that the colon mass and intussusception was missed on the CT, so the MRI was not performed to evaluate the colon mass or liver.
Believe it or not, a different radiologist interpreting the MRI also missed the colon mass and resulting intussusception. Below are coronal T2 (top left), axial T2 (top right), high B value DWI (bottom left), and corresponding ADC (bottom right) images. The red arrows highlight the mass, which is clearly visible in retrospect.
Why did these important findings get missed again?
We can add a few new reasons to the ones described for the CT exam:
- Alliterative error: The interpreting radiologist was influenced by the radiologist interpreting the CT exam. A colon mass was not described in the report for the CT scan performed a few weeks earlier, so there is likely no colon mass on the current MRI exam. To avoid this error, do not look at the prior radiologists report until after you've interpreted and dictated your study. But make sure you read the prior report, otherwise you may miss subtle but important findings on the prior study.
- Framing bias: the study was not performed to evaluate for a colon mass. If the indication was elevated bilirubin and concern for biliary obstruction, the radiologist would likely not be focused on finding an incidental colon mass. I will read the history and then forget it as I review the study using my regular search pattern. After I am done, I go back with the history in mind and double check certain areas. For example, if there is a history of cancer, I will always go back and look at the liver, lymph nodes, and bony structures (especially the pedicles) a second time because I know that's where subtle metastases are missed. Some would say that this is inefficient because you are looking at the study a second time. Yes it is inefficient, but more accurate. So you must decide what is more important, expediency or accuracy.
- Not reviewing the DWI images for unexpected findings. I found this as a contributing factor during a study comparing random versus nonrandom peer review. DWI is not just to further characterize lesions identified on other sequences or studies. It is important to review the DWI images the same way as a CT, looking at each organ and structure individually. I have cases of missed liver metastases, pancreatic masses, bone metastases, colon cancers, soft tissue metastases, and adenopathy because the radiologist wasn't expecting them for various reasons, yet they were most obvious on the DWI images. When you look at DWI images, expect the unexpected.
