Friday, November 28, 2008

SOS and a Rheumatoid Knee

The phenomenon of "satisfaction of search" (SOS) is the bane of all radiologists. ("Bane" comes form the old English word for "slayer, murderer"; it means "that which causes ruin or woe", so it is a felicitous choice for this context). In SOS, the radiologist detects an obvious lesion, becomes satisfied with his perceptions, and misses less obvious abnormalities on the same study.

Satisfaction of search has been described by several authors, including Samuel et al. (Radiology 194:895-902, 1995), who studied this phenomenon in the detection of nodules on chest radiographs. They concluded that "obvious abnormalities capture visual attention and decrease vigilance for more subtle abnormalities". SOS also occurs in musculoskeletal radiology, as documented by Ashman et al (AJR 175:541-544, 2000).

Not surprisingly, radiologists continue to wrestle with this phenomenon. The more striking the findings, the more you have to increase your vigilance for subtle findings.

In this case, a 22 year-old female with rheumatoid arthritis presents with knee pain:

Sagittal and coronal T2 fat sat images show a large joint effusion with rice bodies (yellow arrow) and inflammatory pannus (green arrows). There is also a bone infarct in the tibia (red arrows). There seem to be more than enough findings to explain the patient's pain!

Mindful of the SOS phenomenon, a careful inspection of the entire knee was done. This revealed a tear of the posterior horn of the lateral meniscus:

This case reinforces the idea that the bigger and more spectacular the findings, the more you should look carefully at the entire study. Otherwise, human nature and SOS will tend to lead you astray.

Vic David MD

1 comment:

fiona said...

hi, its very informative, Sports Physiotherapist , thanks