Fig. 5

Lack of knowledge (type 3) error. A 55-year-old male patient underwent lower extremity CTA due to signs of peripheral artery disease in the left lower extremity. The radiology resident who examined the CTA for the preliminary results saw that the left superficial femoral artery was of thin caliber and ended at the knee level. He thought that it was chronically occluded (red arrow, a). He also thought that collaterals between the left deep femoral artery and popliteal artery (blue arrow, a) had developed secondary to the thrombi in the left popliteal artery (green arrow, a). When the radiologist referred the CTA to the attending physician, he learned that the patient’s left internal iliac artery continued as the popliteal artery, which is a variation called persistent sciatic artery. The persistent sciatic artery of the patient was thrombosed throughout its course (yellow arrows, b, c, d). The resident could not recognize this variation and the pathology due to the lack of knowledge. Although this is not a common variation that should be known by every radiologist, in this case, failure to recognize the thrombosed persistent sciatic artery could have adversely affected the possible interventional treatment plan