The authors review and classify errors in 182 cases that were presented at problem case conferences between August 1986 and October 1990. Errors were classified by means of a system developed 20 years ago and by means of a system developed within the past several years. The authors found that sources of error have changed very little. Errors usually involved failure to consult old radiologic studies or reports, limitations in imaging technique, acquisition of inaccurate or incomplete clinical history, location of a lesion outside the area of interest on an image, lack of knowledge, failure to continue to search for abnormalities after the first abnormality was found, and failure to recognize a normal biologic variant. Errors included 126 perceptual errors (64 false-negative, 15 false-positive, and 47 misclassification errors) and 56 mishaps, including 38 complications and 18 communication errors. In seven cases nonperception errors occurred because established departmental routines were not followed, and in nine cases a new departmental routine was established after a complication occurred. Departmental policy exerts less effect on perception and interpretation errors.

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Myxoid tissue forms part of many benign and malignant soft-tissue tumors. The advent of percutaneous needle biopsy has made it important to be aware of the diagnostic implications of biopsy samples containing myxoid tissue. To determine whether the magnetic resonance imaging (MRI) characteristics could help establish the diagnosis, we compared the MR images of 11 tumors containing myxoid tissue with the resected tumor tissue. In our small series of these rare tumors, the MRI characteristics allowed differentiation of intramuscular myxomas from malignant neoplasms containing myxoid tissue. Intramuscular myxomas meet the following conditions: (a) they are well circumscribed; (b) they arise within muscle; (c) T1-weighted images demonstrate uniform, decreased signal intensity; (d) T2-weighted images demonstrate uniform increased signal intensity; (e) contrast-enhanced images exhibit an inhomogeneous increase in signal intensity. If any of these conditions is not met, then a malignancy containing myxoid tissue should be suspected.

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