Screening mammography interpretation test: more frequent mistakes.

Purpose: To present the mammographic cases most commonly misinterpreted by the participants in the mammography self-test proposed by the Italian Society of Medical Radiology (SIRM) National Congress in Rimini, Italy, 2002, by analysing the findings responsible for errors, suggesting reasons for the errors, and assessing possible inadequacies in the format of the test.

Materials And Methods: The self-test was performed on the mammograms of 160 cases (32 positive and 128 negative for cancer as confirmed by histology). The mammograms had been taken in the four standard projections and placed on four multi-panel diaphanoscopes, each displaying a set of 40 cases comprising benign and malignant cases in equal proportions. The participants were given pre-printed forms on which to note down their diagnostic judgement. We evaluated a total of 134 fully-completed forms. Among these, we identified the 23 cases most frequently misread by over 15 participants in percentages varying between 40-90%. Of these cases, 10 were malignancies and 13 were negative mammograms. On review, we also assessed the diagnostic contribution of complementary investigations (not available the participants).

Results: The 134 fully-completed forms (all of the 40 cases) yielded a total of 5360 responses, 1180 of which (22.01%) were incorrect. Of these, 823 out of the 4288 cases expected to be negative (19.2%) were false positive, and 357 out of the 1072 cases expected to be positive (33.3%) were false negative. As regards the 23 most frequently misread cases, these were 10/32 (31.25%) mammograms positive for malignancy and 13/128 (10.15%) negative mammograms or mammograms showing benign disease. The 10 malignancies included 7 infiltrating ductal carcinomas, 1 infiltrating cribriform carcinoma, 1 infiltrating tubular carcinoma, and 1 carcinoma in situ. The 13 cases of benign disease--as established by histology or long-term follow-up--mistaken for malignancies by the test participants were fibrocystic breast disease in 5 cases, surgical scar in 1 case, ABBI scar in 1 case, radial scar in 2 cases, microcalcifications that had remained stable for years in 2 cases, focal sclero-adenosis in 1 case and sclero-elastosis in 1 case.

Conclusions: The errors were due to microcalcifications, benign disease simulating a neoplasm, overlapping tissue, visibility of a lesion in one projection only, lesion site in relation to the corpus mammae, missed areas of asymmetry. Attention must be paid to these signs of focal breast disease since, if correctly evaluated, they enable the early diagnosis of low-grade carcinomas that frequently carry a favourable prognosis.