Medical audit of mammography: a simplified alternative

Assessing radiologists' mammographic interpretation and performing a complete audit of a mammographic practice are notoriously difficult and time consuming. The authors propose a simplified method for accomplishing a satisfactory medical audit. A search of the 1987 pathological reports of St. Michael's Hospital in Toronto yielded 153 patients who underwent excisional biopsy of the breast and for whom preoperatively obtained mammograms were available. The medical records of the patients were reviewed to obtain demographic data, as well as information as to whether the excised lesions had been palpable and the stage of the tumour. The mammograms of the patients were categorized retrospectively by four independent observers. The findings were correlated with the results of the pathological examinations and analysed with receiver-operating characteristic (ROC) curves. Forty-five nonpalpable and 121 palpable lesions were identified, of which 70 were malignant and 96 benign. The positive predictive value of mammography for the nonpalpable lesions was 20%. Three of the 9 nonpalpable cancers and 35 of the 56 palpable ones had metastasized to the axillary lymph nodes. The area under the ROC curves for the four radiologists ranged from 0.84 to 0.89. This audit method in inexpensive and easily applied.