Inadvertent excision of lumps which turn out to be soft tissue sarcomas is still unfortunately quite common. It is known as the “whoops” procedure. Determining whether there is residual disease is key to deciding subsequent management. The value of MRI has been assessed.

All new patients referred to our unit with a potential diagnosis of a “whoops” lesion were routinely reassessed with MR1 6 weeks after the initial operation.

Notwithstanding the result of the scan all patients underwent a further wide excision of the involved area shortly after the MRI. The scans of these patients have been reviewed and classified into positive, equivocal or negative. These results have been compared with the histological assessment of the re- excision specimen to determine the accuracy of MR1 in predicting the presence of residual tumour.

Of 887 patients with newly diagnosed soft tissue sarcomas seen in an 8 year period, 140 (11 %) had previously had a ‘whoops” procedure. Of these 111 had re-evaluation MR1 scans and had also undergone a further re-excision. There was residual tumour in 63 (57%) patients, whilst 48 (43%) had no residual tumour.

The sensitivity of MRI in predicting tumour was 64% but specificity 93%. Positive predictive value was 93% and negative predictive value 67%. Overall accuracy was 77%.

MRI is useful in identifying residual tumour after a whoops procedure but a negative result by no means excludes it. Re-excision remains essential despite the MRI results in most cases to ensure tumour clearance. Preventing the “whoops” procedure is clearly the best option of all!