[Comparison of prostate volume measured by transrectal and abdominal echography and its implication for the measurement of the PSA density for the diagnosis of prostate cancer].

OBJECTIVE

To compare PSA density (PSAD) results based on prostate volume measurements obtained by either transrectal or abdominal ultrasound (US) in the diagnosis of prostate cancer.

METHODS

We prospectively selected 420 consecutive subjects whom at the time of a transrectal US (TRUS) guided biopsy or an abdominal US had the other US evaluation done within the previous 6 months and who did not undergo hormonal, surgical o radiotherapeutic therapy. For both abdominal and transrectal US PSAD (PSA/volume) were obtained from this data and compared, with volumes calculated using the formula: V = antero-posterior diameter2 x transverse diameter/2.

RESULTS

140 patients had prostate cancer (33.8%). Using Student's t test mean differences were 0.27 cm for anteroposterior diameter, 0.39 cm for transverse diameter, 3.36 cc for volume and 0.014 for PSAD, being the differences significative in all cases (p < 0.001). When ROC curves were calculated for TRUS PSAD and abdominal PSAD areas obtained were 0.66 and 0.67 respectively. For a PSAD cut off point of 0.15, in patients with PSA values between 4-10 ng/ml Sensitivity was 0.77 for TRUS and 0.75 for abdominal US, and specificity was 0.40 and 0.49 respectively.

CONCLUSIONS

Although statistically significative differences were found in all measurements between TRUS and abdominal US, most probably due to the high number of patients, these differences have little clinical relevance as the other results show. In our experience PSAD calculation by abdominal US has the same utility than by transrectal US and avoids its mayor inconvenience which is to perform TRUS.