Objectives. To correlate the maximal transverse prostate measurement determined using transabdominal ultrasound with the maximal transverse prostate measurement determined using transrectal ultrasound.

Methods. The records of 287 patients who had undergone both transabdominal pelvic ultrasound for determination of postvoid residual urine volume and transrectal ultrasound for evaluation of elevated serum prostate-specific antigen levels or abnormal digital rectal examinations were reviewed. For all patients, the maximal transverse prostate dimension had been recorded at each study. Linear regression analysis was used to correlate these two data sets.

Results. There was a strong correlation between the maximal transverse prostate dimension determined using transabdominal ultrasound and that determined using transrectal ultrasound. The R² for the regression analysis was 0.448. From the regression analysis, the equation that converts the maximal transabdominal transverse prostate measurement into its equivalent transrectal counterpart was determined: transrectal measurement (cm)=0.5109 [transabdominal measurement (cm)]+2.2935.

Conclusions. A strong mathematical correlation was found between the maximal transverse prostate dimension determined using transabdominal ultrasound and that obtained using transrectal ultrasound. This may have clinical significance when performing transurethral needle ablation of the prostate.