Is the density of transition zone prostate tissue truly 1 gram per milliliter?-an evaluation of HoLEP specimens

Prostate volume is assumed to equal prostate weight (PW), based on a 1:1 conversion between the milliliter (mL) and gram (g). While the 1:1 conversion holds for pure water, the density of transitional zone prostate tissue has not been studied. The aim of this study was to evaluate prostate density (PD) and the factors that affect it.

This was an experimental in vitro study of holmium laser enucleation of the prostate (HoLEP) specimens weighed intraoperatively. Morcellated transition zone tissue was collected. The PW was measured by sterile water displacement. The volume displaced by the tissue was used to measure volume and density. Statistical analysis was performed using correlation analysis and the Wilcoxon rank-sum test. Descriptive statistics were reported as medians with bootstrap-calculated interquartile ranges (IQR).

Specimen data were collected from 50 consecutive HoLEP patients, of whom 45 had complete data. Median resected intraoperative PW was 71 g (IQR, 56-89). Intraoperatively measured prostate volume was 74.2 mL (IQR, 60-89.6). Calculated PD was 0.95 (0.92-0.98). Prostate volume modestly overestimated resected PW by 3.35 mL (95% confidence interval: 1.10-5.35, P=0.005). Finasteride use, prior benign prostatic hyperplasia (BPH) surgery, and cancerous tissue were not associated with PD. Prostates larger than 100 mL on preoperative imaging had a higher PD compared to smaller prostates. Denser prostate tissue was associated with longer morcellation and enucleation times, and higher laser energy utilization.

In transitional zone prostate tissue collected from HoLEP specimens, PW was largely consistent with prostate volume, supporting the notion of 1:1 conversion. However, this did not hold for larger prostates, which were denser and exhibited greater variation in prostate volume. Correlation between PD and pathology needs to be further studied.