Comparative morphometric study of bladder detrusor between patients with benign prostatic hyperplasia and controls

We determined the change in the amount of connective tissue of the detrusor in patients with benign prostatic hyperplasia (BPH) in relation to the degree of bladder hypertrophy by ultrasound estimated bladder weight. The ratio of connective tissue-to-smooth muscle between controls and BPH cases was compared.

For normal controls we used cadaver bladders excised at autopsy from 13 men with no urinary tract diseases. Bladder wall samples were also obtained at subcapsular prostatectomy for BPH in 26 patients. On thin sections stained with Masson trichrome, the ratio of connective tissue-to-smooth muscle was measured using a computer assisted color image analysis. This ratio was compared in BPH cases with estimated bladder weight, which was measured preoperatively using transabdominal ultrasonography.

A connective tissue-to-smooth muscle ratio ranged from 19.8 to 28.2% (mean plus or minus standard deviation 24.7+/-2.4) and from 12.9 to 53.3% (27.3+/-9.9) in control and BPH cases, respectively. In BPH cases a significant correlation was noted between estimated bladder weight and connective tissue-to-smooth muscle ratio (r=0.788, p <0.0001). Interestingly, in BPH cases with an estimated bladder weight of less than 60 gm. the ratio ranged from 12.9 to 30.4% (22.8+/-4.9), which was not significantly different compared to control cases. In contrast, in all BPH cases with an estimated bladder weight of 60 gm. or more connective tissue-to-smooth muscle ratio increased significantly to more than 30% (range 33.4 to 53.3%, mean 42.2+/-13.6%).

These results suggest that abnormal increase of connective tissue in addition to smooth muscle hypertrophy and/or hyperplasia could contribute to advanced bladder hypertrophy caused by infravesical obstruction.