Stereological and biochemical analysis of muscular and connective tissue components in the penile corpus cavernosum adjacent to the fibrous plaque of Peyronie's disease

Abstract

Objective: To investigate the structural organization of the connective tissue in the corpus cavernosum (CC) adjacent to the fibrous plaque in Peyronie's disease (PD) using stereological and biochemical techniques, as most studies on PD have focused on the analysis of the fibrous plaque that forms in the tunica albuginea (TA). Because this fibrotic reaction is mediated by various inflammatory soluble factors, adjacent connective tissues might also be affected and this secondary effect might explain, for example, the erectile dysfunction that occurs in PD.

Patients and methods: During surgery biopsies were taken from the CC adjacent to the fibrous plaque and from the plaque itself in seven patients with PD (mean age 48.3 years). All the patients had normal erections. Control samples were similarly located samples from 'normal' penises obtained during autopsy of five men (mean age 52.3 years). Tissue samples were stained with Weigert's stain (elastic fibres), Van Gieson's stain (connective tissue), and Sirius red (collagen). Stereological analysis was done using a 42-point grid to determine volumetric densities (Vv). Total collagen content was estimated as micrograms of hydroxyproline per milligram dry CC.

Results: The Vv of elastic fibres was significantly reduced in PD by 17.3% compared with controls, at a mean (sd) of 19.49 (3.27)% vs 23.56 (1.87)% (P < 0.05). While in PD the Vv of smooth muscle at 34.46 (2.06)% and connective tissue at 35.39 (6.15)% were not significantly different from those of controls at 38.38 (3.17)% and 38.02 (5.03)%, respectively. The Vv of elastic fibres in the fibrous plaque was decreased by 38.3% compared with the normal TA, at 20.25 (5.49)% vs 32.81 (4.75)% (P < 0.02). The mean (sd) collagen concentration in the CC from controls was 77.94 (24.26) microg/mg and in the patients with PD was 66.57 (19.39) microg/mg, which did not differ significantly. Sirius red-stained sections under polarized light showed that, in the normal CC, collagen-associated colours were homogeneously distributed. However, in the PD samples, stained collagen had a disrupted orientation and had a more heterogeneous birefringence, implying looser collagen bundles.

Conclusions: The quantitative analyses indicated that collagen in the CC close to the fibrous plaque was not affected, although its organization was noticeably altered. The CC elastic fibres were reduced though, and there was a similar change in the fibrous plaque of the TA. These results suggest that, although occurring primarily in the TA, the PD fibrous plaque may induce changes in the adjacent CC.