Microscopic Features

In uncircumcised men the mucosa covering the glans, coronal sulcus, and inner foreskin is formed by a nonkeratinizing stratified squamous epithelium of about 5-7 cells thick (Fig. 3.3a). No sweat glands or other adnexal structures are observed. Underlying it there is a lamina propria composed of connective tissue, about 2-3 mm thick. The glans is composed mainly of corpus spongiosum but the rounded endings of corpora cavernosa frequently protrudes into its deepest region. Both corpus spon-giosum and cavernosum are specialized types of erectile tissues formed by anasto-mosizing venous-like vascular channels immersed in a fibroelastic stroma. However, vascular spaces in the corpus spongiosum are more ample, irregular and spaced

Fig. 3.3 Penile histology. (a) A nonkeratinized squamous epithelium and underlying lamina propria. (b) Corpus spongiosum with ample vascular spaces immersed in a fibroelastic stroma.

(c) Corpus cavernosum with densely packed vascular spaces, irregular lumina, and denser stroma.

(d) Most of the distal urethra is covered by a stratified columnar epithelium with intermingled mucin-producing cells. Note openings of Littré glands in the lower half field

Fig. 3.3 Penile histology. (a) A nonkeratinized squamous epithelium and underlying lamina propria. (b) Corpus spongiosum with ample vascular spaces immersed in a fibroelastic stroma.

(c) Corpus cavernosum with densely packed vascular spaces, irregular lumina, and denser stroma.

(d) Most of the distal urethra is covered by a stratified columnar epithelium with intermingled mucin-producing cells. Note openings of Littré glands in the lower half field from each other while in the corpora cavernosa they are more compacted, vascular lumina are more compressed, and stroma is denser (Fig. 3.3b, c). In the foreskin, beneath the lamina propria, bundles of the dartos muscle, extending from the homologous layer in the shaft, are easily discernable (Fig. 3.4a). The outer surface of the foreskin is formed by a prolongation of the skin of the shaft and shows similar his-tological features. The preputial dermis and the mucosal lamina propria are very similar in its microscopic aspect and differences between them are best noted examining the covering epithelium. Rete ridges of the epidermis are more irregular, kera-tinocytes are more or less pigmented, a thin stratum corneum is observed and adnexal structures are usually found (Fig. 3.4b). In the squamous epithelium of the inner foreskin the basement is almost flat and no pigmentation, stratum corneum, or adnexal structures are normally detected (see Fig. 3.3a).

The penile shaft is covered by the same type of skin found elsewhere, a kerati-nizing stratified squamous epithelium with sweat glands and pilosebaceous units. The dartos layer underneath is composed of interlacing bundles of smooth muscle separated by loose connective tissue. The Buck's fascia, extending from the root

Fig. 3.4 Penile histology. (a) Bundles of smooth muscle fibers typical of the dartos layer in foreskin, coronal sulcus, and shaft. (b) The foreskin outer surface is a keratinizing squamous epithelium with irregular rete ridges, pigmented keratinocytes, and pilosebaceous units

to the coronal sulcus and located beneath the dartos layer, is composed of loose connective tissue with abundant vessels and nerves. Deeper lies the tunica albuginea surrounding both corpora cavernosa. It is composed of dense hypocellular connective tissue that encases them throughout their entire length. The median septum separating the corpora cavernosa depicts similar features. Ventrally located in the angle formed by both corpora cavernosa is the column of corpus spongio-sum which contains the distal (penile) urethra running throughout its entire length from the root to the meatus urethralis. The epithelium of the distal urethra is urothelial only in its most proximal section and from here it changes to a stratified columnar epithelium with interspersed goblet-like cells (Fig. 3.3 d). It maintains this morphology up to the fossa navicularis where it changes to the typical epithelium that covers the glans. Underneath the epithelium of the distal urethra there is a lamina propria of loose connective tissue which imperceptibly merges with the surrounding erectile tissue of the corpus spongiosum. Mucin-secreting glands, named Littre glands, are found in the periurethral area and empty their secretion into the urethral lumen (see Fig. 3.3d).

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