Anatomy of the tunica albuginea
Tunica albuginea is a Latin term used in anatomy to describe a special kind of thin but tough tissue layer that simply means "white covering." This tissue is found in three different areas of the body: tunica albuginea of the penis that covers each of the two corpora cavernosa, as well as tunica albuginea of the testicles, and tunica albuginea of the ovaries.
While this bit of anatomy might be confusing because it is new to you, it is simple to understand with a familiar example: the hot dog. Think of the penis as being made of two hot dogs lying side by side. The substance or meat of the hot dog is the corpora cavernosa, and the casing or skin that surrounds the hot dog is the tunica albuginea. These two hot dogs are sounded by other layers of tissue but for our discussion this should help you to understand the anatomy of the penis that is important to Peyronie’s disease.
The penis is made of three cylinders of spongy tissue, consisting of paired corpora cavernosa and a single corpus spongiosum. The two corpora cavernosa are involved with the erection process, while the corpus spongiosum is involved with the transmission of the urethra through which urine passes. The tunica albuginea only surrounds the two corpora cavernosa.
The tunica albuginea is primarily made of layers of collagen protein that can accommodate a considerable degree of pressure as the corpora cavernosa fill with blood during an erection. About 5% of the tunica is elastin fibers that enable the penis to lengthen during erection. The tunica is built to elongate symmetrically and increase in circumference assuring that a straight erection develops. The physical properties of the tissue that make up the tunica allow for a considerable volume increase of the penis in order for an erection to achieve full hardness and size. If the tunica albuginea does not expand because of the presence of the excess scar material – as in Peyronie’s disease – then the penis will bend when erect of not fill completely resulting in a weak erection.
Tensile strength of the tunica albuginea is 1200-1500 mmHg, making this connective tissue one of strongest in the body. On average, the flaccid penis volume will increase about triple when erect, with a range of 1.7-5 times volume increase.
Tunica albuginea and the Peyronie’s scar
At the heart of the Peyronie’s disease problem is the excess fibrous material, similar in composition to common scar, that develops in the tunica albuginea. Located below the surface of the shaft and within the tunica albuginea of the penis, the internal scar is formed in response to injury or genetic abnormality. All the signs and symptoms of Peyronie’s disease occur only because this scar tissue abnormally affects the tunica albuginea under the surface of the shaft. The distortion of the penis, pain, reduced sexual ability, and reduced size of the penis can be traced back to how the tunica albuginea responds to the foreign scar material.
Peyronie’s pain occurs because the scar nodule presses up against another tissue known as Buck’s fascia that is found directly above the tunica albuginea. The tunica albuginea has no nerve supply, but Buck’s fascia has a very good nerve supply that will cause it to register pain when pressed upon by the scar located in the tunica albuginea below it.
Peyronie’s penis distortion and curvature occurs because the tough fibrous scar prevents full and normal expansion of the two corpora cavernosa cylinders when they attempt to fill with blood as an erection develops. Because the tunica albuginea prevents full expansion of the corpora cavernosa, the erection will be restricted and weak in all or part of the penis. Depending on the size, number and location of these scars that limit expansion during an erection a variety of twists, curves and dents can develop in the penis.
Ability to engage in intercourse can be reduced in two ways. First, the presence of a bend, curve or distortion that is severe enough to prevent entry. Secondly, by reduction of the hardness of the erection if the PD scar prevents the tunica albuginea from pressing against and closing the deep dorsal vein of the penis. If this happens then the blood does not becomes trapped in the penis to create the pneumatic pressure that is necessary for an erection, leading to a variable degree of impotence.
If the scar material is sufficiently large and causes contraction of the tunica albuginea, then the length and circumference or girth of the erect penis will be reduced. Most men report some loss of penile length, typically 1-2 inches shorter than prior to Peyronie’s disease.