Anatomy

The pelvic outlet can be divided into anterior and posterior triangles by drawing a line between the ischial tuberosities with the symphysis pubis and coccyxbeing the apices (Fig. 6.1). Urogenital causes of Fournier's gangrene lead to initial involvement of the anterior triangle, whereas anorectal causes primarily involve the posterior triangle.

The five fascial planes that can be affected are: Colles' fascia, dartos fascia, Buck's fascia, Scarpa's fascia, and Camper's fascia.

Colles' fascia is the fascia of the anterior triangle of the perineum. Laterally it is attached to the pubic rami and fascia lata, posteriorly it fuses with the perineal membrane and perineal body, and anterosuperiorly it is continuous with Scarpa's fascia (Smith et al. 1998). It prevents the spread of infection in a posterior or lateral direction, but provides no resistance to spread in an anterosuperior direction towards the abdominal wall.

The dartos fascia is the continuation of Colles' fascia over the scrotum and penis.

Buck's fascia lies deep to the dartos fascia, covering the penile corpora. It fuses distally with the corona of bulbar urethra anterior triangle symphysis pubis perineal body urogenital membrane the glans and proximallywith the suspensory ligament and crura of the penis.

Camper's fascia is the loose areolar fascial layer deep to the skin of the abdominal wall, but superficial to Scarpa's fascia. Together with Scarpa's fascia it is continuous with Colles' fascia inferomedially.

Scarpa's fascia lies deep to Camper's fascia, covering the muscles of the anterior abdominal wall and thorax. It terminates at the level of the clavicles.

The perineal membrane lies deep to Colles' fascia. It is triangular in shape and lies between the pubic rami from the symphysis pubis to the ischial tuberosities. It has a distinct posterior border, with the central perine-al tendon in the midline. Colles' fascia terminates in this posterior border.

The central perineal tendon (or perineal body) lies between the anus and bulbar urethra. It serves as an attachment for the various perineal muscles and helps to maintain the integrity of the pelvic floor.

Via the internal and external fascial layers of the spermatic cord, the perineal fascia is continuous with the retroperitoneal fascia. This is a potential path for the spread of infection from the perineum to the peri-vesical and retroperitoneal areas, and vice versa (Paty and Smith 1992; Fialkov et al. 1998).

Spread of infection along the fascial planes will follow the path of least resistance (Jones et al. 1979). Infection in the anterior perineal triangle will spread preferentially in an anterosuperior direction along Scarpa's posterior triangle bulbar urethra anterior triangle symphysis pubis perineal body urogenital membrane posterior triangle

ischial tuberosity coccyx sacrotuberous ligament coccyx ischial tuberosity sacrotuberous ligament

Fig. 6.1.The pelvic outlet can be divided into anterior and posterior triangles by drawing a line between the is-chial tuberosities with the symphysis pubis and coccyx being the apices (© Hohenfellner 2007)

suspensory ligament of penis

Scarpa's fascia

Camper's fascia

Fig. 6.2.Diagram of a sagittal section showing the fascial planes of the male external genitalia, perineum, and lower abdomen (© Hohenfellner 2007)

suspensory ligament of penis

Scarpa's fascia

Camper's fascia

Fig. 6.2.Diagram of a sagittal section showing the fascial planes of the male external genitalia, perineum, and lower abdomen (© Hohenfellner 2007)

Buck's fascia dartos fascia external anal sphincter perineal body

Colles' fascia external spermatic fascia

Buck's fascia dartos fascia external anal sphincter perineal body

Colles' fascia external spermatic fascia fascia, whereas lateral spread will be limited by fusion of Colles' fascia to the ischiopubic rami, and posterior spread to the anal region will be limited by the termination of Colles' fascia in the posterior edge of the perineal membrane (Fig. 6.2).

Infection from the perianal region may sometimes penetrate Colles' fascia, which is fenestrated at the level of the bulbocavernosus muscle, leading to spread of infection to the anterior triangle (Tobin and Benjamin 1949). Thus, while anterior triangle infection rarely spreads to the posterior triangle, it is possible for infection to spread from the posterior to the anterior triangle and then to the anterior abdominal wall (Jones et al. 1979; Walker et al. 1984; Laucks 1994).

In the perineum, the vascular supply to the cutaneous and subcutaneous tissues is mainly derived from the perineal branches of the internal pudendal artery. The deep circumflex iliac artery and superficial inferior epigastric artery supply blood to the lower abdominal wall. These arteries traverse the various fascial planes, supplying nutrients and oxygen to the skin and subcutaneous tissues. With the fascial planes infected, these vessels become thrombosed, facilitating the proliferation of anaerobic bacteria.

Blood supply to the testis, bladder, and rectum originates directly from the aorta and not from the perineal vasculature, and for this reason they are rarely affected in Fournier's gangrene. If the testes are affected, it may be from specific testicular pathology such as epididy-mo-orchitis, or from a retroperitoneal infection spreading along the spermatic fascia, causing thrombosis of the testicular arteries.

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