Urinary extravasation from the urinary tract will inﬁltrate speciﬁc anatomic spaces that are deﬁned by well-described fascial planes (see Plate 2-2). Thus, the degree and extent of urine extravasation depends not only on the type and severity of the injury but also on the involved fascial planes, making knowledge of these fasciae important in the treatment of this condition. Urine may extravasate from urethral perforation, resulting from periurethral abscess formation, instrumentation, external trauma (see Plate 2-19), or malignancy.
Most extravasation occurs in the bulbous urethra where the urine escapes into the well-vascularized corpus spongiosum that surrounds it. By this mechanism, infected urine enters the vascular system, often resulting in “urethral chill”—a sign of bacteremia. If the extravasation occurs gradually because of abscess formation in the bulbous urethra, it is at ﬁrst limited by Buck fascia and appears as localized swelling deep in the perineum. If Buck fascia remains intact after penile urethral injury, extravasation causes swelling limited to the ventral penis. If the intercavernous or transverse septum of Buck fascia (seePlate 2-2) is penetrated, then the entire penis becomes symmetrically swollen.
Inﬂammatory processes eventually rupture through Buck fascia, and urine and exudate are then observed deep to Colles fascia in the perineum. Traumatic injury that extends through Buck fascia results in immediate spread of extravasate beneath Colles fascia. In the perineal region, extravasation may at ﬁrst be restricted to the superﬁcial urogenital pouch by the major leaf of Colles fascia. This fascial leaf is, however, easily penetrated, allowing ﬂuid to descend into the superﬁcial space of the scrotal wall, beneath the dartos fascia. The fascial arrangement also permits progression of extravasation superiorly from the superﬁcial urogenital pouch to the space under Colles fascia of the penis. At the base of the penis, extravasated ﬂuid will easily extend beneath the Scarpa fascia and track superiorly into the lower abdomen. This is termed the “butterﬂy” pattern of genital extravasation or bleeding. Extravasation can also extend to the lower abdominal wall from the scrotum by an additional route, along the spermatic cord canals. Importantly, the posterior extension of extravasated ﬂuid into the perineum beneath Colles fascia is restricted at the urogenital diaphragm to which Colles fascia is ﬁrmly attached (seePlates 2-2 and 2-3). Crush injuries to the perineum may rupture Colles fascia at this site of attachment, in which case urine will spread posteriorly and superiorly into the ischiorectal fossa space and perianal areas.
Anatomically, extravasated urine in the scrotum under Colles (dartos) fascia is still superﬁcial to the external spermatic fascia (oblique muscle) of the scrotal wall. Thus, extraperitoneal or retroperitoneal rupture of the urinary bladder can result in extravasation of urine into the scrotum through the inguinal canals. When this occurs, the scrotal ﬂuid is located subcutaneously beneath both the internal spermatic fascia and the external spermatic fascia, which are deep to the dartos fascia (see Plate 2-1).
A typical case of urinary extravasation from injury to the penile urethra is illustrated in the ﬁgure. Urine escapes through Buck fascia to beneath Colles fascia of the penis, where it extends inferiorly into the scrotum and superiorly under Scarpa fascia to the lower abdomen. Note the line of demarcation at Poupart ligament, where Scarpa fascia is ﬁxed to the fascia lata of the thigh, limiting extension in this area (see Plate 2-2). Normal bacterial ﬂora of the urethra include both aerobic and anaerobic organisms that are usually harmless saprophytes. However, they may become pathogenic when extravasated into remote tissues. In the presence of infected urine, intense cellulitis and gangrenous fasciitis may develop (Fournier gangrene) in these tissues that can progress quickly to necrosis and sloughing of the scrotum skin and is extremely lethal if not treated with antibiotics, the urine diverted, and the area surgically drained.