URINARY
EXTRAVASATION
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.
