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104 Benign Anorectal Diseases
Fig. IV.26. Normal mechanism of labor in
left occipitoanterior position from beginning to end
repair but gives the best protection against
sphincter damage, and (3) mediolateral – carries
significant morbidity for the mother in terms of
pain and potential infection.
It has been reported that use of episiotomy can
prevent pelvic floor damage because the wider
opening requires less force to accomplish delivery
[1, 2].However, data from randomized trials failed
to demonstrate any substantial protection against
pelvic floor injuries with episiotomy,and Sultan et
al. [5] found episiotomy to be associated with an
increased risk of internal (IAS) and external
(EAS) anal sphincter injury. Episiotomy also can
damage the perineal body.
Forceps
Forceps operations are of three kinds (Fig. IV.31):
(1) low forceps – the fetal head has reached the
perineal floor and is visible at the vulva, (2) mid
forceps – engagement has taken place, and the
Fig. IV.27. Schematic representation showing mechanism of
labor in occipitoposterior position
Fig. IV.28. During delivery in occipitoposterior position, the
pelvic floor structures are stretched more than in occipitoanterior position
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 105
High
Medium
Low
Fig. IV.29. Delivery in occipitoposterior position often has to
be completed by forcepst
leading part of the head is below the level of the
ischial spines, and (3) high forceps – application
of the forceps when the head is not engaged.
There are many different patterns of forceps, and
they are identified with three main operations
(Fig. IV.32). Donnelly et al. [6] reported that use of
forceps was associated with an eight-fold increase
in risk of anal sphincter injury.
Postero-lateral J-shaped Median
Fig. IV.30. Episiotomy incisions
Fig. IV.31. Different forceps applications
Perineal Tears
These are more common in primigravid patients
where the perineum is more rigid. The most
important factors are the width of the pubic arch
and the size and position of the fetal head. All
malpresentations increase the amount of perineal
distension. Perineal tears are classified in four
degrees (Fig. IV.33): (1) first degree – vaginal
mucosa and perineal skin, (2) second degree –
extending into the perineal muscles, (3) third
degree – involving the IAS and EAS sphincters,
and (4) fourth degree – extending into the rectal
mucosa. The most significant risk factor for
third-degree perineal injury is the first vaginal
delivery [6].
Primiparity
The most important risk factor for mechanical
injury to the anal sphincters and to the pelvic
floor muscles is first vaginal delivery. In contrast,
pudendal nerve injury is more common with successive vaginal deliveries. A meta-analysis of the
literature [21] estimated a 27% incidence of
sphincter defects in primiparous women, an 8%
incidence of new sphincter defects in multiparous
women, and a 30% incidence of symptomatic
defects postpartum. The probability of fecal
incontinence due to a sphincter defect is 77–83%.
106 Benign Anorectal Diseases
Fig. IV.32. Different patterns of forceps (a). Exposition of old
a
b
forceps at Science Museum in London (b)
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 107
Anal
sphincter
a
Torn ends
of anal
sphincter
b
Fig. IV.33. First-degree (a), second-degree (b), and third-
c
degree (c) perineal tears
108 Benign Anorectal Diseases
a
b
Fig. IV.35. Postpartum defect of the internal (white arrows)
and external anal sphincters (black arrows), with presence of
a hypoechoic area of scarring (dots)
Fig. IV.34. Postpartum defect of the
external anal sphincter (open arrows):
axial plane (a), coronal plane (b)
Sultan et al. [5] reported that the risk of sphincter
damage was greatest during the first vaginal deliv-
ery (25%), and only 4% of patients sustained new
defects after subsequent delivery. Altered fecal
continence was experienced by 13% of primiparous and 23% of multiparous women at 6 weeks
postpartum. Donnelly et al. [6] reported similar
results, with 25% of altered fecal continence 6
weeks following first vaginal delivery.In the same
study, instrumental delivery and a second stage of
labor prolonged beyond 60 min were associated
with an 8.1-fold and 1.7-fold risk of anal sphincter
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 109
a
c
injury,respectively.Handa et al. [7] also identified
primiparity as the dominant risk factor of injury
during childbirth. Birth weight over 4,000 g was
also highly significant. Operative delivery
increased the risk of sphincter laceration, with
vacuum delivery presenting a greater risk than
forceps delivery. Episiotomy decreased the likelihood of third-degree lacerations but increased the
risk of fourth-degree lacerations. In a recent
report, Abramowitz et al. [14] found that primiparae and secundiparae have the same risk factors
for sphincter disruption and anal incontinence.
Fig. IV.36. Tear of the left puboanalis
(arrows) (PA ) as a scar in the medial
aspect of the puborectalis (PR): axial
plane (a), three-dimensional reconstruction (b). TP: transverse perineii, BS:bul-
bospongiosus muscle
Endosonographic Assessment
The main indication for EAUS in patients with
fecal incontinence is to detect anal sphincter
defects and damage to the pelvic floor muscles
(Figs. IV.34–38). There is wide variation in the
incidence of clinically occult anal sphincter
injuries diagnosed by ultrasonography (11–35%)
after the first vaginal delivery [7, 8, 10–19].
Donnelly et al. [6] found anal sphincter injury in
35% of primiparous vaginal deliveries using
EAUS. Sultan et al. [5] reviewed EAUS findings on
110 Benign Anorectal Diseases
a
c
b
Fig. IV.37. Tear of the left puboanalis
(open arrows) in the axial (a, b) and coro-
d
nal (c) planes.Volume render mode (d)
Section IV • Endoanal Ultrasonography in the Assessment of Patients with Fecal Incontinence 111
a
b
79 primiparous women before and after vaginal
delivery and identified anal sphincter defects in
28 (35%), of whom nine (32%) reported altered
fecal continence. Sphincter defects were not identified in those women delivered by caesarean section. Deen et al.[13] studied 46 patients with postpartum fecal incontinence symptoms and found
that 87% had a recognizable anal sphincter defect
on EAUS. In a prospective study, de Parades et al.
[8] did not confirm previous observations that
anal sphincter injury is common after forceps
delivery. In a large population of 93 healthy
Fig. IV.38. Three-dimensional recon-
struction in the axial (a) anal coronal (b)
planes showing a tear of the left transverse perineii (TP) as a scar lateral to the
external sphincter ring (EAS)
women, anal sphincter injury was identified by
ultrasonography in <13% of cases after forceps
delivery, and the development of anal inconti-
nence was not related to these defects. The only
factor with significant predictive value for anal
sphincter injury was perineal tear. Pinta et al. [22]
analyzed possible risks factors associated with
sphincter rupture during vaginal delivery.A total
of 52 women with a third- or fourth-degree perineal laceration were compared with 51 primiparous women with no clinically detectable perineal laceration.EAUS found a persistent defect of
112 Benign Anorectal Diseases
the EAS in 39 women (75%) in the rupture group
compared with ten women (20%) in the control
group (p<0.001). An abnormal presentation was
the only risk factor for anal sphincter rupture
during vaginal delivery.
Fecal incontinence related to anal sphincter
defects is likely to occur even in elderly women
who experienced vaginal deliveries earlier in life
[15, 19].Oberwalder et al. [23] reported that 71% of
women with late-onset fecal incontinence had
occult sphincter defects on EAUS results. The
onset of fecal incontinence was at a median age of
61.5 years.
Obstetric trauma can be associated with damage/defects primarily to the distal part of the rectovaginal septum, as well as elongation of the
length of the septum. Fecal incontinence develop-
ing after vaginal delivery can also be caused by
injury to the perineal body [25]. It is the central
portion of the perineum where the external anal
sphincter, the bulbospongiosus, and the transverse perineal muscles meet. The perineal body
has multiple and diverse functions: it anchors the
anorectum, anchors the vagina, provides a physical barrier between the vagina and rectum, and
maintains urinary and fecal continence.
The routine measurement of perineal body
thickness (PBT) during EAUS may be valuable.
Zetterstrom et al.[26] reported that 93% of incontinent women with obstetric trauma to the anal
sphincter had a PBT of 10 mm or less. This result
was confirmed by Fornell et al. [24] who found
that PBT <10 mm was associated with incontinence for flatus and liquid stools and lower anal
squeeze pressures, and also by Oberwalder et al.
[27] who found that a sonographically thin
(< 10 mm) perineal body was associated with anal
sphincter defects in 97% of patients with fecal
incontinence, a PBT of 10–12 mm was associated
with sphincter defect in 36% of cases, and a PBT
of 12 mm was associated with a defect in 23% of
cases.
Benefits of three-dimensional (3-D) EAUS in
the evaluation of fecal incontinence have been
reported [15–17, 28]. Williams et al. [15] assessed
changes to anal canal morphology in the absence
of sphincter trauma. After delivery, there was significant shortening of the length of the anterior
portion of the EAS, which could be demonstrated
only with 3-D reconstructions on sagittal and
coronal planes. This change did not correlate with
any functional symptoms. West et al. [28] found
that incontinence in parous females was not associated with loss of sphincter volume. Williams et
al. [16] reported that only 68% of women with
third-degree tears had 3-D EAUS evidence of
sphincter damage. In another study,Williams et al.
[17] determined the incidence and functional consequences of anal sphincter damage using 3-D
EAUS and anal manometry in 45 women who had
vaginal delivery. They found evidence of postpartum trauma in 29% of cases, involving the external
sphincter in 11% of patients, the puboanalis in 11%
of cases, and the transverse perineii in 7% of cases.
Damage to the EAS was associated with a significant decrease in squeeze pressure and an increase
in incontinence score and represented the only
functionally significant component. Tears to the
puboanalis or transverse perineii did not affect
pressure or incontinence score.
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