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Suprale
Perianal
10 Anorectal Abscess and Fistula in Ano
163
tion while the remainder result from the causes
as listed in Table10.1. Anorectal abscess occurs
more often in males than females, and may
occur at any age, with peak incidence among
20–40-year-olds [9–14].
Table 10.1 Etiology of anorectal abscess
Nonspecic
Cryptoglandular
Specic
Inammatory bowel disease
Crohn’s disease
Ulcerative colitis
Infection
Tuberculosis
Actinomycosis
Lymphogranuloma venereum
Trauma
Impalement
Foreign body
Surgery
Episiotomy
Hemorrhoidectomy
Prostatectomy
Malignancy
Carcinoma—anal, rectal, vaginal, prostate
Leukemia
Lymphoma
Chemotherapy-related immunocompromise
Radiation
Classication
Anorectal abscesses are classied by the anatomic
space in which they develop. They are more common in the perianal and ischiorectal spaces and
less common in the intersphincteric, supralevator,
and submucosal locations (Fig. 10.2) [9, 11–13,
15]. Pus can also spread circumferentially through
the intersphincteric, supralevator and ischiorectal
spaces, resulting in a horseshoe abscess.
Evaluation
Symptoms
Perianal pain and swelling are common with supercial abscesses while drainage or fever occur less
often [11–13, 16]. Deeper abscess, such as those
that form in the supralevator or high ischiorectal
space, may also present with pain that is sometimes
referred to the perineum, low back, or buttocks [15,
17, 18]. Rectal bleeding has been reported. Severe
rectal pain accompanied by urinary symptoms such
as dysuria, retention or inability to void may be suggestive of an intersphincteric or supralevator abscess.
It is always valuable to note the incontinence score
prior to and after any stula surgery [19].
Physical Examination
Physical examination may reveal supercial
erythema and uctuance with tenderness to pal-
Fig. 10.2 Classication
of anorectal abscess
vator
Inter-
sphincteric
Ischiorectal
164
J. D. Vogel and C.-A. Vasilevsky
pation or may be unrevealing in patients with
deeper abscesses despite the patient’s complaint
of pain [13, 17, 20, 21]. An inspection will reveal
erythema, swelling and possible uctuance. It is
crucial to recognize that visible external manifestations will often be absent with intersphincteric
or supralevator abscesses despite the patient’s
complaint of pain [22]. Although digital examination may not be possible because of extreme
tenderness, palpation, if possible, will demonstrate tenderness and a mass. With a supralevator
abscess, a tender mass may be palpated on rectal or vaginal examination [2]. While anoscopy
or sigmoidoscopy is typically unnecessary in the
acute setting, sedation or anesthesia should be
considered when these procedures are required.
The differential diagnosis of anorectal abscess
includes ssure, thrombosed hemorrhoid, pilonidal disease, hidradenitis, Crohn’s disease and
sexually transmitted infections [20, 21, 23].
Diagnostic Imaging
Supercial abscesses generally do not require
diagnostic imaging to guide treatment.
Alternatively, imaging with CT, MRI, or ultrasound has proven useful in the assessment of
less obvious anorectal abscess, in patients with
Crohn’s disease, and in patients with recurrent
stulas who have undergone prior stula surgery [24–27]. In a retrospective study, of patients
with conrmed anorectal abscess, the sensitivity
of CT was 77% and 70% in immunocompetent
and immunocompromised patients, respectively
[28]. MR imaging is helpful to dene anorectal
abscess and stula. In a 2014 study, the presence
and origin of a supralevator abscess was conrmed by MR in 13 patients prior to operation
[24]. In another recent study, MR had a positivepredictive value (PPV) of 93% and a negativepredictive value of 90% for anorectal abscess and
a sensitivity of over 90% for stula-in-ano [29].
Representative studies of endoanal ultrasound
(EUS), in 2 or 3-dimesions, with or without
peroxide enhancement, indicate that this imaging modality is also useful in the diagnosis and
classication of anorectal abscess and stula-inano with concordance with operative ndings in
73–100% of cases [30–33].
Treatment
General Principles
The cornerstone of treatment of an anorectal
abscess is incision and drainage. Watchful waiting under the cover of antibiotics is usually inadequate and may allow the suppurative process to
progress resulting in the creation of a more complicated abscess and thus possible injury to the
sphincter mechanism. Rarely, delay in diagnosis and management of anorectal abscesses may
result in life-threatening necrotizing infection
and death [34].
Operative Management
Incision andDrainage
Perianal abscesses can be effectively drained
under local anesthesia [2, 13]. The area surrounding the abscess is inltrated with lidocaine
or bupivacaine with epinephrine. A linear or cruciate incision is made and the edges are excised
to prevent coaptation which may result in poor
drainage or recurrence (Fig.10.3). Randomized
trials that have demonstrated equivalent or
superior abscess resolution, with less pain and
faster healing, in patients whose wounds are left
unpacked [35–37].
Most ischiorectal abscesses can be incised
and drained in a similar fashion with the site of
incision shifted as close to the anal side of the
abscess, minimizing the complexity of a subsequent stula. Large ischiorectal abscesses may
be better drained under general or regional anesthesia since loculations within the cavity can be
more easily broken down.
Since the diagnosis of an intersphincteric
abscess is entertained when the patient presents
with pain out of proportion to the physical ndings, an examination under anesthesia is generally required to completely assess the cause of
the pain. Once the diagnosis is established, either
by palpation of a protrusion into the anal canal or
by needle aspiration in the intersphincteric plane,
treatment consists of dividing the internal sphincter along the length of the abscess cavity. The
wound is then marsupialized to allow adequate
drainage and quicker healing.
10 Anorectal Abscess and Fistula in Ano
165
a
b
c
d
Fig. 10.3 Drainage of abscess. (a) Injection of local
anesthesia. (b) Cruciate incision. (c) Excision of skin. (d)
Drainage cavity
Prior to the treatment of a supralevator
abscess, it is essential to determine its origin
since it may arise from an upward extension of
an intersphincteric or an ischiorectal abscess, or
downward extension of a pelvic abscess [38].
The treatment in each case will be different. If
the origin is an intersphincteric abscess, it should
be drained through the rectum by dividing the
internal sphincter and not through the ischiorectal fossa, since this will result in the creation of
a suprasphincteric stula. However, if it arises
from an ischiorectal abscess, it should be drained
as such and not through the rectum; otherwise
an extrasphincteric stula will occur (Fig.10.4).
This approach was followed by Prasad who, in
1981, reported his results with the treatment of 13
patients with supralevator abscess [15]. All four
patients with supralevator abscess that resulted
from intersphincteric extension were completely
healed after trans-rectal drainage. Of the nine
patients with a supralevator abscesses that originated from an ischiorectal source, transperineal
drainage led to recurrent abscess in two and stula in six patients, respectively. If the abscess is
of pelvic origin, it may be drained through the
rectum, ischiorectal fossa or abdominal wall via
percutaneous drainage depending on the direction to which it is pointing.
Horseshoe abscesses should be drained with
the patient under a regional or general anesthetic
with the patient in the prone jackknife position.
This type of abscess develops most often originate in the deep posterior anal space, but may also
develop in the deep anterior anal space, and then
progress with unilateral or bilateral extension
into the ischiorectal spaces [17, 39]. The Hanley
procedure, rst described in 1965, is a technique for draining the deep post-anal space via
major stulotomy with additional incisions into
the ischiorectal spaces as needed to completely
drain the abscess [40]. While this procedure has
proven effective in the treatment of the horseshoe abscess, it is debilitating, and comprehensive assessment of its impact on long-term anal
sphincter function were not included in the larger
reported series [17, 39]. A modied Hanley technique, in which a partial sphincterotomy is combined with a seton that is incrementally tightened,
is a less destructive but similarly effective means
of horseshoe abscess resolution with preservation
of anal sphincter function (Fig.10.5) [17, 41, 42].
Catheter Drainage
An alternative method of treatment for selected
patients is catheter drainage. The patient is
placed in the lithotomy, prone jackknife, or
166
Drain
Counter drainage
e
Fig. 10.4 Drainage of a
supralevator abscess
J. D. Vogel and C.-A. Vasilevsky
Fig. 10.5 Drainage of
horseshoe abscess
Don’t
Drain
Don’t
Posterior drainage
lateral (Sim’s) position. The skin is prepared with
an iodine or alcohol solution and the uctuant
point of the abscess is identied. Local anesthesthetic with epinephrine is injected to create 1cm
wheel in the overlying skin and a 4–6mm stab
incision is made to drain the pus and insert the
catheter (Fig.10.6a). A 10–16 French soft latex
External sphincter
Internal sphincter
Counter drainag
Dentate line
mushroom catheter (e.g. Pezzer or Malecot) is
inserted over a probe into the abscess cavity.
When released, the shape of the catheter tip and
the small incision will hold the catheter in place,
obviating the need for sutures. The external portion of the catheter is shortened to leave 2–3cm
outside the skin with the tip in the depth of the
10 Anorectal Abscess and Fistula in Ano
167
Fig. 10.6 Catheter
drainage of an abscess.
(a) Stab incision. (b)
Catheter in abscess
cavity
a
b
abscess cavity (Fig.10.6b). A small bandage is
placed over the catheter.
Several portions of this technique deserve
further comment. First, the stab incision should
be placed as close as possible to the anus, minimizing the amount of tissue that must be opened
if a stula is found following resolution of
inammation (Fig.10.6a). Second, the size and
length of the catheter should correspond to the
size of the abscess cavity (Fig. 10.7a). A cath-
eter that is too small or too short may fall into
the wound (Fig.10.7b). Third, the length of time
that the catheter should be left in place requires
clinical judgement. Factors involved in this
decision should include the size of the original
abscess cavity, the amount of granulation tissue
around the catheter and the character and amount
of drainage. If there is doubt, it is better to leave
the catheter in place for a longer period of time.
While this technique may not allow for com-
168
ab
J. D. Vogel and C.-A. Vasilevsky
Fig. 10.7 Catheter in an abscess cavity. (a) Correct size and length of catheter. (b) Catheter too short
plete disruption of loculations within the abscess
cavity and generally omits primary stulotomy,
comparative analyses of incision and percutaneous drainage of perianal and other soft-tissue
abscess indicate equal efcacy of the two techniques [43–45].
patients underwent anorectal manometry before
surgery and at 6weeks and 12weeks after surgery. Persistent stulas developed in 25% of
patients after incision and drainage alone and
in none of the patients who underwent incision,
drainage, and stulotomy (P = 0.009). Further,
all of the patients remained fully continent.
Primary Fistulotomy
A point of controversy is whether primary stulotomy should be performed at the time of initial abscess drainage. Advocates of this approach
note a decreased incidence of recurrent abscess
or stula while opponents counter that division
of the anal sphincter in the acute setting may be
unnecessary and could result fecal incontinence
[11, 46–49]. While stulotomy would address
the offending crypt, edema and inammation
may obscure the location of the internal opening and overzealous probing could create a false
opening or a larger wound. In 1997, Ho reported
a randomized, prospective trial of incision and
drainage vs. incision, drainage, and stulotomy
in 52 patients with perianal abscess [47]. These
Schouten also reported a signicant decrease
in recurrent abscess with primary stulotomy
compared to incision and drainage alone but
with a twofold increase in continence disturbances in the stulotomy patients [48]. A recent
Cochrane Review that included 6 trials and 479
patients, demonstrated that sphincter division
(stulotomy or stulectomy) at the time of incision and drainage was associated with a signicant decrease in abscess recurrence, persistent
stula or abscess, and the need for subsequent
surgery in comparison to patients who underwent
anorectal abscess drainage alone (Relative Risk
(RR)=0.13, 95% CI 0.07–0.24) [50]. However,
there was an increased, albeit statistically insignicant, incidence of continence disturbances at
10 Anorectal Abscess and Fistula in Ano
169
1-year follow-up (RR=3.06, 95% CI 0.7–13.45).
With some evidence showing safety of primary
stulotomy and others undue risk, one may conclude that stulotomy at the time of abscess incision and drainage can be cautiously performed
by surgeons who have a sound understanding
on the anorectal anatomy and the implications
of stulotomy. One reasonable approach would
be that easily identiable and supercial stula
tracts, in patients who are continent, are treated
with primary stulotomy. Alternatively, when
deep stula tracts are found, a draining seton,
tied loosely in place, is likely a better choice [20].
Antibiotics
In general, the addition of antibiotics to routine incision and drainage of an uncomplicated
anorectal abscess in healthy patients does not
improve healing or reduce recurrence and is not
generally recommended. However, selective use
of antibiotics for patients with anorectal abscess
complicated by cellulitis, systemic illness, or
immunosuppression is recommended [13, 20, 51,
52]. Evidence supporting this approach may be
gleaned from a recent retrospective study of 172
patients with uncomplicated anorectal abscess
in which the outcomes of incision and drainage
alone were compared with incision and drainage plus 5–7days of oral antibiotic therapy [53].
Nine percent of patients had recurrent abscess,
with no difference between the treatment groups.
However, among patients with anorectal abscess
complicated by surrounding cellulitis, induration
or systemic sepsis, there was a twofold increase
in recurrent abscess in patients who were not
treated with antibiotics.
Postoperative Care
Patients are instructed to continue with a regular diet and to take a bulk-forming agent, narcotic analgesic as needed, and Sitz baths. Those
patients in whom catheter drainage has been
performed are seen within 7–10days post procedure. If the cavity has closed around the catheter
and drainage has ceased, the catheter is removed.
If the cavity has not healed, the catheter is left in
place or replaced with a smaller one. In all cases,
patients are seen periodically until complete
healing has occurred.
Complications
Recurrent Abscess
Recurrent abscess occurs in up to 44% of patients,
most often within 1year of initial treatment [13,
46, 48, 53–55]. Inadequate drainage, missed locu-
lations, horseshoe type abscess, and failure to perform primary stulotomy have been identied as
risk factors for recurrent anorectal abscess [17, 48,
54]. In cases of recurrent abscess, extra-anal dis-
ease should be considered once the usual causes of
recurrence have been ruled out. Hidradentis suppurativa and downward extension of a pilonidal
abscess should be considered [2]. A prospective
review of recurrent anorectal abscesses by Chrabot
etal. reported hidradenitis in one third of patients
with recurrent abscesses [16]. In addition the possibility of Crohn’s disease should be suspected.
Incontinence
Incontinence may result after incision and drainage of an abscess either from iatrogenic damage
to the sphincter or inappropriate wound care.
Continence may be compromised if the supercial
external sphincter is inadvertently divided during
drainage of a perianal or deep postanal abscess in
a patient with preoperative borderline continence.
Drainage of a supralevator abscess may lead to
incontinence if the puborectalis is inappropriately
divided [56]. Prolonged packing of a drained
abscess may impair continence by preventing the
development of granulation tissue and promoting
the formation of excess scar tissue [57].
Although advocated to decrease recurrence
rates, primary stulotomy may result in unnecessary division of sphincter muscle in acutely
inamed tissue. Schouten and van Vroonhoven
reported a 39% rate of continence disturbances in
a prospective randomized trial [48]. However, as
described above, other reports and a recent metaanalysis reached different conclusions about primary stulotomy and fecal incontinence.
Special Considerations
Necrotizing Anorectal Infection
Although initially described by Fournier in 1883
as the sudden onset of a rapid progression of gan-
170
J. D. Vogel and C.-A. Vasilevsky
grene without cause in healthy young men, the
denition has been expanded to include a synergistic necrotizing fasciitis of the perineum,
external genitalia and perianal area affecting men
women and rarely children [58]. In fact, recent
reports have noted an increasing age in patients
with Fournier’s gangrene [59]. Contrary to the
original description, the septic focus can usually
be traced to the urinary tract, anorectal area or
local skin trauma [58]. Perianal and rectal causes
have been found in one study to be the most common sites of origin [60]. Anorectal abscess, hemorrhoid banding, rectal carcinoma in association
with radiotherapy, anal dilatation, rectal biopsy
and rectal perforation by foreign body have
been implicated as antecedent events [58, 60].
Pre-disposing co-morbidities such as diabetes,
alcohol abuse, obesity, hypertension, renal insufciency, malnutrition, leukemia and HIV infection have been associated with this infection. It is
thought that impaired cellular immunity and thus
impaired host resistance to invasion by polymicrobial organisms and their produced exotoxins
result in tissue necrosis [58]. This in conjunction
with thrombosis of small supercial blood vessels subsequently result in gangrene of the overlying skin [61].
Symptoms andSigns
Spreading soft tissue infection of the perineum
can be classied into two groups [62]. The
rst group includes anorectal sepsis in which
the infection extends supercially around the
perineum resulting in necrosis of skin, subcutaneous tissue, fascia or muscle. Perianal crepitation, erythematous, indurated skin, blistering
or gangrene may be present. A black spot may
appear early and indicates a necrotizing infection
(Fig.10.8) [63]. The second group includes sepsis in which the preperitoneal or retroperitoneal
spaces have become involved. Subtle signs may
be present which include abdominal wall induration, tenderness or a vague mass. It is important
to realize that systemic symptoms of septic shock
may precede the appearance of overt signs of
infection [64]. CT scan is an excellent diagnostic
modality since it demonstrates the origin as well
as the extent of infection [65].
Treatment
Early recognition and aggressive surgical debridement as well as selection of the appropriate antibiotics result in a decrease in mortality [66]. The
mean interval from onset of symptoms to surgical
intervention is seen as the most important prognostic factor with a signicant impact on outcome
[66]. Patients should be resuscitated in an ICU
setting with vigorous intravenous uid hydration,
restoration of electrolyte balance and insertion of
a Foley catheter. Accompanying coagulopathy,
respiratory insufciency and renal failure must
be aggressively treated. Invasive monitoring and
ventilatory support may be necessary [67]. Pus or
necrotic tissue from the infected region must be
cultured for aerobes and anaerobes. A Gram stain
can be used to distinguish between the presence
of clostridial and non-clostridial organisms [68].
Empiric broad-spectrum antibiotic therapy should
be instituted regardless of Gram stain and culture
results. The chosen antibiotic regimen should
be effective against staphylococci and streptococci, gram-negative coliforms, Pseudomonas,
Bacteroides and Clostridium. Recently
Methicillin-resistant S aureus has emerged as
an etiological microbe associated with a severe
clinical course and fulminant sepsis [59]. A multiantibiotic regimen including a carbapenem or beta
lactam beta lacatamase inhibitor (e.g. piperacillin-tazobactam), clindamycin, and an anti-MRSA
antibiotic (e.g. vancomycin) should be used until
cultures dictate otherwise [69]. Tetanus toxoid
should also be considered [67].
Fig. 10.8 Necrotising anorectal infection
10 Anorectal Abscess and Fistula in Ano
171
Surgical treatment must be prompt and aggressive consisting of wide radical debridement until
healthy tissue is encountered. The goals of surgical debridement are to remove all nonviable
tissue, halt the progression of infection and alleviate the systemic toxicity [64]. It is crucial to
realize that the preoperative skin changes may
be minimal compared to the operative ndings
which may include edema, liquefactive necrosis of subcutaneous tissues, watery pus formation and extensive necrosis of underlying fascia
[67]. Re-examination under anesthesia is usually necessary to ensure that all devascularized
tissue has been removed since this is the only
manner by which adequate wound examination
can be conducted [67]. Vacuum assisted closure
of the resulting wounds may be a useful adjunct
in healing of these wounds which may be rather
extensive [70]. The use of multiple radial incisions and placement of loose draining setons has
been proposed to avoid the massive excision of
tissue and resulting deformities that may occur
with recovery [71]. The need for colostomy is a
debatable issue and has been recommended if the
sphincter muscle is grossly infected, if there is
colonic or rectal perforation, if the rectal wound
is large, if the patient is immunocompromised or
if incontinence is present [62, 64]. While some
authors [68] feel that colostomy creation is seldom necessary, a “medical colostomy” consisting of enteral or parenteral nutrition in addition
to the careful placement of a sealed rectal catheter drainage may be adequate. Controversy also
exists with regards to the need for urinary diversion by suprapubic catheterization. It has been
suggested that this may be indicated in the presence of known stricture and urinary extravasation
with phlegmon.
Although antibiotics and aggressive surgical
drainage are the mainstay of treatment, the use
of hyperbaric oxygen (HBO) has been advocated
as an adjunct particularly in patients with diffuse
spreading infections who do not have chronic
obstructive pulmonary disease [72]. While it
is postulated that HBO has a direct antibacterial effect on anaerobic bacteria, diminishing
the effect of endotoxins, optimizing leukocyte
phagocytic function [63] and promoting healing
by facilitating broblast proliferation [72], its
use remains controversial [60]. It is expensive,
not readily available and has not shown to be
advantageous in terms of reducing morbidity and
mortality [58].
Despite aggressive surgical and multidisciplinary management of anorectal sepsis, mortality rates as few as 3% to as many as 45% have
been reported [58, 73]. Retrospective studies
have suggested that poor prognosis could be
correlated with increasing age, diabetes, delay
in presentation and treatment and extent of soft
tissue involvement [58, 64]. The Fournier’s
Gangrene Severity Index (FGSI) was developed
to stratify risk in this patient population. This
is a numerical score that combines nine physiological parameters such as temperature, heart
rate, respiratory rate, and serum levels of sodium,
potassium, creatinine, white blood cell count,
hematocrit and sodium bicarbonate. A FGSI
greater than 9 was predictive of a 75% probability of mortality while a score of less than 9 predicted a 78% probability of survival [73]. This
was corroborated by another study which also
found that extent of disease beyond the perineum
as well as serum creatinine, bicarbonate, lactate
and calcium were associated with a poor prognosis [61]. This high mortality rate is due in part to
the aggressive nature of the infection and to the
underlying co-morbid diseases that are present in
these patients [64].
Anal Infection andHematologic
Diseases
The reported incidence of perianal sepsis in
patients with hematological diseases ranges from
5–10% [74–76]. The most signicant risk factor for the development of perianal infection is a
low neutrophil count [74]. Although the underlying pathophysiology relating to cryptoglandular
infection is the same as in the immunocompetent
patient, the lack of neutrophils impairs the formation of pus and as a result, the clinical manifestations may be modied. Thus, rather than
present with uctuance, these patients will present with diffuse swelling, edema and erythema
in addition to pain. Perianal infection in neutropenic (ANC<500 cells/mm3) patients has been
172
J. D. Vogel and C.-A. Vasilevsky
found to occur more often in males younger than
40years of age [77]. These infections are often
difcult to diagnose due to lack of typical ndings. In addition, consensus guidelines generally
prohibit digital rectal examination in neutropenic
patients thus causing clinicians to be reluctant
to examine the anorectal area for occult infection for fear of provoking bacteremia [78]. As a
result an accurate diagnosis is made only in 50%
of patients [34]. Untreated sepsis leads to high
mortality rates reportedly as high as 59% [79].
The use of CT and MR imaging have been advocated as useful adjuncts to conrm the presence
of occult infection [80]. A greater local inammatory reaction has been found in association
with perianal sepsis in the immunocompromised
patient on MR [80]. In the absence of clinical features of abscess, imaging studies serve as a guide
to management [74].
Management
Neutropenic patients with perianal pain are
assumed to have perianal infection and are
started on precautionary measures which consist
of no digital rectal examinations, suppositories,
or enemas [78, 81]. Sitz baths, stool softeners,
bulk agents and analgesia are advised. Acutely ill
or otherwise high-risk patients are treated empirically with an anti-pseudomonal beta-lactam drug
such as cefepime, a carbapenem, or piperacillintazobactam with the addition of other antibiotics
as dictated by the results of microbiology cultures or in response to other clinical clues [78].
Since these infections have been found to be
due to E.Coli and group D streptococcus [82] they
are best managed with a third-generation cephalosporin combined with anaerobic coverage or an
extended spectrum penicillin in combination with
an aminoglycoside and an anti-anaerobic antibiotic. This combination has been associated with
an 88% success rate [82]. Although in the past,
an aggressive surgical approach has been advocated [75], subsequent studies have demonstrated
a poorer outcome following surgical treatment of
anorectal sepsis in the neutropenic patient [79]
associating this approach with poor wound healing, expanding soft tissue infection or recurrence
[82]. Thus a highly selective approach is advo-
cated reserving surgery for those patients with
uctuance, non-improvement with conservative
treatment and in those patients who deteriorate
developing soft tissue necrosis [74].
Patients managed conservatively require close
monitoring until they improve or develop uctuance at which time they should be drained in
order to avoid the rare development of necrotizing fasciitis [83].
In the past, radiation therapy has been mentioned in the treatment of perianal sepsis in the
severely neutropenic patient [81]. However a
randomized controlled study failed to conrm the
utility of this approach [84].
Fistula-in-Ano
Pathophysiology
Etiology
A stula is dened as an abnormal communication between any two epithelium-lined surfaces.
A stula-in-ano is an abnormal tract or cavity
communicating with the rectum or anal canal by
an identiable internal opening. As outlined previously, most stulas are thought to arise due to
cryptoglandular infection.
Classication
A simple and often used classication of stulain-ano is that described by Parks et al. [38].
Intersphincteric and transphincteric stulae are
more frequently encountered than suprasphincteric, extrasphincteric, and submucosal types
[12, 38, 85, 86]. Intersphincteric stula are the
sequelae of a perianal abscess. The tract passes
within the intersphincteric space (Fig. 10.9a).
Transphincteric stula-in-ano develop from an
ischiorectal abscess. The tract passes from the
internal opening through the internal and external
sphincters to the ischiorectal fossa (Fig.10.9b).
Suprasphincteric Fistula-in-Ano results from a
supralevator abscess. The tract passes above the
puborectalis after arising as an intersphincteric
abscess. The tract curves downward lateral to
the external sphincter in the ischiorectal space
to the perianal skin (Fig. 10.9c). A high blind