Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_1199_Библиотеки_им_академика_М_И_Перельмана.pdf
Contents
1 Surgical Anatomy of Anal Canal and Rectum . . . . . . . . . . . . . . 1
Ashfaq Hassan and Abdullah Al Mamun
2 Physiology of Defecation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Rauf A. Wani and Natasha Thakur
3 Hemorrhoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
P. Sivalingam , Rama Kant , Vijay Arora ,
and Pravin Padmakumar Gore
4 Anal Fissure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Benjamin Perakath and Niranjan Agarwal
5 Perianal Sepsis and Fistula. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Parvez Sheikh and Prasang Bajaj
6 Pilonidal Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
P. N. Joshi and Shekhar Suradkar
7 Rectovaginal Fistulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Fazl Q. Parray
8 Anorectal Injuries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
Satish B. Dharap
9 Anal Incontinence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
P. N. Joshi , Ashok Kumar , and Kiran Shah
10 Complete Rectal Prolapse in Adults . . . . . . . . . . . . . . . . . . . . . . 131
Ajay K. Khanna
11 Pelvic Floor Dysfunction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Brij B. Agarwal and P. Sivalingam
12 Perianal Dermatology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Iffat Hassan and Parvaiz Anwar Rather
13 Benign Ulcers of the Anorectum . . . . . . . . . . . . . . . . . . . . . . . . . 177
Ahmad Abdul Hai and Niharika Roy
14 Benign Strictures of Anorectum . . . . . . . . . . . . . . . . . . . . . . . . . 195
P. N. Joshi and C. Kale
15 Benign Tumors of the Anorectum . . . . . . . . . . . . . . . . . . . . . . . . 205
Rajshekar Mohan
xi
Surgical Anatomy of Anal Canal and Rectum
Ashfaq Hassan and Abdullah Al Mamun
1
1.1 Rectum
Rectum is a fi xed terminal portion of the large
intestine that serves as a reservoir. It is about
10–14 cm in length, and it is located between the
sigmoid colon above and the anal canal below. It
begins at the level of S3 vertebra and ends by
becoming continuous with the anus which corresponds to the apex of the prostate or lower end of
the vagina and is 2–3 cm in front of and a little
below the tip of the coccyx. The proximal part of
the rectum joins the sigmoid colon at the rectosigmoid junction which is at about 15 cm from
the anal verge, and the distal part joins the anal
canal at the anorectal junction. The cardinal features of large intestine like the taenia, appendices
epiploicae, sacculations, and well-defi ned mesentery are absent in the rectum (Corman 2005 ;
Chapuis et al.
is dilated and is called rectal ampulla. Though the
word rectum means straight, the rectum is not
straight. It is curved both anteroposteriorly and
A. Hassan , MBBS, MS
Department of Anatomy , Sheri Kashmir
Institute of Medical Sciences Medical College ,
Srinagar , Jammu and Kashmir , India
e-mail:
A. Al Mamun , FCPS(Surgery), MRCS(Edin)
Department of Surgery ,
Shaheed Suhrawardy Medical
College Hospital, Dhaka , Bangladesh
e-mail:
2002 ). The lower part of the rectum
ashhassan@rediffmail.com
mamun1973@gmail.com
from side to side. The lateral curves are three in
number. The upper and the lower lateral curves
are convex to the right. The middle lateral curve
is convex to the left. Endoluminally, these folds
are known as valves of Houston. The clinical signifi cance of these folds is that they must be successfully negotiated during successful
proctosigmoidoscopic examination (Corman
2005 ; Nivatvongs and Gordon 1992 ; Neugut and
Pita 1988 ), and it is safer to take biopsies from
these folds which are easily accessible and have
no muscle. There is also minimal risk of perforation at these folds.
The rectum derives its support from Waldeyer’s
fascia, lateral ligaments of rectum, rectovesical
fascia of Denonvilliers, pelvic peritoneum, and
perineal body. These supports may get weakened
in prolapse of rectum. The rectum is a distensible
organ and in view of assumption of erect posture,
needs additional supports for maintaining its
position which is provided by the levator ani
muscle that forms an effective support like a
basin for the rectum.
The anorectal ring is an important landmark
and the prime source of maintaining rectal continence. Damage to this ring results in rectal
incontinence. The anorectal ring is formed by
puborectalis, deep external sphincter, and internal sphincter (Coller
tal examination. The ring is more marked
posteriorly due to a larger number of muscle
fi bers.
1987 ). It can be felt per rec-
© Springer India 2016
N.A. Chowdri, F.Q. Parray (eds.), Benign Anorectal Disorders:
A Guide to Diagnosis and Management, DOI 10.1007/978-81-322-2589-8_1
1
2
A. Hassan and A. Al Mamun
1.1.1 Relations
The relations of rectum are important to know
because of the fact that per rectal examinations, it
can give vital information regarding surrounding
structures. They provide key to the local spread of
rectal cancers and are important in operative
removal of rectum. In males, anteriorly one can
palpate the prostate gland, the seminal vesicles,
and the base of the urinary bladder, and in females,
it is related to the uterus, cervix, and posterior vaginal wall. In females, the perineal body and cervix
are felt anteriorly. A layer of specialized fascia
(Denonvilliers) separates the rectum from anterior
structures (prostate, seminal vesicles, or vagina).
The upper two-thirds of the rectum is covered by
the peritoneum and relates to coils of small intestine which lie in the cul-de- sac of the pouch of
Douglas between the rectum and the bladder in
males or uterus in females. Laterally, only the
upper third is covered by the peritoneum. The
lower third of the rectum is entirely extraperitoneal. In both sexes, the coccyx and sacrum can be
felt posteriorly. These are separated by extraperitoneal connective tissue containing the rectal vessels, lymphatic, and lower sacral nerves, emerging
from the anterior sacral foramina. These nerves
may get infi ltrated by the cancers spreading posteriorly from the rectum, resulting in severe sciatic
pain (Ellis 2002 ). Laterally, the rectum is sup-
ported by the levator ani. The rectum ends anteroinferiorly about 2–3 cm from tip of coccyx from
where it turns back sharply and enters the levator
to become the anal canal. The lateral rectal sheath
or ligaments are formed by condensation of pelvic
fascia laterally. These are triangular in shape with
the apex toward the lateral rectal wall. Branches of
middle rectal vessels pass through these ligaments
only in 20–25 % of cases. These stalks also contain branches from pelvic nerves. Posteriorly, presacral fascia condensation of endopelvic fascia
separates the rectum and mesorectum from the
sacrum and coccyx. Presacral veins, middle sacral
artery, and nerves can be injured with lifethreatening bleeding if the surgeon dissects outside this fascia during surgery. The thick
anteroinferior fascial extension of presacral fascia
toward fascia propria of rectum at S4 level above
the anorectal angle is known as Waldeyer’s fascia.
The mesorectal fat or mesorectum is thicker and
posteriorly is enclosed in fascia propria and contains inferior hemorrhoidal vessels and lymphatics. This is the site of metastasis from rectal
cancers. Inclusion of this mesorectum in resection
specimen of rectal cancers (mesorectal excision)
has reduced the rate of recurrence signifi cantly.
Ureters after crossing the pelvic brim in front
of bifurcation of common iliac artery lie between
the peritoneum and internal iliac artery. In
females, these are closely related to the neck of
the uterus and upper vagina.
1.2 Anal Canal
The anal canal represents the distal most part of the
gastrointestinal tract located in the perineum in the
anal triangle between the right and left ischial fossae. The length of anal canal varies depending on
its defi nition. The surgical or functional anal canal
is approximately 4 cm, extending from the top of
levator ani or anorectal angle to the intersphincteric
groove (the sulcus between internal and external
sphincters) or anal verge (Fig. 1.1 ). The anatomic
or embryologic anal canal is only 2 cm, extending
from the anal verge to dentate line. The anal verge
or anocutaneous line of Hilton represents the lower
most edge of the anal canal and is about 1–2 cm
from dentate line. Anal verge and dentate line
(more precise) are taken as reference levels for
measurement during proctosigmoidoscopy. Anal
orifi ce or anus on the other hand is a cutaneous slit
at the lower part of anal canal.
It is angulated at junction with the rectum
because the pull of the sling-like action of puborectalis muscle forms anorectal angle (Fig.
2–3 cm in front of and slightly below the tip of the
coccyx, which is opposite the apex of the prostate
in males. The anal canal is attached posteriorly to
the coccyx by the anococcygeal ligament. The
anus is surrounded laterally and posteriorly by
loose adipose tissue within the ischioanal fossae, a
potential pathway for the spread of perianal sepsis
from one side to the other. Inferior rectal vessels
and nerves cross it to reach the anal canal.
Anteriorly, the perineal body separates the anal
1.2 ). It lies
1 Surgical Anatomy of Anal Canal and Rectum
3
Anorectal ring
Internal anal sphincter
Column of morgagni
External anal sphincter
Anal crypt
Fig. 1.1 Anatomy of anorectum
Fig. 1.2 Anorectal angle
canal from the membranous urethra and penile
bulb in males or from the lower vagina in females.
The anal complex has two sphincters: internal
and the external. The internal anal sphincter is a
smooth muscle, involuntary in nature, and is
formed by the condensation of circular muscle of
Surgical
anal canal
Dentate line
Anatomical or
embryological
anal canal
Anal verge
the rectum, while the external anal sphincter is
voluntary in nature and is formed by the striated
skeletal muscle (Felt-Bersma et al.
1989 ). The
external sphincter has subcutaneous, superfi cial,
and deep parts (Fig. 1.1 ). It covers the entire
length of internal sphincter tube. It ends little
below it as subcutaneous portion. The intersphincteric groove between lower edges of internal and external sphincter can be palpated more
so when anus is stretched. This groove is used to
enter the intersphincteric space in surgical procedures like internal sphincterotomy for anal fi ssure
and ligation of intersphincteric tract (LIFT) for
fi stulae in ano. Endosonographically external and
internal anal sphincters measure 6–8 and 2–3 mm,
respectively. Internal sphincter appears uniformly
hypoechogenic, while external anal sphincter and
puborectalis are predominantly hyperechogenic.
The external and internal sphincters and puborectalis are important muscles to maintain automatic
continence and prevent fecal leakage at the time
of threatened incontinence. The conjoined longitudinal muscle is formed by continuation of longitudinal layer of rectum along with some fi bers
of levator ani at the level of anorectal angle. It
4
A. Hassan and A. Al Mamun
continues down between the internal and external
sphincters binding them together and traverses
the subcutaneous part of external sphincter as a
corrugator cutis ani to get inserted into perianal
skin. This muscle is supposed to act as skeletal
support that attaches the anorectum to the pelvis.
The levator ani consisting of iliococcygeus, pubococcygeus, and puborectalis forms the pelvic
fl oor and is important for gross fecal continence.
External and internal sphincters control gas and
liquid contents. Puborectalis is a U-shaped sling
which slings the anorectal angle to pubis and
forms anorectal angle.
1.2.1 Inner Lining
The partition line between upper endodermal and
lower ectodermal part (proctodeum) of anal canal
is called dentate or pectinate line. Failure of
breakdown of separating membrane between the
two parts results in an imperforate anus. The
upper part is lined by columnar cells, while the
lower part is lined by squamous epithelium which
is thin, pale, and smooth devoid of hair and
glands. Above the dentate line, it is innervated by
sympathetic and parasympathetic system, while
the distal part is innervated by somatic nerves,
and any infl ammatory process or procedure in
this part of anal canal is painful. The blood supply and venous drainage above the dentate line
come from and go to superior and middle hemorrhoidal vessels and drain to the portal system,
while the part below the dentate line drains into
systemic circulation through inferior hemorrhoidal vessels, thereby making this area site for
portosystemic shunts and cavernoma. Lymphatic
above and below dentate line also drains to different groups of lymph nodes (inferior mesenteric and groin). Anal valves are located at dentate
line. These valves are remnants of proctodeal
membrane. Above each valve, there is an opening
of anal glands known as anal crypts or sinus.
Anal glands are 3–12 in number located in the
submucosa, internal sphincter, or intersphincteric
space. More than one gland may open into the
same crypt. Half of the crypts have no communication with the glands. Obstruction of ducts of
these glands causes stasis, infection, perianal
sepsis, and fi stula formation.
There are 8–14 longitudinal folds known as
columns of Morgagni. These are present cranially
on the dentate line. Anal papillae are present at
the lower end of these columns. A strip of
0.5–1 cm of mucosa consisting of several layers
of cuboidal cells above the dentate line in the area
of column of Morgagni has a deep purple color
because of internal hemorrhoidal plexus and is
known as anal transition zone. Above this zone,
epithelium changes to single layer of columnar
cells (pink color). Just below the dentate line, the
anal canal is lined by modifi ed squamous epithelium which is thus as pale in color. This white
color makes the reference point for taking a purse
string suture in stapled hemorrhoidopexy.
1.3 Blood Supply of Anal Canal
and Rectum
The arterial supply of the rectum comes from
superior, middle, and inferior rectal arteries and
the median sacral artery. The superior and inferior rectal arteries are the main source of blood
supply to anorectum.
The superior rectal or superior hemorrhoidal
artery is the most important source of blood supply to the rectum. It is the continuation of the
inferior mesenteric artery which is the artery of
hind gut. The vessel subdivides opposite the third
sacral vertebrae into two branches, the right and
the left. The superior rectal artery lies just posterior to the right of the sigmoid colon, coming in
close contact with posterior aspect of gut at the
rectosigmoid junction.
The middle rectal or middle hemorrhoidal
arteries are a source of blood supply only to the
superfi cial layers of the lower part of the rectum.
The middle rectal vessels arise usually from anterior division of internal iliac artery and anastomose with the adjacent arteries. In some cases, it
may arise from inferior gluteal arteries. It may be
absent in 40–80 % of cases (Didio et al
Lawson 1974 ).
The median sacral artery is a small vessel arising from the distal part of aorta near its termination.
1986 ;
1 Surgical Anatomy of Anal Canal and Rectum
5
It supplies the rectum in the region of anorectal
junction.
The inferior rectal or hemorrhoidal artery arises
from pudendal artery which is a distal branch of
internal iliac artery. This artery is encountered during perineal dissection of abdominoperineal resection for low rectal cancer. Profuse intramural
anastomotic network in the anorectum maintains
its blood supply even if both superior and inferior
rectal arteries are ligated.
The veins from the rectum drain by virtue of
the superior and middle rectal veins. The superior
rectal vein starts from the internal rectal venous
plexus which ultimately forms three to fi ve veins
which unite to form this vein. The superior rectal
vein continues upward as the inferior mesenteric
vein to end in the splenic vein.
The middle and inferior rectal veins drain the
anal canal and lower rectum and open into the
internal iliac vein and subsequently the inferior
vena cava. Dilatation of subcutaneous venous
plexus situated below the dentate line and one
present above the dentate line gives rise to external and internal hemorrhoids.
The venous drainage is particularly important
to understand the spread of rectal cancer. These
tumors may spread to the liver via the portal
venous system or to other organs via inferior
vena cava.
1.4 Lymphatics of Anal Canal
and Rectum
Lymphatics from the upper two-thirds of rectum
pass along the superior rectal vessels to the inferior mesenteric nodes after going through the
pararectal and sigmoid nodes. From the lower
third of the rectum, lymph passes not only in the
cephalad direction to inferior mesenteric nodes
but also along the middle rectal vessels to the
internal iliac nodes. The carcinoma of rectum
spreads cephalad by virtue of the lymphatics to
the local lymph nodes of the rectum and predominantly to pararectal and subsequently to inferior
mesenteric nodes. Laterally, the lymphatics along
middle rectal and inferior rectal vessels drain into
the internal iliac group of lymph nodes. Lymph
from the anal canal above the dentate line drains
to inferior mesenteric and internal iliac nodes,
and lymph from the anal canal below the dentate
line drains into inguinal nodes though less frequently it may go along inferior hemorrhoidal
artery. In females, lymphatic spread also goes to
genital organs like the uterus, cervix, vagina,
broad ligament, and ovaries. The lymphatics are
an important source of dissemination of cancers
from the rectum.
1.5 Nerve Supply of Anal Canal and Rectum
Sympathetic and parasympathetic innervation of
anorectum comes from L1 to L3 (superior hypogastric plexus around root of inferior mesenteric
artery) and S2 to S4 (nervi erigentes forming pelvic plexus), respectively. The right and left hypogastric nerves carry sympathetic fi bers to pelvic
plexus (inferior hypogastric plexus) from where
these are distributed along with parasympathetic
fi bers to prostate, urethra, ejaculatory ducts, vas
deferens, seminal vesicles, and corpora cavernosa. Sympathetic infl ow inhibits vasoconstriction, while parasympathetic causes vasodilatation
of corpora resulting in erection of penis. These
nerves may be injured in various pelvic procedures including those of anorectal cancers at various levels, i.e., root of inferior mesenteric artery,
sacral promontory or presacral region (pull on
hypogastric nerves leading to retrograde ejaculation and bladder dysfunction), lateral rectal stalks
close to middle rectal arteries (injuring nervi erigentes leading to erectile dysfunction), or near
seminal vesicles and prostate (injuring sympathetic and parasympathetic components leading
to both erectile and bladder dysfunction).
Permanent sexual dysfunction occurs in 100 % of
patients following radical abdominoperineal
resections (APR) (Marcio et al.
bladder dysfunction can occur in 7–59 %,
impotence in 15–45 %, and ejaculatory dysfunction in 32–42 % patients after APR. However,
sexual and bladder complications may not be so
evident in females.
2009 ) . Permanent
6
Peritoneum
Levator ani muscle
Puborectalis muscle
Deep external
sphincter muscle
Internal
sphincter muscle
Transverse septum
Fig. 1.3 Perianal spaces
A. Hassan and A. Al Mamun
Supralevator space
Ischioanal space
Intershincteric space
Perianal space
External anal sphincter is a voluntary muscle
and is innervated by inferior rectal and perineal
branches of pudendal nerve (S2, S3, and S4).
Sensations from anal canal are carried by inferior
rectal branches of the pudendal nerve. Due to
crossover of fi bers at spinal cord sphincter, function of anal canal is still preserved following unilateral division of pudendal nerve.
1.6 Anorectal Spaces
These are potential spaces around the anorectum
which a surgeon should know to understand the
genesis, diagnosis, and treatment of perianal sepsis (Fig.
either side of rectum communicate with each
other through deep postanal space of Courtney
and explain the formation of horseshoe abscess.
The lower part of ischiorectal fossa surrounding
the lower part of anal canal contains the subcutaneous part of external sphincter, lowest portion of
internal sphincter, and external hemorrhoidal
plexus. It is separated from the ischiorectal fossa
by a thin fascia. The intersphincteric space is
important for genesis of perianal abscess as anal
glands; a source of cryptoglandular infection is
located in this region. The presacral or retrorectal
space is a site for embryogenic remnants and
1.3 ). The two ischiorectal spaces on
tumors. The cryptoglandular infection can spread
even to supralevator space above the levators.
Submucous space present above the dentate line
contains internal hemorrhoidal plexus.
Bibliography
Chapuis P, Bokey L, Fahrer M, et al. Mobilisation of the
rectum: anatomic concepts and bookshelf revisited.
Dis Colon Rectum. 2002;45:1.
Coller JA. Clinical application of anorectalmanometry.
Gastroenterol Clin North Am. 1987;16:17.
Corman ML. Colon and rectal surgery. 5th ed. Baltimore:
Lippincott Williams & Wilkins; 2005. p. 1.
Didio LJ, Diaz-Franco C, Schemainda R, et al. Surg
Radiol Anat. 1986;8:229–36.
Ellis H. Clinical anatomy. 10th ed. Hong Kong: Blackwell
Science; 2002. p. 87–8.
Felt-Bersma RJ, Strijers RL, Janssen JJ, et al. The external
anal sphincter. Dis Colon Rectum. 1989;32:112.
Lawson JO. Pelvic anatomy II. Anal canal and associated
sphincters. Ann R Coll Surg Engl. 1974;54:288.
Marcio J, Jorge N, Habr Gamma A, et al. Anatomy and
embryology of the colon, rectum and anus. In: Beck
DE, editor. The ASCRS manual of colon and rectal
surgery. New York: Springer; 2009.
Neugut AI, Pita S. Role of sigmoidoscopy in screening for
colorectal cancer: a critical review. Gastroenterology.
1988;95:492.
Nivatvongs S, Gordon PH. Surgical anatomy. In: Gordon
PH, Nivatvongs S, editors. Principle and practice of
surgery for Colon, Rectum and anus. St Louis: Quality
Medical Publishing; 1992. p. 3.
Physiology of Defecation
Rauf A. Wani and Natasha Thakur
2
2.1 Normal Defecation
Defecation is a refl ex provoked through a sacral
arc by distention of the rectum. In infancy, the
evacuation of the rectum occurs refl exly. The
development of the control over defecation refl ex
is associated with the growth of inhibition over it.
The cerebral cortex cannot only inhibit the refl ex
but can also initiate it when suitable circumstances are available for voiding. Thus, continence is an acquired capacity to suppress the
natural urge to defecate. When this capacity is
impaired, incontinence occurs.
For maintenance of continence, both the rectum and anus play a responsible role. The process
begins with movement of gas, liquid, or solid
contents into the rectum. Distension of the rectum leads to stimulation of pressure receptors
located on the puborectalis muscle and in the
pelvic fl oor muscles, which in turn stimulates the
rectoanal inhibitory refl ex (Fig.
R. A. Wani , MS, MRCS (*)
Department of Colorectal Surgery ,
Sheri Kashmir Institute of Medical Sciences ,
Srinagar , Jammu & Kashmir , India
raufw64@hotmail.com
e-mail:
N. Thakur
Department of General and Minimal Invasive Surgery,
Sherikashmir Institute of Medical Sciences Medical
College , Srinagar , Jammu & Kashmir , India
doc_nats259@yahoo.co.in
e-mail:
2.1 ). The internal
anal sphincter relaxes, allowing sampling of
contents (Miller et al.
deferred, voluntary contraction of the external
anal sphincter and levator ani muscles occurs,
and the rectum accommodates with relaxation
after an initial increase in pressure. This voluntary contraction of the external sphincter can
exercise control for 45–60s. When the anal canal
is deemed to have solid contents and a decision to
defecate is made, the glottis closes, pelvic fl oor
muscles contract, and diaphragm and abdominal
wall muscles contract, all increasing abdominal
pressure (Womachs et al. 1985 ). The puborectalis
muscle relaxes, resulting in straightening of the
anorectal angle and slight descent of pelvic fl oor.
The external anal sphincter relaxes, and anal
canal contents are evacuated. Upon normal complete evacuation, the pelvic fl oor rises and sphincters contract once more in a “closing refl ex”
(Plam et al.
lower rectum and that of anus can distinguish
between the fl atus and fl uid and solid stool. The
cutaneous lining of the anal canal forms a very
sensitive zone which can detect even a minute
quantity of fl atus or feces. Any operative procedure in which this segment is sacrifi ced will lead
to sensory incontinence.
The internal sphincter, the external sphincter,
and the levator ani constitute the motor components. The internal sphincter unconsciously
maintains continence by its sustained contraction. Any damage to the internal sphincter will
1999 ). The mucosal lining of the
1981 ). If defecation is to be
© Springer India 2016
N.A. Chowdri, F.Q. Parray (eds.), Benign Anorectal Disorders:
A Guide to Diagnosis and Management, DOI 10.1007/978-81-322-2589-8_2
7
8
Fig. 2.1 Refl ex mechanisms
involved in defecation process
Glottis diaphragm
abdominal muscle
Increased intra
abdominal pressure
Voluntary motor nerve
to external sphincter
Involuntary motor Nn
(leading to contraction
& relaxation of bowl
muscles for defecation)
Pudendal nerve
(Reflex action)
R.A. Wani and N. Thakur
Cerebral
cortex
Sensory nerve
fibers
Pelvic splanchnic
nerves (parasymp.div.)
Stretch receptors
in wall
External anal
sphincter
(skeletal musle)
result into the partial loss of control. The
puborectalis part of the levator ani gets its attachment to the upper part of the external anal sphincter (Nicholas and Lindsay
2013 ). This constitutes
the puborectalis sling. It gives strength to the
sphincters and prevents retraction of their cut
edges when they are divided during anal operations. If puborectalis sling is also divided, large
gaping occurs, resulting in anal incontinence.
2.1.1 Mechanical Factors
of Continence and Defecation
The puborectalis arises from the pubic bone and
passes horizontally and posteriorly around the
anorectum as the most medial portion of the levator ani muscle. This forms a U-shaped sling
around the anorectum near its anatomic junction
with the anus, pulling the rectum anteriorly and
giving rise to the so-called anorectal angle
Internal anal
sphincter
2.2 ). Parks postulated a mechanism by
(Fig.
which this takes place (Parks et al. 1966 ). The
intra-abdominal pressure increases with sneezing, coughing, or straining. This force is transmitted across the anterior wall of the rectum at
the anorectal angle. The underlying mucosa is
opposed against the upper anal canal, creating a
fl ap valve mechanism that prevents stool from
passing to the lower anal canal, thereby preserving continence. This is now disputed as many
multiparous women have this angle obliterated
and are still fully continent.
2.1.2 Reservoir
The rectum must be able to function as a
temporary storage site for liquid and solid stools.
With the passage of the fecal stream into the
rectum, the pliable rectal walls distend and delay
the defecation sequence until an appropriate