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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_923_Библиотеки_им_академика_М_И_Перельмана.pdf
18
White line of Hilton
External anal sphincter
Anal valv
e
Coulmns of Morgagni
2 Surgical Anatomy ofAnal Canal
Internal anal sphincter
Fig. 2.6 Morgagni columns
Fig. 2.7 Diagram
showing anal valves
Table 2.3
Arterial blood
supply
Venous
drainage
Lymphatic
drainage
Innervations Somatic
Dentate line summarized
Below the dentate
Inferior rectal
artery
Inferior rectal
vein (systemic)
Supercial
inguinal nodes
(Pudendal
nerve)
e
Above the dentate
line
Superior and
middle rectal
artery
Superior rectal
vein (portal)
Internal iliac
nodes
Autonomic
Intermediate
zone
Dentate line
Anal column
Pectinate lin
2.5.5 Anal Papillae
These are remnants of the embryonic anal membrane and represent the junction of the proctodeum with the hindgut. These are present as small
epithelial projections at the dentate line. In 60%
of cases, 1–3 papillae are present, and in 40%, the
number is from 4 to 6. The usual length of papillae is 1.0–5.0mm. Due to their hyperplastic tendency, constant irritation, injury, or infection can
cause enlargement, a condition known as
“Hypertrophic Anal papillae” (Fig.2.9) [12].
Arteries: Superior rectal artery
sympathetic & parasympathetic)
Lymphatics: To internal
Hypertrophic anal
2.5 Upper Columnar Zone: Contents
19
from inferior mesenteric artery
Nerves: Visceral motor (mixed
& sensory innervation
& sensory innervation
Fig. 2.8 Dentate line
Fig. 2.9 Hypertrophic anal papillae
2.5.6 Anal Cushions
The term “anal cushions” was described by Thomson
in 1975 [13, 14]. According to Thomson, the submu-
cosa inside the anal canal forms a discontinuous
series of cushions instead of a continuous ring.
There are three columns of these cushions
along the anal canal—right anterior, right posterior, and left lateral, popularly known as 3, 7, and
11o’clock positions (Fig.2.10) [13]. These cush-
ions represent well-shaped, deep purple, hemi-
Veins: Superior rectal vein
to portal venous system
iliac lymph nodes
Pectinate line Pectinate line
Somatic motor
From internal iliac artery
inferior rectal artery
To caval venous system
inferior rectal vein
To superficial inguinal
lymph nodes
spherical masses that protrude towards the anal
canal lumen. Each cushion has a submucosa con-
papillae
taining loose connective tissue, elastic muscle
ber, and anorectal vascular plexus consisting of
arterioles and venules. The vascular plexus inside
the cushions gives the surgical anal canal a purple
color. The vertical mucosal folds of Morgagni
superimpose the cushions.
The anal cushions are held in their normal
position by the muscle bers of ligament of
Treitz. These bers originate from conjoined longitudinal muscle (CLM), pierce the internal
sphincter, and play a vital role in anchoring anal
cushions (Fig.2.11).
Histology ofMucosa Covering Anal Cushions
The anal canal mucosa has three layers—muscularis mucosae, lamina propria, and endothelium.
The vessels cross muscularis mucosae to enter
lamina propria. Due to momentary displacement
during defecation, the mucosa may become lax
20
External anal sphincter
Internal anal sphincter
2 Surgical Anatomy ofAnal Canal
Fig. 2.10 Positions of
anal cushions
Fig. 2.11 Muscles of
Treitz
11 o’clock
7 o’clock
Conjoined longitudinal
muscle
Anorectal ring
Pectinate line
Anal verge
3 o’clock
Treitz’s muscle
Hemorrhoidal plexus
and friable. A portion of this laxed mucosal moiety might get pinched between the pectinate line
and the passing stool. Trauma due to straining or
passing hard stool may cause damage to the capillaries present in the lamina propria leading to
bleeding [15] (Fig.2.12).
2.5.7 Anal Transitional Zone (ATZ)
ATZ is a mucosal strip above the dentate line 0.5
to 1.0 cm long. The epithelium transforms to a
single layer of columnar cells cephalad to this
region and macroscopically develops the rectal
mucosa’s typical pink color [16] (Fig.2.13).
Dentate line
Surgical Signicance of Anal Transition Zone
Sensory nerves in the anal canal were
described by Duthei and Gairns in 1960. This
showed a high level of sensitivity to touch,
temperature, and pain. Sensation and inner-
vation are lacking in the mucosa [17, 18].
• The external anal sphincter contraction
and internal anal sphincter relaxation
are related to rectum’s distention. Rectal
contents may be sampled by the anal
mucosa in ATZ which differentiates
between gas, liquid, and solid stools.
Muscularis mucosa
Stratified squamous
non - kertinized epithelium
anal sphincter
anal sphincter
2.6 Intermediate Zone
Lamina propria
Fig. 2.12 Histology of anal cushions
Fig. 2.13 Anal
transition zone (ATZ)
21
Arterioles
Submucosa
2.6 Intermediate Zone
Between the dentate line and the white line of
Hilton is the intermediate zone. The intermediate
zone is separated from the lower zone by a line
known as the “White line of Hilton” [19]. It is
approximately 1–1.5cm long and lined with anal
mucosa (anoderm). The mucosa over here is less
mobile than in the upper zone. This area is known
as the “area of pectin.” This area of pectin is lined
by stratied squamous nonkeratinized epithelium
[20] (Fig.2.14).
Levator ani
Dentate line
Internal
External
Anorectal ring
Rectum
Anal transition
zone
Area of
Pectin
Anal margin
Surgical anal
canal
Surgical Signicance of White Line of Hilton
• Because of its white color, the bottom
limit of the pectin is known as the
“White line of Hilton” [19].
• This is seen at the intersphincteric
groove.
• The stratied squamous epithelium that
lines it is pale, thin, glossy, lacks sweat
glands, and indicates the lower limit of
pectin.
• Internal anal sphincter in pectin region
is spastic according to Goligher et al.
[21]. Anal ssures usually extend
between the anal verge and the dentate
line for this reason.
22
Exter
Anal verge
White line of Hilton
Fig. 2.14 Intermediate
zone
2 Surgical Anatomy ofAnal Canal
nal anal sphincter
Internal anal sphincter
2.7 Lower Cutaneous Zone
The lower zone is known as “Zona Certanea”
[20]. It is about 8mm long and extends between
the anal verge and the Hilton’s white line. It is
Intermediate
area
Dentate line
lined by stratied squamous keratinized epithelium and looks like pigmented skin with sebaceous glands, hair follicles, and sweat glands
(Fig. 2.15). Inferiorly, it blends with perianal
skin.
External anal sphincter
Keratinizing stratified squamous epithelium
Internal anal sphincter
2.8 Internal Anal Sphincter (IAS)
23
Rectum
Columnar epithelium
Columns of morgagni
Fig. 2.15 Lower cutaneous zone
Anal transition
Non - keratinizing
squamous epithelium
Lower Zone
2.8 Internal Anal Sphincter (IAS)
IAS is the consolidation of rectum’s circular
muscle layer in distal 2.5–4cm (Fig.2.16) [22].
2.8.1 Origin andInsertion
The IAS may be felt 1.2cm distal to the dentate
line on physical examination. It is a smooth muscle that arises from the rectum’s inner circular
layer. The intersphincteric groove is between the
external and internal anal sphincter [7].
zone
Anal gland
2.8.3 Importance
About 50–80% of the resting anal tone is maintained by IAS [24].
2.8.4 Innervation
This muscle is innervated by para-sympathetic
and sympathetic bers from the splanchnic
nerves and inferior pelvic plexus (S2–S4) [25].
The pudendal nerve does not innervate the IAS.
2.8.2 Thickness
When measured endosonographically, it is
3mm thick and represents a hypoechoic circular
band [23].
2.8.5 Blood Supply
The internal pudendal artery supplies the internal
anal sphincter.
24
Puborectalis part of levator
Fig. 2.16 IAS, CLM
(conjoined longitudinal
muscle), EAS, and
anorectal ring
2 Surgical Anatomy ofAnal Canal
ani
Table 2.4
Salient features
Control Involuntary
Insertion The rectum’s inner circular layer
Termination Approximately 6mm above anal verge
Thickness 3mm
Nerve
supply
Functions
2.8.6 Functions
It helps maintain continence by controlling involuntary liquid stool and gas loss [25].
2.8.7 Features
Table 2.4 lists the most important characteristics
of the IAS.
2.9 Conjoined Longitudinal
CLM [7] is the blending of the puborectalis with
the rectum’s longitudinal muscle coat. This muscle connects the external and internal anal sphincters. It gets inserted in the perianal skin to form
corrugator cutis ani (Fig.2.16). When it descends,
Deep
part
External anal
sphincter
Salient features of the internal anal sphincter
Pelvic splanchnic nerves (S4)
• Keeps anal canal and orice closed
• Helps in the mechanism of
defecation
Superficial
part
Subcutaneous
Muscle (CLM)
Conjoined longitudinal
muscle
Internal anal sphincter
part
it becomes broelastic, forming fan-shaped
medial extensions that cross the IAS and
contribute to the Treitz ligament, a group of
smooth muscles in the submucosa [16].
2.9.1 Thickness
Approximately 2.5mm [26].
2.9.2 Functions
The CLM acts as a skeleton for the external and
internal anal sphincter complex, providing support and connecting them. CLM and extensions
divide adjacent tissues into subspaces [27].
According to Shak etal., the conjoined longitudinal muscle has a minimal role in maintaining
continence [28]. Because of its fan-shaped
insertion in the perianal skin, along with bers of
the subcutaneous segment of the EAS, it is
responsible for septa formation where external
hemorrhoidal plexus is present.
2.10 EAS (External Anal Sphincter)
The pelvic oor muscle includes EAS. It is a
striated muscle covering an inferior section of
the anal canal and is under voluntary control.
2.10 EAS (External Anal Sphincter)
This muscle is relaxed at the time of defecation,
allowing the passage of feces (Fig.2.16).
2.10.1 Origin andInsertion
It extends from the skin and fascia surrounding
the anus and the entire anal canal. The attachment of the supercial part of the EAS into the
coccyx forms the anococcygeal ligament posteriorly. Anteriorly it is inserted into the perineal
body [29].
There are three anatomic components to this
sphincter: subcutaneous, supercial, and deep
[29].
2.10.1.1 Subcutaneous Part
Corrugator cutis ani is formed by inserting the
subcutaneous portion into the perianal skin
along with the CLM bers. It surrounds the
anal verge. The typical creases seen externally
around the anus are the results of the bers of
the EAS. The inferior bers extend past the
IAS. The anal canal mucosa covers it on the
inner side and the lower aspect is covered by
the anal skin.
2.10.1.2 Supercial Part
It is an elliptical ring of muscle bers surrounding the internal sphincter’s lower region. Its two
divergent parts encircle the anal canal’s middle
half. It is inserted anteriorly into the perineal
body and posteriorly into the coccyx through the
anococcygeal ligament.
2.10.1.3 Deep Part
The deep part becomes continuous with puborectalis to form an anorectal sling. According to
some authors, the EAS is a single type 1 skeletal
muscle that contracts on twitching [28]. Instead
of three parts, supercial, subcutaneous, and
deep, there are two parts of an EAS: lower and
upper. The upper portion extends up to the lower
part of the IAS, and the lower part extends beyond
the IAS [6].
25
Fig. 2.17 Endoscopic appearance of IAS and EAS
2.10.2 Thickness
Endosonographically, the EAS is hyperechoic
with a mean thickness of 6mm (Fig.2.17) [23].
2.10.3 Relations ofExternal Anal
Sphincter withMuscles
ofPerineum
Partially blends with
1. Puborectalis muscle
2. Supercial transverse perineal muscle
3. The layer of pelvic diaphragm covering the
inferior aspect of the levator ani
4. Conjoined longitudinal muscle [29]
A space between the external anal sphincter
and the internal anal sphincter is called intersphincteric space. Anal glands are present in this
space. Their blockage can lead to stula or
abscess formation. Surgically this space may be
assessed on bi-digital examination.
2.10.4 Innervation
The external anal sphincter receives somatic
innervations from the inferior anal nerve, a
branch of the pudendal nerve (S2–S4).
26
r
2.10.5 Blood Supply
The external anal sphincter is supplied by inferior
rectal arteries, which are terminal branches of the
internal pudendal artery originating from the
internal iliac artery.
2.10.6 Functions
The EAS maintains approximately 25–30% of
the resting tone [30]. It is under voluntary control, and at the time of defecation, it acts as a piston for easy evacuation.
Surgical Signicance of the EAS
Shak in 1975 postulated the “Triple Loop
System” of the EAS in which each loop is a
separate sphincter [28]. Three main U-shaped
loops comprise external anal sphincter, as
described by Shak. The upper loop is comprised by the deep external sphincter and the
puborectalis, which inserts on the pubis. The
supercial part forms the middle loop, which
is inserted in coccyx. Subcutaneous part
forms the lower loop, which is connected to
the perianal skin (Fig.2.18).
2 Surgical Anatomy ofAnal Canal
Any one of the three loops may serve as
a sphincter for solid stools, but not for atus or liquid.
2.10.7 Features
See Table2.5.
Table 2.5
Salient features
Insertion Posteriorly into the anococcygeal ligament
Divisions Subcutaneous
Thickness 6mm
Innervation Inferior anal nerve
Blood
supply
Functions Voluntary control for defecation
Salient features of EAS
Anteriorly into the perineal body
Supercial
Deep
Pudendal nerve - a branch of
(S2–S4) [29]
Inferior rectal arteries
Helps to support the pelvis along with
the perineal muscles
Fig. 2.18 Triple loop
system
Pubic symphysis
Rectum
Coccyx
Deep
Superficial
Subcutaneous
Perianal skin
External anal sphincte
Inferior rectal branch of
internal pudental artery
Main descending branch
2.11 Blood Supply toAnal Canal
27
2.11 Blood Supply toAnal Canal
2.11.1 Arterial Supply
Three arteries supply the anal canal—the
superior, the middle, and the inferior hemorrhoidal artery (Fig.2.19) [31]. An extension of
the inferior mesenteric artery, the SHA
“Superior hemorrhoidal artery” divides into
two branches at the third sacral vertebral level
(S3) [32]. These branches follow the extramural, transmural, and submucosal course within
the rectal wall to form corpus cavernosum
recti. Of variable origin, the paired middle
hemorrhoidal arteries supply to the distal and
middle rectum. They may arise from the internal iliac artery’s anterior division, or the inferior vesical artery, or both. According to some
authors, it is present only in 40–60% of cases
[33, 34]. The inferior hemorrhoidal artery
originates from the internal pudendal artery, a
branch of the internal iliac artery’s anterior
division.
2.11.2 Venous Supply
The veins follow the arterial supply. The superior
hemorrhoidal vein continues as the inferior mesenteric vein to join the splenic vein [16]. The
internal iliac veins receive drainage from inferior
and middle hemorrhoidal veins. A portocaval
anastomosis is formed through communication
between the hemorrhoidal plexuses. However,
hemorrhoidal engorgement is an uncommon
occurrence. Instead, true rectal varices may
develop in portal hypertension (Fig.2.20).
Surgical Signicance
Venous ow between anal canal and the
rectum is facilitated by systemic and portal
circulation. Always differentiate between
rectal varices and hemorrhoids in cases of
bleeding per rectum (Fig.2.21). The terms
hemorrhoidal/rectal arteries and veins refers
to the same vessels.
Superior rectal artery
Fig. 2.19 Arterial blood supply of anal canal
Levator ani
Anal canal
Right branch
Middle rectal artery
Terminal descending branches
Ascending branches