Abdomen , Pelvis and Perineum - PowerPoint Presentation

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Abdomen, Pelvis and Perineum

ANA 301

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Course Outline

Anterior abdominal wall (femoral and inguinal hernias)

Peritoneal reflections and mesenteriesEsophagus and stomachSmall intestineColon, cecum, appendix, and anal canalLiver, gallbladder, biliary tractsVasculature of the abdomen (portocaval system)Pancreas and spleenPosterior abdominal wall – kidney and adrenal glandLumbar plexusOsteology of the pelvis (sex differences / clinical importance)Pelvis and perineumSacral plexusLevator ani musclesMale internal and external genitaliaFemale internal and external genitalia

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Abdomen

Part

of the trunk between the thorax and the pelvis.Houses organs of the alimentary system and part of the urogenital system. Containment of these organs and their contents is provided by musculo-aponeurotic walls anterolaterally, the diaphragm superiorly, and the muscles of the pelvis inferiorly. Anterolateral musculo-aponeurotic walls are suspended by the inferior margin of the thoracic skeleton superiorly and the pelvic girdle inferiorly and lumbar vertebral column

in the posterior abdominal wall.

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Overview of viscera of thorax and abdomen

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Musculo-aponeurotic

abdominal walls contract to increase intra-abdominal pressure and distend to accommodate expansions Anterolateral abdominal wall (AAW) and several organs lying against the posterior wall are covered on their internal aspects with serosa that reflects onto the abdominal viscera. Peritoneal cavity is formed between the walls and the visceraDouble-layered reflections of peritoneum provide passage for the blood vessels,

lymphatics

, fat and

nerves.

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Abdominal cavity

Forms the superior and major part of the abdominopelvic cavityExtends between the thoracic diaphragm and pelvic diaphragm.Continuous with the pelvic cavity. Plane of the pelvic inlet (superior pelvic aperture) separates the abdominal and the pelvic cavities.Extends superiorly to the thoracic cage to the 4th intercostal space. Superiorly placed abdominal organs (

spleen, liver

, part of the kidneys, and stomach) are protected

by the

thoracic cage.

Greater

pelvis (expanded part

of the

pelvis superior to the pelvic inlet) supports and

partly protects

the lower abdominal viscera (part of the

ileum,

cecum

, appendix, and sigmoid colon).

Location

of most digestive organs, parts of the

urogenital

system

(kidneys and most of the

ureters

), and

the spleen.

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9 Regions

Four planes: two sagittal and two transverse planes. Two sagittal planes are the midclavicular planes that pass from the midpoint of the clavicles to the midinguinal points, midpoints of the lines joining the anterior superior iliac spine (ASIS) and the pubic tubercles on each side. Two transverse planes are the subcostal plane, passing through the inferior border of the 10th costal cartilage on each side, and the transtubercular plane, passing through the iliac

tubercles

and the body of the L5 vertebra

.

Transpyloric

plane

, extrapolated midway between the superior

borders of

the

manubrium

of the sternum and the pubic

symphysis

(L1

vertebral level), transects the pylorus,fundus of the gallbladder, neck of the pancreas, origins of the superior mesenteric artery (SMA) and hepatic portal vein, root of the transverse mesocolon, duodenojejunal junction, and hila of the kidneysInterspinous plane passes through the ASIS on each side.

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Four quadrants of the abdominal cavity defined by two readily defined planes:

Transumbilical plane, passing through the umbilicus (and the intervertebral [IV] disc between the L3 and L4 vertebrae), dividing it into upper and lower halvesMedian plane, passing longitudinally through the body, dividing it into right and left halves.

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Abdominal

wall is

subdivided into the anterior wall, right and left lateral walls, and posterior wall Boundary between the anterior and lateral walls is indefinite, therefore the term anterolateral abdominal wall.Bounded superiorly by the cartilages of the 7th–10th ribs and the xiphoid process of the sternumBounded inferiorly by the inguinal ligament and the superior margins of the anterolateral aspects of the pelvic girdle (iliac crests, pubic crests, and pubic symphysis).

- Consists

of skin and subcutaneous tissue composed of fat

, muscles and their

aponeuroses

and deep fascia,

extraperitoneal

fat

, and parietal

peritoneum.

- Three

musculotendinous

layers; the

fiber bundles of each layer run in different directions. 10

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Subdivisions of the

anterior abdominal wall

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Superficial Fascia

of the Anterolateral Abdominal WallMajor site of fat storage, fat forms sagging folds (panniculi).2 layers inferior to the umbilicus: Superficial fatty layer (Camper fascia) Deep membranous layer (Scarpa fascia).Membranous layer

continues into

the perineal

region as

the

superficial

perineal

fascia (

Colles

fascia)

Investing

fascia cover

the external aspects of the three muscle layersInternal aspect of AAW constitute endoabdominal fascia. Transversalis fascia lines transversus abdominis muscle and its aponeurosis Parietal peritoneum formed by a single layer of epithelial cells and supporting connective tissue.

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Muscles of

Anterolateral Abdominal WallFive (bilaterally paired) muscles in the AAW: three flat muscles and two vertical muscles.Flat muscles are the external oblique, internal oblique, and transversus abdominis. Fibers of the outer two layers runs diagonally and perpendicular to each other,

and the fibers

of the deep layer

runs

transversely.

Between

the

midclavicular

line

(MCL) and the midline, the

aponeuroses

form

the rectus sheath enclosing the rectus abdominis muscle.Aponeuroses interweave with their fellows of the opposite side, forming midline raphe - the linea alba extends from the xiphoid process to the pubic symphysis. Contained

within the rectus sheath, are

rectus

abdominis

and

the

pyramidalis

.

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EXTERNAL OBLIQUE MUSCLE

Largest and most superficial of the three flat AAW muscles. Fibers run inferomedially, approaching a horizontal course. Muscle fibers become aponeurotic at the MCL medially and at the spino-umbilical line inferiorly decussating at the linea alba

Contralateral

external

and internal oblique muscles

form a “

digastric

muscle”

Inferiorly

,

it attaches to the

pubic crest medial to the pubic tubercle.

Inferior margin is thickened and

spans between the ASIS and the pubic tubercle as the inguinal ligament (Poupart ligament).

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Internal oblique

A thin muscular sheet that fans out anteromedially. Fibers run perpendicular to those of the external oblique, running superomediallyFibers also become aponeurotic at the MCL and participate in the formation of the rectus sheath.

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TRANSVERSUS

ABDOMINIS MUSCLE

Innermost of the three flat abdominal musclesRuns more or less transversallyFibers end in an aponeurosis, which contributes to the formation of the rectus sheath.Between the internal oblique and the transversus abdominis muscles is a neurovascular planeNeurovascular plane contains the nerves and arteries supplying the AAW.

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RECTUS ABDOMINIS MUSCLE

A long, broad, strap-like muscleprincipal vertical muscle of the anterior abdominal wall Paired rectus muscles, separated by the linea alba, lie close together inferiorly. Three times as wide superiorly as inferiorly; it is broad and thin superiorly and narrow and thick inferiorly.Most of the rectus abdominis is enclosed in the rectus sheath.

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PYRAMIDALIS

Small, triangular muscle that is absent in approximately 20% of people. Lies anterior to the inferior part of the rectus abdominis and attaches to the anterior surface of the pubis and the anterior pubic ligament. Ends in the linea albaTenses the linea alba. When present, surgeons use the attachment of the pyramidalis to the linea alba as a landmark for median abdominal incision.

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RECTUS SHEATH, LINEA ALBA, AND UMBILICAL RING

Rectus sheath is the strong, fibrous compartment of the rectus abdominis and pyramidalis muscles.Found in the rectus sheath are the superior and inferior epigastric arteries and veins, lymphatic vessels, and distal portions of the thoraco-abdominal nerves (abdominal portions of the anterior rami of spinal nerves T7–T12). Formed by the decussation and interweaving of the aponeuroses of the flat abdominal muscles.

External oblique

aponeurosis

contributes to the anterior wall.

Arcuate

line

demarcates

the

transition between the

posterior

wall of

the sheath

covering the superior three quarters of the rectus and the transversalis fascia covering the inferior quarter.

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FUNCTIONS

OF ANTEROLATERAL ABDOMINAL MUSCLESSupport for the anterolateral abdominal wall. Support the abdominal viscera and protect them from most injuries.Compress the abdominal contents to maintain or increase the intra-abdominal pressureMove the trunk and help to maintain posture.Muscles form a muscular girdle that exerts pressure on the abdominal viscera. Movements

of the trunk at the lumbar

vertebrae.

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Neurovasculature

of Anterolateral Abdominal WallDERMATOMES OF ANTEROLATERAL ABDOMINAL WALLAnterior rami of spinal nerves T7–T12 Dermatome T10 includes the umbilicus, whereas dermatome L1 includes the inguinal fold.NERVES OF ANTEROLATERAL ABDOMINAL WALLSkin and muscles of AAW are supplied by:Thoraco-abdominal nerves: Anterior rami of the inferior six

thoracic spinal

nerves (T7–T11

)

Lateral (thoracic)

cutaneous

branches:

thoracic

spinal nerves T7–T9 or T10.

Subcostal

nerve:

anterior

ramus of spinal nerve T12.Iliohypogastric and ilio-inguinal nerves: terminal branches of the anterior ramus of spinal nerve L1.

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T7–T9

supply the skin superior to the umbilicus.T10 supplies the skin around the umbilicus.T11, plus the cutaneous branches of the subcostal (T12), iliohypogastric, and ilio-inguinal (L1), supply the skin inferior to the umbilicus.Thoraco-abdominal, subcostal, and iliohypogastric nerves communicate with each other.

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VESSELS OF ANTEROLATERAL ABDOMINAL

WALLDrains superiorly to the internal thoracic vein medially and the lateral thoracic vein laterally and inferiorly to the superficial and inferior epigastric veins, tributaries of the femoral and external iliac veins.Cutaneous veins surrounding the umbilicus anastomose with para-umbilical veins and tributaries of the hepatic portal

vein.

Thoraco

-

epigastric

vein

between

the

superficial

epigastric

vein (a femoral vein tributary) and the lateral thoracic vein (an axillary vein tributary). Anastomosis between the inferior epigastric vein (from external iliac vein) and the superior epigastric/internal thoracic veins (subclavian vein tributaries) afford collateral circulation during blockage of either vena cava.

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Blood

vessels of the AAW are the superior epigastric vessels and branches of the musculophrenic vessels from the internal thoracic vessels.Inferior epigastric and deep circumflex iliac vessels from the external iliac vessels.Superficial circumflex iliac and superficial epigastric vessels from the femoral artery and greater

saphenous

vein, respectively.

Posterior

intercostal

vessels of the 11th

intercostal

space and the anterior branches of

subcostal

vessels

.

Superior

epigastric

artery is the continuation of the internal thoracic artery and anastomoses with the inferior epigastric artery approximately in the umbilical region.Inferior epigastric artery arises from the external iliac artery just superior to the inguinal ligament and anastomoses with the superior epigastric artery.

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Lymphatic drainage

• Superficial lymphatic vessels accompany the subcutaneous veins- Those superior to the transumbilical plane drain to the axillary lymph nodesA few drain to the parasternal lymph nodes. Superficial lymphatic vessels inferior to the transumbilical plane drain to the superficial inguinal lymph nodes.• Deep lymphatic vessels accompany the deep veins of the abdominal wall - Drain to the external iliac, common iliac, and right and left lumbar (caval

and aortic) lymph nodes.

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Abdominal

HerniasAAW may be the site of abdominal herniasUmbilical hernias Common in neonates because the anterior abdominal wall is weak in the umbilical ring. SmallResult from increased intra-abdominal pressure in the presence of weakness and incomplete closure of the anterior abdominal wall after ligation of the umbilical cord at birth. Acquired umbilical herniasOccur most commonly in women and obese people. Extraperitoneal fat and/or peritoneum protrude into the hernial sac.

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Injury to Nerves of

Anterolateral Abdominal WallInferior thoracic spinal nerves (T7–T12) and the iliohypogastric and ilio-inguinal nerves (L1) Susceptible to injury in surgical incisions or from trauma at any level of the abdominal wall. Injury to nerves of the anterolateral abdominal wall may result in weakening of the muscles predisposing to development of an inguinal hernia.

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Abdominal Surgical Incisions

Allows access to the abdominal cavity. Follow the cleavage lines (Langer lines) in the skin. Allows adequate exposure, and the best possible cosmetic effect, is chosen. Surgeon avoids injury to motor nerves, maintenance of blood supply, and minimizes injury to muscles and fascia of the abdominal wall while aiming for favorable healing. Surgeon considers the direction

of the muscle

fibers and the location of the

aponeuroses

and

nerves.

Muscles

and viscera are retracted toward, not

away from

, their neurovascular supply.

Cutting a motor nerve paralyzes the muscle

fibers supplied by

it, thereby weakening the

anterolateral abdominal wall.

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LONGITUDINAL

INCISIONSMedian and paramedian incisions offer good exposure and access to the viscera Median incisions can be made along any part or the length of the linea alba from the xiphoid process to pubic symphysis. Linea alba transmits only small vessels and nerves to the skin, a midline incision is relatively bloodless, and avoids major nerves.Paramedian incisions (lateral to the median plane) are made in a sagittal plane and may extend from the costal

margin to

the pubic hairline

.

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OBLIQUE AND TRANSVERSE INCISIONS

Direction of oblique and transverse incisions is related to muscle fiber orientation and minimizes nerve damage. Gridiron (muscle-splitting) incisions are often used for an appendectomy. Oblique McBurney incision is made at the McBurney point, approximately 2.5 cm superomedial to the ASIS on the spino-umbilical line.

Muscles are incised in

the direction of

their fibers and retracted;

iliohypogastric

nerve

, running deep to the internal oblique, is

identified and

preserved.

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Suprapubic

(Pfannenstiel) incisions (“bikini” incisions) are made at the pubic hairline. These incisions—horizontal with a slight convexity—are used for most gynecological and obstetrical operations (e.g., for cesarean section).The iliohypogastric and ilio-inguinal nerves are identified and preserved.

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Transverse incisions

through the anterior layer of the rectus sheath and rectus abdominis provide good access and cause the least possible damage to the nerve supply of the rectus abdominis. Subcostal incisions provide access to the gallbladder and biliary ducts on the right side and the spleen on the left. The incision is made parallel but at least 2.5 cm inferior to the costal margin to avoid the 7th and 8th thoracic spinal nerves.

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HIGH-RISK

INCISIONSPararectus incisions along the lateral border of the rectus sheath are undesirable because they may cut the nerve supply to the rectus abdominis. Inguinal incisions for repairing hernias may injure the ilio-inguinal nerve.INCISIONAL HERNIAA protrusion of omentum or an organ through a surgical incision. If the muscular and

aponeurotic

layers of the abdomen do not heal properly, an

incisional

hernia can result.