5 Neurovascular Systems: Topographical Anatomy
5.1 Anterior Trunk Wall: Surface Anatomy and Superficial Nerves and Vessels
A Superficial cutaneous vessels and nerves of the anterior trunk wall
Superficial vessels: Most of the arterial supply to the anterior trunk wall comes from two sources: the internal thoracic artery and the superficial epigastric artery. The superficial veins drain chiefly into the axillary vein (via the thoracoepigastric vein) and into the femoral vein (via the superficial epigastric and superficial circumflex iliac veins). The peri- and paraumbilical veins provide the main communication between the superficial veins of the trunk wall and the portal veins (portocaval anastomoses). Superficial nerves: The sensory supply to the anterior trunk wall has a largely segmental arrangement (provided, for example, by lateral and anterior cutaneous branches from the intercostal nerves). The cervical plexus (supraclavicular nerves) is additionally involved in the thoracic region, as is the lumbar plexus (e.g., iliohypogastric and ilioinguinal nerves) in the lower abdominal region.
B Segmental (radicular) cutaneous innervation of the anterior trunk wall (dermatomes)
Right half of the trunk and adjacent upper limb, anterior view. Every sensory nerve root (dorsal root) innervates a specific skin area with its fibers. These “dermatomes” (see p. 88), then, correspond to associated spinal cord segments. The dermatomes are arranged in bandlike patterns that encircle the chest wall and upper abdomen. Below the umbilicus, the dermatomes become angled slightly downward toward the median plane. A “segmental gap” exists between the C 4 and T 2 dermatomes because the phylogenetic outgrowth of the human upper limb has removed the sensory fibers of C 5–C 8 and T 1 from the trunk wall (after Mumenthaler).
C Peripheral sensory cutaneous innervation of the anterior trunk wall
Right half of the trunk and adjacent upper limb, anterior view. The color-coded map of the peripheral cutaneous nerve territories follows the branching pattern of the cutaneous nerves in the subcutaneous connective tissue. Besides the cutaneous branches of the intercostal nerves (anterior and lateral cutaneous branches), it is chiefly the supraclavicular nerves and the iliohypogastric and ilioinguinal nerves that supply the skin of the anterior trunk wall (after Mumenthaler).
E Criteria for dividing the abdomen into regions
a The abdomen is divided into four quadrants by two perpendicular lines that intersect at the umbilicus.
b Coordinate system composed of two vertical and two horizontal lines. They divide the abdomen into nine regions, each located in either the upper, middle, or lower abdomen. The two vertical lines represent the left and right midclavicular lines. The two horizontal lines pass through the lowest point of the tenth ribs or the summit of the two iliac crests (see p. 35).
F Projection of the abdominal organs onto the four quadrants of the anterior abdominal wall
a Organs of the anterior layer, b organs of the middle layer, c organs of the posterior layer.
The organs of the anterior layer abut the anterior abdominal wall. The organs of the middle layer are located in the posterior part of the abdominal cavity (some are partially retroperitoneal), and those of the posterior layer are located outside or behind the actual abdominal cavity (i. e., they are retroperitoneal).
5.2 Posterior Trunk Wall: Surface Anatomy and Superficial Nerves and Vessels
A Superficial cutaneous vessels and nerves of the posterior trunk wall
Posterior view. Except for the lower buttocks and lateral portions of the trunk wall, the posterior trunk wall derives its sensory innervation from posterior rami of the spinal nerves and from lateral cutaneous branches of the intercostal nerves. This is a predominantly segmental innervation pattern, analogous to that described in the anterior trunk wall. Both the medial and lateral cutaneous nerve branches pass with the cutaneous vessels through the intrinsic back muscles to the skin of the back. The skin of the buttocks is supplied by lateral branches from the three cranial lumbar and sacral nerves (superior and middle clunial nerves).
Note: The lower part of the buttock is supplied by the inferior clunial nerves, which are branches of the sacral plexus; thus, they are derived from the anterior rami of the spinal nerves.
B Segmental (radicular) cutaneous innervation of the posterior trunk wall (dermatomes)
Right half of the trunk and adjacent upper limb, posterior view (after Mumenthaler).
C Peripheral sensory cutaneous innervation of the posterior trunk wall
Right half of the trunk and adjacent upper limb, posterior view (after Mumenthaler).
D Surface anatomy of the posterior trunk wall
a Male, b female.
In both sexes a spinal furrow runs vertically in the posterior midline of the trunk below the C 7 spinous process. It is formed by the fixation of the subcutaneous tissue to the corresponding spinous processes. At the sacral level in males, the furrow widens to form the sacral triangle (bounded by the right and left posterior superior iliac spines and the upper part of the anal cleft). The corresponding diamond-shaped area in females is called the rhomboid of Michaelis (see F).
E Segmental and peripheral cutaneous innervation of the male perineal region
Lithotomy position. The segments or dermatomes have been mapped on the left side of the body, and the areas supplied by the peripheral cutaneous nerves are shown on the right side (after Mumenthaler).
F Anatomic boundaries of the Michaelis rhomboid
Female gluteal region, posterior view. In women the sacral triangle is expanded to form a diamond-shaped figure with the following boundaries: the left and right posterior superior iliac spines, the spinous process of the L 4 vertebra, and the upper part of the anal cleft. With a normal female pelvis, the vertical and horizontal dimensions of the rhomboid are approximately equal. The shape of the Michaelis rhomboid (named for the German gynecologist G. A. Michaelis, 1798–1848) reflects the width of the female pelvis, providing an indirect indicator of the size of the birth canal.
5.3 Posterior Trunk Wall, Posterior View
A Neurovascular structures of the posterior trunk wall and nuchal region
Posterior view. The segmentally arranged neurovascular structures of the posterior trunk wall (posterior rami of the spinal nerves and posterior branches of the posterior intercostal and lumbar vessels) are demonstrated on the left side of the trunk (all muscle fasciae have been removed except for the superficial layer of the thoracolumbar fascia). On the right side, the trapezius muscle has been detached from its origins and reflected laterally to show the course of the transverse cervical artery in the deep scapular region (compare with B).
Note: On the posterior trunk wall, only the lateral nuchal region (lesser occipital nerve, see C) and the lower gluteal region (inferior clunial nerves) receive their sensory supply from anterior spinal nerve rami.
The latissimus dorsi muscle has been partially removed on the right side to demonstrate the upper costolumbar triangle (of Grynfeltt). The fibrous lumbar triangle (boundaries: twelfth rib, intrinsic back muscles, and internal oblique) is similar to the lower iliolumbar triangle (of Petit, bounded by the iliac crest, latissimus dorsi, and external oblique) in that it creates a site of predilection for rare, usually acquired lumbar hernias (Grynfeltt or Petit hernia, see also p. 223).
B Arteries of the deep scapular region
Right scapular region, posterior view. The trapezius, splenius capitis, deltoid, infraspinatus, and rhomboid major and minor muscles have been completely or partially removed on the right side. The deep scapular region is supplied by the transverse cervical artery, deep cervical artery (see C), suprascapular artery, circumflex scapular artery, and posterior circumflex humeral artery. All of these vessels arise directly or indirectly—via the thyrocervical trunk—from the subclavian artery (neither is visible here). The suprascapular, circumflex scapular, dorsal scapular, and thoracodorsal arteries form the “scapular arcade” (see p. 391). Medial to the mastoid process, the occipital artery appears below the tendon of insertion of the sternocleidomastoid muscle and runs upward with the sensory greater occipital nerve to the skin of the occiput. The greater occipital nerve pierces both the trapezius and semispinalis capitis muscles in the area of their firm tendinous attachments. It may become compressed at these sites, leading to occipital neuralgia.
C Suboccipital triangle (vertebral artery triangle)
Posterior view. The trapezius, sternocleidomastoid, splenius capitis, and semispinalis capitis muscles have been removed to display the suboccipital region on the right side. The suboccipital triangle is bounded by the suboccipital muscles (rectus capitis posterior major and the obliquus capitis superior and inferior). In the deep portion of the triangle, the vertebral artery runs through its groove in the atlas. The suboccipital nerve (C 1), which is purely motor, emerges above the posterior arch of the atlas to supply the short muscles of the head. The greater occipital nerve (C 2) and, at a lower level, the third occipital nerve (C 3) wind posteriorly as they pass the lower margin of the obliquus capitis inferior. The deep cervical artery, a branch of the costocervical trunk, runs between the semispinalis capitis and cervicis muscles.
5.4 Posterior Trunk Wall, Anterior View
A Neurovascular structures on the anterior side of the posterior trunk wall
a Lumbar fossa on the right side after removal of the anterior and lateral trunk wall, the intra- and retroperitoneal organs, the peritoneum, and all the fasciae of the trunk wall. The inferior vena cava has been partially removed.
b Lumbar fossa with the lumbar plexus of the right side after removal of the superficial layer of the psoas major.
The lumbar plexus (see p. 536) is formed by the anterior rami of the T 12–L 4 nerves lateral to the lumbar spine and is partially covered by the psoas major muscle. The nerves run laterally and obliquely downward to the abdominal wall and thigh, except for the obturator nerve (see b), which runs through the lateral wall of the lesser pelvis and the obturator foramen (not visible here) to the medial part of the thigh.
Note: The sites of emergence of the lumbar and iliolumbar vessels are located below the psoas major muscle. They run almost horizontally across the quadratus lumborum and iliacus muscles. Medial to the psoas major (and covered by the inferior vena cava) is the lumbar sympathetic trunk.
B Neurovascular structures of the posterior trunk wall at the thoracic level
Transverse section through the thorax after removal of the thoracic organs, parietal pleura, and part of the endothoracic fascia, anterosuperior view. The chest wall receives its arterial blood supply from the posterior intercostal arteries and is drained by the intercostal veins, which empty into the azygos system. The intercostal vessels run with the intercostal nerves along the inferior border of the associated rib, lodged in the costal sulcus.
5.5 Anterior Trunk Wall: Overview and Location of Clinically Important Nerves and Vessels
A Neurovascular structures on the anterior side of the anterior trunk wall
Anterior view. The superficial (subcutaneous) neurovascular structures are demonstrated on the left side of the trunk and the deep neurovascular structures on the right side. For this purpose the pectoralis major and minor muscles have been completely removed on the right side, and the external and internal oblique muscles have been partially removed. Portions of the right rectus abdominis muscle have been removed or rendered transparent to demonstrate the inferior epigastric vessels. Finally, the intercostal spaces have been exposed to display the course of the intercostal vessels and nerves.
B The arterial supply of the anterior trunk wall
Anterior view. The anterior trunk wall receives its blood supply from two main sources: the internal thoracic artery, which arises from the subclavian artery, and the inferior epigastric artery, which arises from the external iliac artery. It is also supplied by smaller vessels arising from the axillary artery (superior thoracic artery, thoracodorsal artery, and lateral thoracic artery) and from the femoral artery (superficial epigastric artery and superficial circumflex iliac artery).
C Importance of the superficial circumflex iliac artery in harvesting skin flaps for plastic surgery
a Dissection of a skin flap based on the superficial circumflex iliac artery.
b The groin flap transferred to the dorsum of the right hand (after Weber).
D Preserving the intercostal vein, artery, and nerve during the insertion of a chest tube
A chest tube may be inserted to drain an abnormal fluid collection from the pleural space, such as a pleural effusion due to bronchial carcinoma. The best site for placing the chest tube can be determined by percussion or ultrasound examination. Generally, one optimum puncture site in the sitting patient is at the level of the seventh or eighth intercostal space on the posterior axillary line (see e and p. 34). The drain should always be introduced at the upper margin of a rib to avoid injuring the intercostal vein, artery, and nerve. For additional puncture sites, see textbooks on surgery.
a–d Steps in the placement of a chest tube (anterior view; after Henne-Bruns, Dürig, and Kremer):
a A skin incision is made under local anesthesia, and the drainage tube is introduced perpendicular to the chest wall.
b On reaching the ribs, the tube is angled 90° and advanced cephalad in the subcutaneous plane, parallel to the chest wall.
c On reaching the next higher intercostal space, the tube is passed through the intercostal muscles above the rib.
d The tube is then advanced into the pleural cavity.
e Longitudinal section through the chest wall at the level of the posterior axillary line, after placement of the chest tube in the presence of pleural effusion.
5.6 Anterior Trunk Wall: Nerves, Blood Vessels, and Lymphatics in the Female Breast
A Shape and appearance of the female breast
Right breast, anterior view. The female breast is shaped like a cone that is more rounded in its lower half than in the upper quadrants. It consists of the glandular tissue (mammary gland) and a fibrous stroma that contains fatty tissue. The excretory ducts of the glandular tissue open on the cone-shaped nipple, which lies at the center of the more heavily pigmented areola. Numerous small protuberances mark the openings of apocrine sweat glands and free sebaceous glands (areolar glands).
B The mammary ridges
The rudiments of the mammary glands form in both sexes along the mammary ridges, appearing as an epidermal ridge extending from the axilla to the inguinal region on each side. Although rarely the mammary ridges may persist in humans to form accessory nipples (polythelia), normally all the rudiments disappear except for the thoracic pair. By the end of fetal development, lactiferous ducts have sprouted into the subcutaneous tissue from the two remaining epithelial buds. After menarche, breast development in females is marked by growth of the fibrous stroma and proliferation of the glandular tree in response to stimulation by sex hormones.
C Gross and microscopic anatomy of the breast
a The base of the adult female breast extends from the second to the sixth rib along the midclavicular line and directly overlies the pectoralis major, serratus anterior, and external oblique muscles. It is loosely attached to the pectoralis fascia and adjacent fascial planes (axillary and superficial abdominal fascia) by connective tissue. The breast is additionally supported, especially in its upper portion, by permeating bundles of connective tissue (the suspensory ligaments of the breast, or Cooper’s ligaments). The glandular tissue is composed of 10 to 20 individual lobes, each of which has its lactiferous major duct that opens on the nipple by way of a dilated segment, the lactiferous sinus (structure of the lobe shown in b). The glands and lactiferous ducts are surrounded by firm, fibrofatty tissue that has a rich blood supply.
b Sagittal section of the duct system and portions of a lobe. A mammary lobe resembles a tree composed of branching lactiferous ducts, which terminate in smaller lobules (approximately 0.5 mm in diameter). In the nonlactating breast (as shown here), these lobules contain rudimentary acini that are arranged in clusters of small epithelial buds without a visible lumen.
c The terminal duct lobular unit (TDLU). One lobule and its terminal duct make up the basic secretory unit of the female breast. Each lobule is composed of acini that empty into a terminal ductule. The associated intralobular connective tissue (mantle tissue) contains stem cells that give rise to the tremendous cell growth (proliferation of the duct system and differentiation of the acini) that occurs during the transformation to the lactating breast. The TDLU is of key importance in pathohistology because it is the site where most malignant breast tumors originate (after Lüllmann).
D Blood supply to the breast
The breast derives its blood supply from perforating branches of the internal thoracic artery (= medial mammary branches from the second through fourth intercostal spaces), branches of the lateral thoracic artery (lateral mammary branches), and direct branches from the second through fifth intercostal arteries (mammary branches). The breast is drained by the internal and lateral thoracic veins.
E Nerve supply to the breast
The sensory innervation of the breast has a segmental arrangement and is supplied by branches of the second through sixth intercostal nerves (lateral and medial mammary branches). Branches of the cervical plexus (supraclavicular nerves) also supply the upper portion of the breast.
F Lymphatic drainage of the breast
The lymphatic vessels of the breast can be divided into a superficial, subcutaneous, and deep system. The deep system begins with lymphatic capillaries at the acinar level (see Cb and c) and is particularly important as a route for tumor metastasis. The main regional filtering stations are the axillary and parasternal lymph nodes, the approximately 30 to 60 axillary lymph nodes receiving most of the lymphatic drainage. They are the first nodes to be affected by metastasis (see G) and therefore have major oncological significance. The axillary lymph nodes are subdivided into levels (see p. 360):
• Level I: lower axillary group (lateral to the pectoralis minor):
– Pectoral axillary lymph nodes
– Subscapular axillary lymph nodes
– Lateral axillary lymph nodes
– Paramammary lymph nodes
• Level II: middle axillary group (at the level of the pectoralis minor):
– Interpectoral axillary lymph nodes
– Central axillary lymph nodes
• Level III: upper infraclavicular group (medial to the pectoralis minor):
– Apical axillary lymph nodes
The parasternal lymph nodes, which are distributed along the thoracic vessels, chiefly drain the medial portion of the breast. From there, tumor cells may spread across the midline to the opposite side. The survival rate in breast cancer patients correlates most strongly with the number of involved lymph nodes at the various axillary nodal levels. The parasternal lymph nodes are rarely important in this regard. According to Henne-Bruns, Dürig, and Kremer, the 5-year survival rate is approximately 65% with metastatic involvement of level I, 31% with involvement of level II, but approaches 0% in patients with level III involvement. This explains the key prognostic importance of a sentinel lymphadenectomy (removal of the sentinel lymph node). This technique is based on the assumption that every point in the integument drains via specific lymphatic pathways to a particular lymph node, rarely draining to more than one. Accordingly, the lymph node that is the first to receive lymph from the primary tumor will be the first node to contain tumor cells that have spread from the primary tumor by lymphogenous metastasis. The specific lymphatic drainage path, and thus the sentinel node, can be identified by scintigraphic mapping with radio-labeled colloids (99mTC sulfur microcolloid), which has superseded the older technique of patent blue dye injection. The first lymph node to be visualized is the sentinel node. That node is selectively removed and histologically examined for the presence of tumor cells. If the sentinel node does not contain tumor cells, generally the rest of the axillary nodes will also be negative. This method is 98% accurate in predicting the level of axillary nodal involvement prior to surgery.
G Distribution of malignant tumors by quadrant in the female breast
The numbers indicate the average percentage location of malignant breast tumors.
5.7 Anterior Trunk Wall: The Inguinal Canal
A Location of the inguinal canal in the male
Right inguinal region, anterior view. Approximately 4 to 6 cm long, the inguinal canal passes obliquely forward, downward, and medially above the inguinal ligament to pierce the anterior abdominal wall. It begins internally at the deep inguinal ring (D and E) in the lateral inguinal fossa (see p. 214) and opens externally at the superficial inguinal ring, lateral to the pubic tubercle. With the superficial abdominal fascia removed, this “external opening” of the canal can be identified as a slitlike orifice in the aponeurosis of the external oblique muscle (external oblique aponeurosis). It is bounded by the medial crus superomedially and by the lateral crus inferolaterally. Both crura are interconnected by the intercrural fibers. The superficial inguinal ring is completed internally by arched fibers from the inguinal ligament (reflex ligament), forming a deep groove. The inguinal canal in the male provides a pathway for the descent of the testis during fetal life (see p. 226). Its contents in the male (after testicular descent) include the spermatic cord, and its contents in the female include the round ligament of the uterus.
B Sagittal section through the inguinal canal in the male
Medial view. Note the structures that form the walls of the inguinal canal above and below the spermatic cord and on the anterior and posterior sides (compare with C). The openings and wall structures of the inguinal canal bear an important relationship to the pathophysiology of hernias (after Schumpelick).
C Openings and wall structures of the inguinal canal
The inguinal canal resembles a flattened tube with an internal and external opening (see below), a floor, a roof, and anterior and posterior walls. A lumen is present only after its contents have been removed (the spermatic cord in males, the uterine round ligament and its artery in females, the ilioinguinal nerve and lymphatic vessels in both sexes). The inguinal canal remains patent for life, especially in males, and thus forms a path for potential herniation through the abdominal wall (see p. 215).
Openings of the inguinal canal (see A)
Superficial inguinal ring
Opening in the external oblique aponeurosis bounded by the medial crus, lateral crus, intercrural fibers, and reflected inguinal ligament
Deep inguinal ring
Opening between the interfoveolar ligament, inguinal ligament, and lateral umbilical fold; formed by an outpouching of the transversalis fascia (becomes the internal spermatic fascia) (see p. 214)
Wall structures of the inguinal canal (see B)
Inguinal ligament (densely interwoven fibers of the lower external oblique aponeurosis and adjacent fascia lata of the thigh)
Transversus abdominis and internal oblique muscles
External oblique aponeurosis
Transversalis fascia and peritoneum (partially thickened by the interfoveolar ligament)
D Contribution of the oblique abdominal muscles to the structure of the male inguinal canal
Right inguinal region, anterior view.
a–c Progressive removal of the abdominal wall muscles.
E The inguinal canal, progressively opened to expose the spermatic cord
a Division of the external oblique aponeurosis reveals the internal oblique muscle, some of whose fibers are continued onto the spermatic cord as the cremaster muscle. The genital branch of the genitofemoral nerve runs with it below the cremasteric fascia (see p. 538). The ilioinguinal nerve runs through the inguinal canal on the spermatic cord. Its sensory fibers pass through the superficial inguinal ring to the skin over the pubic symphysis and are distributed to the lateral portion of the scrotum or labia majora and medial thigh.
b With the internal oblique muscle divided and the cremaster muscle split, the full course of the spermatic cord through the inguinal canal can be displayed. The spermatic cord appears at the deep inguinal ring, where the transversalis fascia is invaginated into the inguinal canal (and encloses the spermatic cord on its way to the testis as the internal spermatic fascia). It runs below the transversus abdominis along the posterior wall of the inguinal canal (transversalis fascia and peritoneum). The wall at the midportion of the canal is formed by the interfoveolar ligament and is reinforced medially by the reflected inguinal ligament. Medial to the interfoveolar ligament, deep to which run the epigastric vessels, and superior to the inguinal ligament is the medial inguinal fossa, a weak spot in the abdominal wall that is a common site for direct inguinal hernias (after Schumpelick; see also p. 215).
5.8 Anterior Abdominal Wall: Anatomy and Weak Spots
A Internal surface anatomy of the anterior abdominal wall in the male
Coronal section through the abdominal and pelvic cavity at the level of the hip joints, posterior view. All of the abdominal and pelvic organs have been removed except for the urinary bladder and prostate. Por-tions of the peritoneum and transversalis fascia have also been removed on the left side. The internal surface anatomy of the lower abdominal wall is marked by five peritoneal folds, which extend toward the umbilicus:
• An unpaired median umbilical fold on the midline (contains the obliterated urachus).
• Paired left and right medial umbilical folds (contain the left and right obliterated umbilical artery).
• Paired left and right lateral umbilical folds (contain the left and right inferior epigastric vessels)
Located between the peritoneal folds on each side are three more or less distinct fossae, which are sites of potential herniation through the anterior abdominal wall:
• The supravesical fossa, located between the median and medial umbilical folds above the apex of the bladder
• The medial inguinal fossa (Hesselbach’s triangle), located between the medial and lateral umbilical folds
• The lateral inguinal fossa, located lateral to the lateral umbilical fold (site of the deep inguinal ring)
B Internal and external openings for abdominal hernias
Above the inguinal ligament, the median, medial, and lateral umbilical folds (see A) form three sites of weakness on each side of the abdominal wall where indirect and direct inguinal hernias and suprapubic hernias typically occur. Another weak spot is located below the inguinal ligament and medial to the femoral vein in the femoral ring. At that site the femoral ring is covered only by loose, compliant connective tissue, the femoral septum, which is permeated by numerous lymphatic vessels. The sharp-edged lacunar ligament forms the medial border of the femoral ring and can contribute to the incarceration of a femoral hernia (see p. 217).
Above the inguinal ligament:
Superficial inguinal ring
Direct inguinal hernia
Medial inguinal fossa (Hesselbach’s triangle)
Superficial inguinal ring
Indirect inguinal hernia
Lateral inguinal fossa (deep inguinal ring)
Superficial inguinal ring
Below the inguinal ligament:
* The internal opening is where the hernia starts and the external opening is where it is observed clinically.
C Internal hernial openings in the male inguinal and femoral region
Detail from A, posterior view. The peritoneum and transversalis fascia have been partially removed to reveal the hernial openings more clearly. The internal openings (see A and B) for indirect and direct inguinal hernias, femoral hernias, and suprapubic (= supravesical) hernias are indicated by color shading.
D Triangle of doom and triangle of pain
In two key regions in the preperitoneal space known respectively as the “triangle of pain” and the “triangle of doom,” it is important to avoid placing clips to secure mesh implants, particularly in laparoscopic hernia repairs (see p. 221). The iliopubic tract (the union of the transverse fascia and the inguinal ligament) defines the superior border of both triangles. The triangle of pain lies lateral to the testicular vessels, the triangle of doom medial to them. The triangle of pain contains both branches of the genitofemoral nerve, the femoral nerve, and the lateral femoral cutaneous nerve. Injury to these nerves can result in pain and dysesthesia. The testicular vessels and the major vessels of the leg (the external iliac vessels) course through the triangle of doom. Injury to these vessels can lead to poorly controllable bleeding.
A Definition, occurrence, and structure of a hernia
Between the thorax and the bony pelvis lies an extensive gap in the skeleton which is bridged by a multi-layered abdominal wall of broad muscles, fasciae, aponeuroses, and peritoneum. The muscular layer is absent at certain specific locations in the abdominal wall. At these locations, the abdominal wall is composed of connective tissue structures such as the transverse fascia, which also forms the posterior aspect of the inguinal canal. These areas are weak points in the abdominal wall. Especially where the connective tissue is weakened, as occurs in elderly persons, they occasionally fail to resist intra-abdominal pressure and become sites of hernias. Triggering events include lifting heavy objects or even coughing. The term hernia (Latin hernia = rupture) refers to the protrusion of the parietal peritoneum through a preexisting gap (inguinal or femoral hernia) or an acquired gap (hernia through a scar). A hernia that exits the abdominal space and is visible on the surface of the body is referred to as an external hernia; a protrusion into a peritoneal pocket is referred to as an internal hernia. As to the time of occurrence, one differentiates congenital hernias (such as an umbilical hernia or indirect inguinal hernia in a patent processus vaginalis) and acquired hernias (such as a direct inguinal hernia or femoral hernia). The following components of a hernia are important from a surgical standpoint:
• Hernial opening: the orifice or defect through which the viscus herniates (inguinal, femoral, or scar hernia).
• Hernial sac: the pouch, generally lined by parietal peritoneum, that contains the herniated viscus. Its size is highly variable, depending on the extent of the hernia.
• Hernial contents: may be almost any intra-abdominal viscus but usually consist of greater omentum or loops of small bowel.
• Coverings: the tissue layers surrounding the hernial sac. The composition of the coverings depends on the location and mechanism of the hernia.