Chapter 45 Abdominal Wall, Umbilicus, Peritoneum, Mesenteries, Omentum, and Retroperitoneum

Abdominal Wall And Umbilicus

Embryology

The abdominal wall begins to develop in the earliest stages of embryonic differentiation from the lateral plate of the embryonic mesoderm. At this stage, the embryo consists of three principal layers—an outer protective layer termed the ectoderm, an inner nutritive layer, the endoderm, and the mesoderm.

The mesoderm becomes divided by clefts on each side of the lateral plate, which ultimately develop into somatic and splanchnic layers. The splanchnic layer with its underlying endoderm contributes to the formation of the viscera by differentiating into muscle, blood vessels, lymphatics, and connective tissues of the alimentary tract. The somatic layer contributes to the development of the abdominal wall. Proliferation of mesodermal cells in the embryonic abdominal wall results in the formation of an inverted U-shaped tube that in its early stages communicates freely with the extraembryonic coelom.

As the embryo enlarges and the abdominal wall components grow toward one another, the ventral open area, bounded by the edge of the amnion, becomes smaller. This results in the development of the umbilical cord as a tubular structure containing the omphalomesenteric duct, allantois, and fetal blood vessels, which pass to and from the placenta. By the end of the third month of gestation, the body wall has closed, except at the umbilical ring. Because the alimentary tract increases in length more rapidly than the coelomic cavity increases in volume, much of the developing gut protrudes through the umbilical ring to lie within the umbilical cord. As the coelomic cavity enlarges to accommodate the intestine, the latter returns to the peritoneal cavity so that only the omphalomesenteric duct, allantois, and fetal blood vessels pass through the shrinking umbilical ring. At birth, blood no longer courses through the umbilical vessels, and the omphalomesenteric duct has been reduced to a fibrous cord that no longer communicates with the intestine. After division of the umbilical cord, the umbilical ring heals rapidly by scarring.

Anatomy

There are nine layers to the abdominal wall—skin, subcutaneous tissue, superficial fascia, external oblique muscle, internal oblique muscle, transversus abdominis muscle, transversalis fascia, preperitoneal adipose and areolar tissue, and peritoneum (Fig. 45-1).

FIGURE 45-1 The nine layers of the anterolateral abdominal wall.

(From Thorek P: Anatomy in surgery, ed 2, Philadelphia, 1962, JB Lippincott, p 358.)

Subcutaneous Tissues

The subcutaneous tissue consists of Camper’s and Scarpa’s fascia. Camper’s fascia is the more superficial adipose layer that contains the bulk of the subcutaneous fat, whereas Scarpa’s fascia is a deeper denser layer of fibrous connective tissue contiguous with the fascia lata of the thigh. Approximation of Scarpa’s fascia aids in the alignment of the skin after surgical incisions in the lower abdomen.

Muscle and Investing Fascias

The muscles of the anterolateral abdominal wall include the external and internal oblique and transversus abdominis. These flat muscles enclose much of the circumference of the torso and give rise anteriorly to a broad flat aponeurosis investing the rectus abdominis muscles, termed the rectus sheath. The external oblique muscles are the largest and thickest of the flat abdominal wall muscles. They originate from the lower seven ribs and course in a superolateral to inferomedial direction. The most posterior of the fibers run vertically downward to insert into the anterior half of the iliac crest. At the midclavicular line, the muscle fibers give rise to a flat strong aponeurosis that passes anteriorly to the rectus sheath to insert medially into the linea alba (Fig. 45-2). The lower portion of the external oblique aponeurosis is rolled posteriorly and superiorly on itself to form a groove on which the spermatic cord lies. This portion of the external oblique aponeurosis extends from the anterior superior iliac spine to the pubic tubercle and is termed the inguinal or Poupart’s ligament. The inguinal ligament is the lower free edge of the external oblique aponeurosis posterior to which pass the femoral artery, vein, and nerve and the iliacus, psoas major, and pectineus muscles. A femoral hernia passes posterior to the inguinal ligament, whereas an inguinal hernia passes anterior and superior to this ligament. The shelving edge of the inguinal ligament is used in various repairs of inguinal hernia, including the Bassini and the Lichtenstein tension-free repair (see Chapter 46).

FIGURE 45-2 A, External oblique, internal oblique, and rectus abdominis muscles and anterior rectus sheath. B, Lateral view of the external oblique muscle and its aponeurosis as it enters the anterior rectus sheath. Inset, Origin of the external oblique muscle fibers from the lower ribs and their costal cartilages.

(From McVay C: Anson and McVay’s surgical anatomy, ed 6, Philadelphia, 1984, WB Saunders, pp 477–478).

The internal oblique muscle originates from the iliopsoas fascia beneath the lateral half of the inguinal ligament, from the anterior two thirds of the iliac crest and lumbodorsal fascia. Its fibers course in a direction opposite to those of the external oblique—that is, inferolateral to superomedial. The uppermost fibers insert into the lower five ribs and their cartilages (Fig. 45-3; see Fig. 45-2A). The central fibers form an aponeurosis at the semilunar line, which, above the semicircular line (of Douglas), is divided into anterior and posterior lamellae that envelop the rectus abdominis muscle. Below the semicircular line, the aponeurosis of the internal oblique muscle courses anteriorly to the rectus abdominis muscle as part of the anterior rectus sheath. The lowermost fibers of the internal oblique muscle pursue an inferomedial course, paralleling that of the spermatic cord, to insert between the symphysis pubis and pubic tubercle. Some of the lower muscle fascicles accompany the spermatic cord into the scrotum as the cremasteric muscle.

FIGURE 45-3 Lateral view of the internal oblique muscle. The external oblique muscle has been removed to show the underlying internal oblique muscle originating from the lower ribs and costal cartilages.

(From McVay C: Anson and McVay’s surgical anatomy, ed 6, Philadelphia, 1984, WB Saunders, p 479.)

The transversus abdominis muscle is the smallest of the muscles of the anterolateral abdominal wall. It arises from the lower six costal cartilages, spines of the lumbar vertebra, iliac crest, and iliopsoas fascia beneath the lateral third of the inguinal ligament. The fibers course transversely to give rise to a flat aponeurotic sheet that passes posterior to the rectus abdominis muscle above the semicircular line and anterior to the muscle below it (Fig. 45-4). The inferiormost fibers of the transversus abdominis originating from the iliopsoas fascia pass inferomedially along with the lower fibers of the internal oblique muscle. These fibers form the aponeurotic arch of the transversus abdominis muscle, which lies superior to Hesselbach’s triangle and is an important anatomic landmark in the repair of inguinal hernias, particularly Bassini’s operation and Cooper’s ligament repairs. Hesselbach’s triangle is the site of direct inguinal hernias and is bordered by the inguinal ligament inferiorly, lateral margin of the rectus sheath medially, and inferior epigastric vessels laterally. The floor of this triangle is composed of transversalis fascia.

FIGURE 45-4 A, Anterolateral view of the investing fascia of the transversus abdominis muscle and the muscle itself with the fascia removed (inset). The external and internal oblique muscles have been removed. Also note the appearance of the intercostal nerves lying between the fascia of the transversus abdominis muscle and internal oblique muscle. B, Anterior view of the transversus abdominis muscle (left) and the transversalis fascia (right). Note that the transversalis fascia is shown by reflecting the overlying transversus abdominis muscle medially.

(From McVay C: Anson and McVay’s surgical anatomy, ed 6, Philadelphia, 1984, WB Saunders, pp 480–481.)

The transversalis fascia covers the deep surface of the transversus abdominis muscle and, with its various extensions, forms a complete fascial envelope around the abdominal cavity (Fig. 45-5; see Fig. 45-4B). This fascial layer is regionally named for the muscles that it covers—for example, the iliopsoas fascia, obturator fascia, and inferior fascia of the respiratory diaphragm. The transversalis fascia binds together the muscle and aponeurotic fascicles into a continuous layer and reinforces weak areas where the aponeurotic fibers are sparse. This layer is responsible for the structural integrity of the abdominal wall and, by definition, a hernia results from a defect in the transversalis fascia.

FIGURE 45-5 Rectus abdominis muscle and contents of the rectus sheath. Note the semicircular line below which the posterior rectus sheath is absent; the rectus abdominis muscle overlies the transversalis fascia, preperitoneal areolar tissue, and peritoneum.

(From McVay C: Anson and McVay’s surgical anatomy, ed 6, Philadelphia, 1984, WB Saunders, p 482.)

The rectus abdominis muscles are paired muscles that appear as long, flat triangular ribbons wider at their origin on the anterior surfaces of the fifth, sixth, and seventh costal cartilages and the xiphoid process than at their insertion on the pubic crest and pubic symphysis. Each muscle is composed of long parallel fascicles interrupted by three to five tendinous inscriptions (Fig. 45-5), which attach the rectus abdominis muscle to the anterior rectus sheath. There is no similar attachment to the posterior rectus sheath. These muscles lie adjacent to each other, separated only by the linea alba. In addition to supporting the abdominal wall and protecting its contents, contraction of these powerful muscles flexes the vertebral column.

The rectus abdominis muscles are contained within the rectus sheath, which is derived from the aponeuroses of the three flat abdominal muscles. Superior to the semicircular line, this fascial sheath completely envelops the rectus abdominis muscle, with the external oblique and anterior lamella of the internal oblique aponeuroses passing anterior to the rectus abdominis and aponeuroses from the posterior lamella of the internal oblique muscle, transversus abdominis muscle, and transversalis fascia passing posterior to the rectus muscle. Below the semicircular line, all these fascial layers pass anterior to the rectus abdominis muscle, except the transversalis fascia. In this location, the posterior aspect of the rectus abdominis muscle is covered only by transversalis fascia, preperitoneal areolar tissue, and peritoneum.

The rectus abdominis muscles are held closely in apposition near the anterior midline by the linea alba. The linea alba consists of a band of dense, crisscrossed fibers of the aponeuroses of the broad abdominal muscles that extends from the xiphoid to the pubic symphysis. It is much wider above the umbilicus than below, thus facilitating the placement of surgical incisions in the midline without entering the right or left rectus sheath.

Preperitoneal Space and Peritoneum

The preperitoneal space lies between the transversalis fascia and parietal peritoneum and contains adipose and areolar tissue. Coursing through the preperitoneal space are the following:

1 Inferior epigastric artery and vein

2 Medial umbilical ligaments, which are the vestiges of the fetal umbilical arteries

3 Median umbilical ligament, which is a midline fibrous remnant of the fetal allantoic stalk or urachus

4 Falciform ligament of the liver, extending from the umbilicus to the liver

The round ligament, or ligamentum teres, is contained within the free margin of the falciform ligament and represents the obliterated umbilical vein, coursing from the umbilicus to the left branch of the portal vein (Fig. 45-6). The parietal peritoneum is the innermost layer of the abdominal wall. It consists of a thin layer of dense, irregular connective tissue covered on its inner surface by a single layer of squamous mesothelium.

FIGURE 45-6 Umbilicus. A, In the fetus, the umbilical vein superiorly and the two umbilical arteries and urachus inferiorly radiate from the umbilicus. B, View of the umbilicus from within the peritoneal cavity showing the round ligament of the liver (derived from the obliterated umbilical vein) superiorly and the median umbilical ligament (derived from the obliterated urachus) and medial umbilical ligaments (also called the lateral umbilical ligaments, derived from the obliterated umbilical arteries).

(From Thorek P: Anatomy in surgery, ed 2, Philadelphia, 1962, JB Lippincott, p 375.)

Vessels and Nerves of the Abdominal Wall

Vascular Supply

The anterolateral abdominal wall receives its arterial supply from the last six intercostals and four lumbar arteries, superior and inferior epigastric arteries, and deep circumflex iliac arteries (Fig. 45-7). The trunks of the intercostal and lumbar arteries, together with the intercostal, iliohypogastric, and ilioinguinal nerves, course between the transversus abdominis and internal oblique muscles. The distalmost extensions of these vessels pierce the lateral margins of the rectus sheath at various levels and communicate freely with branches of the superior and inferior epigastric arteries. The superior epigastric artery, one of the terminal branches of the internal mammary artery, reaches the posterior surface of the rectus abdominis muscle through the costoxiphoid space in the diaphragm. It descends within the rectus sheath to anastomose with branches of the inferior epigastric artery. The inferior epigastric artery, derived from the external iliac artery just proximal to the inguinal ligament, courses through the preperitoneal areolar tissue to enter the lateral rectus sheath at the semilunar line of Douglas. The deep circumflex iliac artery, arising from the lateral aspect of the external iliac artery near the origin of the inferior epigastric artery, gives rise to an ascending branch, which penetrates the abdominal wall musculature just above the iliac crest, near the anterior superior iliac spine.

FIGURE 45-7 Arteries and nerves of the anterolateral abdominal wall.

(From McVay C: Anson and McVay’s surgical anatomy, ed 6, Philadelphia, 1984, WB Saunders, p 501.)

The venous drainage of the anterior abdominal wall follows a relatively simple pattern in which the superficial veins above the umbilicus empty into the superior vena cava by way of the internal mammary, intercostal, and long thoracic veins. The veins inferior to the umbilicus—the superficial epigastric, circumflex iliac, and pudendal veins—converge toward the saphenous opening in the groin to enter the saphenous vein and become a tributary to the inferior vena cava (Fig. 45-8). The numerous anastomoses between the infraumbilical and supraumbilical venous systems provide collateral pathways whereby venous return to the heart may bypass an obstruction of the superior or inferior vena cava. The paraumbilical vein, which passes from the left branch of the portal vein along the ligamentum teres to the umbilicus, provides important communication between the veins of the superficial abdominal wall and portal system in patients with portal venous obstruction. In this setting, portal blood flow is diverted away from the higher pressure portal system through the paraumbilical veins to the lower pressure veins of the anterior abdominal wall. The dilated superficial paraumbilical veins in this setting are termed caput medusae.

FIGURE 45-8 Venous and lymphatic drainage of the anterolateral abdominal wall.

(From Thorek P: Anatomy in surgery, ed 2, Philadelphia, 1962, JB Lippincott, p 345.)

The lymphatic supply of the abdominal wall follows a pattern similar to the venous drainage. Those lymphatic vessels arising from the supraumbilical region drain into the axillary lymph nodes, whereas those arising from the infraumbilical region drain toward the superficial inguinal lymph nodes. The lymphatic vessels from the liver course along the ligamentum teres to the umbilicus to communicate with the lymphatics of the anterior abdominal wall. It is from this pathway that carcinoma in the liver may spread to involve the anterior abdominal wall at the umbilicus (Sister Mary Joseph node [or nodule]).

Innervation

The anterior rami of the thoracic nerves follow a curvilinear course forward in the intercostal spaces toward the midline of the body (see Fig. 45-7). The upper six thoracic nerves end near the sternum as anterior cutaneous sensory branches. Thoracic nerves 7 to 12 pass behind the costal cartilages and lower ribs to enter a plane between the internal oblique muscle and the transversus abdominis. The seventh and eighth nerves course slightly upward or horizontally to reach the epigastrium, whereas the lower nerves have an increasingly caudal trajectory. As these nerves course medially, they provide motor branches to the abdominal wall musculature. Medially, they perforate the rectus sheath to provide sensory innervation to the anterior abdominal wall. The anterior ramus of the 10th thoracic nerve reaches the skin at the level of the umbilicus and the 12th thoracic nerve innervates the skin of the hypogastrium.

The ilioinguinal and iliohypogastric nerves often arise in common from the anterior rami of the 12th thoracic and first lumbar nerves to provide sensory innervation to the hypogastrium and lower abdominal wall. The iliohypogastric nerve runs parallel to the 12th thoracic nerve to pierce the transversus abdominis muscle near the iliac crest. After coursing between the transversus abdominis muscle and internal oblique for a short distance, the nerve pierces the latter to travel under the external oblique fascia toward the external inguinal ring. It emerges through the superior crus of the external inguinal ring to provide sensory innervation to the anterior abdominal wall in the hypogastrium. The ilioinguinal nerve courses parallel to the iliohypogastric nerve, but closer to the inguinal ligament. Unlike the iliohypogastric nerve, the ilioinguinal nerve courses with the spermatic cord to emerge from the external inguinal ring, with its terminal branches providing sensory innervation to the skin of the inguinal region and scrotum or labium. The ilioinguinal nerve, iliohypogastric nerve, and genital branch of the genitofemoral nerve are commonly encountered during the performance of inguinal herniorrhaphy.

2 Infantile umbilical hernia

3 Acquired umbilical hernia

(From McVay C: Anson and McVay’s surgical anatomy, ed 6, Philadelphia, 1984, WB Saunders, p 576.)

Persistence of the intestinal end of the omphalomesenteric duct results in Meckel’s diverticulum. These true diverticula arise from the antimesenteric border of the small intestine, most often the ileum. A Rule of 2s is often applied to these lesions in that they are found in approximately 2% of the population, are within 2 feet of the ileocecal valve, are often 2 inches in length, and contain two types of ectopic mucosa (gastric and pancreatic). Meckel’s diverticula may be complicated by inflammation, perforation, hemorrhage, or obstruction. GI bleeding is caused by peptic ulceration of adjacent intestinal mucosa from hydrochloric acid secreted by ectopic parietal cells within the diverticulum. Intestinal obstruction associated with Meckel’s diverticulum is usually caused by intussusception or volvulus around an abnormal fibrous connection between the diverticulum and posterior aspect of the umbilicus. These lesions are discussed in Chapter 50.

Abnormalities Resulting from Persistence of the Allantois

The allantois is the cranialmost component of the embryologic ventral cloaca. The intra-abdominal portion is termed the urachus and connects the urinary bladder with the umbilicus, whereas the extra-abdominal allantois is contained within the umbilical cord. At the end of gestation, the urachus is converted into a fibrous cord that courses between the extraperitoneal urinary bladder and umbilicus as the median umbilical ligament. Persistence of part or all of the urachus may result in the formation of a vesicocutaneous fistula, with the appearance of urine at the umbilicus, an extraperitoneal urachal cyst presenting as a lower abdominal mass, or an urachal sinus with the drainage of a small amount of mucus. Treatment is excision of the urachal remnant with closure of the bladder, if necessary.

Acquired Abnormalities

Diastasis Recti

Diastasis recti refers to a thinning of the linea alba in the epigastrium and is manifested as a smooth midline protrusion of the anterior abdominal wall. The transversalis fascia is intact, and hence this is not a hernia. There are no identifiable fascial margins and no risk for intestinal strangulation. The presence of diastasis recti may be particularly noticeable to the patient on straining or when lifting the head from the pillow. Appropriate treatment consists of reassurance of the patient and family regarding the innocuous nature of this condition.

Anterior Abdominal Wall Hernias

Epigastric hernias occur at sites through which vessels and nerves perforate the linea alba to course into the subcutaneum. Through these openings, extraperitoneal areolar tissue and, at times, peritoneum may herniate into the subcutaneous tissue. Although these hernias are often small, they may produce significant localized pain and tenderness because of direct pressure of the hernia sac and its contents on the nerves emerging through the same fascial opening. Spigelian hernias occur through the fascia in the region of the semilunar line and present with localized pain and tenderness. The hernia sac is only rarely palpable because it is often small and tends to remain beneath the external oblique aponeurosis. Ultrasonography of the abdominal wall or computed tomography (CT) with thin cuts through the abdomen, after careful marking of the suspected site, should be diagnostic. Treatment consists of simple operative closure of the fascial defect. These hernias are discussed in Chapter 46.

Rectus Sheath Hematoma

Rectus sheath hematoma is an uncommon condition characterized by acute abdominal pain and the appearance of an abdominal wall mass. It is more common in women than men and in older than younger individuals. A review of 126 patients with rectus sheath hematomas treated at the Mayo Clinic found that almost 70% were receiving anticoagulants at the time of diagnosis. A history of nonsurgical abdominal wall trauma or injury is common (48%), as is the presence of a cough (29%).¹ In young women, rectus sheath hematomas have been associated with pregnancy.

Patients with rectus sheath hematomas usually present with the sudden onset of abdominal pain, which may be severe and is often exacerbated by movements requiring contraction of the abdominal wall. Physical examination will demonstrate tenderness over the rectus sheath, often with voluntary guarding. An abdominal wall mass may be noted in some patients, 63% in the Mayo Clinic series.¹ Abdominal wall ecchymosis, including periumbilical ecchymosis (Cullen’s sign) and blue discoloration in the flanks (Grey Turner’s sign), may be present if there is a delay from the onset of symptoms to presentation. The pain and tenderness associated with this process may be severe enough to suggest peritonitis. In those cases in which the hematoma expands into the perivesical and preperitoneal spaces, the hematocrit level may fall, although hemodynamic instability is uncommon.

Ultrasonography or CT will confirm the presence of the hematoma and localize it to the abdominal wall in almost all cases. Usually, these patients may be managed successfully with rest and analgesics and, if necessary, blood transfusion. In the Mayo Clinic series, almost 90% of patients were managed successfully in this manner.¹ In general, coagulopathies are corrected, although continued anticoagulation of selected patients may be prudent, depending on the indications for anticoagulation and seriousness of the bleeding. Progression of the hematoma may necessitate angiographic embolization of the bleeding vessel or, uncommonly, operative evacuation of the hematoma and hemostasis.

Malignancies of the Abdominal Wall

The most common primary malignancies of the abdominal wall are desmoid tumors and sarcomas. Although unusual, a variety of common cancers may metastasize through the bloodstream to the soft tissue of the abdominal wall, where it presents as a soft tissue mass. Metastatic melanoma, in particular, may present in this manner. Finally, transperitoneal seeding of the abdominal wall by intra-abdominal malignancies may complicate transabdominal biopsies or operative procedures.

Desmoid Tumor

Desmoid tumor, also known as fibromatosis or aggressive fibromatosis, is an uncommon neoplasm that occurs sporadically or as part of an inherited syndrome, most notably, familial adenomatous polyposis (FAP) and Gardner’s syndrome, an autosomal dominant syndrome of GI adenomatous polyps or adenocarcinoma, osteomas, and skin and soft tissue tumors. These tumors arise from fibroaponeurotic tissue and typically present as a slowly growing mass. Although they lack metastatic potential, they are locally aggressive and invasive, with a high propensity for recurrence.

Desmoid tumors are typically classified by location as extra-abdominal or extremity desmoids (i.e., those tumors occurring in the proximal extremities or limb girdle), abdominal wall tumors, and intra-abdominal desmoids, which involve the mesentery, pelvis, or bowel wall.

The frequency of desmoid tumors in the general population is 2.4 to 4.3 cases/million; this risk increases 1000-fold in patients with FAP.^2,³ The vast majority of desmoid tumors are sporadic, typically in young women during pregnancy or within a year of childbirth. Oral contraceptive use has also been associated with the occurrence of these tumors. These associations, combined with the detection of estrogen receptors within the tumor, suggest a regulatory role for estrogen in this disease.

Patients with a desmoid tumor present with an asymptomatic mass or with symptoms related to mass effect from the tumor. There is often a temporal association between the discovery of the tumor and an antecedent history of abdominal trauma or operation.³ Imaging (CT or MRI) is necessary to delineate the extent of tumor involvement fully, but otherwise there is no need to perform staging for metastatic disease. On CT, a desmoid tumor appears as a homogeneous mass arising from the soft tissue of the abdominal wall (Fig. 45-10). A desmoid tumor will appear as a homogeneous and isointense mass compared with muscle on T1-weighted MRI images, whereas T2-weighted images demonstrate greater heterogeneity and a signal slightly less intense than fat.

FIGURE 45-10 CT scan of the abdomen demonstrating a desmoid tumor arising within the left rectus sheath. The tumor appears as a homogeneous soft tissue mass.

Biopsy is required to establish the diagnosis. Core needle biopsy or incisional biopsy will demonstrate a tumor composed of bundles of spindle cells and an abundant fibrous stroma. The center of the tumor is often acellular, whereas the periphery contains most of the fibroblasts. The histology can be similar to that of a low-grade fibrosarcoma, but diagnosis is usually not difficult because the fibroblasts are highly differentiated and lack the mitotic activity found in malignancy. Immunohistochemistry can help clarify difficult diagnoses; the tumors typically stain positive for β-catenin, actin, and vimentin and stain negative for cytokeratin and S-100.

Resection of the tumor with a wide margin of normal tissue is currently considered the optimal treatment. Often, the extent of this resection will require abdominal wall reconstruction with local tissue flaps or mesh prostheses. The completeness of resection is an important prognostic factor; Stojadinovic and colleagues ⁴ have reported that 68% of desmoids tumors resected with a positive margin recur within 5 years, compared with none of the tumors in which the resection margin was free of disease.

Abdominal wall desmoids are responsive to radiation therapy, although the treatment effect is slow and may be progressive over several years. Radiotherapy alone is an acceptable treatment option for patients with unresectable desmoid tumors or tumors for which resection will be associated with high morbidity risks or major functional loss. A retrospective review from the M.D. Anderson Cancer Center has reported 10-year recurrence rates of 38% for surgery alone (27% for those with negative margins), 25% for combined surgery and radiation, and 24% for radiation therapy alone.⁵ It was also concluded that radiation therapy can assuage the adverse effect of positive margins on local tumor recurrence. Similar large studies have reported local control rates of approximately 80% with radiotherapy alone, rates that are consistently equivalent or even superior to surgery alone.⁶

Adjuvant radiation therapy is controversial, with most centers reserving this modality for patients with positive margins, or close margins, because of critical structures. The use of neoadjuvant radiation therapy is less well accepted than adjuvant radiation therapy because of the slow response times, often 1 year or more, with the potential for making subsequent abdominal wall reconstruction more difficult, and few studies demonstrating a clear benefit.

Estrogen receptor antagonists, nonsteroidal anti-inflammatory drugs (NSAIDs), and systemic chemotherapy have been used successfully in the treatment of patients with locally advanced, recurrent or unresectable desmoid tumors. The use of these agents in an adjuvant or neoadjuvant setting is not well studied and they would be best used in the setting of a clinical trial.

The detection of estrogen receptors on desmoids tumors, as well as the association with pregnancy and oral contraceptives, provide some support for the use of antiestrogens, such as tamoxifen. Clinical improvement has been reported in 43% of patients receiving antiestrogens, although the response rate varies among studies. Tumor responses to antiestrogens are slow in onset but often last for several years.^7,⁸ Most reports of NSAID treatment use sulindac but indomethacin has also been used. A study using combination high-dose tamoxifen and sulindac recommended this regimen as initial treatment for FAP-associated desmoid tumors.⁹

Various cytotoxic chemotherapy regimens have been used in the treatment of patients with inoperable desmoids. Methotrexate with vinblastine, doxorubicin-based therapy, and ifosfamide-based regimens have been reported, with positive responses in 20% to 40% of patients.^7,¹⁰ For desmoids with rapid growth, medical oncologists may recommend therapies typically used for sarcomas, such as doxorubicin and dacarbazine. Recent reports have also suggested imatinib, a tyrosine kinase inhibitor, as another effective treatment option for patients with these tumors.¹¹

Abdominal Wall Sarcoma

Abdominal wall sarcoma are classified as truncal sarcoma—including the chest or abdominal wall—and account for 10% to 20% of sarcomas overall. In general, sarcomas are rare and abdominal wall sarcomas are exceedingly rare. Similar to desmoid tumors, these neoplasms most often present as a painless mass, although as many as one third of patients with abdominal wall sarcomas will have pain at the site of the tumor. Pertinent history, such as a history of retinoblastoma, FAP, neurofibromatosis, radiation therapy, or Li-Fraumeni syndrome, should be sought. The differential diagnosis includes many common conditions, such as lipomas, hematomas, ventral hernias, endometriosis, and inflammatory processes, such as needle site granulomas in diabetics. Histologic subtypes include liposarcoma, fibrosarcoma, leiomyosarcoma, rhabdomyosarcoma, and malignant fibrous histiocytoma.

Axial imaging with MRI or CT will provide important information regarding the location and extent of the tumor as well as involvement of contiguous structures. Chest CT should be included to rule out metastatic disease. Definitive diagnosis requires biopsy, which may be performed with a core needle or by incision. The accuracy of core needle biopsy is consistently reported as more than 90% and can be performed under CT guidance for deep lesions. If an incisional biopsy is performed, it is optimally done by the surgeon who will perform the definitive resection; it should be oriented in the same plane as the underlying muscle to minimize unnecessary tissue loss during the definitive procedure and facilitate reconstruction. No attempt is made to develop tissue flaps around the lesion, and hemostasis is meticulous to avoid dissemination of the tumor along the tissue planes by a postoperative hematoma.

Definitive treatment of abdominal wall sarcomas is resection with tumor-free margins, with most surgeons attempting to obtain at least a 2-cm margin around the tumor. Lymph node metastases are rare (2% to 3%). Reconstruction of the abdominal wall defect may be accomplished primarily, with myocutaneous flaps, or with prosthetic meshes, depending on the site and extent of resection. Response rates with radiation and chemotherapy are low.

Soft tissue sarcomas are discussed in greater detail in Chapter 33.

Metastatic Disease

Metastases to the abdominal wall may occur by direct seeding of the abdominal wall during biopsy or resection of an intra-abdominal malignancy or by hematogenous spread of an advanced tumor. The risk of tumor implantation at the port site after laparoscopic colon resection for adenocarcinoma is 0.9% and has been shown in randomized controlled trials to be no different than the risk of tumor recurrence in the wound after open colon resections.¹² The most common tumors that metastasize to soft tissue are lung, colon, melanoma, and renal cell tumors. Although metastases to soft tissue are unusual, the abdominal wall is the site of such recurrence in approximately 20% of cases.¹³ Similar to desmoids tumors or sarcomas, metastases to the abdominal wall present as a painless mass. Immunohistochemistry staining of the tumor may allow specific identification of the type of primary tumor and facilitate differentiation from primary sarcomas of the abdominal wall. The Sister Mary Joseph nodule is often described and seldom seen but represents a palpable nodule in the region of the umbilicus representing metastatic abdominal or pelvic cancer.

Symptoms of Intra-Abdominal Disease Referred to the Abdominal Wall

Abdominal pain may be categorized as visceral, somatoparietal, and referred. Visceral pain is caused by stimulation of visceral nociceptors by inflammation, distention, or ischemia. The pain is dull in nature and poorly localized to the epigastrium, periumbilical regions, or hypogastrium, depending on the embryonic origin of the organ involved. Inflammation of the stomach, duodenum, and biliary tract (derivatives of the embryonic foregut) localizes visceral pain to the epigastrium. Stimulation of nociceptors in midgut-derived organs (small intestine, appendix, right colon) causes the sensation of pain in the periumbilical region, whereas inflammation or distention of hindgut-derived organs (left colon, rectum) causes hypogastric pain. The pain is felt in the midline because these organs transmit sympathetic sensory afferents to both sides of the spinal cord. The pain is poorly localized because the innervation of most viscera is multisegmental and contains fewer nerve receptors than highly sensitive organs such as the skin. The pain is often characterized as cramping, burning, or gnawing and may be accompanied by secondary autonomic effects such as sweating, restlessness, nausea, vomiting, perspiration, and pallor.

Somatoparietal pain arises from inflammation of the parietal peritoneum; it is more intense and more precisely localized than visceral pain. The nerve impulses mediating parietal pain travel within the somatosensory spinal nerves and reach the spinal cord in the peripheral nerves corresponding to the cutaneous dermatomes from the T6 to the L1 region. Lateralization of parietal pain is possible because only one side of the nervous system innervates a given part of the parietal peritoneum.

The difference between visceral and somatoparietal pain is well illustrated by the pain associated with acute appendicitis, in which the early, vague, periumbilical visceral pain is followed by the localized somatoparietal pain at McBurney’s point. The visceral pain is produced by distention and inflammation of the appendix, whereas the localized somatoparietal pain in the right lower quadrant of the abdomen is caused by extension of the inflammation to the parietal peritoneum.

Referred pain is felt in anatomic regions remote from the diseased organ. This phenomenon is caused by convergence of visceral afferent neurons innervating an injured or inflamed organ with somatic afferent fibers arising from another anatomic region. This occurs within the spinal cord at the level of second-order neurons. Well-known examples of referred pain include shoulder pain on irritation of the diaphragm, scapular pain associated with acute biliary tract disease, and testicular or labial pain caused by retroperitoneal inflammation.

Peritoneum And Peritoneal Cavity

Anatomy

The peritoneum consists of a single sheet of simple squamous epithelium of mesodermal origin, termed mesothelium, lying on a thin connective tissue stroma. The surface area is 1.0 to 1.7 m², approximately that of the total body surface area. In males, the peritoneal cavity is sealed, whereas in females it is open to the exterior through the ostia of the fallopian tubes. The peritoneal membrane is divided into parietal and visceral components. The parietal peritoneum covers the anterior, lateral, and posterior abdominal wall surfaces and the inferior surface of the diaphragm and the pelvis. The visceral peritoneum covers most of the surface of the intraperitoneal organs (i.e., stomach, jejunum, ileum, transverse colon, liver, spleen) and the anterior aspect of the retroperitoneal organs (i.e., duodenum, left and right colon, pancreas, kidneys, adrenal glands).

The peritoneal cavity is subdivided into interconnected compartments or spaces by 11 ligaments and mesenteries. The peritoneal ligaments or mesenteries include the coronary, gastrohepatic, hepatoduodenal, falciform, gastrocolic, duodenocolic, gastrosplenic, splenorenal, and phrenicocolic ligaments and the transverse mesocolon and small bowel mesentery (Fig. 45-11). These structures partition the abdomen into nine potential spaces—right and left subphrenic, subhepatic, supramesenteric and inframesenteric, right and left paracolic gutters, pelvis, and lesser space. These ligaments, mesenteries, and peritoneal spaces direct the circulation of fluid in the peritoneal cavity and thus may be useful in predicting the route of spread of infectious and malignant diseases. For example, perforation of the duodenum from peptic ulcer disease may result in the movement of fluid (and the development of abscesses) in the subhepatic space, right paracolic gutter, and pelvis. The blood supply to the visceral peritoneum is derived from the splanchnic blood vessels, whereas the parietal peritoneum is supplied by branches of the intercostals, subcostal, lumbar, and iliac vessels. The innervation of the visceral and parietal peritoneum is discussed earlier.