Patologia do peritoneu e retroperitoneu

Question 1

Anatomy

Answer 1

• The peritoneum consists of a single sheet of simple squamous epithelium of mesodermal origin, termed mesothelium, lying on a thin connective tissue stroma.
• The peritoneal membrane is divided into parietal and visceral components

Question 2

Physiology

Answer 2

• The peritoneum is a bidirectional, semipermeable membrane that controls the amount of fluid in the peritoneal cavity, pro- motes the sequestration and removal of bacteria from the peri- toneal cavity, and facilitates the migration of inflammatory cells from the microvasculature into the peritoneal cavity.
• The amount of fluid in the peritoneal cavity may increase to many liters in some dis- eases, such as cirrhosis, nephrotic syndrome, and peritoneal carcinomatosis.
• The peritoneum and peritoneal cavity respond to infection in five ways:
  1. Bacteria are rapidly removed from the peritoneal cavity through the diaphragmatic stomata and lymphatics.
  2. Peritoneal macrophages release proinflammatory mediators that promote the migration of leukocytes into the peritoneal cavity from the surrounding microvasculature.
  3. Degranulation of peritoneal mast cells releases hista- mine and other vasoactive products, causing local vasodilation and the extravasation of protein-rich fluid containing complement and immunoglobulins into the peritoneal space.
  4. Protein in the peritoneal fluid opsonizes bacteria, which, along with activation of the complement cascade, promotes neutrophil- and macrophage- mediated bacterial phagocytosis and destruction.
  5. Bacteria become sequestered within fibrin matrices, thereby promoting abscess formation and limiting the generalized spread of the infection.

Question 3

Peritoneal Disorders

Ascites

Answer 3

• Ascites is the pathologic accumulation of fluid in the peritoneal cavity.
• Cirrhosis is the most common cause of ascites in the United States, accounting for approximately 85% of cases
• The onset of ascites is an important prognostic factor for poor outcome in patients with cirrhosis because of its association with the occurrence of spontaneous bacterial peritonitis, renal failure, a worsened quality of life, and an increased likelihood of death within 2 to 5 years
• The two principal factors underlying the formation of ascites in cirrhotic patients are renal sodium and water retention and portal hypertension.
• Renal sodium retention is driven by activation of the renin-angiotensin-aldosterone and sympathetic nervous systems, which cause proximal and distal renal tubule sodium reabsorption.
• It is postulated that the abnormal release of nitric oxide within the splanchnic circulation causes vasodila- tion and a decrease in the effective circulating blood volume. Renin, aldosterone, and other hormones are generated as a coun- terregulatory mechanism to restore the effective circulating blood volume to normal.
  Portal hypertension is produced by postsinusoidal vascular obstruction from the deposition of col- lagen in the cirrhotic liver. Increased hydrostatic pressure within the hepatic sinusoids and splanchnic vasculature drives the extravasation of fluid from the microvasculature into the extra- cellular compartment. Ascites results when the capacity of the lymphatic system to return this fluid to the systemic circulation is overwhelmed. Some recent studies have reviewed the patho- physiology underlying fluid retention, hyponatremia, and ascites formation that characterizes patients with cirrhosis

-Obstruction of the portal or hepatic venous blood flow in the absence of cirrhosis (e.g., portal vein thrombosis or Budd- Chiari syndrome, respectively) also causes ascites formation by increasing hydrostatic pressure within the splanchnic microvas- culature. A similar pressure-based mechanism contributes to ascites formation in patients with heart failure, although the release of vasopressin and renin-angiotensin-aldosterone also promote sodium and water retention in these patients.

-Patients with malignancies develop ascites by one of three mechanisms:
1. Multiple hepatic metastases cause portal hyperten- sion by narrowing or occluding branches of the portal venous system.
2. Malignant cells scattered throughout the peritoneal cavity release protein-rich fluid into the peritoneal cavity, as in peritoneal carcinomatosis.
3. Obstruction of retroperitoneal lymphatics by a tumor, such as lymphoma, causes rupture of major lymphatic channels and the leakage of chyle into the peritoneal cavity.
Finally, ascites may result from the leakage of pancreatic
juice, bile, or lymph into the peritoneal cavity after an iatrogenic or inflammatory disruption of a major pancreatic, bile, or lym- phatic duct

Question 4

Clinical presentation and Diagnosis

Answer 4

The diagnosis of ascites is made on the basis of the medical history and appearance of the abdomen. Obviously, risk factors for hepatitis or cirrhosis are sought, as is evidence of cardiac or renal disease or malignancy. A full bulging abdomen with dullness of the flanks on percussion is suggestive of the presence of ascites. Approximately 1.5 liters of fluid must be present before dullness can be detected by percussion. Physical evidence of cirrhosis is also sought, such as palmar erythema, dilated abdominal wall collateral veins, and multiple spider angiomas. Patients with cardiac ascites have impressive jugular venous distention and other evidence of con- gestive heart failure.

Question 5

Ascitic Fluid Analysis

Answer 5

• Paracentesis with ascitic fluid analysis is the most rapid and cost-effective method of determining the cause of ascites and should be performed on patients with new-onset ascites
• Another important indication for early paracentesis in a patient with ascites is the occurrence of signs and symptoms of infection, such as abdominal pain or tenderness, fever, encepha- lopathy, hypotension, renal failure, acidosis, and/or leukocytosis
• Paracentesis can be performed safely in most patients, including those with cirrhosis and mild coagulopathy.
• It is usually per- formed in the lower abdomen, with the left lower quadrant preferred over the right. Ultrasound guidance may be useful in obese patients and in those with a history of laparotomy.
• Examination of the ascitic fluid begins with its gross appearance. Normal ascitic fluid is slightly yellow and transpar- ent. The presence of more than 5000 leukocytes/mm3 will cause the fluid to be cloudy, whereas ascitic fluid specimens with fewer than 1000 cells/mm3 are almost clear. Blood in the ascitic fluid may be caused by a traumatic tap, in which case the fluid may be blood-streaked and will often clot unless immediately trans- ferred to a tube containing an anticoagulant. Nontraumatic blood-tinged ascitic fluid does not clot because the required factors have been depleted by previous clotting in the peritoneal cavity. Lipid in the ascitic fluid, such as that which accompanies chylous ascites, causes the fluid to appear opalescent, ranging from cloudy to completely opaque. If placed in the refrigerator for 48 to 72 hours, the lipids usually layer out.
• Examination of the ascitic fluid begins with its gross appearance. Normal ascitic fluid is slightly yellow and transpar- ent. The presence of more than 5000 leukocytes/mm3 will cause the fluid to be cloudy, whereas ascitic fluid specimens with fewer than 1000 cells/mm3 are almost clear. Blood in the ascitic fluid may be caused by a traumatic tap, in which case the fluid may be blood-streaked and will often clot unless immediately trans- ferred to a tube containing an anticoagulant. Nontraumatic blood-tinged ascitic fluid does not clot because the required factors have been depleted by previous clotting in the peritoneal cavity. Lipid in the ascitic fluid, such as that which accompanies chylous ascites, causes the fluid to appear opalescent, ranging from cloudy to completely opaque. If placed in the refrigerator for 48 to 72 hours, the lipids usually layer out.
• The most valuable laboratory tests on ascitic fluid are the cell count, differential, and determination of ascitic fluid albumin and total protein concentrations. The leukocyte count in uncomplicated cirrhotic ascites is usually less than 500 cells/ mm3, and approximately 50% of these cells are neutrophils. More than 250 neutrophils/mm3 of ascitic fluid suggests an acute inflammatory process, the most common of which is spon- taneous bacterial peritonitis. In this case, the total white blood cell and absolute neutrophil counts are elevated, with neutro- phils accounting for more than 70% of the total cell count
• The serum-ascites albumin gradient (SAAG) is the most reliable method to categorize the various causes of ascites. The SAAG is calculated by measuring the albumin concentration of serum and ascitic fluid specimens and subtracting the ascitic fluid value from the serum value. If the SAAG is greater than or equal to 1.1 g/dL, the patient has portal hypertension; a SAAG of less than 1.1 g/dL is consistent with the absence of portal hypertension. Examples of high- and low-gradient causes of ascites are shown in Table 45-1. The accuracy of this measure- ment in predicting the presence or absence of portal hyperten- sion is approximately 97%.

Question 6

treatment of ascites in Cirrhotic patients

Answer 6

• The standard treatment protocol for patients with ascites caused by cirrhosis is a stepwise approach beginning with sodium restriction, diuretic therapy, and paracentesis
• The initial goal of medical therapy is to induce a state in which renal sodium excretion exceeds sodium intake, a situation that will reduce the extracellular volume and improve ascites
• Large-volume paracentesis, in which more than 5 liters of ascites fluid is removed from the peritoneal cavity, may be useful for patients with ascites that has been unresponsive to sodium restriction and diuretic treatment;
• The continuation of diuretics and salt restriction will prevent or delay the reaccumulation of ascites after paracen- tesis. Others have suggested that weekly albumin administra- tion, independent of large-volume paracentesis, may be a useful adjunct to salt restriction and diuretic therapy in patients with refractory ascites. Transjugular intrahepatic portosystemic shunt and, ultimately, hepatic transplantation have been used to manage ascites refractory to simpler, less invasive options.

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Question 7

Chylous ascites

Answer 7

Chylous ascites is the collection of chyle in the peritoneal cavity and may result from one of three principal mechanisms:

1. Obstruction of major lymphatic channels at the base of the mesentery or the cisterna chyli, with exudation of chyle from dilated mesenteric lymphatics
2. Direct leakage of chyle through a lymphoperitoneal fistula caused by abnormal or injured retroperitoneal lymphatic vessels
3. Exudation of chyle through the walls of retroperitoneal megalymphatics, without a visible fistula or thoracic duct obstruction

In adults, the most common cause of chylous ascites is an
intra-abdominal malignancy obstructing the lymphatic channels at the base of the mesentery or in the retroperitoneum
Lym- phoma is the most common malignancy associated with chylous ascites, although chylous ascites has also been associated with ovarian, colon, renal, prostate, pancreatic, and gastric malignancies. Carcinoid tumors may cause chylous ascites by obstructing the lymphatics at the base of the mesentery through direct invasion and the dense fibrosis characteristic of this neo- plasm
Chylous ascites may also result from injury of the retro- peritoneal lymphatics during surgical procedures such as operations on the abdominal aorta and retroperitoneal lymph node dissections. Blunt and penetrating traumatic injuries are also important causes of chylous ascites, particularly in children. Chylous ascites in children may be caused by congenital lym- phatic abnormalities, such as primary lymphatic hypoplasia, resulting in lower extremity lymphedema, chylothorax, and chylous ascites.

Patients with chylous ascites most often present with pain- less abdominal distention. Malnutrition and dyspnea occur in approximately 50% of cases. Paracentesis yields a characteristic milky fluid with a high protein and fat content. The SAAG will be less than 1.1 mg/dL and the triglyceride level will be higher than that of plasma, often two to eight times higher that of plasma. CT, lymphoscintigraphy, and lymphangiography may provide information regarding the site of obstruction, although the latter two modalities are rarely available.

Question 8

Management of patients with chylous ascites includes the maintenance or improvement of nutrition, reduction in the rate of chyle formation, and correction of the underlying disease process. A low-fat, medium-chain triglyceride diet, combined with diuretics, has been used successfully to treat adults with chylous ascites complicating retroperitoneal lymph node dissec- tions. It is postulated that reducing long-chain triglyceride intake will reduce the rate of chyle flow because their metabolites are transported through the splanchnic lymphatics as chylomi- crons. In contrast, medium-chain triglycerides are directly absorbed by enterocytes and transported to the liver through the splanchnic blood vessels as free fatty acids and glycerol. Fasting with total parenteral nutrition, alone or in combination with somatostatin, has also been used successfully to manage patients with retroperitoneal lymphatic leak. Paracentesis may temporar- ily relieve the dyspnea and abdominal discomfort associated with chylous ascites; however, repeated paracentesis leads to hypopro- teinemia and malnutrition. Experience with peritoneovenous shunts to treat chylous ascites has generally been disappointing. Surgical exploration of the abdomen and retroperitoneum is generally reserved for patients who fail to improve with nonop- erative management. In some cases, the application of fibrin glue has been a beneficial adjunct to surgical exploration of the retroperitoneum.

Answer 8

continuação

Question 9

peritonitis

Answer 9

Peritonitis is inflammation of the peritoneum and peritoneal cavity, usually caused by a localized or generalized infection.

• Primary peritonitis results from bacterial, chlamydial, fungal, or mycobacterial infection in the absence of perforation of the GI tract, whereas secondary peritonitis occurs in the setting of GI perforation
• causes of secondary bacterial peritonitis include peptic ulcer disease, acute appendicitis, colonic diverticulitis, and pelvic inflammatory disease.

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Question 10

Spontaneous Bacterial Peritonitis

Answer 10

• Spontaneous bacterial peritoni- tis (SBP) is defined as a bacterial infection of ascitic fluid in the absence of an intra-abdominal, surgically treatable source of infection. Although usually associated with cirrhosis, SBP may also occur in patients with nephrotic syndrome and, less com- monly, congestive heart failure. It is extremely rare for patients with ascitic fluid containing a high protein concentration to develop SBP, such as those with peritoneal carcinomatosis. The most common pathogens in adults with SBP are the aerobic enteric flora Escherichia coli and Klebsiella pneumoniae. In chil- dren with nephrogenic or hepatogenic ascites, group A strepto- coccus, Staphylococcus aureus, and Streptococcus pneumoniae are common isolates.
• Bacterial translocation from the GI tract is thought to be an important step in the pathogenesis of SBP. Impaired GI motility in cirrhotics is thought to alter normal gut microflora and impaired local and systemic immune function prevents the effective clearance of translocated bacteria from the mesenteric lymphatics and bloodstream. A low protein concentration in ascitic fluid prevents effective opsonization of bacteria and hence clearance by macrophages and neutrophils.\
• The diagnosis of SBP is made initially by demonstrating more than 250 neutrophils/mm3 of ascitic fluid in a clinical setting consistent with this diagnosis—that is, abdominal pain, fever, or leukocytosis in a patient with low-protein ascites. It is unusual to document bacterascites on Gram staining of ascitic fluid, and delay of appropriate antibiotic management until the ascitic fluid cultures grow bacterial isolates risks the development of overwhelming infection and death. Bedside screening of ascitic fluid for leukocyte esterase, using colorimetric leukocyte esterase reagent strips, has been used to shorten the time from paracentesis to treatment, although its widespread use remains controversial

Question 11

Tuberculous Peritonitis

Answer 11

Tuberculosis is common in impoverished areas of the world and is encountered with increasing frequency in the United States and other developed countries. Since 1985, the number of cases of tuberculosis in the United States and European nations has increased dramatically as the number of immigrants, refugees, and individuals with acquired immuno- deficiency syndrome (AIDS) has increased. Others have described an association between peritoneal tuberculosis and alcoholic cirrhosis and chronic renal failure.25 Peritoneal tuber- culosis is the sixth most common site of extrapulmonary tuber- culosis, after lymphatic, genitourinary, bone and joint, miliary, and meningeal. Most cases result from reactivation of latent peritoneal disease that had been previously established hematog- enously from a primary pulmonary focus. Only approximately 17% of cases are associated with active pulmonary disease.

• The illness often presents insidiously, with patients having had symptoms for several weeks to months at the time of pre- sentation. Abdominal swelling caused by ascites formation is the most common symptom, occurring in more that 80% of cases. Similarly, most patients complain of a nonlocalized, vague abdominal pain. Constitutional symptoms such as low-grade fever and night sweats, weight loss, anorexia, and malaise are reported in approximately 60% of patients. The concomitant presence of other chronic conditions such as uremia, cirrhosis, and AIDS makes these symptoms difficult to interpret. Abdomi- nal tenderness is present on palpation in approximately 50% of patients with peritoneal tuberculosis.25
• A positive tuberculin skin test is present in most cases, whereas only approximately 50% of these patients will have an abnormal chest radiograph. The ascitic fluid SAAG is less than 1.1 g/dL, consistent with a high protein concentration in the ascitic fluid. Microscopic examination of the ascites shows erythrocytes and an increased number of leukocytes, most of which are lymphocytes. Recently, measurement of ascitic fluid adenosine deaminase activity and polymerase chain reaction assays have been used as noninvasive and rapid tests for tuberculous peritonitis. Ascitic fluid adenos- ine deaminase activity, in particular, appears to be highly sensi- tive and specific for tuberculous peritonitis.
• Abdominal imaging with ultrasound or CT may suggest the diagnosis but lacks the sensitivity and specificity to be diag- nostic. Ultrasound may demonstrate the presence of echogenic material in the ascitic fluid, seen as fine mobile strands or par- ticulate matter. CT will demonstrate the thickened and nodular mesentery with mesenteric lymphadenopathy and omental thickening.
• The diagnosis is made by laparoscopy with directed biopsy of the peritoneum. In more than 90% of cases, laparoscopy demonstrates a number of whitish nodules (<5 mm) scattered over the visceral and parietal peritoneum; histologic examination demonstrates caseating granulomas. Multiple adhesions are commonly present between the abdominal organs and parietal peritoneum. The gross appearance of the peritoneal cavity is similar to that of peritoneal carcinomatosis, sarcoidosis, and Crohn’s disease, thus reiterating the importance of biopsy.
• Treatment of peritoneal tuberculosis consists of antituber- culous drugs. Drug regimens useful in treating pulmonary tuberculosis are also effective for peritoneal disease, with isonia- zid and rifampin daily for 9 months being a commonly used and effective regimen. The presence of associated alcoholic cir- rhosis may complicate the use of these agents because of hepatotoxicity.

Question 12

Peritonitis Associated With Chronic Ambulatory Peritoneal Dialy- sis

Answer 12

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Question 13

Malignant Neoplasms of the Peritoneum

Answer 13

Primary malignancies of the peritoneum are rare; these include malignant mesothelioma, primary peritoneal carcinoma, and sarcomas (e.g., angiosarcoma). Most malignancies that involve the peritoneum are transperitoneal metastases originating from carcinomas of the GI tract (especially the stomach, colon, and pancreas), the genitourinary tract (usually, ovarian) or, more rarely, an extra-abdominal site (e.g., breast). When metastatic cancer deposits diffusely coat the visceral and parietal peritoneum, these peritoneal metastases are referred to as carcinomatosis

Question 14

pseudomyxoma peritoneu

Answer 14

Pseudomyxoma peritonei describes mucinous ascites arising from a ruptured ovarian or appendiceal adenocarcinoma. In this disease, the peritoneum becomes coated with a mucus-secreting tumor that fills the peritoneal cavity with tenacious semisolid mucus and large, loculated cystic masses.

• here we will focus on pseudomyx- oma peritonei resulting from ruptured epithelial neoplasms of the appendix
• Pseudomyxoma peritonei occurs most commonly in patients who are 40 and 50 years of age and occurs with equal frequency in men and women. Patients are often asymptomatic until late in the course of their disease. On presentation, they will often describe a global deterioration in their health long before the diagnosis is made. Symptoms of abdominal pain and distention and nonspecific complaints are common. Physical examination may reveal a new hernia, ascites, distended abdomen with nonshifting dullness and, occasionally, a palpable abdomi- nal mass.
• CT of the chest, abdomen, and pelvis may provide impor- tant information regarding the diagnosis and the ability to resect the tumor completely or perform an adequate cytoreduction. The latter is often limited by involvement of the small bowel or porta hepatis by tumor. Preoperative colonoscopy will differenti- ate a mucinous neoplasm of the appendix from that arising from the colon. Often, the diagnosis is made at laparotomy, when the surgeon is presented with a peritoneal cavity containing tena- cious semisolid mucus and large, loculated cystic masses. If the surgeon is unprepared to perform a definitive procedure, the best approach is to establish the diagnosis by the least invasive pro- cedure possible and relieve symptoms of intestinal obstruction, if present. The patient can then be referred to a center experi- enced in the management of these patients.
• The treatment of patients with pseudomyxoma peritonei involves resection of as much of the tumor as possible (cytore- duction) and intraperitoneal heated chemotherapy (IPHC). Operative management includes omentectomy, stripping of involved peritoneum, resection of involved organs, and appen- dectomy, if not previously performed. There should be no resid- ual tumor nodules larger than 2 mm in diameter after resection to facilitate penetration of the chemotherapy into any residual disease. Generally, a right hemicolectomy is performed for these tumors, although a review of 501 patients with mucinous tumors of the appendix has suggested that this is unnecessary if the resection margin at appendectomy is negative.28 IPHC can be performed using an open technique, in which the abdomen is left open to ensure adequate chemotherapy distribution through- out the peritoneal cavity, or a closed technique, in which the abdomen is closed after inflow and outflow cannulas are placed. The latter allows for easier maintenance of hyperthermia (Fig. 45-12). There are many variations of surgical technique and chemotherapy administration but one commonly used technique 29 has been reported extensively by Stewart and associates.

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