Appendix and Peritoneum Lecture Notes PDF

APPENDIX AND PERITONEUM Dr. M Jele Department of Anatomical Pathology Date: 16 August 2022 LECTURE OUTLINE APPENDIX Normal histology Congenital/developmental/acquired anatomic abnormalities Inflammatory diseases Malignancy...

APPENDIX AND PERITONEUM Dr. M Jele Department of Anatomical Pathology Date: 16 August 2022 LECTURE OUTLINE APPENDIX Normal histology Congenital/developmental/acquired anatomic abnormalities Inflammatory diseases Malignancy Benign Malignant PERITONEUM Normal histology Inflammatory diseases Neoplastic disorders of the peritoneal cavity and retroperitoneal space Appendix o Normal true diverticulum of the caecum o Adult appendix: average 8 cm in length Appendix Has no known function Has the same four layers as the remainder of the gut and possesses a colonic-type mucosa. Has an extremely rich lymphoid tissue of the mucosa and submucosa In young individuals forms an entire layer of germinal follicles and lymphoid pulp. In the elderly, particularly the distal portion, sometimes undergoes fibrous obliteration Congenital/developmental/acquired anatomic abnormalities Atypical location Duplication Type A: incomplete duplication. 1 base between the two appendices Type B: complete duplication. The first appendix arises from the normal position, the second at various sites of the colon Type C: complete duplication of the caecum with each having its own appendix Absence and atresia o Rare o Absence: an abnormally located appendix must be excluded o Congenital absence may be associated with other congenital abnormalities like congenital diaphragmatic hernia o Atresia may be associated with atresia of the entire ileocaecal region Appendiceal septa Incomplete or complete septa formation within the appendiceal lumen Seen in children and young adults Contributing factors: congenital abnormality, postinflammatory fusion of mucosal folds, ischaemia ( due to thrombosed vessels) Diverticular disease of the appendix Congenital: muscular wall Acquired: eg cystic fibrosis (no muscular wall) Fibrous obliteration of the appendiceal lumen Obliteration of the appendiceal lumen: spindle cells within a collagenous and myxoid background The distal tip of the appendix is usually affected ACUTE APPENDICITIS Acute Appendicitis Most common in adolescents and young adults May occur in any age group. Males are affected slightly more often than females The diagnosis can be difficult to confirm preoperatively Acute Appendicitis: Causes Obstruction with superimposed bacterial infection o Faecolith ( small stone-like mass of stool) o Foreign body o Lymphoid hyperplasia o Tumour or polyp o Mucin accumulation (like in cystic fibrosis) Acute Appendicitis: Causes Infection o Parasitic: amoebiasis, Cryptosporidium, Enterobius vermicularis and Schistosomiasis. o Bacterial: Yersinia, Campylobacter,MTB o Viral: Epstein-Barr virus, cytomegalovirus, varicella zoster virus, measles virus o Fungal: Candida, mucormyosis, aspergillosis Acute Appendicitis: Causes Inflammatory bowel disease Stump appendicitis Diverticular disease Pathogenesis It is thought to be initiated by progressive increases in intraluminal pressure that compromise venous outflow. Ischaemic injury and stasis of luminal contents, which favour bacterial proliferation, trigger inflammatory responses including tissue oedema and neutrophilic infiltration of the lumen, muscular wall, and periappendiceal soft tissues Morphology In early acute appendicitis Subserosal vessels are congested There is a modest perivascular neutrophilic infiltrate within all layers of the wall. Inflammatory reaction transforms the normal glistening serosa into a dull, granular, erythematous surface. Morphology Diagnosis requires neutrophilic infiltration of the muscularis propria Mucosal neutrophils and focal superficial ulceration Serosal fibrinopurulent reaction occurs in more severe cases Morphology Later, focal abscesses may form within the wall (acute suppurative appendicitis) In severe cases, haemorrhagic ulceration and gangrenous necrosis that extends to the serosa creating acute gangrenous appendicitis can occur This is often followed by rupture and suppurative peritonitis Clinical features Most often signs and symptoms are absent In young children & the very elderly the diagnosis can be difficult since o they are more likely to have atypical clinical presentations. o other causes of abdominal emergencies are prevalent in these populations Clinical features Symptoms Periumbilical pain in the right lower quadrant Nausea, vomiting, low-grade fever A mildly elevated peripheral white cell count. Right flank or pelvic pain in a retrocaecal appendix and a malrotated colon may give rise to appendicitis in the left upper quadrant Clinical features Signs Deep tenderness located two thirds of the distance from the umbilicus to the right anterior superior iliac spine (McBurney's point). o Also known as McBurney's sign - a classic physical finding Complications of acute appendicitis Pyelophlebitis (portal vein) Portal venous thrombosis Liver abscess Bacteraemia Differential Diagnoses Mesenteric lymphadenitis -often secondary to unrecognized Yersinia infection or viral enterocolitis Mittelschmerz (female) - pain caused by minor pelvic bleeding at the time of ovulation Salpingitis (female) Ectopic pregnancy (female) Meckel diverticulitis Incarcerated inguinal hernia TUMOURS OF THE APPENDIX Tumours of the appendix Carcinoid Mucinous cystadenoma Mucinous cystadenocarcinoma Non-mucin-producing adenocarcinomas Carcinoid o Most common tumour of the appendix o Incidental discovery at the time of surgery or examination of a resected appendix. o Frequently involves the distal tip of the appendix, where it produces a solid bulbous swelling up to 2 to 3 cm in diameter. o Intramural and transmural extension may be evident. o Nodal metastases are very infrequent, and distant spread is exceptionally rare. Mucocoele A dilated appendix filled with mucin May represent an obstructed appendix containing inspissated mucin or be a consequence of mucinous cystadenoma or mucinous cystadenocarcinoma. In the latter instance, invasion through the appendiceal wall can lead to intraperitoneal seeding and spread. Mucocoele In women, resulting peritoneal implants may be mistaken for mucinous ovarian tumours In the most advanced cases the abdomen fills with tenacious, semisolid mucin, a condition called Pseudomyxoma peritoneii. Mucinous cystadenoma The most common benign mucinous neoplasm Replaces the appendiceal mucosa Histologically identical to analogous tumours in the ovary The luminal dilation is associated with appendiceal perforation in 20% of cases, producing localized collections of mucus attached to the serosa of the appendix or lying free within the peritoneal cavity. Microscopically the mucus reveals no malignant cells. Mucinous cystadenocarcinoma Malignant mucinous neoplasm One fifth as common as cystadenomas Macroscopically : mucin-filled cystic dilatation of the appendix indistinguishable from that seen with benign cystadenomas. Mucinous cystadenocarcinoma Penetration of the appendiceal wall by invasive cells and spread beyond the appendix in the form of localized or disseminated peritoneal implants, is frequently present. In its fully developed state, continued cellular proliferation and mucin secretion fills the abdomen with tenacious, semisolid mucin—pseudomyxoma peritoneii Mucinous cystadenocarcinoma Anaplastic adenocarcinomatous cells can be found, distinguishing this process from mucinous spillage Instances in which pseudomyxoma peritoneii is accompanied by both appendiceal and ovarian mucinous adenocarcinomas are usually ascribed to spread of an appendiceal primary lesion. Non-mucin-producing adenocarcinomas Also occur in the appendix. May cause obstruction and enlargement that mimics acute appendicitis PERITONEUM PERITONEUM Inflammatory & infectious processes More common Neoplastic disorders of the peritoneal cavity and retroperitoneal space. Less common Can carry a grave prognosis Normal histology Is composed of a single layer of mesothelial cells which cover the visceral and parietal surfaces and are supported by a thin layer of connective tissue to form the peritoneum. Lines the peritoneal cavity which houses the abdominal viscera Inflammatory diseases Peritonitis May result from bacterial invasion or chemical irritation. Commonly occurs due to a number of causes Common causes of peritonitis Leakage of bile or pancreatic enzyme; which produces sterile peritonitis. Perforation or rupture of the biliary system; evokes a highly irritating peritonitis, usually complicated by bacterial superinfection. Common causes of peritonitis Acute hemorrhagic pancreatitis o associated with leakage of pancreatic enzymes and fat necrosis. o Globules of fat may be found in the peritoneal fluid. o Damage to the bowel wall may allow bacteria to spread to the peritoneal cavity, leading to a frank suppurative exudate after 24 to 48 hours Foreign material Can be introduced surgically (e.g., talc and sutures) induces foreign body–type granulomas and fibrous scarring. Common causes of peritonitis Endometriosis; which causes hemorrhage into the peritoneal cavity, where it acts as an irritant Ruptured dermoid cysts; release keratins that invoke an intense granulomatous reaction Perforation of abdominal viscera Infections Bacterial peritonitis When bacteria from the gastrointestinal lumen are released into the abdominal cavity. Typically following perforation Most commonly as a complication of o acute appendicitis, peptic ulcer, cholecystitis, diverticulitis, and intestinal ischemia. o Acute salpingitis, abdominal trauma, and peritoneal dialysis are other potential sources of contaminating bacteria. Causative bacteria Any bacteria can be associated with bacterial peritonitis. Commonly implicated bacteria E. coli Streptococci S. aureus Enterococci C. perfringens Spontaneous bacterial peritonitis Develops in the absence of an obvious source of contamination. It is an uncommon disorder Often in 10% of patients with cirrhosis and ascites May also develop in children with nephrotic syndrome The manner by which bacteria gain access to the peritoneal cavity is unknown. Commonly identified organisms are E. coli and pneumococci MORPHOLOGY Normally glistening serosal and peritoneal surfaces become dull and lusterless. Serous or slightly turbid fluid begins to accumulate within 2 to 4 hours of infection. As the infection progresses, creamy suppurative material that may be extremely viscous accumulates. The volume of fluid may be localized by the omentum and viscera to a small area or fill the abdominal cavity. Exudate may collect around the liver to form subhepatic and sub diaphragmatic abscesses.  The cellular inflammatory response is composed primarily of dense collections of neutrophils and fibrinopurulent debris that coat the viscera and abdominal wall. The reaction usually remains superficial and does not penetrate deeply. One exception is tuberculous peritonitis, which typically studs the serosal and peritoneal surfaces with small, pale granulomas.  Bacterial peritonitis can be fatal. The inflammatory process can Heal, either spontaneously or as a result of therapy. It may resolve completely; Undergo organization into fibrous adhesions; Become walled off in abscesses that may persist (potentially serving as new sources of infection) or heal SCLEROSING RETROPERITONITIS Also known as idiopathic retroperitoneal fibrosis or Ormond disease. Is characterized by dense fibrosis that may extend to involve the mesentery. The cause of sclerosing retroperitonitis is unknown, however it is thought to be an inflammatory process. Frequently compresses the ureters. BENIGN LESIONS CYSTS Cysts may develop within the abdominal cavity Are frequently attached to the peritoneum. They can be quite large, sometimes presenting as palpable abdominal masses. The origins of such cysts are diverse; they can develop from “blind” lymphatic channels; foregut or hindgut diverticulae that pinch off during development; the urogenital ridge or its derivatives (i.e., the urinary tract and male and female genital tracts); walled-off infections; as a sequela of pancreatitis (pseudocysts). BENIGN TUMOURS Primary benign soft-tissue tumors can develop within the peritoneum and retroperitoneum MALIGNANT TUMOURS Can be primary or secondary Primary tumours : Less common Examples include mesothelioma and desmoplastic small round cell tumour Mesotheliomas Are similar to tumors of the pleura and pericardium. Almost always associated with significant asbestos exposure. It has been hypothesized that swallowed asbestos fibers somehow penetrate through the intestinal wall to reach the peritoneum. Histopathologic diagnosis can be difficult and the differential diagnosis includes metastatic adenocarcinoma, which can be distinguished from mesothelioma using a variety of immunohistochemical markers Desmoplastic Small Round Cell Tumour This is the most commonly occurring primary malignant soft-tissue tumour. It is an aggressive tumor that occurs in children and young adults. It is characterized by a reciprocal chromosomal translocation, that results in fusion of genes associated with Ewing sarcoma (EWS) and Wilms tumor (WT1). Morphologically, the tumor bears a resemblance to Ewing sarcoma and related tumors. Secondary tumours Are quite common. In any form of advanced cancer, direct spread to the serosal surface or metastatic seeding (peritoneal carcinomatosis) may occur. The most common tumours producing diffuse serosal implants are ovarian and pancreatic adenocarcinoma. Appendiceal mucinous carcinomas may produce pseudomyxoma peritoneii. Any intra-abdominal malignancy, as well as a wide variety of tumors of extra-abdominal origin, may spread to the peritoneum. Thank you