L acute appendicitis

For Pathology students

1. Acute Appendicitis Dr Mohammad Manzoor Mashwani

2. Appendix: NORMAL STRUCTURE The appendix is a blind-ending tubular diverticulum of the cecum, usually lying behind the caecum and varies in length from 4 to 20 cm (average 7 cm ).The wall of the appendix consists of all the four typical coats of the digestive tube: mucosa, submucosa, muscularis externa & serosa. A  diverticulum   is an outpouching of a hollow (or a fluid-filled) structure in the body. 

3. Histology The appendix is characterized by a thick wall but a relatively narrow lumen which is stellate or irregular in outline. Intestinal villi are absent. Mucosa: Epithelium, Lamina propria, muscularis mucosa Epithelium: The mucosa is lined mainly by absorptive cells (enterocytes) which are columnar cells; only a few/numerous goblet cells are present.

4. Histology The lamina propria shows intestinal glands (crypts of Lieberkühn) . The intestinal glands in the appendix are less well developed , shorter , and often spaced farther apart than those in the colon. The lamina propria of the appendix is heavily infiltrated with lymphocytes and contains numerous lymphoid nodules , which form the most conspicuous histologic feature of this organ. These lymphoid nodules show germinal centers and are not confined to the lamina propria, but penetrate the muscularis mucosae to extend into the submucosa ( present often in the submucosa) . Argentaffin and nonargentaffin endocrine cells are present in the base of mucosal glands just as in the small intestine.

5. The submucosa has numerous blood vessels. The connective tissue of the submucosa of appendix is characterized by the abundance of fat cells. The submucosa has abundant lymphoid tissue. The muscularis externa (propria)of the appendix is thin but has two layers of smooth muscle cells (inner circular and outer longitudinal) as elsewhere in the alimentary tract. Teniae coli are absent. The parasympathetic ganglia of the myenteric plexus are located between the inner and outer smooth muscle layers of the muscularis externa. Serosa forms the outermost coat of the appendix under which are seen adipose cells .

6. Acute Appendicitis - Epidemiology Acute inflammation of the appendix, acute appendicitis, is the most common acute abdominal condition confronting the surgeon. The condition is seen more commonly in older children and young adults, and is uncommon at the extremes of age. The disease is seen more frequently in the West and in affluent societies which may be due to variation in diet— a diet with low bulk or cellulose and high protein intake more often causes appendicitis.

7. ETIOPATHOGENESIS The most common mechanism is obstruction of the lumen from various etiologic factors that leads to increased intraluminal pressure . This presses upon the blood vessels to produce ischaemic injury which in turn favours the bacterial proliferation and hence acute appendicitis. Acute appendicitis is thought to be initiated by progressive increases in intraluminal pressure that compromises venous outflow. In 50% to 80% of cases, acute appendicitis is associated with overt luminal obstruction, usually by a small, stonelike mass of stool, or fecalith, or, less commonly, a gallstone, tumor, or mass of worms. Ischemic injury and stasis of luminal contents, which favor bacterial proliferation, trigger inflammatory responses including tissue edema and neutrophilic infiltration of the lumen, muscular wall, and periappendiceal soft tissues.

8. The common causes of appendicitis are as under: A. Obstructive 1. Faecolith/ Fecalith 2. Calculi (Stones) 3. Foreign body 4. Tumour 5. Worms (especially Enterobius vermicularis) 6. Diffuse lymphoid hyperplasia, especially in children. B. Non-obstructive 1. Haematogenous spread of generalised infection 2. Vascular occlusion 3 . Inappropriate diet lacking roughage.

9. Phlegmon  is a spreading  diffuse   inflammatory  process with formation of suppurative/ purulent exudate  or  pus . This is the result of acute purulent inflammation which may be related to bacterial infection, however the term ' phlegmon ' mostly refers to a walled-off inflammatory mass without bacterial infection, one that may be palpable on physical examination. Aposteme : A swelling filled with purulent matter.

10. MORPHOLOGIC FEATURES Grossly, the appearance depends upon the stage at which the acutely-inflamed appendix is examined. In early acute appendicitis , the organ is swollen and serosa shows hyperaemia . In welldeveloped acute inflammation called acute suppurative appendicitis , the serosa is coated with fibrinopurulent exudate and engorged vessels on the surface. In further advanced cases called acute gangrenous appendicitis , there is necrosis and ulcerations of mucosa which extend through the wall so that the appendix becomes soft and friable and the surface is coated with greenish-black gangrenous necrosis.

11. Gross description ● Fibrinopurulent exudate on serosa , prominent vessels ● Lumen may contain blood-tinged pus ● Variable perforation, mucosal ulceration, fecalith or other obstructing agent The inflammatory reaction transforms the normal glistening serosa into a dull, granular appearing, erythematous surface.

12. Microscopy Microscopically, the most important diagnostic histological criterion is the neutrophilic infiltration of the muscularis propria . In early stage , the other changes besides acute inflammatory changes, are congestion and oedema of the appendiceal wall . In later stages , the mucosa is sloughed off , the wall becomes necrotic, the blood vessels may get thrombosed and there may be neutrophilic abscesses in the wall. Diagnosis of acute appendicitis requires neutrophilic infiltration of the muscularis propria.

13. Micro description ● Mucosal ulceration ● Minimal (if early) to dense neutrophils in muscularis propria with necrosis , congestion, perivascular neutrophilic infiltrate ● Late: absent mucosa , necrotic wall , prominent fibrosis , granulation tissue , marked chronic inflammatory infiltrate in wall, thrombosed vessels

14. Acute appendicitis. Microscopic appearance showing diagnostic neutrophilic infiltration into the muscularis propria. Other changes present are necrosis of mucosa and periappendicitis.

15. CLINICAL COURSE The patient presents with features of acute abdomen as under: 1. Colicky pain, initially around umbilicus but later localised to right iliac fossa 2. Nausea and vomiting 3. Pyrexia of mild grade 4. Abdominal tenderness 5. Increased pulse rate 6. Neutrophilic leucocytosis.

16. Clinical features A classic physical finding is McBurney’s sign, deep tenderness noted at a location two thirds of the distance from the umbilicus to the right anterior superior iliac spine (McBurney’s point ). Complications: Peritonitis Abscess Adhesions Portal Pylephlebitis Mucocele

17. COMPLICATIONS If the condition is not adequately managed , the following complications may occur: 1. Peritonitis. A perforated appendix as occurs in gangrenous appendicitis may cause localised or generalised peritonitis. 2. Appendix abscess. This is due to rupture of an appendix giving rise to localised abscess in the right iliac fossa . This abscess may spread to other sites such as between the liver and diaphragm ( subphrenic abscess ), into the pelvis between the urinary bladder and rectum, and in the females may involve uterus and fallopian tubes.

18. Complications 3. Adhesions. Late complications of acute appendicitis are fibrous adhesions to the greater omentum, small intestine and other abdominal structures. 4. Portal pylephlebitis. Spread of infection into mesenteric veins may produce septic phlebitis and liver abscess . 5. Mucocele. Distension of distal appendix by mucus following recovery from an attack of acute appendicitis is referred to as mucocele. It occurs generally due to proximal obstruction but sometimes may be due to a benign or malignant neoplasm in the appendix. An infected mucocele may result in formation of empyema of the appendix .

19. TUMOURS OF APPENDIX Tumours of the appendix are quite rare. These include: Carcinoid tumour ( the most common), Pseudomyxoma peritonei and Adenocarcinoma. CARCINOID TUMOUR. Both argentaffin and argyrophil types are encountered, the former being more common. Appendiceal carcinoids, occur more frequently in 3 rd and 4th decades of life without any sex predilection, are often solitary and behave as locally malignant tumours.

20. Morphology Grossly, carcinoid tumour of the appendix is mostly situated near the tip of the organ and appears as a circumscribed nodule, usually less than 1 cm in diameter, involving the wall but metastases are rare. Histologically, carcinoid tumour of the appendix resembles other carcinoids of the midgut. Appendiceal carcinoids commonly involve the tip of the organ and are solitary

21. Tumors of Appendix PSEUDOMYXOMA PERITONEI. Pseudomyxoma peritonei is appearance of gelatinous mucinous material around the appendix admixed with epithelial tumour cells. It is generally due to mucinous collection from benign mucinous cystadenoma of the ovary or mucin-secreting carcinoma of the appendix. ADENOCARCINOMA. It is an uncommon tumour in the appendix and is morphologically similar to adenocarcinoma elsewhere in the alimentary tract.

22. THANKS Have a good day.