Acute Appendicitis

Dr Mohammad Manzoor Mashwani

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.

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.

HistologyThe 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.

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 .

Acute Appendicitis - Epidemiology

Acute inflammation of the appendix, acute appendicitis, isthe most common acute abdominal condition confronting thesurgeon. The condition is seen more commonly in older children and young adults, and is

uncommon at the extremesof age. The disease is seen more frequently in the West andin affluent societies which may be due to variation in diet—a diet with low bulk or cellulose and high protein intake moreoften causes appendicitis.

ETIOPATHOGENESISThe 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.

The common causes of appendicitis are as under:

A. Obstructive 1. Faecolith/ Fecalith2. Calculi (Stones)3. Foreign body4. Tumour5. Worms (especially Enterobius vermicularis)

6. Diffuse lymphoid hyperplasia, especially in children.

B. Non-obstructive 1. Haematogenous spread of generalised infection

2. Vascular occlusion3. Inappropriate diet lacking roughage.

Phlegmon is a spreading diffuse inflammatory process with formation of suppurative/purulentexudate 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.

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 andfriable and the surface is coated with greenish-blackgangrenous necrosis.

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.

MicroscopyMicroscopically, the most important diagnostic histologicalcriterion is the neutrophilic infiltration of the muscularis

propria.

Inearly stage, the other changes besides acute inflammatorychanges, are congestion and oedema of the appendicealwall. In later stages, the mucosa is sloughed off, the wallbecomes necrotic, the blood vessels may get thrombosedand there may be neutrophilic abscesses in the wall.

Diagnosis of acute appendicitis requires neutrophilic infiltration of the muscularis propria.

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

Acute appendicitis. Microscopic appearance showing diagnostic neutrophilic infiltration into the muscularis propria. Other changes

present are necrosis of mucosa and periappendicitis.

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 vomiting3. Pyrexia of mild grade4. Abdominal tenderness5. Increased pulse rate6. Neutrophilic leucocytosis.

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:1. Peritonitis2. Abscess3. Adhesions4. Portal Pylephlebitis5. Mucocele

COMPLICATIONSIf the condition is not adequately managed, the following

complications may occur:1. Peritonitis. A perforated appendix as occurs ingangrenous appendicitis may cause localised or generalisedperitonitis.2. Appendix abscess. This is due to rupture of an appendixgiving rise to localised abscess in the right iliac fossa. Thisabscess may spread to other sites such as between the liverand diaphragm (subphrenic abscess), into the pelvis betweenthe urinary bladder and rectum, and in the females mayinvolve uterus and fallopian tubes.

3. Adhesions. Late complications of acute appendicitis arefibrous adhesions to the greater omentum, small intestineand other abdominal structures.4. Portal pylephlebitis. Spread of infection into mesentericveins may produce septic phlebitis and liver abscess.5. Mucocele. Distension of distal appendix by mucusfollowing recovery from an attack of acute appendicitis isreferred to as mucocele. It occurs generally due to proximalobstruction but sometimes may be due to a benign ormalignant neoplasm in the appendix. An infected mucocelemay result in formation of empyema of the appendix.

TUMOURS OF APPENDIXTumours 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 3rd and 4th decades of life without any sex predilection, are often solitary and behave as locally malignant tumours.

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 appendixresembles other carcinoids of the midgut.

Appendiceal carcinoids commonly involve the tip of the organ and are solitary

Tumors of AppendixPSEUDOMYXOMA PERITONEI. Pseudomyxoma peritoneiis appearance of gelatinous mucinous material around theappendix admixed with epithelial tumour cells. It is generallydue to mucinous collection from benign mucinouscystadenoma of the ovary or mucin-secreting carcinoma ofthe appendix.ADENOCARCINOMA. It is an uncommon tumour in theappendix and is morphologically similar to adenocarcinomaelsewhere in the alimentary tract.

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