Appendix ...& acute appendicitis

Anatomy

The appendix is a narrow, hollow tube connected to the cecum. It has large aggregations of lymphoid tissue in its walls and is suspended from the terminal ileum by the mesoappendix, which contains the appendicular vessels . Its point of attachment to the cecum is consistent with the highly visible free taenia leading directly to the base of the appendix, but the location of the rest of the appendix varies .
It may be:

posterior to the cecum or the lower ascending colon, or both, in a retrocecal or retrocolic position;
suspended over the pelvic brim in a pelvic or descending position;
below the cecum in a subcecal location;
anterior to the terminal ileum, possibly contacting the body wall, in a preileal position or

posterior to the terminal ileum in a postileal position posterior to the terminal ileum in a postileal position

The surface projection of the base of the appendix is

at the junction of the lateral and middle one-thirds of a line from the anterior superior iliac spine to the umbilicus (McBurney's point). People with appendicular problems may describe pain near this location.

HISTOLOGY

The general structure of the appendix conforms to that of the rest of the large intestine. In some mammals, the appendix is capacious and involved in prolonged digestion

of cellulose, but in humans its function is unknown.

the suspensory mesentery M in continuity with the outer serosal layer S. The serosa contains extravasated blood resulting from haemorrhage during surgical removal. The mesenteries conduct blood vessels, lymphatics and nerves .
The most characteristic feature of the appendix, particularly in the young, is the presence of masses of lymphoid tissue in the mucosa and submucosa

the lamina propria LP and upper submucosa SM are diffusely infiltrated with lymphocytes. Note that the mucosal glands are much less closely packed than in the large intestine. the lymphoid tissue also forms follicles F often containing germinal centres . These follicles bulge into the lumen and, like the follicles of Peyer's patches in the small intestine, are invested by a simple epithelium of M cells , which presumably facilitates sampling of antigen in the lumen

PATHOLOGY :

appendicitis is the most common acute abdominal condition the surgeon is called on to treat. Appendicitis is one of the best-known medical entities and yet may be one of the most difficult diagnostic problems to confront the emergency physician. A differential diagnosis must include virtually every acute process that can occur within the abdominal cavity, as well as some emergent conditions affecting organs of the thorax.Acute Appendicitis

(Inflammation in the right lower quadrant was considered a nonsurgical disease of the cecum (typhlitis or perityphlitis) until Fitz recognized acute appendicitis as a distinct entity in 1886)

causes :

Appendiceal inflammation is associated with obstruction in 50% to 80% of cases, usually in the form of a fecalith and, less commonly, a gallstone, tumor, or ball of worms (oxyuriasis vermicularis). Note .. Continued secretion of mucinous fluid in the obstructed viscus presumably leads to a progressive increase in intraluminal pressure sufficient to cause eventual collapse of the draining vein

Ischemic injury then favors bacterial proliferation with additional inflammatory edema and exudation, further embarrassing the blood supply. Nevertheless, a significant minority of inflamed appendices have no demonstrable luminal obstruction, and the pathogenesis of the inflammation remains unknown.

Morphology.

At the earliest stages, only a scant neutrophilic exudate may be found throughout the mucosa, submucosa, and muscularis propria. Subserosal vessels are congested, and often there is a modest perivascular neutrophilic infiltrate. The inflammatory reaction transforms the normal glistening serosa into a dull, granular, red membrane; this transformation signifies early acute appendicitis for the operating surgeon. At a later stage, a prominent neutrophilic exudate generates a fibrinopurulent reaction over the serosa . As the inflammatory process worsens, there is abscess formation within the wall, along with ulcerations and foci of suppurative necrosis in the mucosa. This state constitutes acute suppurative appendicitis. Further appendiceal compromise leads to large areas of hemorrhagic green ulceration of the mucosa and green-black gangrenous necrosis through the wall, extending to the serosa, creating acute gangrenous appendicitis, which is quickly followed by rupture and suppurative peritonitis.



Acute appendicitis. The inflamed appendix shown below is red, swollen, and covered with a fibrinous exudate.

The histologic criterion for the diagnosis of acute appendicitis is neutrophilic infiltration of the muscularis propria. Usually, neutrophils and ulcerations are also present within the mucosa. Since drainage of an exudate into the appendix from alimentary tract infection may also induce a mucosal neutrophilic infiltrate, evidence of muscular wall inflammation is requisite for the diagnosis.

Clinical Features

(1) pain, at first periumbilical but then localizing to the right lower quadrant; (2) nausea and/or vomiting; (3) abdominal tenderness, particularly in the region of the appendix; (4) mild fever; and (5) an elevation of the peripheral white blood cell count up to 15,000 to 20,000 cell/µL.

complications

perforation, uncommon complications of appendicitis include pyelophlebitis with thrombosis of the portal venous drainage, liver abscess, and bacteremia

diffrential diagnosis

mesenteric lymphadenitis, usually secondary to an enterocolitis (often unrecognized) caused by Yersinia or a virus; systemic viral infection; acute salpingitis; ectopic pregnancy; mittelschmerz (pain caused by trivial pelvic bleeding at the time of ovulation); cystic fibrosis; and Meckel diverticulitis.

TREATMENT

APPENDECTOMY .

Reference :

Gray's anatomy For Student

Wheater's Functional Histology 5th Edition

ROBBINS _ pathologic bases 7th edition