Acute appendicitis anatomy and function icon

Acute appendicitis anatomy and function

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The appendix first becomes visible in the eighth week of development as a protuberance off the cecum. During development the growth rate of the cecum exceeds that of the appendix, displacing the appendix medially toward the ileocecal valve. The relationship of the base of the appendix to the cecum remains constant, whereas the tip can be found in a retrocecal, pelvic, subcecal, preileal, or right pericolic position. The three taenia coli converge at the junction of the cecum with the appendix. The appendix can vary in length from less than 1 cm to greater than 30 cm; most appendices are 6.9 cm in length.

The appendix is an immunologic organ that participates in the secretion of immunoglobulins, particularly immunoglobulin A (IgA). Although the appendix is an integral component of the gut-associated lymphoid tissue (GALT) system, its function is not essential and appendectomy is not associated with any manifestation of immune compromise. Lymphoid tissue first appears in the appendix approximately 2 weeks after birth. The amount of lymphoid tissue increases throughout puberty, remains steady for the next decade, and then begins a steady decrease with age.


Historical Background

The greatest contributor to the treatment of appendicitis is Charles McBurney. In 1889, he published his landmark paper in the New York Medical Journal describing the indications for early laparotomy for the treatment of appendicitis. It is in this paper that he described McBurney’s point as the point of maximum tenderness, when one examines with the fingertips is, in adults, one-half to two inches inside the right anterior spinous process of the ileum on a line drawn to the umbilicus. McBurney subsequently published a paper describing the incision that bears his name in 1894. Semm is widely credited with performing the first successful laparoscopic appendectomy in 1982. Incidence The lifetime rate of appendectomy is 12 percent for men and 25 percent for women, with approximately 7 percent of all people undergoing appendectomy for acute appendicitis. Over a 10-year period from 1987 to 1997, the overall appendectomy rate decreased parallel to a decrease in incidental appendectomy. However, the rate of appendectomy for appendicitis has remained constant at 10 per 10,000 patients per year. Appendicitis is most frequently seen in patients in their second through fourth decades of life, with a mean age of 31.3 years and a median age of 22 years. There is a slight male to female predominance. Despite increased use of ultrasonography, computed tomography (CT) scanning, and laparoscopy between 1987 and 1997, the rate of misdiagnosis of appendicitis has remained constant (15.3 percent), as has the rate of appendiceal rupture. The percentage of misdiagnosis of appendicitis is significantly higher among women than men (22.2 vs. 9.3 percent), negative appendectomy rate for women of reproductive age is 23.2 percent, with the highest rates identified in women age 40.49 years. The highest negative appendectomy rate is reported for women older than 80 years of age.

Aetiology and Pathogenesis

There is a predictable sequence of events leading to appendiceal rupture. Proximal obstruction of the appendiceal lumen produces a closed-loop obstruction, and continuing secretion by the appendiceal mucosa produces distention. Distention of the appendix stimulates nerve endings of visceral afferent stretch fibers, producing vague, dull, diffuse pain in the mid-abdomen or lower epigastrium.

Peristalsis is also stimulated by the sudden distention, so that some cramping may be superimposed on the visceral pain early in the course of appendicitis. Distention continues from continued mucosal secretion and from multiplication of the resident bacteria of the appendix. Distention of this magnitude causes reflex nausea and vomiting, and the diffuse visceral pain becomes more severe. As pressure in the organ increases, venous pressure is exceeded. Capillaries and venules are occluded, but arteriolar inflow continues, resulting in engorgement and vascular congestion. The inflammatory process soon involves

the serosa of the appendix and in turn parietal peritoneum in the region, producing the characteristic shift in pain to the right lower quadrant. The mucosa of the appendix is susceptible to impairment of blood supply, thus its integrity is compromised early in the process, allowing bacterial invasion. As progressive distention encroaches on first the venous return and subsequently the arteriolar inflow, the area with the poorest blood supply suffers most. As distention, bacterial invasion, compromise of vascular supply,

and infarction progress, perforation occurs, usually through one of the infracted areas on the antimesenteric border. Perforation generally occurs just beyond the point of obstruction rather than at the tip. This sequence is not inevitable, however, and some episodes of acute appendicitis apparently subside spontaneously.


The bacteriology of the normal appendix is similar to that of the normal colon. The bacteria cultured in cases of appendicitis are therefore similar to those seen in other colonic infections such as diverticulitis. The principal organisms seen in the normal appendix, in acute appendicitis, and in perforated appendicitis are Escherichia coli and Bacteroides fragilis. However, a wide variety of both facultative and anaerobic bacteria and mycobacteria may be present. Appendicitis is a polymicrobial infection, with some series reporting up to 14 different organisms cultured in patients with perforation.

Common Organisms Seen in Patients with Acute Appendicitis:

Aerobic and facultative Anaerobic

Gram-negative bacilli Gram-negative bacilli

E. coli Bacteroides fragilis

Pseudomonas aeruginosa Bacteroides species

Klebsiella species Fusobacterium species

Gram-positive cocci Gram-positive cocci

Streptococcus anginosus Peptostreptococcus species

Streptococcus species Gram-positive bacilli

Enterococcus species Clostridium species

^ Clinical Manifestations


Abdominal pain is the prime symptom of acute appendicitis. Classically, pain is initially diffusely centered in the lower epigastrium or umbilical area, is moderately severe, and is steady, sometimes with intermittent cramping superimposed. After a period varying from 1-12 h, the pain localizes to the right lower quadrant. This classic pain sequence, although usual, is not invariable. In some patients, the pain of appendicitis begins in the right lower quadrant and remains there. Variations in the anatomic location of the appendix account for many of the variations in the principal locus of the somatic phase of the pain.

Anorexia nearly always accompanies appendicitis. It is so constant that the diagnosis should be questioned if the patient is not anorectic. Although vomiting occurs in 75 percent of patients, it is neither prominent nor prolonged. Most patients give a history of obstipation beginning prior to the onset of abdominal pain, and many feel that defecation would relieve their abdominal pain. However, diarrhea occurs in some patients, particularly children, so that the pattern of bowel function is of little differential diagnostic value. The sequence of symptom appearance has great differential diagnostic significance.

In more than 95 percent of patients with acute appendicitis, anorexia is the first symptom, followed by abdominal pain, which is followed, in turn, by vomiting. If vomiting precedes the onset of pain, the diagnosis of appendicitis should be questioned.


Physical findings are determined principally by the anatomic position of the inflamed appendix, and by whether the organ has already ruptured when the patient is first examined. Vital signs are minimally changed by uncomplicated appendicitis. Temperature elevation is rarely more than 1.C (33.8.F) and the pulse rate is normal or slightly elevated. Changes of greater magnitude usually indicate that a complication has occurred or that another diagnosis should be considered. Patients with appendicitis usually prefer to lie supine, with the thighs, drawn up, because any motion increases pain. The classic right lower quadrant physical signs are present when the inflamed appendix lies in the anterior position.

Tenderness is often maximal at or near the McBurney point. Direct rebound tenderness is usually present. Additionally, referred or indirect rebound tenderness is present. This referred tenderness is felt maximally in the right lower quadrant, indicating localized peritoneal irritation. The Rovsing sign.pain in the right lower quadrant when palpatory pressure is exerted in the left lower quadrant also indicates the site of peritoneal irritation. Cutaneous hyperesthesia in the area supplied by the spinal nerves on the right at T10, T11, and T12 frequently accompanies acute appendicitis. Muscular resistance to palpation of the abdominal wall parallels the severity of the inflammatory process. Anatomic variations in the position of the inflamed appendix lead to deviations in the usual physical findings. The psoas sign indicates an irritative focus in proximity to that muscle. The test is performed by having patients lay on their left side as the examiner slowly extends the right thigh, thus stretching the iliopsoas muscle. The test is positive if extension produces pain. Similarly, a positive obturator sign of hypogastric pain on stretching the obturator internus indicates irritation in the pelvis. The test is performed by passive internal rotation of the flexed right thigh with the patient supine.

^ Laboratory Findings

Mild leukocytosis, ranging from 10,000.18,000/mm3, is usually present in patients with acute, uncomplicated appendicitis and is often accompanied by a moderate polymorphonuclear predominance.However, white blood cell counts are variable. It is unusual for the white blood cell count to be greater than 18,000/mm3 in uncomplicated appendicitis. White blood cell counts above this level raise the possibility of a perforated appendix. Urinalysis is useful to rule out the urinary tract as the source of infection. Although several white or red blood cells can be present from ureteral or bladder irritation as a result of an inflamed appendix, bacteriuria in a catheterized urine specimen is not seen with acute appendicitis.

^ Additional methods of investigation

Plain films of the abdomen, although frequently obtained as part of the general evaluation of a patient with an acute abdomen, are rarely helpful in diagnosing acute appendicitis. However, plain radiographs can be of significant benefit in ruling out other pathology. In patients with acute appendicitis, one often sees an abnormal bowel gas pattern (Klemma’s sign), which is a nonspecific finding. The presence of a fecalith is rarely noted on plain films, but if present, is highly suggestive of the diagnosis. Graded compression sonography has been suggested as an accurate way to establish the diagnosis of appendicitis. The technique is inexpensive, can be performed rapidly, does not require contrast, and can be used in pregnant patients. Sonographically, the appendix is identified as a blind-ending, nonperistaltic

bowel loop originating from the cecum.With maximal compression, the diameter of the appendix is measured in the anteroposterior dimension. A scan is considered positive if a noncompressible appendix 6 mm or greater in the anteroposterior direction is demonstrated. The presence of an appendicolith establishes the diagnosis. The presence of thickening of the appendiceal wall and periappendiceal fluid is highly suggestive. Sonographic demonstration of a normal appendix excludes the diagnosis of acute appendicitis. The study is considered inconclusive if the appendix is not visualized and there is no

pericecal fluid or mass. When the diagnosis of acute appendicitis is excluded by sonography, a brief survey of the remainder of the abdominal cavity should be performed to establish an alternative diagnosis. In females of child-bearing age, the pelvic organs must be adequately visualized. The sonographic diagnosis of acute appendicitis has a reported sensitivity of 55 -96 percent and a specificity of 85 -98 percent.

High-resolution, helical, computer tomography also has been used to diagnose appendicitis. On CT scan, the inflamed appendix appears dilated and the wall is thickened.

^ Alvarado Scale for the Diagnosis of Appendicitis

Manifestations Value

Symptoms Migration of pain 1

Anorexia 1

Nausea/vomiting 1

Signs RLQ tenderness 2

Rebound 1

Elevated temperature 1

Laboratory values Leukocytosis 2

Left shift 1

Total Points 10

RLQ = right lower quadrant.

Source: From Alvarado, with permission.

Laparoscopy can serve as both a diagnostic and therapeutic maneuver for patients with acute abdominal pain and suspected acute appendicitis. Laparoscopy is most useful in the evaluation of females with lower abdominal complaints because appendectomy is performed on a normal appendix in as many as 30-40 % of these patients. Differentiating acute gynaecologic pathology from acute appendicitis can be effectively accomplished by using the laparoscope.

^ Appendiceal Rupture

Immediate appendectomy has long been the recommended treatment of acute appendicitis because of the risk of rupture. The overall rate of perforated appendicitis is 25,8 %. Children younger than age 5 years and patients older than age 65 years have the highest rate of perforation (45 and 51 %, respectively). It has been suggested that delays in presentation are responsible for the majority of perforated appendices. There is no accurate way of determining when and if an appendix will rupture prior to resolution of the inflammatory process. Although it has been suggested that observation and antibiotic therapy alone may be an appropriate treatment for acute appendicitis, nonoperative treatment exposes the patient to the increased morbidity and mortality associated with a ruptured appendix. Appendiceal rupture should be suspected in the presence of fever greater than 39.C (102.F) and a white blood cell count greater than 18,000/mm3. In the majority of cases, rupture is contained and patients display localized rebound tenderness. Generalized peritonitis will be present if the walling-off process is ineffective in containing the rupture. In 2-6 % of cases, an ill-defined mass will be detected on physical examination. This could represent a phlegmon or a periappendiceal abscess. Patients who present with a mass have a longer duration of symptoms, usually at least 5-7 days. The ability to distinguish acute, uncomplicated appendicitis from acute appendicitis with perforation on the basis of clinical findings is often difficult, but it is important to make the distinction because their treatment differs. CT scan may be beneficial in guiding therapy. Phlegmons and small abscesses can be treated conservatively with intravenous antibiotics; well localized abscesses can be managed with percutaneous drainage; complex abscesses should be considered for surgical drainage. If operative drainage is required, it should be performed by using an extraperitoneal approach, with appendectomy reserved for cases in which the appendix is easily accessible. Interval appendectomy performed at least 6 weeks following the acute event

has classically been recommended for all patients treated either nonoperatively or with simple drainage of an abscess.

^ Differential Diagnosis

The differential diagnosis of acute appendicitis is essentially the diagnosis of the acute abdomen. This is because clinical manifestations are not specific for a given disease, but are specific for disturbance of a physiologic function or functions. Thus, an essentially identical clinical picture can result from a wide variety of acute processes within or near the peritoneal cavity.

The accuracy of preoperative diagnosis should be approximately 85 percent. If it is consistently less, it is likely that some unnecessary operations are being performed, and a more rigorous preoperative differential diagnosis is in order. A diagnostic accuracy rate consistently greater than 90 percent should also cause concern, because this may mean that some patients with atypical, but bona fide cases of, acute appendicitis are being observed when they should have prompt surgical intervention.

The differential diagnosis of acute appendicitis depends on four major factors: the anatomic location of the inflamed appendix; the stage of the process (i.e., simple or ruptured); the patient’s age; and the patient’s sex.

^ Acute Appendicitis in Older Adults

Although the incidence of appendicitis in older adults is lower than in younger patients, the morbidity and mortality are significantly increased in this patient population. Delays in diagnosis, a more rapid progression to perforation, and co morbid disease are all contributing factors. The diagnosis of appendicitis may be subtler and less typical than in younger individuals, and a high index of suspicion should be maintained. In patients older than age 80 years, perforation rates of 49 percent and mortality rates of 21 percent have been reported.

^ Acute Appendicitis during Pregnancy

Appendicitis is the most frequently encountered extrauterine disease requiring surgical treatment during pregnancy. The incidence is approximately 1 in 2000 pregnancies. Acute appendicitis can occur at any time during pregnancy, but is more frequent during the first two trimesters. As fetal gestation progresses,

the diagnosis of appendicitis becomes more difficult as the appendix is displaced laterally and superiorly. Nausea and vomiting after the first trimester or new-onset nausea and vomiting should raise the consideration of appendicitis. Abdominal pain and tenderness will be present, although rebound and guarding are less frequent because of laxity of the abdominal wall. Elevation of the white blood cell count above the normal pregnancy levels of 15,000 -20,000 КL, with a predominance of polymorphonuclear cells, is usually present. When the diagnosis is in doubt, abdominal ultrasound may be beneficial. Laparoscopy may be indicated in equivocal cases, especially early in pregnancy. The performance

of any operation during pregnancy carries a risk of premature labor of 10.15 %. The most significant factor associated with both fetal and maternal death is appendiceal perforation. Fetal mortality increases from 3.5 % in early appendicitis to 20 percent with perforation. The suspicion of appendicitis during pregnancy should prompt rapid diagnosis and surgical intervention.


Once the decision to operate for presumed acute appendicitis has been made, the patient should be prepared for the operating room. Adequate hydration should be ensured; electrolyte abnormalities corrected; and preexisting cardiac, pulmonary, and renal conditions should be addressed. Many trials have

demonstrated the efficacy of preoperative antibiotics in lowering the infectious complications in appendicitis.

^ Open Appendectomy

Most surgeons employ either a McBurney (oblique) or Rocky-Davis (transverse) right lower quadrant muscle-splitting incision in patients with suspected appendicitis. The incision should be centered over either the point of maximal tenderness or a palpable mass. If an abscess is suspected, a laterally placed incision is imperative to allow retroperitoneal drainage and to avoid generalized contamination of the peritoneal cavity. If the diagnosis is in doubt, a lower midline incision is recommended to allow a more extensive examination of the peritoneal cavity. This is especially relevant in older patients with possible

malignancy or diverticulitis. Several techniques can be used to locate the appendix. Because the cecum

is usually visible within the incision, the convergence of the taeniae can be followed to the base of the appendix. A sweeping lateral to medial motion can aid in delivering the appendiceal tip into the operative field. Occasionally, limited mobilization of the cecum is needed to aid in adequate visualization.

Once identified, the appendix is mobilized by dividing the mesoappendix, taking care to ligate the appendiceal artery securely. The appendiceal stump can be managed by simple ligation or by ligation

and inversion with either a purse-string or Z stitch. As long as the stump is clearly viable and the base of the cecum not involved with the inflammatory process, the stump can be safely ligated with a nonabsorbable suture. The mucosa is frequently obliterated to avoid the development of mucocele. The

peritoneal cavity is irrigated and the wound closed in layers. If perforation or gangrene is found in adults, the skin and subcutaneous tissue should be left open and allowed to heal by secondary intent or closed in 4-5 days as a delayed primary closure. If appendicitis is not found, a methodical search for an alternative

diagnosis must be performed.

^ Laparoscopic appendectomy is performed under general anesthesia. A nasogastric tube and a urinary catheter are placed prior to obtaining a pneumoperitoneum. Laparoscopic appendectomy usually requires the use of three ports. Four ports may occasionally be necessary to mobilize a retrocecal appendix.

The surgeon usually stands to the patient’s left. One assistant is required to operate the camera. One troacar is placed in the umbilicus (10 mm), with a second trocar placed in the suprapubic position. Some surgeons will place this second port in the left lower quadrant. The suprapubic trocar is either 10 or

12 mm, depending on whether a linear stapler will be used. The placement of the third trocar (5 mm) is variable and is usually either in the left lower quadrant, epigastrium, or right upper quadrant. Placement is based on location of the appendix and surgeon preference. Initially, the abdomen is thoroughly

explored to exclude other pathology. The appendix is identified by following the anterior taeniae to its base. Dissection at the base of the appendix enables the surgeon to create a window between the mesentery and base of the appendix. The mesentery and base of the appendix are then secured and divided separately. When the mesoappendix is involved with the inflammatory process, it is often best to divide the appendix first with a linear stapler, and then to divide the mesoappendix immediately adjacent to the appendix. The base of the appendix is not inverted. The appendix is removed from the abdominal

cavity through a trocar site or within a retrieval bag. The base of the appendix and the mesoappendix should be evaluated for hemostasis. The right lower quadrant should be irrigated. Trocars are removed under direct vision.

The largest meta-analysis comparing open to laparoscopic appendectomy included 47 studies, 39 of which were studies of adult patients. This analysis demonstrated that the duration of surgery and operation costs were higher for laparoscopic appendectomy than for open appendectomy. Wound infections were approximately half as likely after laparoscopic appendectomy than after open appendectomy. However, intraabdominal abscess was three times greater after laparoscopic appendectomy than after open appendectomy.

^ Interval Appendectomy

The accepted algorithm for the treatment of appendicitis associated with a palpable or radiographically documented mass (abscess or phlegmon) is conservative therapy with interval appendectomy 6-10 weeks later. This technique has been quite successful and provides much lower morbidity and mortality rates

than immediate appendectomy. This treatment is associated with added expense and longer hospitalization. The initial treatment consists of intravenous antibiotics and bowel rest. Although generally effective, there is a 9 -15 % failure rate, with operative intervention required at 3-5 days after presentation.

Percutaneous or operative drainage of abscesses is not considered a failure of conservative therapy.

The timing of interval appendectomy is controversial. Appendectomy may be required as early as 3 weeks following conservative therapy. Two thirds of the cases of recurrent appendicitis occur within 2 years, and this is the outside limit.


The mortality from appendicitis in the United States has steadily decreased from a rate of 9,9 per 100,000 in 1939, to 0.2 per 100,000 as of 1986. Principal factors in mortality are whether rupture occurs before surgical treatment and the age of the patient. The overall mortality rate for a general anesthetic is 0.06 %. The overall mortality rate in ruptured acute appendicitis is about 3 %. The mortality rate of ruptured appendicitis in older adults is approximately 15 %Complications occur in 3 percent of patients with nonperforated appendicitis and in 47 percent of patients with perforations. Most of the serious early complications are septic and include abscess and wound infection. Wound infection is common, but

is nearly always confined to the subcutaneous tissues and promptly responds to wound drainage. Wound infection predisposes the patient to wound dehiscence.

The sites of predilection for abscesses are the appendiceal fossa, pouch of Douglas, subhepatic space, and between loops of intestine. The latter are usually multiple. Transrectal drainage is preferred for an abscess that bulges into the rectum.


The existence of chronic appendicitis as a clinical entity has been questioned for many years. Recent clinical data document the existence of this uncommon disease. Histologic criteria have been established. The pain lasts longer and is less intense than that of acute appendicitis, but is in the same location. There is a much lower incidence of vomiting, but anorexia and occasionally nausea, pain with motion, and malaise are characteristic. Leukocyte counts are predictably normal and CT scans are generally nondiagnostic. At operation, surgeons can establish the diagnosis with 94 percent specificity

and 78 percent sensitivity. There is an excellent correlation between clinical symptomatology, intraoperative findings, and histologic abnormalities. Laparoscopy can be effectively used in the management of this clinical entity. Appendectomy is curative. Symptoms resolve postoperatively in 82 -93% of patients. Many of those whose symptoms are not cured or recur are ultimately diagnosed with Crohn disease.


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