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The Appendix
Appendicitis remains one of the most common diseases faced by the surgeon in practice. It is the most common urgent or emergent general surgical operation performed in the United States and is responsible for as many as 300,000 hospitalizations annually. Although appendectomy is frequently the first “major” case performed by the surgeon in training, the impact of a timely diagnosis and prompt treatment is as impressive as that of any other major surgical intervention. It is estimated that as much as 6% to 7% of the general population will develop appendicitis during their lifetime, with the incidence peaking in the second decade of life. Despite its high prevalence in Western countries, the diagnosis of acute appendicitis can be challenging and requires a high index of suspicion on the part of the examining surgeon to facilitate prompt treatment of this condition, thereby avoiding the substantial morbidity (and even mortality) associated with delayed diagnosis and subsequent perforation. Appendicitis is much less common in underdeveloped countries, suggesting that elements of the Western diet, specifically a low-fiber, high-fat intake, may play a role in the development of the disease process.
Anatomy and Embryology
The appendix is a midgut organ and is first identified at 8 weeks of gestation as a small outpouching of the cecum. As gestation progresses, the appendix becomes more elongated and tubular as the cecum rotates medially and becomes fixed in the right lower quadrant of the abdomen. The appendiceal mucosa is of the colonic type, with columnar epithelium, neuroendocrine cells, and mucin-producing goblet cells lining its tubular structure. Lymphoid tissue is found in the submucosa of the appendix, leading some to hypothesize that the appendix may play a role in the immune system. In addition, evidence suggests that the appendix may serve as a reservoir of “good” intestinal bacteria and may aid in recolonization and maintenance of the normal colonic flora. Although historically removal of the appendix was not felt to result in any adverse sequelae, this has recently been challenged. For example, patients who have had previous appendectomy have been demonstrated to have a more difficult clinical course and overall poorer outcomes in recurrent cases of Clostridium difficile infection when compared with patients who have not undergone appendectomy. The theory is that the microbiome of the appendix has a protective function and that the loss of this eliminates an element of beneficial immunologic redundancy. In addition, a recently published epidemiological study found a significant link between appendectomy prior to age twenty and the development of prostate cancer, although a precise causative mechanism could not be elucidated.
As a midgut organ, the blood supply of the appendix is derived from the superior mesenteric artery. The ileocolic artery, one of the major named branches of the superior mesenteric artery, gives rise to the appendiceal artery, which courses through the mesoappendix . The mesoappendix also contains lymphatics of the appendix, which drain to the ileocecal nodes, along with the blood supply from the superior mesenteric artery. ,
The appendix is of variable size (5–35 cm in length) but averages 8 to 9 cm in length in adults. Its base can be reliably identified by defining the area of convergence of the taeniae at the tip of the cecum and then elevating the appendiceal base to define the course and position of the tip of the appendix, which is variable in location. The appendiceal tip may be found in a variety of locations, with the most common being retrocecal (but intraperitoneal) in approximately 60% of individuals, pelvic in 30%, and retroperitoneal in 7% to 10%. Agenesis of the appendix has been reported, as has duplication and even triplication. , Knowledge of these anatomic variations is important to the surgeon because the variable position of the appendiceal tip may account for differences in clinical presentation and in the location of the associated abdominal discomfort. For example, patients with a retroperitoneal appendix may present with back or flank pain, just as patients with the appendiceal tip in the midline pelvis may present with suprapubic pain. Both of these presentations may result in a delayed diagnosis, as the symptoms are distinctly different from the classically described anterior right lower quadrant abdominal pain associated with appendiceal disease.
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Appendicitis
History
The first appendectomy was reported in 1735 by a French surgeon, Claudius Amyand, who identified and successfully removed the appendix of an 11-year-old boy that was found within an inguinal hernia sac and that had been perforated by a pin. Although autopsy findings consistent with perforated appendicitis appeared sporadically thereafter in the literature, the first formal description of the disease process, including the common clinical features and a recommendation for prompt surgical removal, was in 1886 by Reginald Heber Fitz of Harvard University.
Notable advances in surgery for appendicitis include McBurney’s description of his classic muscle-splitting incision and technique for removal of the appendix in 1894 and the description of the first laparoscopic appendectomy by Kurt Semm in 1982. Laparoscopic appendectomy has become the preferred method for management of acute appendicitis among surgeons in the United States and may be accomplished using several (typically three) trocar sites or through single-incision laparoscopic surgical techniques. Finally, but of no less significance, was the development of broad-spectrum antibiotics, interventional radiologic techniques, and better surgical critical care strategies, all of which have resulted in substantial improvements in the care of patients with appendiceal perforation and its subsequent complications.
Pathophysiology and Bacteriology
Appendicitis is caused by luminal obstruction. The appendix is vulnerable to this phenomenon because of its small luminal diameter in relation to its length. Obstruction of the proximal lumen of the appendix leads to elevated pressure in the distal portion because of ongoing mucus secretion and production of gas by bacteria within the lumen. With progressive distention of the appendix, the venous drainage becomes impaired, resulting in mucosal ischemia. With continued obstruction, full-thickness ischemia ensues, which ultimately leads to perforation. Bacterial overgrowth within the appendix results from bacterial stasis distal to the obstruction. This is significant because this overgrowth results in the release of a larger bacterial inoculum in cases of perforated appendicitis. The time from onset of obstruction to perforation is variable and may range anywhere from a few hours to a few days. The presentation after perforation is also variable. The most common sequela is the formation of an abscess in the periappendiceal region or pelvis. On occasion, however, free perforation occurs that results in diffuse peritonitis.
Because the appendix is an outpouching of the cecum, the flora within the appendix is similar to that found within the colon. Infections associated with appendicitis should be considered polymicrobial, and antibiotic coverage should include agents that address the presence of both gram-negative bacteria and anaerobes. Common isolates include Escherichia coli , Bacteroides fragilis , enterococci, Pseudomonas aeruginosa , Klebsiella pneumoniae , and others ( Table 51.1 ). The choice and duration of antibiotic coverage and the controversies surrounding the need for cultures are discussed later in the chapter.
Table 51.1
Bacteria commonly isolated in perforated appendicitis.
Adapted from Song DW, Park BK, Suh SW, et al. Bacterial culture and antibiotic susceptibility in patients with acute appendicitis. Int J Colorectal Dis . 2018;33:441–447.
| Type of Bacteria | Isolates (n = 694) |
|---|---|
| Gram-Negative Bacteria | |
| Escherichia coli | 448 (64.6%) |
| Pseudomonas aeruginosa | 114 (16.4%) |
| Klebsiella pneumoniae | 37 (5.3%) |
| Citrobacter species | 18 (2.6%) |
| Enterobacter species | 10 (1.4%) |
| Serratia marcescens | 3 (0.4%) |
| Raoultella planticola | 3 (0.4%) |
| Comamomas testosteroni | 2 (0.3%) |
| Aeromonas species | 2 (0.3%) |
| Proteus species | 2 (0.3%) |
| Acinetobacter species | 1 (0.1%) |
| Yersinia species | 1 (0.1%) |
| Morganella species | 1 (0.1%) |
| Gram-Positive Bacteria | |
| Enterococcus species | 27 (3.9%) |
| Streptococcus species | 20 (2.9%) |
| Staphylococcus species | 5 (0.7%) |
The causes of the luminal obstruction are many and varied. These most commonly include fecal stasis and fecaliths but may also include lymphoid hyperplasia, neoplasms, fruit and vegetable material, ingested barium, and parasites such as ascaris or pinworm infestation. Pain associated with appendicitis has both visceral and somatic components. Distention of the appendix is responsible for the initial vague abdominal pain (visceral) often experienced by the affected patient. The pain typically does not localize to the right lower quadrant until the tip becomes inflamed and irritates the adjacent parietal peritoneum (somatic) or perforation occurs, resulting in localized peritonitis. ,
Differential Diagnosis
Appendicitis must be considered in every patient (who has not had an appendectomy) who presents with acute abdominal pain. Knowledge of disease processes that may have similar presenting symptoms and signs is essential to avoid an unnecessary or incorrect operation. Consideration of the patient’s age and gender may help narrow the list of possible diagnoses. In children, other considerations include but are not limited to mesenteric adenitis (often seen after a recent viral illness), acute gastroenteritis, intussusception, Meckel diverticulitis, inflammatory bowel disease, and (in males) testicular torsion. Nephrolithiasis and urinary tract infection may be manifested with right lower quadrant pain in either gender. ,
In women of childbearing age, the differential diagnosis is expanded even further. Gynecologic pathology may be mistaken for appendicitis and result in a higher negative appendectomy rate than in male patients of comparable age. These processes include ruptured ovarian cysts, mittelschmerz (midcycle abdominal pain occurring with ovulation), endometriosis, ovarian torsion, ectopic pregnancy, and pelvic inflammatory disease. ,
Two other patient populations deserve mention. In the elderly, consideration must be given to acute diverticulitis and malignant disease as possible causes of lower abdominal pain. In the neutropenic patient, typhlitis (also known as neutropenic enterocolitis) should also be considered within the differential diagnosis. Appendicitis in these special populations is discussed in greater detail later in the chapter.
Presentation
History
Patients presenting with acute appendicitis typically complain of vague abdominal pain that is most commonly periumbilical in origin and reflects the stimulation of visceral afferent pathways through the progressive distention of the appendix. Anorexia is often present, as is nausea with or without associated vomiting. Either diarrhea or constipation may be present as well. As the condition progresses and the appendiceal tip becomes inflamed, resulting in peritoneal irritation, the pain localizes to its classic location in the right lower quadrant. This phenomenon remains a reliable symptom of appendicitis , and should serve to further increase the clinician’s index of suspicion for appendicitis ( Fig. 51.1 ).
Whereas these symptoms represent the “classic” presentation of appendicitis, the clinician must be aware that the disease may be manifested in an atypical fashion. For example, patients with a retroperitoneal appendix may present in a more subacute manner, with flank or back pain, whereas patients with an appendiceal tip in the pelvis may have suprapubic pain suggestive of urinary tract infection. , Although cases such as these are less common than the typical presentation, knowledge of these variations is essential to maintain the necessary index of suspicion to permit a prompt and accurate diagnosis.
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