Appendicitis

CHAPTER 37

APPENDICITIS

D. PATRICK BRYANT AND HEIDI FRANKEL

In the time of Leonardo da Vinci, the appendix was ascribed a function as an organ capable of expanding and contracting, to deal with excessive wind and prevent perforation of the cecum. Over the ensuing years, others have recognized that the appendix served an immune function as well, namely, in the lymphocyte response. This is particularly true in ruminators.¹ Bollinger et al.² theorize that the appendix is responsible for maintaining homogeneity in the flora of the colon.

EMBRYOLOGY

The appendix is an organ derived from the midgut. It begins as a outpouching of the embryonic cecum and then lines up at the confluence of the taeniae. The vermiform appendix becomes visible in the eighth week of gestation (when fetal length is 10–12 cm), and the first accumulations of lymphatic tissue develop during the 14th and 15th weeks directly below the epithelium. Some lymphocytes penetrate into the epithelial layer of the vermiform appendix that distinctly contains fewer goblet cells than the other colic mucosa. The vermiform appendix, tonsils, and Peyer’s patches possess no draining lymphatic vessels.

ANATOMY

The appendix varies in size, but on average it is generally 6–9 cm in length and may be in a retrocecal, pelvic, retroileal, or right pericolic position, and at times within the wall of the cecum. The blood supply is from the appendiceal artery; the terminal branch of the ileocolic artery. It is an end artery and the ischemia that is part of the process in acute appendicitis is the result of no collateralized flow. Occasionally, the artery itself becomes thrombosed as part of the inflammatory process, resulting in a gangrenous appendix with perforation.

HISTORY

Perityphlitis was a diagnosis without a known causative factor until Dr. Reginald Fitz published his work in 1886 demonstrating that perityphlitis and perforated appendicitis were one and the same disease. In 1889, Dr. Charles McBurney presented his report on the early surgical intervention of appendicitis to the New York Surgical Society. In 1894, he presented his paper on the muscle splitting incision that bears his name. The procedure for appendectomy was largely unchanged for almost a century.

The first laparoscopic appendectomy was performed by Dr. Kurt Semm in May of 1980.³ Currently, well over half of the approximately 250,000 appendectomies performed annually in the United States are laparoscopically done. In addition to laparoscopy, the major advances in the care of appendicitis included the introduction of broad spectrum antibiotics, the improvement in preoperative diagnostic testing, and the use of interventional radiology to perform drainage procedures for periappendiceal abscesses.

EPIDEMIOLOGY

The incidence of appendicitis peaks in the mid to late teens with a slight male predominance (∼1.3: 1). The incidence of 84 per 100,000 patients has remained stable over time.⁴ The overall mortality of appendicitis is 0.5%, 1.7% in cases with perforation, and over 20% in patients over the age of 70.⁵

PATHOPHYSIOLOGY

Acute appendicitis is the most common surgical emergency treated in the acute care setting. Its classic presentation remains relatively unchanged over time; present in about 80% of those who present with lower abdominal pain. The standard presentation in a relatively young person is a result of luminal obstruction of the appendix. This obstruction may be related to hyperplasia of the germinal follicles or from a fecalith impacted in the appendiceal orifice. The capacity of the appendix is about 0.5 mL. With the orifice obstructed, the pressure in the lumen quickly rises above 60 mm Hg and ischemia results. The ensuing distension stimulates the visceral afferent nerves, leading to the nausea and emesis, as well as the periumbilical pain, which is emblematic of early disease. As the inflammatory process continues, the pain localizes to McBurney’s point when the inflamed appendix comes in contact with the peritoneum and the somatic afferent nerves are stimulated. As the pressure increases, vascular compromise develops and along with it, bacterial overgrowth, after which, perforation can be expected.

Perforation is clearly more of a problem in the pediatric population. Nearly one-half of young pediatric patients with acute appendicitis present to care after perforation.^5,6 Perforation is associated with vomiting, prolonged illness, and higher body temperatures. Perforation is also an important factor in morbidity and mortality, including prolongation of the hospital stay, development of a secondary abscess (pelvic, psoas, hepatic, tubo-ovarian), urinary retention, hematuria, and subacute and delayed bowel obstruction. Alternatively, patients with acute appendicitis who perforate may develop a “contained” abscess.

The entity of chronic appendicitis describes a disease process with symptoms over 7 or more days. The pathology tends to show more lymphocytic or eosinophilic infiltration. These patients have a greater diversity of abdominal complaints as well; pelvic, back, and bilateral lower abdominal pain, which makes diagnosis more difficult.

DIAGNOSIS

The “classic” history for appendicitis involves the patient presenting with periumbilical pain, which subsequently localizes to the right lower quadrant. At this point, the pain character changes from a dull ache or vague discomfort to a sharp “finger point” pain. This change is due to the change in the neurologic pathway involved. Periumbilical pain is due to the distenson of the appendix sending nociceptive signals via the celiac pathway through visceral afferents. Localized right lower quadrant pain develops from the irritation of the parietal peritoneum that corresponds to the dermatomal distribution of the somatic afferent nerve roots at McBurney’s point. Patients generally have a low-grade fever; it is rare for them to have a very high fever. They will invariably have malaise and lethargy. After the pain starts, patients often have some degree of nausea and emesis. These symptoms transpire over a 12–24 hours period; however, that can be variable as well.

On physical exam, the patient will often delineate the area of maximal tenderness (McBurney’s point). Rovsing’s sign is a peritoneal sign elicited by pressing on the left lower quadrant with resultant pain in the right lower quadrant. The psoas sign pertains to irritation of the psoas muscle that is described as pain in the pelvis after the patient extends his/her right thigh while lying on the left side. The obturator sign is demonstrated with the patient in the supine position and rotating a flexed right lower extremity medially.

A child with acute retrocecal or retroileal appendicitis (appendix deep to distal ileal bowel loops) may walk with exaggerated lumbar lordosis and have a slightly flexed right hip as a result of right psoas muscle spasm. Pain with extension of the right hip with the patient in left lateral decubitus position (psoas sign) and with internal rotation of the thigh (obturator sign) may be found with retrocecal appendicitis. If present, this indicates peritonitis.

Symptoms are contingent on the location of the appendix. For those patients with a retrocecal appendix, the pain is often posterior radiating to the groin, simulating the pain of renal colic. The patient may have associated microscopic hematuria. The anterior abdominal findings of tenderness and localized rebound are often less impressive in the patient with a retrocecal appendix. Those patients with an appendix lying in the pelvis can have pelvic pain with urinary symptoms.

LABORATORY DATA

The most diagnostic laboratory value for most patients with acute appendicitis is an elevated white blood count. This finding is most reliable in young persons, but less so in the elderly. If the WBC is normal without left shift, then the diagnosis of acute appendicitis should be reconsidered, although a normal WBC occurs in up to 30% of those with appendicitis. Of course, a markedly elevated WBC should raise the possibility of perforation. Urinalysis should be obtained to exclude nephrolithiasis. The presence of microhematuria may be caused by ureteral or bladder irritation from the adjacent appendicitis. In females of child-bearing age, a serum pregnancy test should be obtained. Additionally, a liver panel with amylase and lipase levels can be useful; pancreatitis should be considered in the differential diagnosis. Another marker that may be helpful is the C-reactive protein level. A normal C-reactive protein level has been associated with the absence of acute appendicitis.⁶

RADIOLOGY

An abdominal x-ray series (flat and upright) is a mainstay of the workup for abdominal pain, but generally will be unrevealing in appendicitis, with the rare exception of the radio-opaque fecalith. The other benefit of the plain radiograph is when it suggests bowel obstruction in a patient without a hernia or previous surgery. This can be the sign of a perforated appendicitis in someone with an atypical presentation.

The accuracy of ultrasound (US) depends upon the skill level of the sonographer. US findings suggestive of acute appendicitis include a noncompressible appendix of at least 6 mm in diameter. US has become a mainstay of diagnosis in the pediatric population. US does have its limitations, and while the ranges of reported specificity (88%–99%) and accuracy (82%–99%) for US have been acceptable, sensitivity (50%–100%) has varied considerably. Furthermore, US is relatively inexpensive and safe. Its biggest drawback is that negative findings do not exclude appendicitis with a high degree of confidence unless a normal appendix is visualized. However, appendiceal visualization rates in normal individuals without appendicitis vary widely in the published literature, from a high of 98%,⁷ to a low of 22%.⁸ A meta-analysis of three United States and three European studies with varied prevalence of acute appendicitis indicated that US was inferior to computed tomography (CT) in all instances.⁹

CT has become the diagnostic test of choice in many emergency departments and primary care facilities. CT findings of acute appendicitis include a visualized appendix >6 mm in size with periappendiceal stranding or wall thickening. A fecalith can be visualized in one quarter of cases of acute appendicitis. A contrast-filled appendiceal lumen without other abnormalities on CT essentially eliminates the diagnosis of acute appendicitis. If the appendix cannot be visualized on CT, the diagnosis cannot be excluded. Current generation high-resolution scanners produce sensitivity rates of 91%–97% and specificity rates of 91%–93%¹⁰ (Fig. 37.1). Particularly in centers where OR access is at a premium, utilization of CT to eliminate the negative appendectomy appears prudent. Further, a recent review suggests that a noncontrast CT compared to CT with contrast may provide equivalent diagnostic accuracy, expediting the workup.¹¹ Mere introduction of CT into a care algorithm in and of itself does not lower the published 10%–20% negative appendectomy rate. However, integrating its use into a management strategy that uses senior surgeon consultation early in the workup can dramatically lower this rate as reported by Antevil et al.¹² Clearly, the best use of this technology is in the premenopausal female, where Wagner and colleagues have demonstrated a nearly two-thirds reduction in the negative appendectomy rate.¹³ On the other hand, liberal use of CT does not appear to affect the rate of perforation. As a general rule, however, with a reliable history and physical exam, there is little reason for an adjunctive CT scan.¹⁴ The benefit of CT is in the patient with an unreliable exam or the inconsistent story. In addition, in elderly populations where other surgical conditions are common (ischemic colitis, Clostridium difficile colitis, colon cancer), CT may provide essential information. There is certainly concern for exposing the pediatric population to unnecessary radiation. This must be balanced with the morbidity of delaying the diagnosis in this population, one with a high perforation rate—20% in recent study.¹⁵