eMedicine Specialties > General Surgery > Abdomen

Vermiform Appendix: Workup

Author: Steven L Lee, MD, Chief, Pediatric Surgery, Department of Surgery, Kaiser-Permanente, Los Angeles Medical Center
Coauthor(s): Shant Shekherdimian, MD, Consulting Surgeon, Department of Surgery, Kaiser Foundation Hospital; Jeffrey J DuBois, MD, Consulting Staff, Division of Pediatric Surgery, Kaiser Permanente, North Sacramento Medical Center
Contributor Information and Disclosures

Updated: Nov 24, 2008

Workup

Laboratory Studies

• Complete blood cell (CBC) count with manual differential
  • The WBC count is often mildly elevated, and a left shift is present. When an extremely elevated WBC count is present, either the patient has a perforated appendix, or another process, such as a viral illness, is responsible.
  • Both pediatric patients and adult patients do not always manifest an elevated WBC count.³ Thus, an increased percentage of bands on manual cellular differential may be just as reliable. Because an accurate history and physical is often more difficult to obtain, a persistently elevated percentage of bands may be the only objective finding of appendicitis in the pediatric patient.
• Urinalysis (UA): Although not mandatory, a UA is often obtained to rule out urinary tract infections; however, pyuria (WBCs in the urine) is commonly observed in appendicitis because the inflammatory process may lie adjacent to the right ureter.
• Electrolyte and renal panel: This test is not required but may be useful to help guide electrolyte resuscitation prior to appendectomy.

Imaging Studies

• No imaging studies are needed in patients with classic appendicitis. This has been confirmed by a retrospective study determining predictive values for appendicitis (Alvarado score) based on history and physical findings. Prospective comparison of the accuracy of the Alvarado score with ultrasound findings was similar.¹¹
• Additional imaging studies may be required in the workup of atypical appendicitis. Controversy exists as to the most accurate, rapid, and cost-effective method of diagnosing atypical appendicitis while avoiding delays that may increase morbidity.
• Plain abdominal radiographs - Abdominal series
  • For the most part, abdominal roentgenograms are not helpful in making the diagnosis of appendicitis. Roughly 85% of radiograph findings are normal, and 10% have nonspecific findings.³
  • The 2 most common nonspecific findings associated with appendicitis are ileus and small bowel obstruction. A more specific abnormality is a fecalith in the RLQ, but this is observed in only 4-5% of radiographs.
  • Rarely, free air under the diaphragm may also be present in patients with perforated appendicitis.
• Abdominal/pelvic ultrasound
  • Ultrasound is an ideal noninvasive means to visualize the abdominal cavity. It is inexpensive and portable, and it can be rapidly performed with little or no patient preparation. Most importantly, it poses no ionizing radiation risk to the patient; therefore, it is particularly safe to use in children and pregnant women. On the other hand, it is operator-dependent, which means that it requires some experience and expertise to produce consistent quality results.
  • The wall elements of the appendix have a typical "target" appearance and can be visualized using graded ultrasonography compressive technique with a high resolution transducer, occasionally with supplement of color Doppler.
  • Appendicitis is suspected when the study demonstrates wall thickening (>8-10 mm), luminal distention, and lack of compressibility. In addition, ultrasound is useful in detecting free intraperitoneal fluid and fluid collections consistent with abscess formation.
  • Prospective studies have shown excellent results, with an average sensitivity of 86% and a specificity of 94% under the conditions of well-controlled clinical trials, namely in the hands of experienced examiners.¹² In addition, many reported studies included patients with classic appendicitis instead of patients with equivocal clinical histories and physical findings. Such good results reported in prospective clinical trials were not frequently duplicated in routine clinical conditions. In fact, the accuracy of ultrasonography was no better than that based on clinical evaluation by the surgeons, and low sensitivity and high false-negative rates have been reported.^3,13,14
  • Ultrasound is most useful for excluding other diagnoses. In women, pelvic pathology, such as pelvic inflammatory disease, ruptured Graafian follicle, twisted ovarian cyst or tumor, endometriosis, and ruptured ectopic pregnancy, can be readily detected by ultrasonography.
• Contrast-enhanced CT scans
  • CT scan findings become more prominent with enhanced disease. Specific findings include an edematous, thick-walled appendix, inflammatory streaking of surrounding fat, and the presence of an appendicolith. Abscess formation, a small amount of free air in the RLQ, and a pericecal phlegmon suggest a perforated appendix.
  • In most clinical trials, CT appears superior to ultrasonography in the evaluation of the acute abdomen. Since CT scans have shown to yield precise information, it has increasingly become a screening tool for acute appendicitis in the emergency department. In well-conducted clinical trials, CT scans have excellent sensitivity and specificity, in the range of 87-100% and 91-97%, respectively.^15,16,17 Again, such good results reported in prospective clinical trials were not frequently duplicated in routine clinical conditions. Use of CT scans in patients who have acute appendicitis had risen from 25% to 68% over a 5-year period and yet the rate of negative appendectomy remained largely unchanged, suggesting the information obtained from the imaging studies may not have much influence on the clinical decision-making process.¹⁸
  • One of the potential clinical dilemmas involves the failure of CT scan to identify a normal appendix. The difficulty in identifying the normal appendix by CT scan ranges from 44-51% in asymptomatic patients.^19,20 It is probably unsafe to assume that nonvisualization of the appendix excludes the diagnosis of acute appendicitis unless there is a collaborating history or physical findings. In a patient who has no evidence of inflammation in the ileocecal region and the appendix is not visualized, there is a chance that the patient indeed still has acute appendicitis.
• Tc-labeled WBC scan: Despite a reported sensitivity of 98% and specificity of 95%, the time required for performing the scan and its lack of around-the-clock availability make this a less-than-ideal diagnostic test for appendicitis.²¹
• Barium contrast studies
  • Historically, a single-contrast barium enema was used to diagnose patients with atypical signs and symptoms. The goal was to assess the patency of the appendiceal lumen. In addition, the colonic wall could be examined for extrinsic mass effects caused by appendicitis.
  • Although this remains a simple, inexpensive, and safe study, it has been largely replaced by ultrasound and CT scanning and is rarely used today.

Diagnostic Procedures

• The only diagnostic procedure for acute appendicitis short of open exploration is diagnostic laparoscopy.

Histologic Findings

A small percentage of normal-appearing appendices have focal appendicitis on microscopic examination. In addition, early appendicitis may be encountered in the form of increased interleukin (IL)-2 and tumor necrosis factor (TNF)-alpha secretion, which may not be detected on gross examination. Approximately 1% of patients have appendicitis from carcinoid or adenocarcinoma.³

Staging

Appendicitis progresses through the following stages: acute or focal appendicitis, suppurative appendicitis, gangrenous appendicitis, and perforated appendicitis.⁹

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