Work Up of Suspected Appendicitis

Historically, appendicitis has been a clinical diagnosis, however, when the clinical impression is relied upon for diagnosis, a normal appendix is removed in approximately every fifth patient who undergoes appendectomy. Additionally, the diagnosis is initially clinically overlooked in every fifth patient who has appendicitis. The national average false positive rate of 20% on clinical examination rises even further in the subgroup of women in their reproductive years, where the clinical impression of appendicitis may be wrong 40-45% of the time.

Imaging is no replacement for clinical judgement, especially in today's era of cost containment. However, in the diagnosis of acute appendicitis, currently available imaging technology has the potential to spare many patients an unnecessary invasive procedure and may often establish other diagnoses, which may be non-surgical. Routine use of preoperative imaging can result in a significant decrease in the cost of treating patients with suspected appendicitis by deferring the cost of unnecessary surgery in 20% of patients, as well as the cost of delayed diagnosis in another 20% of patients. Preoperative CT scanning in patients with suspected appendicitis will improve patient care, and has the potential to lower the total global U.S. costs of treating patients with this diagnosis by up to $187,000,000 per year.

Click for large, high-resolution images:
CT image of a normal appendix
CT image of appendicitis
Coronal reconstructed CT of mesenteric lymphadenitis

Spiral CT can be a very useful tool in the evaluation of appendicitis. Within the last few years, there has been a significant improvement in CT technology with the advent of spiral scanning. A recent study from the Massachusetts General Hospital found the sensitivity of spiral CT for the diagnosis of acute appendicitis to be 100%, with an accuracy rate of 98%. A normal appendix was seen in all patients without appendicitis that were scanned using their technique, which utilized oral and rectal, but no intravenous contrast. Thin section spiral scanning is performed, usually within an hour of administration of water-soluble oral contrast after patients are clinically evaluated in an office or urgent care setting. Although the normal appendix can frequently be seen on non-contrast CT's of the urinary system, the use of rectal contrast improves visualization of the appendix and cecum. This technique can be replicated with any spiral CT scanner and as this focused study does not use intravenous contrast, the cost of the exam is decreased.

In addition to excluding the diagnosis of appendicitis, CT also has utility in preoperative planning when appendicitis is present. CT is sensitive to the presence of peri-appendiceal abscess and phlegmon, extensive cecal inflammatory changes, or free fluid, which are relative contraindications to laproscopic appendectomy. If these findings are discovered at the time of laparoscopic appendectomy, then the surgeon may be obligated to convert to an open appendectomy, which not only increases unnecessary costs for laproscopic disposables, but also contributes to an overall longer procedure time. We have found this use of CT to be an effective and sensitive test in our hands, and appendiceal CT is frequently ordered by both the ER and surgical staff at Hilo Medical Center. CT also allows us to frequently visualize non-surgical causes of RLQ pain, such as mesenteric adenitis and ileitis, precluding the need for hospitalization and observation.

Ultrasound may visualize an abnormal appendix, particularly if the patient has a small body habitus. Visualization of the normal appendix, however, can be quite technically difficult and is operator-dependent. A normal appendix is only occasionally seen, especially in obese patients. We still perform ultrasound of the appendix using the graded compression technique, particularly if the examination is performed in conjunction with a pelvic ultrasound for a female in whom adnexal pathology is of primary concern. Ultrasound may not be a cost-effective test in those patients in whom appendicitis is of primary concern, because the appendix is frequently ultrasonically occult.

In the past a barium enema was an occasional requested examination for appendicitis. The appendix was felt to be normal if the lumen filled with barium. The normal appendix, however, fills with barium only about 70% of the time, which gives a potential false positive rate of 30%. Additionally, we have seen several cases in which a normal appendix appears to fill on plain films, but CT confirms inflammatory changes isolated to the appendix tip.

REFERENCES:

Rao PM, Rhea JT, et al. Helical CT technique for the diagnosis of appendicitis: prospective evaluation of a focused appendix CT examination. Radiology 1997; 202: 139-144

Rao PM, Rhea JT, et al. CT diagnosis of mesenteric adenitis. Radiology 1997; 202: 145-149

Rao PM, Rhea JT, et al. Appendicitis: use of arrowhead sign for diagnosis at CT. Radiology 1997; 363-366

Balthazar EJ, Megibow AJ, et al. CT of appendicitis. AJR 1986;147: 705-710

Grosskreutz SR, Goff WB, et al. CT of the normal appendix. J Comput Assist Tomogr 1991;vol 15: 575-577

Rhea TR, Rao PM, et al. A focused appendiceal CT technique to reduce the cost of caring for patients with clinically suspected appendicitis. AJR 1997; 169: 113-118