Ultrasound could precede CT in acute appendicitis diagnosis

Color Doppler sonography should be the first imaging modality for triage of adult patients with suspected acute appendicitis, according to a study from Israel. Findings suggest CT should complement the examination, and only in selected cases.

Acute appendicitis is a common finding in emergency rooms worldwide that indicates urgent surgery. The accurate diagnosis of the condition is key, especially for elderly and pregnant patients for whom misdiagnosis or unnecessary surgery carry exponential risks.

The use of imaging, particularly CT, has significantly reduced the rates of negative laparotomies and death. But optimal imaging protocols now call for cost and radiation safety considerations as well, according to principal investigator Dr. Diana Gaitini of Rambam Health Care Campus in Haifa.

"CT has a slightly higher specificity rate and a higher sensitivity rate than ultrasound, but ultrasound can help the radiologist make a definitive diagnosis in most patients," she said.

Gaitini and colleagues at Rambam and the Technion-Israel Institute of Technology, also in Haifa, reviewed the medical records of 420 consecutive patients, aged 18 and older, who presented to the ER with clinically suspected acute appendicitis between January 2003 and June 2006. Patients underwent sonography of the right upper abdomen and pelvis and Doppler ultrasound of the right lower quadrant. One hundred and thirty-two patients with inconclusive results from clinical or ultrasound exams also underwent CT.

Although ultrasound missed the diagnosis in 23 patients with acute appendicitis, it correctly ruled out the condition in 312 of 326 negative cases. The investigators published their findings in the May issue of the American Journal of Roentgenology.

Two of the 420 cases were lost to follow-up. Sonography correctly diagnosed acute appendicitis in 66 of 75 patients. In the group of 132 inconclusive cases, CT correctly diagnosed 38 of 39 patients with the condition. Ultrasound and CT allowed alternative diagnoses in 82 and 42 patients, respectively. Sensitivity, specificity, positive and negative predictive values, and accuracy were 74.2%, 97%, 88%, 93%, and 92%, respectively, for sonography and 100%, 98.9%, 97.4%, 100%, and 99% for CT.

The higher diagnostic performances of CT needs to be evaluated against its disadvantages, according to Gaitini. The main rationales for trying color Doppler ultrasound first are its lack of ionizing radiation, which is key for a condition affecting predominantly a young patient population, higher availability, lower cost, and high specificity, she said.

"When the patient does not have acute appendicitis, the negative result of the color Doppler ultrasound examination is highly confident," Gaitini said.

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