The sensitivity gap: US less reliable in kids with early appendicitis

Physicians should consider the duration of symptoms as they decide on an imaging strategy for children with suspected appendicitis. Ultrasound (US) delivered 81 percent sensitivity among children who presented in the first 12 hours of abdominal pain, and increased to 96 percent after 48 hours of pain, according to a study published in the November issue of <i>Annals of Emergency Medicine.</i>

Appendicitis is a common diagnosis among children. However, many patients present with atypical findings, and CT and ultrasound are often employed in the diagnostic evaluation of children who present with suspected appendicitis. Although CT provides higher accuracy than ultrasound, concerns about radiation exposure have resulted in increased use of ultrasound at pediatric hospitals.

As protocols evolve, research gaps remain. For example, researchers have not evaluated the performance of either imaging modality with respect to duration of pain. Imaging performed early in the disease process when the disease may be less “macroscopic” could result in false-negative findings, according to Richard G. Bachur, MD, of the division of emergency medicine at Children’s Hospital Boston, and colleagues.

Bachur and colleagues designed a study to evaluate the effect of duration of abdominal pain on diagnostic accuracy of CT and ultrasound. This analysis included 1,810 children, aged three to 18 years with suspected appendicitis.   

Sixty-eight percent of children underwent CT, 46 percent underwent ultrasound and 13 percent underwent both exams. A pediatric emergency physician categorized the duration of abdominal pain in hours: less than 12, 13 to 24, 25 to 36, 37 to 48 or 49 to 72.

A total of 38 percent of children were diagnosed with appendicitis, and 26 percent of these had perforated appendicitis.

The sensitivity or specificity of CT was not tied to duration of pain, according to the researchers. The sensitivity of CT ranged from 94 to 98 percent, and its specificity from 96 to 97 percent. The equivocal CT rate decreased with duration of pain.

Bachur and colleagues observed increasing sensitivity and negative predictive value for ultrasound as the duration of pain increased. They calculated sensitivity at 81 percent in the first 12 hours, with the rate rising to 96 percent for patients reporting more than 48 hours of abdominal pain. The researchers did not find an association between pain duration and the rate of equivocal ultrasound exams.

“With these findings, clinicians should not rely on ultrasonography early in the course of illness,” wrote Bachur et al. The researchers suggested observation and repeat ultrasound imaging, as necessary, for early negative or inconclusive ultrasound results. Other options include repeat clinical exams for patients with less than 24 hours of mild focal right lower quadrant pain. In contrast, when perforation or abscess is suspected, imaging should not be delayed even if duration of pain is short, according to the researchers.

“Clinicians should incorporate this time-dependent accuracy of imaging when deciding to obtain imaging for suspected appendicitis,” concluded Bachur et al.  

For more about CT, ultrasound and pediatric appendicitis, please read “Pediatric CT: Growing Pains,” in Health Imaging.