Detection of acute appendicitis by technetium 99 HMPAO scanning

The diagnosis of acute appendicitis can be difficult. Barium enemas, computed tomography (CT) scans, ultrasound examinations and Indium scans are used to aid in making the diagnosis with varying degrees of success. This blinded, prospective study reports the use of a Technetium 99-m Hexamethylpropyleneamineoxide (HMPAO) labelled white blood cell scan in 30 patients with suspected appendicitis. Autologous white blood counts from 25 cc of whole blood labelled with Tc-99 HMPAO were reinjected into patients. Abdominal imaging was performed at a half hour postinjection and repeated at 2 to 4 hours postinjection. A positive study showed an increased isotope uptake in the right lower quadrant. Nineteen patients had histologically proven appendicitis. Three of these patients were excluded because they were operated on before scan completion. Thirteen of the remaining 16 patients with appendicitis had positive studies (false negative rate = 19%). All patients without appendicitis had either negative scans or scans that detected other intra-abdominal diseases, such as diverticulitis, tubo-ovarian abscess, or small bowel infarction (false positive rate = 0%). Overall, this Tc-99 HMPAO study had a sensitivity of 81 per cent, a specificity of 100 per cent and an overall accuracy of 89 per cent. The 4-hour Tc-99 HMPAO WBC scan is a useful, noninvasive test for confirming the clinical diagnosis of acute appendicitis, but it may prove more valuable as a diagnostic study to rule out appendicitis in patients that have abdominal pain of unclear etiology.