The role of radiolabeled leukocyte imaging in the management of patients with acute appendicitis.

Acute appendicitis is a clinically challenging surgical disease particularly difficult to diagnosis in women and children. An atypical presentation of acute appendicitis is a major factor leading to delay in diagnosis and unnecessary surgery. Delay in diagnosis is associated with morbidity from perforation, abscess and prolonged hospitalization. The routine use of adjunctive imaging studies has not improved the diagnostic accuracy for acute appendicitis nor has impacted clinical outcome. 99mTc HMPAO-labeled leukocyte imaging is one diagnostic imaging test that has the potential of altering the clinical management of acute appendicitis. 99mTc HMPAO-labeled leukocyte imaging is highly sensitive for detecting even small inflammatory processes in the abdomen because of high target to background and early rapid uptake at sites of inflammation. We studied the use of 99mTc HMPAO-labeled leukocytes for diagnosis and management of suspected acute appendicitis in 124 patients with an atypical clinical presentation. Emergent imaging was performed immediately following injection of labeled leukocytes and continued until positive or through 2 hours if negative. The scan correctly and rapidly detected acute appendicitis in 50 of 51 patients with surgical confirmation for a sensitivity of 98%. The specificity was 82% leading to an overall accuracy of 90%. The high negative predicted value of 98% allowed early discharge from the emergency department and avoided costly observation in the hospital and potentially unnecessary surgery in these patients with negative scans. The negative exploratory laparotomy rate was 4% in this patient population compared to 9% in a similar population of patients who were not scanned. These data have been confirmed now in over 600 patients scanned in our department. The main drawbacks of 99mTc HMPAO-labeled leukocyte imaging are the requirement of blood handling and a delay in diagnosis because of the 2-hours preparation time prior to imaging. There are new radiopharmaceuticals on the horizon which have the potential of replacing 99mTc HMPAO-labeled leukocyte imaging and offer advantages of a shorter preparation time and no blood handling. These include 99mTc labeled monoclonal antibodies and chemotactic peptides. The 99mTc anti-SSEA-1 IgM antibody (LeuTech) is currently under investigation for use in acute appendicitis. In summary, nuclear medicine can play a key role in the diagnosis of acute appendicitis in patients with an atypical presentation. This technique is cost effective and appears to impact favorably on clinical outcome.