Multiple static images from a Tc99m-HMPAO (Ceretec) WBC study were obtained 30 minutes after tracer injection. Normal activity is seen within spleen, liver, bone marrow, and bladder. Abnormal WBC accumulation is seen to involve a long segment of the right and transverse colon (arrows).

Differential Diagnosis

The liver, spleen, and bone marrow normally accumulate Tc99m-HMPAO–labeled leukocytes. Normal excretion of technetium complexes are also seen within the bladder and bowel on later imaging (unlike WBCs labeled with indium 111-oxine, which should not normally show bladder/bowel excretion).

•  Inflammatory bowel disease (IBD): Tc99m-HMPAO–labeled WBC activity is seen in a pattern corresponding to large bowel that is abnormal (on early imaging) and compatible with colonic inflammation or infection.

•  Pseudomembranous colitis: Bowel infection cannot be reliably differentiated from inflammation on WBC scan. A history of prolonged antibiotic use would favor this diagnosis.

•  Gastrointestinal bleeding: This can look similar to IBD if active. Tracer will move over time if sequential images are obtained.

Essential Facts