Presentation
Active gastrointestinal bleeding. Desire localization prior to intervention.
Patient Data
99mTc tagged RBCs (Ultratag)
Tagged red blood cell scan performed using 20 mCi of 99mTc-Ultratag IV.
Anterior planar images acquired for 1-minute demonstrate an abnormal focus of radiotracer (RBCs) in the central abdomen. The activity conforms to bowel, increases in intensity over time and moves antegrade and/or retrograde in a serpiginous pattern; consistent with an active small bowel bleed.
Incidental note is made of a vertically oriented collection of radiotracer in the low midline pelvis representing physiologic penile activity. Knowledge of this variant is helpful to avoid the false-positive diagnosis of a rectal bleed.
Case Discussion
Gastrointestinal bleeding (GIB) scintigraphy is indicated for evaluation of overt GIB. The goal of the examination is to determine if there is active bleeding, and if so, localize the site of intestinal bleeding and to possibly estimate the rate of blood loss.
The normal biodistribution of tagged red blood cells (RBCs) includes the blood pool (heart and vessels), liver, and spleen. Mild radiotracer activity is also often seen in the kidneys and urinary bladder due to the presence of unbound (free) pertechnetate. Physiologic penile activity can also be present in men.
The scintigraphic results of GIB scintigraphy will only be positive if the patient is actively bleeding at the time of imaging and hence the exam is typically performed for 1-2 hours in order to maximize sensitivity. Delayed imaging out to 24-hours is an option if the initial exam is negative and there is new clinical evidence of GIB.
The diagnostic criteria for a gastrointestinal bleed are that the focus of activity should be present outside the normal biodistribution, increase in intensity over time, move anterograde or retrograde, and conform to the path of bowel.
A large bowel source of bleeding is typically located peripherally and may show an inverted U-shaped configuration. A small bowel source, as in this case, is typically more centrally located and demonstrates a serpiginous pattern.