G.I. Bleeding: Radionuclide Scan Gianni Bisi Torino, March 31, 2006

G.I. Bleeding scintigraphy has been used for over 20 years for localizing sites of gastrointestinal bleeding (small or large bowel). The most relevant features of G.I. Bleeding Scintigraphy are: high sensitivity, non invasiveness, absence of contraindications. Requirements for an effective use of G.I. Bleeding scintigraphy are: availability of a 24H/7 days open Nuclear Medicine dept., ready answer to clinical questions, and therefore inclusion of G.I. Bleeding Scintigraphy into the emergency N.M. procedures (Pulmonary Embolization, Brain death, AMI rule out, Scrotal torsion, etc..)

G.I. Bleeding Scintigraphy: technical aspects Two different (and opposite) methods and radiopharmaceuticals may be used: *99mTc-labeled sulfur colloid (SC) *99mTc-labeled red blood cells (RBC) A further method can be used to localize ectopic gastric mucosa, such as in Meckel’s diverticulum.

G.I. Bleeding scintigraphy with 99mTc-SC 99mTc-SC showes a rapid intravascular clearace (half time of 2-3 min), since colloids are trapped in the reticuloendothelial system (liver, spleen, bone marrow), so that extravasation into the Gut remains visible as a hot spot in the otherwise “cold” abdomen. To be an effective diagnostic tool, it requires the presence of active bleeding at the time of tracer administration (not useful in intermittent bleeding). It takes a short time to be accomplished, it is sensitive, but with limited ability to precisely identify the site of bleeding (if a simple gamma-camera is used instead of a more sophisticated SPECT/CT system). G.I. bleeding may be difficult to identify in the upper abdomen, due to the shadowing effect of “hot” liver and spleen.

99mTc-SC: bleeding at the hepatic flexure

G.I. Bleeding scintigraphy with 99mTc-RBC 99mTc-RBC have a stable persistence within the blood pool, allowing the possibility of imaging over a prolonged period. Since gastointestinal bleeding is typically intermittent and episodic, this feature is attractive, by increasing the yield of positive studies, in presence of intermittent bleeding. A frequent evaluation is required: typically a half hour dynamic scan followed by 6 and 24 hours static images, if the early phase is negative. Theoretically the underlying background due to circulating RBC may result in an increase of the threshold for the amount of bleeding for detectability. The positivity only in delayed images is only confirmatory of intermittent bleeding, not useful in identifying the bleeding site.

99mTc-RBC: bleeding in the cecum A: dynamic study B: 5 min C: 10 min

Sensitivity for gastrointestinal bleeding detection Method Bleeding rate Angiography 0.5-1 ml/min 99mTc-SC 0.05-0.1 ml/min 99mTc-RBC 0.1 ml/min (rate dependent time until positive)

Potential causes of Angiographic failure to detect gastrointestinal bleeding, for which radionuclide scan may be helpful Hemorrhage less than 0.5 ml/min Venous bleeding Technical failure Resolution of bleeding Temporary cessation of bleeding Hypotension Intermittent source

99mTc-RBC: bleeding in the small bowel in patient with cirrhosis. It is possible to appreciate the typical progression of activity in the bowel over time, due to peristaltic movements

99mTc-RBC: criteria to identify the site of bleeding Central abdomen location: small bowel Peripheral abdomen location: large bowel Since extravasated blood into the bowel usually progresses forward (but sometimes also backwards), it is important to identify the earliest site of bleeding more than the most proximal site of blood in the bowel, by using the dynamic sequence of images.

99mTc-RBC: bleeding in the hepatic flexure It is possible to appreciate forward and backwards progression of radioactive blood in the bowel

Early images (10-30 sec) Late images (24-25 min) 99mTc-RBC in G.I. bleeding with rapid forward transit Early images (10-30 sec) Late images (24-25 min)

Early images (1-3 min) Late images (45-48 min) 99mTc-RBC in G.I. bleeding with backwards transit Early images (1-3 min) Late images (45-48 min)

Early images (1-5 min) Late images (45-50 min) 99mTc-RBC in G.I. intermittent bleeding Early images (1-5 min) Late images (45-50 min)

99mTc-RBC in G.I. minimal bleeding 10-40 sec 26-29 min 79-82 min 162-165 min

Accuracy of G.I. Bleeding scintigraphy with 99mTc-RBC (pooled data from the literature in more than 1500 cases) Rate of positive studies: 52% (range 22%-96%) Correct identification of bleeding site: 81% (range 20%-96%) Whilst the rate of positive studies is linked to the rate of actual bleeding during the study time, the correct identification of the bleeding site is linked to correct methodology (i.e. the correct sequence of images).

Identification of G.I. Bleeding from Meckel’s diverticulum When G.I. bleeding is suspected to originate from a Meckel’s diverticulum (ectopic gastric mucosa), it is preferable to use, as radiopharmaceutical, 99mTc-pertechnetate, with the patient pretreated with cimetidine or pentagastrine. With this method the Meckel’s diverticulum can also be identified in the absence of active bleeding at the time of the study

Meckel’s diverticulum

Meckel’s diverticulum Scintigraphic study performed with 99mTc-pertechnetate, premedication with cimetidine

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