Lower gastrointestinal bleeding occurs distal to the ligament of treitz and may involve the small bowel, colon and rectum .

Active lower gastrointestinal bleeding is a common, potentially life threatening medical presentation that can be challenging to localize and treat .

There are many diseases that may cause lower gastrointestinal bleeding, including angiodysplasia, diverticulosis, benign or malignant bowel neoplasm, inflammatory bowel disease, ischemic bowel disease, and infectious bowel disease.

Often, gastrointestinal bleeding will stop spontaneously, but in approximately 25% of patients, bleeding is massive or recurrent, requiring imaging localization and directed therapy.

Accurate and prompt diagnosis of the bleeding source is crucial because mortality can be as high as 40%if there is hemodynamic instability in patients .

Because of the length of GI tract, the multitude of pathologic processes that can result in GI bleeding, imaging plays a primary role in the diagnosis .

Multislice CT angiography (MSCTA) provides a relatively non-invasive and effective way of localising the source of bleeding, especially in patients with continuous bleeding .

MSCTA is being increasingly used because it is a widely available, non-invasive and fast diagnostic technique that allows for the visualization of the entire intestinal tract and its lesions, the identification of the vascularity and possible vascular abnormalities. In addition, this technique does not require preparation in patients with acute bleeding.

Inclusion Criteria:

• Patients presenting to assiut university hospital with active lower gastrointestinal bleeding.

Exclusion Criteria:

• Patients whom are sensitive to contrast. Pregnant women. Patients with renal insufficiency