Observational and retrospective case-control study based on a series of patients with LGIB who underwent CTA for suspected active bleeding in a tertiary hospital.

Cases and controls were defined according to whether CTA was positive or negative for active bleeding, respectively. Several sociodemographic, clinical and blood test-related variables were collected. The analytical parameters were collected immediately prior to CTA and from the previous results within the previous 7 days. Hemodynamic instability was defined as a mean arterial pressure (MAP) < 65 mmHg and/or a systolic blood pressure (SBP) < 90 mmHg.

The radiological finding that confirms the active nature of the bleeding is the extravasation of iodinated contrast. It is defined as an accumulation of contrast material in the intestinal lumen, which changes in size and attenuation in successive phases. In our study, depending on the phase in which the extravasation was observed, the bleeding was classified as arterial (detected in the arterial phase) or venous (detected in the portal venous and/or delayed phases but not in the arterial phase).

Figure 1 and Figure 2 show examples of patients with LGIB with active bleeding on CTA, arterial and venous, respectively, from our sample. Figure 3 shows an example of a patient with LGIB without active bleeding on CTA from our sample.

Fig 1: Figure 1: 76-year-old patient with a history of diverticulosis and on anticoagulant treatment, who arrives to the emergency department with rectal bleeding and hemodynamic and analytical repercussion. Axial CT images of the abdomen and pelvis show an active arterial bleeding in the transverse colon. Pre-contrast study (A) and after intravenous iodinated contrast in the late arterial phase (B), portal venous phase (C), and late venous phase (D). Contrast extravasation into the colonic lumen in the arterial phase (white arrow in B), which changes shape and increases in size in the subsequent phases (black arrows in C and D).

Fig 2: Figure 2: An 81-year-old patient with a history of ulcerative colitis arrives to the emergency department due to an isolated episode of rectal bleeding with hemodynamic repercussion. Axial CT images of the abdomen and pelvis show active venous bleeding in the rectal lumen. The pre-contrast study (A) and post-contrast with iodinated intravenous contrast in the late arterial phase (B), portal venous phase (C), and late venous phase (D) demonstrate contrast extravasation into the rectal lumen, not visible in the arterial phase and only evident in the portal venous phase (white arrow in C).

Fig 3: Figure 3: 81-year-old patient with no relevant medical history, who arrives to the emergency department with episodes of frank rectal bleeding without hemodynamic or analytical repercussions. Axial CT images of the abdomen and pelvis show no evidence of active bleeding. Pre-contrast study (A) and after intravenous iodinated contrast in the late arterial phase (A), portal venous phase (C), and late venous phase. No signs of contrast extravasation suggestive of active bleeding are observed. There is irregular circumferential mural thickening of the upper rectum-sigmoid with marked heterogeneous enhancement, consistent with a neoplastic process (*). Note the presence of diverticula in the sigmoid colon, without signs of acute complication (white arrows).

Descriptive and contrastive analyses were performed between the two groups, as well as according to whether the active bleeding was arterial or venous in the group of cases. Subsequently, univariate and multivariate logistic regression analyses were performed to predict active bleeding and area under the curve (AUC) values were obtained.