Dynamic contrast-enhanced computed tomography for small bowel bleeding: Two cases of arteriovenous malformation and gastrointestinal stromal tumor

Case 1

An elderly woman in her 80s was referred to our hospital for the evaluation of persistent anemia. Approximately 1 year before presentation, anemia had been detected and upper and lower gastrointestinal endoscopy as well as CT had been performed; however, no bleeding source was identified. Although the imaging protocol used at the referring institution 1 year earlier was unavailable, it is likely that CT without a dedicated arterial phase, such as DCE-CT, was not performed, which may explain why the lesion was not detected at that time. Thereafter, she received intermittent blood transfusions at another outpatient clinic, but her anemia did not improve, prompting referral for further investigation. Her medical history included hypertension, right femoral fracture, status post right inguinal hernia repair, paroxysmal atrial fibrillation, neurogenic bladder, and osteoporosis. She was taking multiple antihypertensive agents, a gastric acid–suppressive agent, hemostatic agents, and medications for bone metabolism. She was not receiving any anticoagulant or antiplatelet therapy. Laboratory findings on admission were as follows: white blood cell count, 4.2 × 10³/μL; red blood cell count, 317 × 10⁴/μL; hemoglobin, 10.1 g/dL; mean corpuscular volume, 95.7 fL; hematocrit, 30.3%; platelet count, 143 × 10³/μL; prothrombin time– international normalized ratio, 0.91; activated partial thromboplastin time, 21.5 s; aspartate aminotransferase, 20 U/L; alanine aminotransferase, 10 U/L; alkaline phosphatase, 44 U/L; total bilirubin, 0.4 mg/dL; albumin, 3.2 g/dL; blood urea nitrogen, 35.5 mg/dL; creatinine, 0.80 mg/dL; and estimated glomerular filtration rate, 51.1 mL/min/1.73 m². These findings indicated normocytic anemia accompanied by hypoalbuminemia and mild renal dysfunction, while no apparent abnormalities were observed in coagulation parameters.

On non-contrast CT, no definite lesion was identified [Figure 1a]. DCE-CT demonstrated a mass-like lesion within the small bowel wall showing marked enhancement in the arterial phase [Figure 1b]. In the delayed phase, the enhancement of the lesion was reduced compared with that in the arterial phase [Figure 1c]. In addition, early opacification of a vein continuous with the lesion was observed in the arterial phase, consistent with early venous drainage [Figure 1b, d and e]. The mean CT attenuation values of the lesion were 38 Hounsfield units (HU) on non-contrast CT, 494 HU in the arterial phase, and 191 HU in the delayed phase, indicating prominent washout from the arterial to the delayed phase. In this case, DCE-CT was performed using 80 mL of iopamidol (300 mg iodine/mL) injected at a rate of 2.7 mL/s, and the arterial phase was acquired 40 s after the start of contrast injection. The mean CT attenuation values of the left common iliac artery measured on the same slice were 552 HU in the arterial phase and 224 HU in the delayed phase, demonstrating enhancement comparable to that of the lesion in both phases. No evidence of contrast extravasation was observed. Double-balloon enteroscopy revealed an approximately 10-mm mass with partial ulceration in the small bowel [Figure 1f], without the evidence of active bleeding. Based on these findings, a small bowel tumor, most likely a vascular lesion causing chronic bleeding and anemia, was suspected. As the patient was hemodynamically stable, elective partial resection of the small bowel was performed on hospital day 9. Macroscopic examination of the resected specimen revealed an ulcer on the small bowel mucosa [Figure 1g]. Histopathological examination demonstrated dilated, tortuous, and thick-walled abnormal vessels in the submucosa, leading to a diagnosis of AVM [Figure 1h].

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Figure 1: Small bowel arteriovenous malformation (AVM) in Case 1. An elderly woman in her 80s presented with persistent anemia. Dynamic contrast-enhanced computed tomography (CT) demonstrates a small bowel lesion with marked arterial-phase hyperenhancement and early venous drainage, which are characteristic imaging features of a vascular lesion such as AVM. Elective surgical resection was subsequently performed, and histopathology confirmed the diagnosis. (a) Axial non-contrast CT of the abdomen shows no definite lesion. The mean attenuation value measured at the site later identified as the lesion on contrast-enhanced CT (arrow) was 38 Hounsfield units (HU). (b) Axial arterial-phase contrast-enhanced CT image at the level of the small bowel demonstrates a small mass-like lesion in the small bowel wall with intense enhancement (mean attenuation value, 494 HU) (arrow), comparable to that of the adjacent left common iliac artery (thin arrow). The yellow arrowhead demonstrates early opacification of a vein continuous with the lesion, consistent with early venous drainage. (c) Axial delayed-phase contrast-enhanced CT image at the level of the small bowel shows reduced enhancement of the lesion compared with the arterial phase (mean attenuation value, 191 HU) (arrow). The attenuation value of the left common iliac artery measured on the same slice was 224 HU (thin arrow), demonstrating enhancement comparable to that of the lesion in the delayed phase and indicating washout from the arterial phase. The yellow arrowhead demonstrates early opacification of a vein continuous with the lesion, consistent with early venous drainage. (d and e) Coronal arterial-phase contrast-enhanced CT images at the level of the small bowel demonstrate early opacification of a vein continuous with the lesion, consistent with early venous drainage (yellow arrowheads). (f) Double-balloon enteroscopy image of the small bowel reveals an approximately 10-mm small bowel lesion with partial ulceration (yellow arrow), without evidence of active bleeding. (g) Gross specimen of the resected small bowel shows an ulcer on the small bowel mucosa (boxed area). (h) Histopathological examination (hematoxylin and eosin stain) with low power view (approximately ×30) demonstrates dilated, tortuous, and thick-walled abnormal vessels in the submucosa, consistent with arteriovenous malformation. Red arrows indicate arteries, blue arrows indicate veins, and green arrows indicate the ulcerated mucosa.

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Case 2

A man in his 70s was transported to the emergency department with complaints of abdominal discomfort, general fatigue, nausea, and dark red stools. His medical history included hypertension, dyslipidemia, status post cholelithiasis surgery, and appendectomy. He was taking antihypertensive and lipid-lowering medications. On arrival, his vital signs were as follows: Blood pressure, 117/66 mmHg; pulse rate, 73 beats/min; respiratory rate, 24 breaths/min; and body temperature, 35.6°C. Physical examination revealed a flat and soft abdomen without tenderness. Digital rectal examination demonstrated the presence of red stool. Laboratory findings on admission were as follows: White blood cell count, 10.4 × 10³/μL; red blood cell count, 371 × 10⁴/L; hemoglobin, 11.3 g/dL; mean corpuscular volume, 91.6 fL; hematocrit, 34.0%; platelet count, 223 × 10³/μL; prothrombin time–international normalized ratio, 1.08; activated partial thromboplastin time, 21.3 s; aspartate aminotransferase, 15 U/L; alanine aminotransferase, 16 U/L; alkaline phosphatase, 41 U/L; total bilirubin, 1.1 mg/dL; albumin, 2.9 g/dL; blood urea nitrogen, 35.0 mg/dL; creatinine, 1.12 mg/dL; and estimated glomerular filtration rate, 49.3 mL/min/1.73 m². These findings indicated mild normocytic anemia accompanied by hypoalbuminemia and mild renal dysfunction, while no apparent abnormalities were observed in coagulation parameters. DCE-CT demonstrated a well-defined mass lesion arising from the small bowel wall and protruding extraluminally, which was obscure on non-contrast CT [Figure 2a] but evident in both the arterial and delayed phases [Figure 2b and c]. The CT attenuation value of the lesion was 46 HU on non-contrast CT [Figure 2a] and 227 HU in the arterial phase, which was markedly lower than that of the abdominal aorta (606 HU) measured on the same slice. In the delayed phase, the CT attenuation value of the lesion was 201 HU, which was comparable to that in the arterial phase. In addition, contrast extravasation was observed around the lesion, indicating active bleeding [Figure 2b and c]. Based on these findings, active bleeding from a small bowel tumor was suspected. After admission, conservative management with fasting and administration of hemostatic agents was initiated; however, anemia progressed, with the hemoglobin level decreasing from 11.3 to 9.5 g/dL, and the patient became hemodynamically unstable with a systolic blood pressure of 78 mmHg. Therefore, emergency partial resection of the small bowel was performed. Macroscopic examination of the resected specimen revealed an ulcerated lesion on the mucosal surface and a well-circumscribed submucosal mass measuring 20 × 18 × 9 mm [Figure 2d and e]. Histopathological examination demonstrated a tumor composed predominantly of spindle-shaped cells [Figure 2f]. Immunohistochemical staining showed positivity for c-kit and CD34 [Figure 2g and h], leading to a diagnosis of GIST.

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Figure 2: Small bowel gastrointestinal stromal tumor (GIST) in Case 2. A man in his 70s presented with dark red stools and hemodynamic deterioration. Dynamic contrast-enhanced computed tomography (DCE-CT) demonstrates a well-defined small bowel mass with contrast extravasation, indicating active bleeding from a neoplastic lesion. Emergency surgical resection was performed, and histopathology with immunohistochemistry confirmed the diagnosis of GIST. (a) Axial non-contrast CT image of the abdomen at the level of the small bowel demonstrates a well-defined mass lesion arising from the small bowel wall (arrow), with a mean attenuation value of 46 hounsfield units (HU). (b) Axial arterial-phase contrast-enhanced CT image at the level of the small bowel shows enhancement of the mass (227 HU) (arrow), which is markedly lower than that of the abdominal aorta measured on the same slice (606 HU). Contrast extravasation adjacent to the lesion is also observed, indicating active bleeding (yellow arrowhead). (c) Axial delayed-phase contrast-enhanced CT image at the level of the small bowel demonstrates persistent enhancement of the lesion (201 HU), comparable to that in the arterial phase (arrow), with continued contrast extravasation (yellow arrowheads). (d) Gross specimen of the resected small bowel shows an ulcerated lesion on the mucosal surface (boxed area). (e) Cut sections of the resected specimen reveal a well-circumscribed submucosal mass (yellow arrow). (f) Histopathological examination (hematoxylin and eosin stain) with high power view (approximately ×200) demonstrates a tumor composed predominantly of spindle-shaped cells (white arrow). (g) Immunohistochemical staining shows diffuse positivity for c-kit (white arrow). (h) Immunohistochemical staining shows positivity for CD34 (white arrow), confirming the diagnosis of GIST.

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Differential diagnosis of small bowel bleeding

The causes of small bowel bleeding can be broadly categorized into vascular lesions, neoplastic lesions, inflammatory or ulcerative diseases [Table 1].^[7] In clinical practice, differential diagnosis requires integration of multiple factors, including the clinical course such as recurrent bleeding or chronic anemia, medication history (e.g., nonsteroidal anti-inflammatory drugs), patient age, the presence or absence of abdominal pain, and hemodynamic status, as well as imaging and endoscopic findings.^[1] In the present report, both cases were attributed to relatively uncommon but clinically important causes of small bowel bleeding, specifically AVM and GIST.

Differential diagnosis of small bowel bleeding based on CT findings

DCE-CT plays an important role in localizing the bleeding source and estimating the underlying cause of small bowel bleeding.^[6] In particular, systematic evaluation of the following imaging features is useful for differentiating vascular from neoplastic lesions: (1) The degree and morphology of arterial-phase enhancement (punctate or linear vs. mass-like), (2) The presence of abnormal vessels, such as dilated feeding arteries or a nidus-like vascular network, (3) the presence or absence of early venous drainage, and (4) evidence of contrast extravasation into the bowel lumen [Table 1].^[2] In Case 1 (AVM), the lesion demonstrated marked arterial-phase enhancement (mean attenuation value, 494 HU), comparable to that of the left common iliac artery measured on the same slice. In addition, early opacification of a vein continuous with the lesion was observed, strongly suggesting the presence of an arteriovenous shunt. These findings are consistent with imaging features typically described for small bowel AVMs or arteriovenous fistulas, including focal intense early enhancement accompanied by abnormal vessels and early venous drainage,^[8] and therefore strongly supported a vascular etiology. The fact that the lesion was difficult to detect on non-contrast CT further indicates the diagnostic importance of arterial-phase imaging. In contrast, in Case 2 (GIST), a well-defined mass demonstrated relatively persistent enhancement in both the arterial and delayed phases, with enhancement intensity clearly lower than that of the abdominal aorta. This difference in enhancement behavior was evident, with the GIST showing relatively persistent delayed-phase enhancement (201 HU) and the AVM demonstrating prominent washout from a much higher arterial-phase peak (494–191 HU), supporting differential diagnosis. Furthermore, contrast extravasation was observed around the lesion, suggesting active bleeding associated with a neoplastic process. From an educational perspective, these cases highlight the value of DCE-CT in the evaluation of obscure or intermittent small bowel bleeding, particularly when upper and lower gastrointestinal endoscopy fails to identify the bleeding source.

Treatment selection

Treatment strategies for small bowel bleeding are determined by bleeding activity, the patient’s overall condition, and the location and characteristics of the lesion. In cases of AVM, endoscopic or endovascular treatments may be considered; however, surgical resection is often effective for preventing rebleeding, particularly when the lesion is localized.^[9] In Case 1, although the patient was hemodynamically stable and imaging findings suggested the absence of active bleeding, recurrent anemia persisted. Because the lesion was clearly localized by DCE-CT and double-balloon enteroscopy, elective surgical resection was considered an appropriate treatment strategy.

In contrast, for neoplastic lesions including GISTs, surgical resection of the primary tumor is the standard treatment. In particular, emergency surgery may be required when active bleeding or hemodynamic deterioration is present.^[10] In Case 2, contrast extravasation on CT suggested active bleeding, and subsequent progression of anemia and hypotension after admission indicated hemodynamic instability. Consequently, emergency surgical resection was performed, allowing simultaneous definitive diagnosis and hemostasis.

Overall, DCE-CT can provide imaging findings that support both etiological assessment (vascular vs. neoplastic) and treatment decision-making (elective vs. emergency) in patients with small bowel bleeding. In particular, intense arterial-phase enhancement comparable to that of adjacent arteries and the presence of early venous drainage in AVM are key findings that suggest a vascular etiology. Understanding these features in contrast to the mass-forming lesions and contrast extravasation observed in GIST is helpful for accurate differential diagnosis and appropriate treatment selection.