Evaluation of Suspected Small Bowel Ischemia Using Contrast-Enhanced Ultrasound with Computed Tomography Fusion.

Small bowel ischemia can lead to fatal complications such as necrosis, perforation, and sepsis. Clinical examinations and laboratory tests are usually inconclusive in critically ill patients. The need for surgical exploration is decided based on imaging, examination, and clinical judgment. The decision to operate is time-critical and can be lifesaving, but surgical intervention has the potential to cause additional morbidity, especially in unstable patients. Contrast-enhanced computed tomography (CECT) is the study of choice in suspected small bowel ischemia but has poor specificity. Contrast-enhanced ultrasound (CEUS) provides real-time visualization of the bowel wall vascularity. In this case report, we used a CEUS with CT fusion examination to rule out small bowel ischemia in a critically ill patient with suspected closed loop small bowel obstruction on CECT and in whom surgical exploration would have not been well tolerated. The patient's condition later improved, and an abdominal CT showed no evidence of obstruction. Copyright:

INTRODUCTION

Small bowel ischemia is a potentially fatal complication of common conditions. It can lead to perforation, necrosis, and sepsis. Clinical signs of small bowel ischemia include pain out of proportion to the physical examination, nausea, vomiting, and fever. In addition, abdominal tenderness, guarding and absent bowel sounds can be detected if the patient develops peritonitis. However, these signs can be absent in many cases. The diagnosis is typically based on contrast-enhanced computed tomography (CECT) alone or in combination with physical examination, and laboratory tests. In patients with ongoing or impending vascular compromise, urgent exploratory laparotomy is indicated to restore blood flow or resect the necrotic bowel. However, impending small bowel ischemia can be a challenging diagnosis in many cases. Modern ultrasound systems allow the reconstruction and integration of prior cross-sectional scans (CT/magnetic resonance imaging [MRI]) with live ultrasound imaging in the same plane.[1] Contrast-enhanced ultrasound (CEUS) fusion requires image registration from different modalities which can be automated, semiautomated, or manual. The scan can be performed by technicians after validating the registration process by examining anatomical landmarks. It is an inexpensive, accessible technology, and can be done at the patient's bedside. This case demonstrates the benefits of CEUS with CT fusion as a rule-out test for small bowel ischemia in a critically ill patient.

CASE REPORT

A 23-year-old female with a 10-year history of Crohn's disease was admitted to the inpatient unit due to intractable abdominal pain. The patient stated that she had suffered from abdominal pain for 3 months and also described night sweats and weight loss of 20–25 lbs. in 1 month. The patient looked thin and frail. Physical examination revealed mild diffuse tenderness in the abdomen, clear chest, and no peripheral adenopathy. Laboratory examination was significant for elevated lipase level (427 U/L). She previously underwent bowel resection for Crohn's disease approximately 10 years ago. Subsequently, her Crohn's disease was managed by immunosuppressive therapy.

On admission, her abdominal CT scan was notable for multiple masses throughout the pancreas which were later diagnosed with diffuse large B-cell lymphoma. Her hospital course was complicated by systemic inflammatory response syndrome, Crohn's colitis, and hemorrhagic shock from bleeding localized to the second part of the duodenum. The patient received several units of packed red blood cells and underwent angioembolization of the proximal branch of the superior mesenteric artery. Her condition later deteriorated into sepsis and encephalopathy prompting endotracheal intubation.

On hospital day 34, an abdominal CT was obtained due to rising white blood cells (32,700/mm3) and elevated lactate (2.3 mmol/L), it showed a loop of the small bowel (15 cm from the ileocecal valve) in the pelvis with apparent stasis [Figure 1]. There was an associated dilation of the short segment, the duodenum, and the stomach concerning for closed-loop obstruction and possible bowel ischemia. Exploratory laparotomy was considered potentially fatal given the patient's unstable condition. Following surrogate consent, a CEUS-CT fusion exam was performed, as part of an ongoing clinical trial, to evaluate for bowel ischemia. Following ultrasound-CT registration, CEUS was performed using a bolus intravenous injection of ultrasound contrast agent (0.4 ml Definity, Lantheus Medical Imaging, N. Billerica MA) during nonlinear contrast imaging mode on a Logiq E10 ultrasound scanner with C1-6 probe (GE Healthcare, Milwaukee WI). Fused CEUS-CT images [Figure 2] revealed a rapid enhancement pattern in the small bowel wall excluding bowel malperfusion and ischemia. Second contrast injection was performed (without CT fusion) approximately 10 min following the initial injection to reevaluate the loop identified on CT fusion while also scanning for pan-ischemia [Figure 2]. Prompt enhancement of the bowel wall relative to the surrounding subcutaneous tissue was again seen, ruling out bowel malperfusion. Her clinical course improved over the next several days with antibiotics and intravenous fluids. A repeat CT of her abdomen was obtained 2 days later which showed nonspecific nondilated fluid-filled small bowel with no evidence of obstruction [Figure 1].

Figure 1

Abdominal computed tomography scans depicting the suspected bowel obstruction before and after its resolution. Top panel scan is notable for a loop of small bowel in the pelvis with dilation of the short segment measuring 3.23 cm (arrow). Bottom panel scan was obtained 2 days postcontrast-enhanced ultrasound, it demonstrates nondilated small bowel (solid white arrow) after the suspected obstruction has subsided

Figure 2

Top panel (a) Shows B-mode ultrasound (left) with contrast-enhanced ultrasound (right) 36 s postcontrast injection where bowel wall enhancement can be observed (white arrows). Bottom panel (b) Shows contrast-enhanced ultrasound (left) with computed tomography (right) fusion where simultaneous bowel wall (white arrow) and subcutaneous tissue (yellow arrow) enhancement is seen

DISCUSSION

Small bowel ischemia remains a challenging diagnosis, especially in critically ill patients. This case report describes the capability of CEUS with CT fusion in ruling out small bowel ischemia in patients with small bowel obstruction. At present, CECT is the diagnostic study of choice in most cases. It can detect conspicuous signs of small bowel ischemia or its complications.[2] CECT has a sensitivity of 89% but suffers from a lower specificity of 67%.[3] Despite including clinical examination and laboratory tests, only 32% of patients are accurately diagnosed before surgical exploration.[4]

Ultrasound is readily available at the bedside and does not involve ionizing radiation. Ultrasound contrast agents are approved by the United States Food and Drug Administration for heart and liver imaging, but can be used off-label for multiple applications like cross-sectional contrast agents.[5] They are safe in patients with renal and hepatic insufficiency and provide real-time visualization of the vasculature in tissues with higher temporal resolution than CT and MRI.[6] Previously, CEUS has been used to quantify the hyperemia of the bowel wall in Crohn's disease.[7] However, it has been scarcely explored to evaluate small bowel ischemia.[89] CEUS can dynamically visualize the vascularity of the bowel wall and the enhancement pattern can be classified relative to the surrounding subcutaneous tissue. We categorized bowel wall enhancement as rapid enhancement, delayed enhancement, or no enhancement. Rapid enhancement rules out bowel malperfusion. Delayed/no enhancement would prompt surgical exploration as malperfusion cannot be excluded.[10]

Localization of a specific bowel segment can be challenging on ultrasound. To confidently identify and evaluate the area of concern, CT fusion was used. When utilized, CEUS can exclude small bowel ischemia and avoid surgical exploration which could be fatal in critically ill patients. In conclusion, CEUS can be employed as a rapid bedside exam to exclude small bowel ischemia in critically ill patients without the risk of surgical exploration.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given her consent for his images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

Research quality and ethics statement

The authors followed applicable EQUATOR Network (http://www.equator-network.org/) guidelines, notably the CARE guideline, during the conduct of this report.

Financial support and sponsorship

The ultrasound contrast agent used in this study was provided by Lantheus Medical Imaging (N. Billerica, MA).

Conflicts of interest

There are no conflicts of interest.