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Home / Education / Journal Watch - December 2020 (2)

Journal Watch - December 2020 (2)

Adhesive Small Bowel Obstruction: Predictive Radiology to Improve Patient Management

Marc Zins, Ingrid Millet, Patrice Taourel

Radiology 2020; 00:1-13. https://doi.org/10.1148/radiol.2020192234

Dr. Bruno Giesteira, 2nd year Radiologist Resident, Department of Radiology, Oporto Hospital and University Center, Oporto (Portugal).
Prof. Dr. Manuela França, Hospitalar Assistant and Head of Radiology Department, Oporto Hospital and University Center, Oporto (Portugal).

 

Small bowel obstruction (SBO) is a main reason of emergency room admissions, with adhesions being its most common cause. The management of SBO has been changing in recent years, with increasing non-surgical attitude instead of performing immediate surgery. Clinical and laboratory signs lack sensibility in predicting the need of surgery and, conversely, imaging studies have been playing a major role for treatment guidance. Imaging is performed to confirm the diagnosis of SBO, to locate the site of obstruction, to identify its cause and to evaluate for potential complications. In this paper, Zins et al. review the ability of imaging to personalize management decisions, namely, highlighting predictors of ischemia, bowel infarction and need for bowel resection, differentiators of open-loop from closed-loop adhesive SBO and, moreover, how to distinguish single band from matted adhesions.

In spite of being widely used for evaluating small bowel loop dilation or air-fluid levels, abdominal radiographs lack sensibility and specificity compared to CT scans and are unable to identify the cause of SBO and its main complications. Nowadays, abdominal radiographs are not recommended as part of the work-up of suspected SBO by the American College of Radiology (ACR) appropriateness criteria (1) and Bologna guidelines (2). Ultrasound examination also fails in the identification of the transient point and the cause of obstruction. Therefore, it is not used as a first-line imaging technique, except in pregnancy and pediatrics patients.

CT is the modality of choice for patients with a suspected SBO, being strongly recommended in both ACR appropriateness criteria (1) and Bologna guidelines (2). The authors suggest a multidetector CT protocol, with unenhanced acquisition plus intravenous contrast-enhanced acquisition on a portal venous phase, with multiplanar reconstruction. Oral contrast administration is not advised. Although not recommended by the ACR guidelines, the acquisition of unenhanced images may increase the detection of decreased bowel wall enhancement (3). Furthermore, they allow detecting increased bowel wall attenuation related to ischemia and transmural necrosis (4).

Although MRI is nearly as accurate as CT imaging, it is limited by low availability and the need of patient cooperation.

Strangulation with ischemia is the main source of morbi-mortality in patients with SBO and it requires emergent surgery. Determining signs of ischemia is the most important task for the radiologist. A recent meta-analysis concluded that decreased bowel wall enhancement had the highest specificity for strangulation and the absence of mesenteric fluid was reliable to exclude the diagnosis (5). Three major signs were associated with ischemia: decreased bowel wall enhancement, mesenteric haziness and closed-loop obstruction (6). The presence of at least two of these signs had a high positive likehood ratio and suggest a need for surgical intervention, whereas their total absence had a high negative predictive value suggesting non-surgical management.

CT findings potentially associated with bowel resection include parietal pneumatosis, lack of bowel wall enhancement in portal venous phase, and increased bowel wall attenuation at unenhanced CT. The later has high specificity for necrosis but low sensitivity and, when present, it indicates irreversible ischemia and requires emergent bowel resection (4,7).

The differentiation of the mechanism of adhesive SBO, as open-loop or closed-loop variants, is important because closed-loop adhesive is associated with a higher risk of bowel ischemia and failure of non-surgical treatment. The diagnosis of closed-loop SBO on CT is challenging. Characteristically, fusiform tapering of the loops is seen at the two adjacent transition zones as well as indirect signs, such as a C-/U-shaped bowel loop and radial distribution of the loops pointing to the transition zone. It is not straightforward that identifying a closed-loop SBO requires surgical intervention. In fact, a distance greater or equal to 8 mm between the two transition zones was predictive of a successful nonoperative treatment (8), still additional studies are needed.

Usually, single band adhesion is more common in the absence of previous abdominal surgery and is more likely to cause strangulation. Extraluminal bowel compression by the band may be seen at the transition zone (fat notch sign) (9). In turn, matted adhesions cause obstruction by angulation, kinking and twisting the bowel (10).

In conclusion, the authors review the major role of imaging in the management of adhesive SBO. They highlight the CT findings that indicate the mechanism of obstruction (open-loop vs closed-loop as well as single band vs matted adhesions), and those which predict ischemia or the need for bowel resection.
 

References

  1. American College of Radiology. ACR Appropriateness Criteria Suspected Small Bowel Obstruction. acsearch.acr.org/docs/69476/Narrative/. pdf. Accessed January 2, 2020.
  2. Ten Broek RPG, Krielen P, Di Saverio S, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO): 2017 update of the evidence-based guidelines from the world society of emergency surgery ASBO working group. World J Emerg Surg 2018;13(1):24.
  3. Chuong AM, Corno L, Beaussier H, et al. Assessment of Bowel Wall Enhancement for the Diagnosis of Intestinal Ischemia in Patients with Small Bowel Obstruction: Value of Adding Unenhanced CT to Contrast-enhanced CT. Radiology 2016;280(1):98–107.
  4. Rondenet C, Millet I, Corno L, Boulay-Coletta I, Taourel P, Zins M. Increased unenhanced bowel-wall attenuation: a specific sign of bowel necrosis in closed-loop small-bowel obstruction. Eur Radiol 2018;28(10):4225–4233
  5. Millet I, Taourel P, Ruyer A, Molinari N. Value of CT findings to predict surgical ischemia in small bowel obstruction: A systematic review and metaanalysis. Eur Radiol 2015;25(6):1823–1835.
  6. Millet I, Boutot D, Faget C, et al. Assessment of Strangulation in Adhesive Small Bowel Obstruction on the Basis of Combined CT Findings: Implications for Clinical Care. Radiology 2017;285(3):798–808.
  7. Nakashima K, Ishimaru H, Fujimoto T, et al. Diagnostic performance of CT findings for bowel ischemia and necrosis in closed-loop small-bowel obstruction. Abdom Imaging 2015;40(5):1097–1103.
  8. Rondenet C, Millet I, Corno L, et al. CT diagnosis of closed loop bowel obstruction mechanism is not sufficient to indicate emergent surgery. Eur Radiol 2020;30(2):1105–1112.
  9. Petrovic B, Nikolaidis P, Hammond NA, Grant TH, Miller FH. Identification of adhesions on CT in small-bowel obstruction. Emerg Radiol 2006;12(3):88–93; discussion 94–95.
  10. Osada H, Watanabe W, Ohno H, et al. Multidetector CT appearance of adhesion-induced small bowel obstructions: matted adhesions versus single adhesive bands. Jpn J Radiol 2012;30(9):706–712.

 

Dr. Bruno Giesteira is a 2nd year radiology resident at the Centro Hospitalar Universitário do Porto, in Portugal. He completed his undergraduate medical degree at Escola de Ciências da Saúde, Universidade do Minho, Braga, in 2017. He is an active member of the ESGAR and has been developing a particular interest in diagnostic genitourinary and abdominal radiology, especially in gastrointestinal imaging.

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