Small Bowel Disease: An Approach to Optimise Imaging Technique and Interpretation

Abstract

Small bowel imaging presents a challenge from the variety of clinical presentations and types of disease affecting a long organ. Emergency presentation most often involves suspicion of bowel obstruction, unexplained acute abdominal pain with or without signs of sepsis and overt obscure GI bleeding. Conversely non-emergency referrals relate to non-specific constitutional symptoms including weight loss, abdominal patient, and altered bowel habit suggesting malignancy or inflammatory bowel disease, while iron deficiency anaemia after negative colonoscopy and endoscopy indicates occult obscure GI bleeding. CT is the commonest and best-established method of evaluation, except in the setting of known inflammatory bowel disease where MRI or ultrasound are advantageous because they avoid radiation.

The CT protocol must be tailored to the clinical situation. Oral preparation is avoided for acute imaging, with the main focus around prompt contrast enhanced scanning: acute obscure bleeding should include non-contrast, arterial and portal venous phases, while obstruction and acute abdominal pain needs portal venous phase assessment. Pre-contrast imaging allows assessment of intramural haemorrhage where there is prior clinical concern for intestinal ischaemia. Conversely non-urgent assessment allows oral luminal preparation with a neutral contrast such as polyethylene glycol or mannitol and enteric or portal venous phase contrast assessment depending on the indication.

FormalPara Learning Objectives

• To understand the main clinical presentations of patients with small bowel disease.

• To know the place of radiological assessment for investigation compared with endoscopic techniques.

• To know how to select an appropriate CT protocol to evaluate patients from the clinical presentation.

• To know imaging features that warrant consideration of emergency surgery.

19.1 Introduction

The aim of this chapter is to provide an approach to deal with small bowel disease in routine clinical practice. It will provide advice on imaging protocols and the imaging signs to search for to produce a diagnosis, particularly those which indicate urgent clinical intervention. The focus is on common conditions and the usual management. Rare conditions are mentioned to illustrate that not everything is common or usual!

19.2 Setting the Scene: Case Presentation and Patient Factors

Small bowel diseases form a small contribution to the total workload of an abdominal radiologist but are challenging because of the length of small bowel being evaluated and the difficulty detecting abnormalities while trying to avoid false-positive diagnosis. Generally, patients present either as an emergency after acute admission or in a more indolent manner as an outpatient. The chapter will be divided into those two distinct referral sources to reflect daily radiology practice.

Furthermore, the approach will focus on the main clinical presentations leading to a request for imaging to assist in diagnosis of small bowel disease. In the emergency setting, three main presenting scenarios are presented; overt or obscure GI bleeding; suspicion of bowel obstruction; and unexplained acute abdominal pain, with or without signs of sepsis. In outpatients the assessment focuses on two presentations; symptoms of weight loss, abdominal pain and altered bowel habit, where there is concern for malignancy or inflammatory bowel disease; and iron deficiency anaemia with occult obscure GI bleeding.

19.2.1 Emergency Small Bowel Conditions: Common Clinical Presentations

CT has an established critical role in the assessment of the acute abdomen. While some patient diagnoses are quite clear at the time of presentation, like acute GI haemorrhage, others are not, such as small bowel ischaemia or perforation and the radiologist may be the first to consider or confirm the diagnosis. This presents difficulties when deciding the optimal protocol as the clinical differential diagnosis can be quite wide and a compromise must be made to prevent routine excessive radiation exposure in all cases while providing an accurate diagnosis for a majority of patients.

19.2.1.1 CT Intravenous Contrast Considerations

A weight-based iso- or hypo-osmolar intravenous iodinated contrast should be preferred. Evaluation of renal function should not delay CT scans in a critical care setting where prompt accurate diagnosis is the greatest priority [1]. Estimated Glomerular Filtration Rate assessment may be helpful before CT for clinicians to understand potential impact of contrast on renal function and reduction in renal function can be supported with renal replacement therapy if necessary. Where possible a rapid contrast injection (3–5 mL/s) allows optimal identification of vessels, hypervascular lesions, and bleeding locations with 350 mg/mL Iodinated contrast dose at 1.2–1.5 mL/kg.

Key Point

• In emergency small bowel CT rapid contrast injection is needed with a weight-based iodinated contrast protocol and a pre-selection of the phases of acquisition according to the clinical situation. Oral contrast is not required.

19.2.1.2 CT Scan Phase Choices for Acquisition

• Non-contrast CT for detection of free gas, dilated small bowel in the presence of obstruction, blood in the lumen of the bowel from bleeding and intramural haemorrhage which is associated with ischaemia and infarction.

• Late arterial phase CT (10 s post peak aortic enhancement) for acute gastrointestinal bleeding to optimise arterial enhancement to see occlusions and arterial jets of contrast at the site of brisk haemorrhage.

• Enteric phase CT (45–50 s post injection) for optimal evaluation of small bowel enhancement and detection of focal bowel lesions.

• Portal venous phase CT (65–75 s post injection) for delayed or slow contrast pooling from extravasation and global assessment of bowel and other viscera in the setting of ischaemia or obstruction.

Routine thin slice reconstructions (1 mm or less) are important for evaluation of vessels and detection of sites of bleeding and multiplanar reformation to appreciate global small bowel enhancement patterns and to detect focal abnormalities like strictures, transition points in obstruction and bleeding [2].

19.2.1.3 CT Luminal Contrast: What Role?

Luminal contrast has a very limited role emergency small bowel CT. Oral contrast delays scanning and it is not appropriate in patients with small bowel obstruction or perforation because of subsequent general anaesthesia and risk of aspiration, in addition to unpleasantness of drinking contrast when patients are unwell with an acute abdomen.

Positive oral contrast should be avoided as it obscures many signs being sought (such as intramural or intraluminal haemorrhage), and the contrast density makes it more difficult to appreciate reduced bowel enhancement.

Specific neutral contrast agents (like Mannitol or Polyethylene Glycol) are usually unnecessary in an acute setting since most of the diseases that might cause an acute hospital admission, such as enteritis from infection or Crohn’s disease, are easily appreciated without it. Water may be given for pre-hydration to reduce the opportunity for contrast induced kidney injury in a sub-acute situation.

19.2.1.4 What Role for MR and Ultrasound?

MRI offers a global assessment of the small bowel without radiation. This may be advantageous in young patients and in pregnancy but relies on sufficient expertise in interpretation and access out of normal working hours (Fig. 19.1). The examinations are longer (20–30 min) and require greater patient cooperation with multiple breath holds and the enclosed environment may not be appropriate if patients are acutely unwell with risk of vomiting. MR enterography is particularly useful in reassessing patients with Crohn’s disease with deterioration in symptoms requiring hospital admission and sub-acute reassessment for complications and evaluation of disease activity, as they may have multiple examinations and accumulate a high lifetime radiation dose from CT. However in the situation of possible perforation, it is inappropriate to wait for MRI and CT is an acceptable test to plan emergency patient management.

Fig. 19.1

Acute admission with vomiting at 34 weeks gestation and previous RYGB. MR abdomen with FISP coronal showing obstruction at the J-J anastomosis with dilatation and obstruction of the biliopancreatic limb (white arrow). Laparoscopic revision of the anastomosis post MRI with a healthy baby delivered 6 weeks later

Ultrasound also allows evaluation of patients with small bowel disease but a global assessment of acute small bowel diseases is challenging particularly in the setting of obstruction or in the presence of high volumes of bowel gas or intraperitoneal perforation. Its role is limited and may be in the incidental detection of important abnormalities when acute ultrasound is being performed for other reasons.

Key Point

• CT is the imaging technique of choice for acute abdomen emergency assessment of the small bowel. MR enterography is preferred to assess patients with Crohn’s disease where this is feasible.

19.2.1.5 Relevant Diseases and Imaging Signs

19.2.1.5.1 Overt or Obscure GI Bleeding

19.2.1.5.1.1 Clinical Context

CT has an important role to detect the source of acute GI bleeding where an upper GI endoscopy has failed to detect the source. Overt denotes visible bleeding (usually melaena or hematochezia in proximal or distal small bowel bleeding, respectively), whereas obscure bleeding describes a bleeding source which is undetected after previous full assessment of the GI system with upper and lower GI endoscopy and small bowel [3]. The role of CT is to detect the source of haemorrhage and direct management to arrest bleeding using endovascular or endoscopic interventional therapies.

Upper GI bleeding is usually excluded by negative endoscopy to the second part of duodenum. Bleeding in the distal duodenum and rest of the small bowel makes up a minority of cases (around 10%). Video capsule endoscopy and double balloon enteroscopy both have a higher yield than CT for detection of the source of bleeding and should be the first line investigation, with CT reserved for unstable patients where there is active haemorrhage [3].

Since CT detection requires the identification of contrast extravasation then immediate access to scanning is the key.

19.2.1.5.1.2 Recommended CT Protocol

Triple phase CT protocol with weight-based iodinated contrast injection and non-contrast, late arterial and portal venous acquisition without oral contrast.

19.2.1.5.1.3 Relevant Conditions and Imaging Signs

Inflammatory bowel disease and Meckel diverticulum are frequent causes of small bowel bleeding in younger patients and NSAID enteropathy (Fig. 19.2) and angioectasia (Fig. 19.3) in older patients, while small bowel neoplasia is seen in both groups including benign polyposis syndromes (e.g., Peutz-Jeghers), lymphoma, neuroendocrine tumours, and adenocarcinoma [3, 4].

Fig. 19.2

(a, b) Axial arterial phase and coronal portal venous phase with contrast extravasation from a jejunal loop in the pelvis from NSAID-induced ulceration. The affected jejunal loop is not thickened

Fig. 19.3

(a–c) Coronal portal venous phase. A 50-year-old male on dialysis with obscure overt GI bleeding. Initial negative CT angiography and further bleeding. Characteristic multifocal angioectasia. Benefit of narrow windows for better visualization

Acute bleeding is best appreciated by careful evaluation for contrast leak from vessels or tumours into the bowel lumen on thin slice reconstructions. Underlying structural lesions causing bleeding like tumours and benign small bowel strictures are better appreciated on enteric and portal venous phase imaging. Tumours and polyps typically enhance uniformly and maximally in the enteric and portal venous phase, while neuroendocrine tumours tend to hyper enhance in late arterial phase and wash out. Malignant tumours are indicated by transmural abnormalities extending into the perienteric fat and presence of metastatic disease in enlarged local lymph nodes or elsewhere on the scan [5]. Layered and homogenous enhancement patterns of diffuse or multifocal small bowel thickening are recognised in Crohn’s disease whereas in other forms of enteritis a multifocal ‘skip’ pattern is less likely.

Angioectasia is a common condition and associated with valvular heart disease in elderly patients. They are typically multiple and detected as a small 2–5 mm rounded enhancing lesion in the jejunum, best appreciated on a narrow abdominal window in an enteric or portal venous phase and detection may be aided with maximum intensity projection [2]. Varices may also be detected as a source of small bowel bleeding but are much less common (Fig. 19.4).

Fig. 19.4

(a, b) Coronal and axial CT in a 56-year-old male with occult overt bleeding. Ileal submucosal varices (arrows) and occult cryptogenic cirrhosis unsuspected clinically treated with TIPPS

19.2.1.5.2 Suspicion of Bowel Obstruction

19.2.1.5.2.1 Clinical Context

CT is an accurate method for diagnosis of small bowel obstruction which is a common cause for acute abdominal presentation. Conservative management is favoured except where obstruction fails to resolve after a period of supportive care or where there are signs of strangulation and small bowel ischaemia. CT is an essential tool to confirm the diagnosis and underlying cause for small bowel obstruction and to search for signs that predict adverse outcomes such as ischaemia, warranting emergency surgery.

19.2.1.5.2.2 Recommended CT Protocol

A CT protocol with rapid weight-based iodinated contrast injection and portal venous acquisition without oral contrast. Where there is pre-scan concern for strangulation/ischaemia or perforation a non-contrast assessment can assist in detection of intramural haemorrhage [6]. Thin slice acquisition and multiplanar reformation are required to assess for the site and cause of obstruction.

19.2.1.5.2.3 Relevant Conditions and Imaging Signs

‘Open loop’ obstruction describes a single transition point (Fig. 19.5), whereas a ‘closed loop’ is formed by a double transition point and leads to increased pressure in a localised small bowel segment which leads to ischaemia and necrosis. Adhesions are the commonest cause by far, from either focal bands or diffuse adhesions. Other causes include hernias (abdominal wall or internal), intrinsic small bowel diseases (Crohn’s disease or tumour), obstructing intraluminal body (gallstone or bezoar), or peritoneal infiltration from tumour.

Fig. 19.5

(a, b) Axial and coronal portal venous phase CT with obstructing mid jejunal adenocarcinoma with focal annular tumour (arrow) at the transition of dilated small bowel (asterisk). Note grossly distended stomach (St)

Assessment of the transition point requires a careful thin slice multiplanar assessment to look for an abrupt transition from dilated obstructed bowel to collapsed distal small bowel. Finding the transition point can be challenging when there are multiple dilated loops. The ‘small bowel faeces sign’ can be helpful when it is present to give a clue of the relevant bowel section to focus on [7].

Adhesions are indicated by absence of other findings, since a ‘mass’ or wall thickening at the transition points to an alternate pathology such as a tumour or inflammatory stricture which is unlikely to resolve with conservative management. Particular signs of a band adhesion are a ‘fat notch sign’ at the point of obstruction, whereas more diffuse adhesions cause generalised angulation and kinking of bowel loops from fixation instead of the expected unimpeded natural looping in the peritoneal cavity. An open loop adhesive obstruction has a single transition while the two transition points forming a closed loop are typically very close, leading to a C or U-shaped dilated segment. The closed loop is most commonly dilated, along with dilatation of the upstream small bowel; however other patterns are recognised with isolated dilatation of the closed loop alone and normal upstream small bowel (flat belly closed loop obstruction); or a non-dilated closed loop and upstream dilatation [6].

Critical ancillary features predicting ischaemia in closed loop should be specifically searched for and consist of decreased bowel enhancement and diffuse mesenteric haziness (Fig. 19.6). Increased unenhanced bowel wall attenuation on non-contrast CT is also highly predictive of ischaemia in closed loop obstruction from intramural haemorrhage, and this is a potential benefit for including it in routine assessment of bowel ischaemia [6].

Fig. 19.6

(a) Closed loop small bowel obstruction from band adhesions. Previous EVAR for aortic aneurysm. Non-contrast CT with small bowel obstruction and two adjacent transition points (arrows) as well as stranding in the ileal mesentery (asterisks) in the right side of the abdomen from closed loop obstruction. No hyper density to indicate intramural haemorrhage. (b) axial and (c) sagittal portal venous phase images showing preserved small bowel enhancement

Key Point

• Closed loop obstruction has an increased risk of ischaemia. A double transition should be sought in any small bowel obstruction, along with decreased bowel enhancement and diffuse mesenteric haziness or increased unenhanced bowel wall attenuation on non-contrast CT.

19.2.1.5.3 Unexplained Acute Abdominal Pain with or Without Signs of Sepsis

19.2.1.5.3.1 Clinical Context

Small bowel disease can present acutely without obstruction. The main aetiologies relate to diseases causing perforation or ischaemia. Localised or free perforation may present with pain and sepsis and result from intrinsic small bowel diseases, such as Crohn’s disease or diverticular disease, or from foreign bodies or trauma. Ischaemia (unrelated to closed loop obstruction) is another important cause and may be related to occlusion of arterial inflow (Fig. 19.7) or venous outflow or diseases of smaller vessels, such as vasculitis and typically presents with sudden onset symptoms. Non-obstructive mesenteric ischaemia is another explanation which is often multifactorial and related to hypoperfusion from cardiovascular disease producing reduced inflow. This can be exacerbated by other factors such as small or large vessel disease (e.g. related to diabetes or atherosclerosis) or medications causing vasoconstriction in critical care environments [8, 9].

Fig. 19.7

(a) axial CT with dilated pelvic small bowel (asterisk) with lack of enhancement of the wall (arrowhead). (b, c) axial images of the SMA origin showing thrombosis with lack of contrast opacification (arrows)

Positive oral contrast is not advised as it delays the scan, it is not necessary for the diagnosis of perforation and it interferes with the assessment of bowel enhancement which is critical for the diagnosis of ischaemia [9].

19.2.1.5.3.2 Recommended CT Protocol

Unexplained acute abdominal pain with or without signs of sepsis: weight-based iodinated contrast injection without oral contrast and portal venous acquisition.

High clinical suspicion of ischaemia: weight-based iodinated contrast injection without oral contrast. A triple phase assessment is recommended with non-contrast, early arterial and portal venous acquisition without oral contrast.

19.2.1.5.3.3 Relevant Conditions and Imaging Signs

Perforation is accompanied by localised or free gas, with or without accompanying fluid, peritoneal thickening and enhancement and increased attenuation of mesenteric fat. While the features or Crohn’s disease and bowel tumours are well known, diverticular disease of the jejunum and ileum are a diagnostic challenge. These diverticula can be large and very diffuse and initially appear as additional gas and fluid-filled bowel loops. However, careful inspection reveals diverticula along the mesenteric border of the bowel which may solve an unexplained localised small bowel perforation (Fig. 19.8). Typically, these are elderly patients and managed conservatively with a confident diagnosis [10].

Fig. 19.8

(a) axial CT in elderly female with abdominal pain and mass centred on the jejunum (arrowheads). (b, c) Coronal reconstructions show multiple adjacent diverticula in the jejunum (arrows) indicating that this is inflammation from jejunal diverticulitis which resolved with antibiotics

Foreign bodies present a challenge and difficult to detect without close evaluation of thin slice CT. Short linear densities protrude through the small bowel (most often fish bones or wood fragments) (Fig. 19.9). These are not expected clinically and patients can have recurrent admissions with relatively little related accompanying changes in bowel wall around the foreign body [11].

Fig. 19.9

(a, b) Axial and coronal CT in male with pyrexia post appendicectomy. The appendix was normal and faecal material was seen at peritoneal washout. Linear foreign body in the wall of the ileum (arrow) which was a wooden toothpick at repeat surgery

Key Point

• Foreign bodies including fish bones can be challenging to detect without thin slice evaluation and jejunal diverticulitis and perforation requires careful assessment for other diverticula on the mesenteric border of the small bowel to make the diagnosis.

Mesenteric arteries and veins need careful inspection on any CT performed for acute abdominal pain. Occlusive vascular diseases require thin slice reconstruction and multiplanar reformation to accurately detect and characterise arterial emboli from a cardiac source (atrial fibrillation or left ventricular mural thrombus) or thrombosis or vascular occlusion from atherosclerotic stenosis. This can be a challenging diagnosis as an unexpected finding on a portal venous phase study. Venous thrombosis may be accompanied by a primary condition or acute inflammatory processes elsewhere (such sigmoid diverticulitis). However, a pitfall for false-positive diagnosis relates to uneven mixing of contrast in the portal venous system, for example, caused by heart failure. Conversely non-occlusive mesenteric ischaemia shows vascular patency but has the other imaging features associated with ischaemia.

Small bowel ischaemia is accompanied by various additional signs including; bowel wall thickening; thinning of the bowel (which may be associated with dilatation); alteration of enhancement with hypo or absent perfusion or conversely hyper enhancement in acute ischaemia from reflex dilatation of small vessels; localised dilatation from ileus; pneumatosis intestinalis and portal venous gas (which is not specific to ischaemia); and inflammatory changes in the mesenteric fat and ascites in the peritoneum [8]. Signs of ischaemia may also be present in other organs such as the spleen and kidneys. Acute intramural haemorrhage is seen in ischaemia as well as close loop obstruction, caused from reperfusion in arterial occlusion or venous occlusion with vascular engorgement. If this is not appreciated, then haemorrhage may be mistaken for preserved enhancement in the bowel wall when it is in fact ischaemic or infarcted [8].

19.2.2 Outpatient Presentation: Common Clinical Presentations

CT is a common tool for the investigation of patients with unexplained symptoms with suspicion of GI tract origin. These symptoms are often non-specific, which once again presents difficulties when deciding the optimal protocol as the clinical differential diagnosis is wide and an optimal imaging approach balances excessive radiation against an accurate diagnosis for a majority of patients.

19.2.2.1 CT Intravenous Contrast Considerations

CT Scan Phase Choices for Acquisition

• Non-contrast CT not indicated because of a low likelihood of haemorrhage being present and tumour calcification is easily detected on contrast enhanced scans.

• Late arterial phase CT (10 s post-peak aortic enhancement) may assist in the diagnosis of arterialised tumours (e.g. NET and metastases).

• Enteric phase CT (45–50 s post injection) for optimal evaluation of small bowel enhancement and detection of focal bowel lesions.

• Portal venous phase CT (65–75 s post injection) for global assessment of the viscera in the abdomen and pelvis.

19.2.2.2 CT Luminal Contrast: What Role?

Optimal small bowel assessment requires luminal distension with neutral contrast. Enteroclysis is advocated by some authors but this is invasive, challenging for patients and clinicians as it requires placement of a nasojejunal tube and a dedicated contrast pump for even delivery of contrast for distension. Enterography is more attractive requiring 1–1.5 L of Mannitol or PEG orally over 40–60 min. While luminal distension is less than enteroclysis, it is an effective and more practical diagnostic tool particularly if used for problem-solving in combination with prior video capsule endoscopy. Intravenous contrast is essential in combination.

Key Point

• CT enterography requires 1–1.5 L of neutral contrast over 40–60 mins prior to scanning and an enteric phase of contrast enhancement between 45–50 s after injection.

19.2.2.3 Weight Loss, Abdominal Pain, and Altered Bowel Habit? Malignancy? Inflammatory Bowel Disease

19.2.2.3.1 Clinical Context

Patients with an established diagnosis of Crohn’s disease should have MR enterography assessment. However, some patients will have this diagnosis proposed after a CT scan for non-specific abdominal symptoms. Likewise, small bowel tumours may be detected when investigating these symptoms.

19.2.2.3.2 Recommended CT Protocol

CT protocol with rapid weight-based iodinated contrast injection and portal venous acquisition with water oral contrast (for prehydration).

High clinical suspicion of small bowel disease: CT enterography with 1–1.5 L Mannitol or PEG over 40–60 min and rapid (4 mL/s) weight-based iodinated contrast injection and enteric phase acquisition.

19.2.2.3.3 Relevant Conditions and Imaging Signs

The imaging features of Crohn’s disease are well known [12]. The length and distribution of abnormal bowel segments should be reported in addition to complications such as fistula, abscess, or obstruction [12, 13]. Note that Crohn’s disease has a bimodal age distribution with a significant proportion presenting over 60 years.

Small bowel tumours are rare. Patients with polyposis are often detected after screening but sporadic cases occur, and these can be very difficult to detect without optimal distension as they have similar post contrast enhancement to normal small bowel folds. Malignant tumours will usually appear as focal bowel thickening, as a large mass, as a transition point in incomplete small bowel obstruction or as a smaller abnormality related to a much more obvious abnormality, such as extensive lymphadenopathy in lymphoma or NET. Few signs are specific. Nodes are uncommon in GIST and metastasis should be considered particularly with a history of melanoma, breast, and lung cancer [5] (Fig. 19.10).

Fig. 19.10

(a, b) Abdominal pain and anaemia. Axial and coronal reconstructions showing polypoid enhancing tumour in the mid small bowel (arrows). Prior history of melanoma resection 2 years previously with metastasis confirmed at small bowel resection

19.2.2.4 Iron Deficiency Anaemia with Occult Obscure GI Bleeding

19.2.2.4.1 Clinical Context

Radiological assessment is reserved for problem-solving after indeterminate video capsule endoscopy or where there is high suspicion of abnormality after negative capsule [3] (Fig. 19.10). Occasionally, CT is requested for ‘road mapping’ to plan the optimal route for double balloon enteroscopy (antegrade or retrograde via the colon) or where DBE is not possible because of adhesions and an operative approach is being considered. Active bleeding is highly unlikely and the detection is focused on optimal contrast enhancement.

19.2.2.4.2 Recommended CT Protocol

CT enterography with 1–1.5 L Mannitol or PEG over 40–60 min and rapid (4 mL/s) weight-based iodinated contrast injection and enteric phase acquisition (± portal venous phase).

Ct enteroclysis (selected cases: 2–3 L (Mannitol or PEG) pump infused via NJ tube (100–150 mL/min) and rapid (4 mL/s) weight-based iodinated contrast injection and enteric phase acquisition (± portal venous phase).

19.2.2.4.3 Relevant Conditions and Imaging Signs

Most tumours and vascular lesions are best detected with an enteric phase assessment and optimal distension [2, 5].

19.2.2.5 Small Bowel Intussusception

Intussusception is a common observation on CT performed for abdominal symptoms and is related to normal physiology from bowel contraction. Most cases can be dismissed where there is no visible mass as a lead point, where the length of intussusception is less than 5 cm and there is no associated obstruction [14, 15] (Fig. 19.11).

Fig. 19.11

(a, b) CT for intermittent abdominal pain in a 34-year-old male with short mid small bowel intussusception. There is no pathological lead point and the intussusception is short, consistent with an incidental physiological event rather than abnormality

Key Point

• Small bowel intussusception detected by CT does not require additional tests unless there is a pathological lead point, signs of associated obstruction or it is greater than 5 cm in length.

19.3 Concluding Remarks

Optimal CT technique tailored to the clinical situation is essential to detect the imaging signs that influence patient care and requires appropriate pre-selection of scan phases and adequate iodinated contrast rate and volume. The most important emergency considerations relate to the effective detection of active bleeding, the diagnosis of small bowel ischaemia and reliable identification of closed loop obstruction while outpatient assessment particularly requires detection of inflammatory bowel disease and malignancy with a minor role in the evaluation of obscure GI bleeding to supplement endoscopic techniques.

Take Home Messages

• Consider non-contrast CT before contrast administration for ischaemia to look for intramural haemorrhage.

• Remember enteric phase CT is optimal for small bowel assessment and is earlier than standard portal venous phase.

• Remember luminal contrast should not delay emergency CT, but neutral contrast is important for outpatient evaluation.