12 Tips for Interpreting Abdominal CT Scans (2020) - Medical Teacher PDF

Medical Teacher ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/imte20 Twelve tips for interpreting abdominal CT scans Sailantra Sivathasan , Jakub Nagrodzki & David McGowan To cite this article: Sailantra Sivathasan , Jakub Nagrodzki & David McGowan (2020): Twelve...

Medical Teacher ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/imte20 Twelve tips for interpreting abdominal CT scans Sailantra Sivathasan , Jakub Nagrodzki & David McGowan To cite this article: Sailantra Sivathasan , Jakub Nagrodzki & David McGowan (2020): Twelve tips for interpreting abdominal CT scans, Medical Teacher, DOI: 10.1080/0142159X.2020.1839033 To link to this article: https://doi.org/10.1080/0142159X.2020.1839033 Published online: 03 Nov 2020. Submit your article to this journal Article views: 57 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=imte20 MEDICAL TEACHER https://doi.org/10.1080/0142159X.2020.1839033 TWELVE TIPS Twelve tips for interpreting abdominal CT scans Sailantra Sivathasana, Jakub Nagrodzkib and David McGowana a Addenbrooke’s Hospital, Cambridge University Hospital Trust, Cambridge, UK; bPeterborough City Hospital, North West Anglia NHS Foundation Trust, Peterborough, UK ABSTRACT KEYWORDS Background: Abdominal computerised tomography (CT) scans are a crucial tool in the diagnosis CT abdomen; interpreting and management of the acute abdomen. Currently, medical students are not widely and exten- abdominal CT scans; sively trained in the interpretation of abdominal scans. systematic approach to CT scans; abdominal Aim: We aim to provide advice about interpreting abdominal CT scans. computerised tomography Methods: We used the critical reflection of our experiences, both in clinical practice and in teach- interpretation ing, alongside advice from the literature to develop these tips. Results: Twelve tips following the ‘4As, 3Bs, 2Cs and 1D’ approach are presented to assist doctors and medical students with interpreting abdominal CT scans. Conclusion: The early identification of pathology on CT scans has been demonstrated to improve patient outcomes in certain cases, while a formal radiologist’s report is awaited. Following a sys- tematic approach, such as the one we presented here, may aid trainees in looking at abdominal CT scans. Introduction example, is it a contrast scan for renal colic? If so, it may not be helpful. Abdominal computerised tomography (CT) scans are a core component of the modern surgical assessment of the acute abdomen, which is offered to a significant proportion of The four ‘A’s patients (Stoker et al. 2009; Paolantonio et al. 2016). Tip 2 In spite of that, evidence suggests that on average only 5% of total teaching time in medical schools in the UK is The 1st A: air. Assess for (1) pneumoperitoneum, (2) dedicated to radiology (Heptonstall et al. 2016), with stu- intramural bowel gas and (3) fluid-gas level within dents reporting low confidence in interpreting abdominal collections imaging (Jacob et al. 2016) and performing poorly at the Firstly, the CT scan needs to be assessed for pneumoperito- recognition of life-threatening CT images (Nguyen et al. neum (free gas in the abdominal cavity). It is a sign of per- 2017). At the same time, interpreting abdominal CTs is con- foration of a hollow viscus and prompt identification of sidered to be an important skill by residency program this sign is crucial (Tanner et al. 2018). In order to maximise the ability to see pneumoperitoneum, consider changing directors in the US (Kondo and Swerdlow 2013). We developed a basic systematic approach to viewing the image window to ‘lungs’, which will make air appear black in contrast to the relatively bright abdominal viscera. abdominal and pelvic CT scans, which can be taught to Look at all the images to ensure that small localised perfo- junior members of the medical profession. It follows a rations are not missed. simple ‘4As, 3Bs, 2Cs and 1D’ approach. It is not, however, Some air within the abdominal cavity is not patho- intended as a comprehensive methodology for interpreting logical, such as gas within the bowel lumen and free air abdominal/pelvic CT scans, and formal reports should be after laparoscopic surgery. It has previously been reported sought where possible. that 23% of post-laparoscopy CT scans have pneumoperito- neum visible for up to 3 weeks post-operatively with only a Tip 1 small percentage of these patients requiring any interven- tion for this finding (Chapman et al. 2015). Perform the pre-interpretation checks Secondly, check for gas contained within the bowel It is vital to make sure that pre-interpretation checks are wall. Pneumatosis intestinalis (intramural bowel gas) appears made. These include: name and date of birth of the as gas bubbles within the bowel wall, indicating a disrup- patient, date of scan, type of scan and images—are there tion in the integrity of bowel mucosa which leads to arterial and venous phase scans or pre- and post-contrast increased permeability. It may indicate bowel ischaemia, images and if so, are you viewing the right one? Finally, necrosis or, less commonly infection and others (Treyaud does the scan allow you to see what you want to see, for et al. 2017). Its management can be challenging, but CONTACT Jakub Nagrodzki [email protected] Peterborough City Hospital, North West Anglia NHS Foundation Trust, Bretton Gate, Peterborough PE3 9GZ, UK These authors contributed equally to this work. ß 2020 Informa UK Limited, trading as Taylor & Francis Group 2 S. SIVATHASAN ET AL. emergency surgery is often required (Tahiri et al. 2015; The appendix, as an anatomical variant, can be found in Ross et al. 2018). many locations throughout the abdominal cavity including Thirdly, one should also check for air within a fluid col- the pelvis, posterior to the urinary bladder, and in the left lection, in the form of an air-fluid level or ‘bubbles’, as this upper quadrant (Barlow et al. 2013). Therefore, it is often can be a sign of gas-forming organisms within the fluid, easier to follow the colon proximally from the rectum until indicating an active infection. the ileo-caecal junction, at which point the appendix can be identified as a blind-ended appendage of the caecum. Signs of inflammation include peri-appendiceal fat strand- Tip 3 ing, extraluminal air, peri-appendiceal fluid or appendix The 2nd A: aorta. Assess for (1) aneurysms and (2) abscess (Kim et al. 2018). atherosclerosis It is important to follow the aorta from the aortic valve (if visible on the scan) down to the common iliac bifurcation The three ‘B’s and then along each of the iliac/femoral vessels until the Tip 6 inferior most image of the scan. Observe for signs of an abdominal aortic aneurysm and any associated leakage of The 1st B: bowel. Assess the bowel for pathology blood, as well as the ‘tennis ball sign’ of aortic dissection When looking at the bowel, consider the following: (1) look (Lal et al. 2017). Aneurysms can occur anywhere along the at the whole bowel and (2) focus on the area which indi- vessel and may involve the aorta or any of its branches, to cates pathology from your clinical assessment. the common iliac arteries and beyond. The bowel needs to be followed from the pylorus to In addition to aneurysms, identification of the main the rectum in a systematic manner. It is often possible branches of the aorta allows for other potential causes of to use clinical signs to pinpoint the likely point of con- abdominal pain to be seen, such as mesenteric ischaemia cern, but the presentation can be misleading, for and infarction. In non-contrast images atherosclerotic calci- example in cases of pelvic inflammatory disease due to fication of these vessels, often at their origin, can raise the pus collection in the dependent areas of the peritoneal suspicion of potential vascular compromise (Wang et al. cavity secondary to peptic or duodenal ulcer perforation 2018). In the presence of contrast look for transition areas (Su et al. 2005). within the vascular tree, indicating the loss of blood flow. It is important to be able to clinically identify the signs of perforation, obstruction, bowel infarction and large malignancy encroaching on the bowel lumen, Tip 4 amongst others. These common conditions can all be The 3rd A: ascites. Check if there is any fluid in part of the acute abdomen and identifying them prior to the abdomen the full radiologist’s report allows for basic interventions, Ask yourself two questions: (1) is the fluid ascites or blood?; such as nasogastric tube and intravenous fluids in bowel (2) if it is ascites, is it exudative or transudative? Identifying obstruction, to be instigated to mitigate the poten- the presence and the likely origin of fluid in the abdomen tial damage. can give clinicians useful clues to the underlying pathology and the necessary management. Tip 7 Firstly, it is important to try to decide whether the fluid is ascites or blood. A large volume of intraabdominal fluid The 2nd B: bladder. Assess the kidneys, bladder and without a compensatory haemodynamic response (tachy- collecting system cardia ± hypotension) generally indicates ascites, rather Diseases of the genitourinary tract are among the top than blood. If the volume is small, it can be difficult to dis- 10 primary inpatient diagnoses in the UK (NHS Digital tinguish ascites from hemoperitoneum on the scan alone, 2019b) and therefore the urological tract is one of the but clinical assessment may give further clues. areas of the abdominal CT scan that needs to be care- Secondly, it may be beneficial to establish if the ascites fully considered. is transudative or exudative. This is also quite difficult Initially, identify the kidneys and note any asymmetry based on the scan alone, however one way is to note if in size or location and any anatomical variations. Look the fluid is loculated or not. The presence of septa within for the bladder and any signs of obvious pathology such the fluid may indicate an exudative cause, but fluid can as cysts, tumours or gross dilatation. Then identify the also become loculated through its confinement by adhe- collecting system of one of the kidneys and follow the sions or malignancy (Rudralingam et al. 2017) and the lack ureter closely from the renal pelvis to the bladder. of septations does not rule out an infective element. Repeat this for the opposite side. Look for any obvious dilatation and/or asymmetry in size or location of the kidneys and ureters, potentially indicating polycystic kid- Tip 5 neys, a tumour or obstructive uropathy. Also look for The 4th A: appendix. Assess this common site signs of calculi, such as bright white signal in the lumen of pathology of the renal pelvis, ureter or bladder. If stone disease is This is an important step due to the relatively high inci- suspected clinically and there is contrast present within dence of acute appendicitis paired with the ability of this the lumen of the ureter it can make the test difficult to condition to mimic a large variety of other conditions interpret, unless there are signs of absolute blockage (Bhangu et al. 2015). with no contrast after a certain point.  MEDICAL TEACHER 3 Tip 8 Tip 10 The 3rd B: biliary tree. Look for pathology of the (1) The 2nd C: cutaneous/soft tissue. Examine the images common bile duct and hepatic duct and (2) for pathology within the skin and soft tissues of the gall bladder abdominal wall The biliary tree is another common cause of patients Once the internal aspect of the peritoneal cavity has been presenting with an acute abdomen (NHS Digital 2019a). interrogated, examining the images for problems within Common diagnoses include choledocholithiasis, obstruc- the skin and soft tissues of the abdominal wall may eluci- tion from external compression such as in pancreatic date the cause of the presenting complaint or a second malignancy or sphincter of Oddi stricture, or biliary sep- abnormality, either related or not. sis, usually secondary to cholecystitis and ascending Examples of causes of presentations resembling the cholangitis. acute abdomen from these structures include rectus sheath The entire biliary tree should be identified, starting from haematomas, abdominal wall cellulitis, or an injury that did the sphincter of Oddi and working proximally to notice any not penetrate the parietal peritoneum. common bile duct or hepatic duct dilatation or collapse, as well as identifying the gall bladder and any signs of perfor- The one ‘D’ ation—in the form of pericholecystic fluid—or inflamma- tion, in the form of fat stranding around the gall bladder Tip 11 (Morris et al. 2007). The D: doctors’ interventions. Check (1) drains, (2) signs of previous surgery, (3) complications of recent interventions The two ‘C’s Look for any signs of drains (including biliary, ascitic, post- operative, etc.) within the abdominal cavity. These can be Tip 9 signs of active pathology and may need to be investigated The 1st C: cancer. Check for any sign of malignancy further as iatrogenic causes of a patient’s presentation— We recommend the following: (1) identify gross abnor- e.g. is the drain blocked? Is it in the wrong location? malities within abdominal and pelvic organs, as well as Surgical clips or intravascular prostheses can be signs of an abdominal wall; (2) consider whether it is likely to be a underlying disease and may modify the differen- malignant (primary or metastatic) or non-malig- tial diagnosis. nant lesion. In post-operative patients, it is particularly important to Examples of gross abnormalities that may be identified consider iatrogenic causes for their presentation. For include malignancies within the liver, both primary and example, surgical procedures performed around the pelvic metastases; malignancies of the kidneys, bowel, ovaries or region and retroperitoneal abdominal space can lead to stomach, as well as tumours in the abdominal wall, to urinary tract injuries (Esparaz et al. 2015). Post-pancreatic name a few. Metastatic masses can grow rapidly, have a surgery complications include bile leak, bile tract obstruc- similar radiological appearance to their primary site lesion, tion and infection (Angileri et al. 2019). and should especially be considered in the differential if the patient has a history of malignancy and/or has other Bringing it all together sites of metastases (Li et al. 2019). Non-radiology trainees, however, are not expected to be competent at identifying Tip 12 the nuances of small malignancies. Summarise the findings In the acute admission, cancers are usually diagnosed Once all 10 aspects of the CT scan have been systematic- based on their sequelae, for example complete bowel ally reviewed, the next step is to corroborate the findings obstruction in colorectal malignancy (Guimaraes et al. of the CT scan with the clinical history and examination, 2014), or as a clinical sign, such as obstructive jaundice and any other investigations. in a patient with liver malignancy (Lai and Lau 2006). Usually the interpretation of CT images for patients with However, the diagnosis of malignancy can be incidental, an acute abdomen by a non-radiologist will allow for initial such as the finding of a markedly enlarged kidney rela- management to be started. Should imaging point to a tive to the contralateral organ in the case of renal pathology that may require surgical intervention, appropri- cell carcinoma. ate senior escalation and discussion with a radiologist to Early identification of neoplasms and their sequelae may confirm the diagnosis is necessary, especially if there is aid decision making, but usually warrants conservative any ambiguity. treatment until a full radiologist report is available. An exception might be cases of faecal peritonitis, where an emergency laparotomy may be indicated, following appro- Conclusions priate escalation to a senior and a direct discussion with a We presented a simple structure for looking at abdominal radiologist (Ross et al. 2018). and pelvic CTs, which can aid junior members of the med- Remember that the differential for masses in the ical profession. The importance of ensuring that junior abdominal wall includes benign tumours, such as lipomas, trainees receive good-quality radiology training is widely as well as tumour-like lesions, such as hernias and endo- recognised (Jacob et al. 2016). It has been demonstrated metriosis (Li et al. 2019). that the cautious use of CT findings prior to a formal 4 S. SIVATHASAN ET AL. radiology report by staff in the emergency department Jacob J, Paul L, Hedges W, Hutchison P, Cameron E, Matthews D, improves outcomes by early recognition and treatment Whiten S, Driscoll P. 2016. Undergraduate radiology teaching in a (Bagheri-Hariri et al. 2017). UK medical school: a systematic evaluation of current practice. Clin Radiol. 71(5):476–483. Kim HY, Park JH, Lee YJ, Lee SS, Jeon J-J, Lee KH. 2018. Disclosure statement Systematic review and meta-analysis of CT features for differentiat- ing complicated and uncomplicated appendicitis. Radiology. 287(1): The authors report no conflicts of interest. 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