Abdominal radiograph and acute imaging decisions — formative SAQs

Short-answer question 1 (10 marks)

A 7-year-old boy presents to the emergency department with a 24-hour history of central abdominal pain that has migrated to the right iliac fossa, anorexia, and a low-grade fever. He is alert, perfusing well, and focal tenderness with voluntary guarding is present in the right lower quadrant. The registrar asks you whether an abdominal radiograph should be requested. [3]

a) State the clinical question the imaging must answer, and name the first-line imaging modality for this presentation. (2 marks) [3]

b) Explain why the abdominal radiograph is not the appropriate first test, and state the role of the pARC risk calculator in guiding the imaging decision. (3 marks) [4]

c) State the ALARA principle and summarise the Pearce 2012 evidence that underpins the radiation-aware practice in the young child. (3 marks) [1]

d) Under what circumstances would computed tomography be the appropriate next step, and what dose-modification principles apply? (2 marks) [3]

Model answer

a) The clinical question is whether this is acute appendicitis. The first-line imaging modality is ultrasound, because it uses no ionising radiation and it directly visualises the appendix. [3]

b) The abdominal radiograph has a very low yield in suspected appendicitis, it cannot see the appendix in the well child, it rarely changes the management, and it delivers a small radiation dose without benefit. The pARC calculator of Kharbanda and colleagues uses the age, the sex, the pain duration and migration, the right-lower-quadrant tenderness, the guarding, the rebound, the anorexia, and the nausea to stratify the probability of appendicitis; the high-probability child proceeds to surgical review and the intermediate-probability child has ultrasound as the deciding test. [4][3]

c) ALARA means that the radiation dose is kept As Low As Reasonably Achievable, because the young child is more radiation-sensitive than the adult owing to the longer remaining lifespan and the faster-dividing tissues. The Pearce 2012 retrospective cohort study of nearly 180,000 children who had CT scans in the United Kingdom estimated a small but statistically significant increase in the risk of leukaemia and brain tumours with increasing cumulative dose, which underpins the radiation-aware practice and the Image Gently campaign. [1][2]

d) Computed tomography is the appropriate next step when the ultrasound is equivocal and the clinical concern persists, or when the child is unstable and the team needs the answer quickly. The scan is dose-modified to the size of the child, the region is limited to the question, and the intravenous contrast is used when the soft-tissue detail is needed. [3]

Short-answer question 2 (10 marks)

A 5-week-old previously well infant presents with bilious (green) vomiting for 6 hours, with reduced feeds and irritability. The abdomen is soft and non-distended. [6]

a) State the most urgent diagnosis to exclude and the definitive imaging test. (2 marks) [6]

b) Explain why this presentation is a surgical emergency and what the consequence of delay is. (3 marks) [6]

c) Contrast this with the imaging pathway for a 3-year-old with episodic colicky abdominal pain, drawing of the knees to the chest, and a current-jelly stool. (3 marks) [5]

d) State why the abdominal radiograph is not the diagnostic test in either of these two children. (2 marks) [5]

Model answer

a) The diagnosis to exclude is malrotation with midgut volvulus. The definitive imaging test is the upper gastrointestinal contrast study, which demonstrates the abnormal position of the duodenojejunal flexure. [6]

b) The midgut volvulus can infarct the entire small bowel within hours because the mesentery twists on its narrow pedicle and cuts off the arterial supply. The bilious vomit in the infant is green and is a surgical emergency until proven otherwise; the consequence of the delay for less-urgent imaging or overnight observation is short bowel syndrome, lifelong parenteral nutrition dependence, or death. [6]

c) The 3-year-old with episodic colicky pain and a current-jelly stool has suspected intussusception. The first-line imaging test is ultrasound, which demonstrates the target lesion of the telescoped bowel and any pathological lead point. The therapeutic step is the enema reduction under fluoroscopic or ultrasound guidance; the delayed repeated reduction is appropriate in the stable child after a failed first attempt, with surgery reserved for the failed reduction, the peritonitis, or the pathological lead point. [5][6]

d) The abdominal radiograph is neither sensitive nor specific for the intussusception, because the target sign and the crescent sign are often absent or non-specific, and the radiograph cannot see the appendix or the malrotation. The ultrasound is the diagnostic test for the intussusception, and the upper gastrointestinal contrast study is the diagnostic test for the malrotation. [5][6]