Acute abdominal pain

It’s 3 o’clock on a Friday afternoon. A new school term has started. Children sit in the ED waiting room clutching their tummies. Some will have constipation. Many will have non-organic pain. Most will be fine. One will be serious. Our hands are drawn to the right iliac fossa, ready to diagnose appendicitis. Spotting an acute abdomen isn’t the problem, it’s the rarer serious causes that can be the challenge. Myocarditis? Pancreatitis? A mass? How do we sieve through the haystack of non-specific abdominal pain to find the child who needs investigation or treatment?

Clues in the history

I was taught at medical school that most diagnoses will be made on history alone. There are certainly some clues in paediatric abdominal pain that will help guide our approach. There are rules. Fever plus abdominal pain – think infection, in particular appendicitis, urinary tract infection (UTI) or gastroenteritis (generally in that order – I tend to work from most serious to least serious rather than most common to least common, it’s that needle in a haystack concept). Diarrhoea plus abdominal pain – think gastroenteritis. Vomiting plus abdominal pain – think obstruction, urinary tract infection or gastro. But how helpful are these rules?

Let’s start with fever. In an old, but much-cited, study from the late 1990s, 1141 children aged 2 to 12 presenting over a 10-month period to unscheduled care with acute (≤ 3 days), atraumatic abdominal pain were retrospectively evaluated. These children accounted for 5.1% of all attendances to the study team’s ED and a walk-in clinic. 64% of these children had fever. That’s a lot of children. The five most common infective diagnoses in descending order ranged from an upper respiratory tract infection (including otitis media) in 18.6%, pharyngitis in a further 16.6%, “viral syndrome” in 16.0%, gastroenteritis in 10.9% and “viral illness” in 7.8%. Urinary tract infections accounted for only 1.6% and appendicitis for only 0.9% of presentations. You’ll be struck by the number of non-abdominal febrile illnesses presenting with abdominal pain. In the era of COVID-19, the differential of abdominal pain plus fever must also make you think of PIMS-TS, the great appendicitis mimic.

You might wonder whether a history of vomiting is any more helpful in pointing us in the right diagnostic direction. Abdominal pain plus vomiting sweeps me in the direction of obstruction, UTI or gastritis. It’s a common symptom. The same study showed that of the 1141 children with abdominal pain, 42% also had a history of vomiting. Perhaps not so helpful then. You’ll have spotted my needle-in-a-haystack approach again listing gastritis as my last differential. Don’t jump to the conclusion that this child has a GI infection until you’ve ruled out the serious diagnoses you don’t want to miss – obstruction (easy when the vomiting is bilious, but it won’t always be bilious), diabetic ketoacidosis (DKA) and (I don’t want to scare you, but you have to think of it) raised intracranial pressure. All those URTIs and pharyngitis – can cause vomiting too.

Add diarrhoea to the mix and it’s easier to conclude that the child has gastroenteritis. And that will be the case, most of the time. But diarrhoea is not as specific a symptom as you may think. Lots of things can make the gut unhappy and an unhappy gut can lead to diarrhoea. UTIs (particularly in babies), intussusception, haemolytic uraemic syndrome (HUS), Meckel’s diverticulum… this list goes on. A child with appendicitis might have diarrhoea – the inflamed appendix irritates the bowel (a little like bladder or urethral irritation in appendicitis leading to leucocytes on urinalysis). And sepsis. An unhappy gut in sepsis can cause diarrhoea.

What about the location of the pain? The classic history of a central abdominal pain migrating to the right iliac fossa will help point towards a diagnosis of appendicitis, but the right iliac fossa is also the home of the right ovary so in post-menarche girls presenting with severe right iliac fossa pain, you’ve got to also think about ovarian torsion. The left ovary sits in the left iliac fossa (generally no appendix there unless the child also has malrotation) so ovarian torsion should be high in your differential in a post-menarche female with pain and tenderness in either iliac fossa. It always makes me a little sad that boys presenting with a suspected testicular torsion are referred to a surgeon within minutes of arrival, but adolescent girls with abdominal pain are often sat in a bed pending bloods and urine until someone thinks ‘ovaries’.

While we’re on the subject of abdominal pain in female adolescents, don’t forget pelvic pain secondary to pregnancy or pelvic inflammatory disease, and if it’s acute and severe, think ectopic pregnancy. Don’t forget to check a urine beta-HCG. For either gender, never skip a HEEADSSS assessment.

The pain from constipation often, although not always, is left-sided and is colicky. The pain from gastroenteritis is diffuse. The pain from liver or gallbladder disease is in the right upper quadrant, while the pain from pancreatitis is periumbilical and can radiate to the back.

What about the character of the pain? Intermittent abdominal pain in a toddler makes me suspicious of intussusception. The classic red currant jelly stool is a late sign and, in my 17-year career as a paediatrician, I’ve only seen it once.

If the pain is aggravated by movement, be suspicious of localised peritoneal irritation. If speed bumps are agonising, or if the child or young person is doubled over walking from the waiting room to a cubicle, you’ve got to think of peritonitis. If, on the other hand, the child hops, skips and jumps up onto the examination couch, you can be pretty reassured that there’s nothing too severe going on.

The peritonitic child will also lie as still as possible on the bed, trying desperately not to move. The child with visceral pain from, say, renal stones, will be the polar opposite, writhing around on the bed in pain, desperately trying to get comfortable.

The child’s age might help. It can be difficult to ascribe abdominal pain in a neonate, but in a neonate with a distended abdomen, particularly if they’re vomiting, think of malrotation with volvulus. In an infant or toddler make sure to look for evidence of an incarcerated hernia or intussusception. In an older child we’re moving into the realm of appendicitis, testicular or ovarian torsion or DKA, although in reality, these can all affect a child of any age – the younger the child, the sicker they are at diagnosis because we tend not to suspect these diagnoses until quite late in the disease process.

Past history can be gold

Although this post is really about the child without significant comorbidities, don’t forget to cover the past medical history as this will raise your level of suspicion and lower your bar to investigate. Previous abdominal surgery? Think adhesions. Hirschprung’s Disease? Think Hirschprung’s enterocolitis. Sickle cell disease or cystic fibrosis? Think cholecystitis, sickle splenic sequestration or a vaso-occlusive girdle crisis. Diabetes? Think DKA. Nephrotic syndrome? Think Primary / Spontaneous Bacterial Peritonitis. Don’t forget to ask about past medical history.

Clues in the examination

The easy part is discerning whether the abdomen is soft or rigid, distended or concave, tender or, well, not tender. Is there focal tenderness, organomegaly, or a mass? Are bowel sounds absent, normal or tinkling (in obstruction)?

But don’t forget, an abdominal examination goes beyond the abdomen. You must, must, must examine the inguinal region and, in a boy, the scrotum. Testicular torsions, incarcerated hernias (yes, in older children too) and other pathologies in the nether regions can all present with abdominal pain with or without vomiting.

Then go further still. Listen to the chest. Are the heart sounds normal? Are they muffled? Is there a gallop rhythm or a murmur? Although rare, abdominal pain and vomiting, often misdiagnosed as gastritis, are recognised presentations of pericarditis and myocarditis. Listen to the breath sounds. Are they normal or focally reduced? Are there crepitations? Percuss the chest. Is there focal dullness? Diaphragmatic irritation presenting with abdominal pain is a fairly common symptom of lower lobe pneumonia, although in these children with abdominal pain the abdomen won’t be tender.

Examine the skin. Jaundice is a big clue that something hepatobiliary is happening. A red, rough sandpapery rash points to scarlet fever. Purpura in the legs suggests Henoch Shonlein Purpura (HSP).

And the bread and butter of any paediatric illness examination? The ears, nose and throat exam. Pharyngitis, tonsillitis, otitis media and viral URTIs can all present with abdominal pain.

What if it’s not the first presentation?

Many of those children clutching their bellies in your ED waiting room on a Friday afternoon will have presented with abdominal pain before. Recurrent or chronic abdominal pain deserves a post in its own right and I’m not going to delve into any detail here other than to suggest you seek evidence in the history and examination for diagnoses like constipation, gastro-oesophageal reflux disease, inflammatory bowel disease and ask about B symptoms that might flag a malignancy. And if you’re happy there are no red flags in the history, always explore a psychosocial HEEADSSS history that might lead you to a diagnosis of functional / non-organic abdominal pain.

And finally, when might you investigate?

Most children with abdominal pain who look well, have no red flags in their history and have a normal or reassuring exam don’t need to be investigated.

If you are concerned, the following tests might help downsize your haystack into a more manageable size.

• Blood sugar – to look for hyperglycaemia in DKA or, the other extreme, hypoglycaemia in the child whose oral intake has been poor or GI losses have been large.
• Urine – to use urinalysis to investigate for UTI, haematuria (pointing towards renal stones, HUS or Heinloch Schonlein Purpura) or pregnancy. Don’t forget that some white cells can slip into the urine in appendicitis due to bladder irritation by the inflamed appendix or in infections outside the abdomen.
• Lab bloods – to look for signs of acute infection (white cell count or CRP, although these might be normal in appendicitis so don’t be falsely reassured if your suspicion of appendicitis remains high); low haemoglobin in Sickle Cell Disease or HUS following bloody diarrhoea (which also has low platelets), deranged liver function or a raised amylase if you suspect hepatobiliary or pancreatic disease.
• Blood gas – to investigate for metabolic acidosis or raised lactate in DKA, dehydration, obstruction, peritonitis or sepsis.
• Abdominal x-ray – when you suspect obstruction (fluid levels in bowel loops), perforation (free air), or foreign body ingestion (beware button batteries or multiple magnets).
• Chest x-ray – may help find a lower lobe pneumonia, although if your clinical findings support pneumonia and the child is well enough to go home, they generally don’t need you to prove the diagnosis with an x-ray. If your examination points you towards pericarditis or myocarditis, a chest x-ray will help evaluate heart size.
• Upper GI contrast – in suspected malrotation with volvulus
• Ultrasound – to look for the classic donut sign in intussusception, to investigate the appendix or ovaries, or when you suspect gallstones, kidney stones or a mass.

And on that last note – a mass. Specifically a mass secondary to a tumour. It’s the diagnosis I’m most concerned about missing. Abdominal tumours are rare in children and although the abdomens of children with abdominal tumours tend to be painless, there may be associated pain if there’s bleeding into the tumour. If you can feel a mass, remember the following. A right-sided mass in a toddler with colicky pain could point towards intussusception, particularly if the right lower abdomen feels empty (Dancer’s Sign). Liver or renal masses may suggest a hepatoblastoma or Wilm’s (kidney) tumour. Two-thirds of neuroblastomas present with abdominal masses and two-thirds of these arise from the adrenal glands. As well as ultrasound, urinary catecholamines will help you here. Hepatomegaly or splenomegaly can be related to leukaemia. And of course, the mass you’re far more likely to feel – the left iliac fossa fullness secondary to poo in the constipated child.

Needles in haystacks

And so, in this whistle-stop tour of abdominal in children, I’ve hopefully helped you gain a bit of a strategy to risk evaluate belly pain in children to help you weed out the severe from the benign and find the needle in the haystack.

And if you’ve ever wondered whether it’s possible to actually find a needle in a haystack, Sven Sachsalber has proven that it is. Have a chuckle while reading this review of his discovery in Man Finds Needle In Haystack published in Modern Farmer in 2014. Enjoy.

Selected references

Chang YJ, Chao HC, Hsia SH and Yan DC. Myocarditis Presenting as Gastritis in Children. Pediatric Emergency Care 2006;22(6):439-440

Scholer, Pituch and Dittus. Clinical outcomes of children with acute abdominal pain. Pediatrics 1996;98:680