Abdominal x ray

Indications: Free air? 80% sensitive Obstruction? 50% sensitive Constipation? (clinical diagnosis!! Limited) Stones? (non contrast CT, US) Masses?

1 = 35 chest radiograph dose

fat less dense so can create outline! This guide provides a structured approach to abdominal X-ray interpretation and includes examples of relevant pathology.

Confirm details

Begin abdominal X-ray interpretation by checking the following details:

Patient details: name, date of birth and unique identification number.

Date and time the film was taken

Previous imaging: useful for comparison.

Assess image type and quality

Projection of image

Assess the projection of the abdominal X-ray.

Typical projections of an abdominal X-ray include:

Anterior-posterior (AP) supine

Anterior-posterior (AP) erect

Decubitus ⇒ suitable for unstable patient for free air and left because wont confuse with gastric bubles

KUB?? ⇒ do with IV urogram or IV pyelogram but now replaced by CT

Can have lateral as well

Exposure of image

Assess the X-ray to ensure the whole abdomen is visible from the level of the diaphragm to the pelvis.

Ensure the exposure is adequate to allow radiological assessment of both the small and large bowel.

Abdominal X-rays do not provide a good view of posterior abdominal structures due to overlying bowel and gas.

If bowel perforation is being considered, you don’t usually require an abdominal film, instead you need an erect chest X-ray, as this allows free gas under the diaphragm to be identified (the patient needs to have sat upright for at least 15-20 minutes prior to the X-ray to allow time for the air to rise).

vertebra bodies seen

A structured approach to interpretation

It’s important to have a systematic approach to interpreting abdominal X-rays as this decreases the risk of missing pathology.

In this guide we use the BBC approach:

Bowel and other organs: small bowel, large bowel, lungs, liver, gallbladder, stomach, psoas muscles, kidneys, spleen and bladder.

Bones: ribs, lumbar vertebrae, sacrum, coccyx, pelvis and proximal femurs.

Calcification and artefact (e.g. renal stones)

Bowel and other organs

Small and large bowel

Differentiating between the small and large bowel on an abdominal X-ray is not always straightforward but there are a number of clues that may help you:

The small bowel usually lies more centrally, with the large bowel framing it.

The small bowel’s mucosal folds are known as valvulae conniventes and are visible across the full width of the bowel.

The large bowel wall features pouches or sacculations that protrude into the lumen, known as haustra. In between the haustra are spaces known as plicae semilunaris. The haustra are thicker than the valvulae conniventes of the small bowel and typically do not appear to completely traverse the bowel. This distinction is unfortunately unreliable as dilated large bowel can have a haustral pattern that does, in fact, traverse the bowel. (plica circulares which transverse vs haustra that doesnt)

Faeces have a mottled appearance and are most often visible in the colon, due to trapped gas within solid faeces.

Bowel diameter

The upper limits for the normal diameter of different bowel segments are as follows:

Small bowel: 3cm

Colon: 6 cm

Caecum: 9 cm

This is often referred to as the ‘3/6/9 rule’.

A normal abdominal X-ray showing large bowel (white arrow) framing the small bowel (black arrow) 5Example of faeces and its typical mottled appearance 7The small bowel’s mucosal folds are called valvulae conniventes and cross the full width of the bowel 5Haustra (white arrow) and plicae semilunaris (black arrow) 5

Small bowel obstruction

Typical abdominal X-ray features of small bowel obstruction include 1 dilation of the small bowel (>3cm diameter) and much more prominent valvulae conniventes creating a 2 ‘coiled-spring appearance‘.

3. Air fluid level differing >2 cm in height within the same bowel loop

Adhesions are the most common cause of small bowel obstruction in the developed world accounting for 75% of all cases. Some other causes include abdominal hernias (10%) and either intrinsic or extrinsic compression by neoplastic masses. 9

When interpreting an abdominal X-ray you should always inspect the inguinal regions, particularly if considering a hernia as a cause of small bowel obstruction, as they are often fairly obvious (even on plain abdominal X-rays).

Small bowel obstruction (note the dilated loops of small bowel creating a “coiled-spring” appearance).

Large bowel obstruction

The most common causes of large bowel obstruction include colorectal carcinoma and diverticular strictures. Less common causes include hernias and volvulus.

Volvulus involves a twisting of the bowel on its mesentery and most commonly occurs at the sigmoid colon or caecum. Patients with volvulus are at high risk of bowel perforation and/or bowel ischaemia secondary to vascular compromise.

Typical abdominal X-ray findings in volvulus differ depending on the sub-type:

Sigmoid volvulus: a characteristic ‘coffee bean’ appearance.

Caecal volvulus: often described as having a fetal appearance.

Large bowel obstruction 1 Sigmoid volvulus 2

Rigler’s (double wall) sign

In healthy individuals, only the inner wall of the bowel should be visible on an abdominal X-ray. The presence of free air within the abdomen (pneumoperitoneum) can result in both sides of the bowel wall becoming visible (this is known as Rigler’s sign).

Causes of pneumoperitoneum include a perforated abdominal viscus (e.g. perforated bowel, perforated duodenal ulcer) and recent abdominal surgery.

You should look closely for free air under the diaphragm on an erect chest X-ray if you suspect pneumoperitoneum. (pt should wait for 15 mins standing) Free air ⇒ below the diaphargm if erect (crescentic sign) If supine ⇒ will go below and cause riglers double wall sign (black in both side) Falciform ligament sign

hyperlucency of liver, traingular lucencies

Rigler’s sign 1 Pneumoperitoneum (free gas under the diaphragm) 2

Inflammatory bowel disease

Features of inflammatory bowel disease on abdominal X-ray include:

Thumbprinting: mucosal thickening of the haustra due to inflammation and oedema causing them to appear like thumbprints projecting into the lumen.

Lead-pipe (featureless) colon: loss of normal haustral markings secondary to chronic colitis.

Toxic megacolon: colonic dilatation without obstruction associated with colitis.

Toxic megacolon in a patient with ulcerative colitis. Note the lead-pipe colon with loss of the normal haustral folds due to chronic colitis.6

Other organs and structures

Although abdominal X-ray isn’t an ideal imaging modality for assessing the structures listed below, it’s useful to be able to recognise them to help orientate yourself and identify relevant pathology:

Lungs: inspect the lung bases for pathology (e.g. consolidation) as abdominal pain can, in some cases, be caused by basal pneumonia.

Liver: a large right upper quadrant structure.

Gallbladder: rarely visible on an abdominal X-ray, however, you should quickly inspect for calcified gallstones and cholecystectomy clips.

Stomach: visible between the left upper quadrant and midline, containing a variable amount of air.

Psoas muscles: the lateral edge is marked by a relatively straight line either side of the lumbar vertebrae and sacrum.

Kidneys: both are often visible, the right kidney is lower than the left due to the presence of the liver on the right.

Spleen: located in the left upper quadrant, superior to the left kidney.

Bladder: has a variable appearance depending on the fullness of the bladder.

Other structures visible on an abdominal X-ray

Bones

Lots of bones are visible on an abdominal X-ray and it’s important that you can identify each and screen for pathology. In addition, bones on an abdominal X-ray provide useful landmarks which allow you to approximate the location of soft tissue structures (e.g. the ischial spines are the usual level of the vesicoureteric junction).

Bony structures commonly visible on abdominal X-ray include:

Ribs

Lumbar vertebrae

Sacrum

Coccyx

Pelvis

Proximal femurs

A wide range of bony pathologies can be identified on abdominal X-ray including fractures, osteoarthritis, Paget’s disease and bony metastases. Like on CXR stuff

Sclerotic bony metastases (arrows) in a male patient with prostate cancer. 3

Calcification and artefact

Various high density (white) areas of calcification or artefact may be noted on abdominal X-ray including:

Calcified gallstones in the right upper quadrant

Renal stones/staghorn calculi

Pancreatic calcification

Vascular calcification

Costochondral calcification

Contrast (e.g. following a barium meal)

Surgical clips

Jewelery

Abdominal X-ray showing ureteric stent placement.Staghorn calculus on the left and multiple renal stones on the right. 4Belly button piercing

Presenting an abdominal X-ray

Having a structured approach to summarising your findings is key to ensuring you communicate the salient points.

“This is a supine AP abdominal radiograph of Jayne Lister, date of birth 11th April 1970. The film is of good quality with adequate exposure. No prior imaging is available for comparison. Both the small and large bowel appear within normal limits. Other abdominal viscera appear normal within the limits of this projection. No obvious bony pathology is identified. No abnormal calcification is visible. In summary, this is a normal plain radiograph of the abdomen.”