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• Abdomen X-rays are radiographic images used for medical imaging.

Learning Objectives for Abdomen X-rays

• Understanding the anatomy of the abdomen and identifying the position of organs.
• Knowing the technical factors for radiography of the abdomen.
• Explaining the exposures for an acute abdomen.
• Describing patient positioning in radiography of the abdomen.
• Evaluating radiographs of the abdomen.
• Demonstrating knowledge of pathology using terminology and outlining pathology, including technique modifications.

Abdominal Anatomy

• Internal organs of the abdomen include liver, gallbladder, pancreas, large/small intestine, kidney, ureter, bladder, urethra, stomach, and spleen.
• Other abdominal organs include the diaphragm, esophagus, falciform ligament, ascending/transverse/descending colon, ileum, and appendix.
• The digestive system consists of the stomach duodenum, jejunum, ileum, colon, appendix, and rectum.
• In an X-ray, observable anatomy includes the liver, splenic flexure, transverse colon, right and left kidneys, transverse processes of L1 vertebra, ascending/descending colon, psoas major, small bowel, pelvic bone, spinous process of L4 vertebra, left pedicle of L3 vertebra, left sacroiliac joint, bladder, and right femur

Abdominal Quadrants

• The abdomen can be divided into quadrants:
• RUQ, or right upper quadrant.
• LUQ, or left upper quadrant.
• RLQ, or right lower quadrant.
• LLQ, or left lower quadrant.
• The diaphragm, liver, faeces, spleen, right and left kidney, and normal bowel gas can observed in a normal abdominal X-ray.

Common Indications for abdominal X-rays

• They include examination for free fluid (blood), presence of foreign bodies, and pathology such as obstruction, metastatic disease, renal calculi, inflammatory disease (ascites), and hernia.
• In cases of trauma, they can be used to find penetrating trauma, free air, stabbing, gunshot and impaling.
• Abdominal X-rays can identify gases, masses, bones, stones, fluid, or foreign bodies.

Gases

• In abdominal X-rays is essential to check for abnormal gas patterns
• These include free gas (extraluminal gas) or dilated small and large bowels (intraluminal gas).
• Pneumoperitoneum indicates gas or air trapped within the peritoneal cavity, but outside the lumen of the bowel.
• Pneumoperitoneum can be due to bowel perforation or insufflation of gas (CO2 or air) during laparoscopy; both have identical x-ray appearances but different clinical significance.
• On an erect x-ray, the free gas will be trapped under the diaphragm.
• An upright chest x-ray detects a Pneumoperitoneum easier than an abdominal X-ray.
• Rigler's/double wall sign is the appearance of lucency (gas) on both sides of the bowel wall.
• Usually, only the inner wall of the bowel is visible.
• Gas separates the bowel segments, and it forms sharp angles.
• Another sign is the Football sign, where a large volume of free gas rises to the front of the peritoneal cavity, resulting in a large, round, black area

Bowel Obstruction

• Bowel obstructions account for 20% of admissions with "surgical abdomens".
• Radiology confirms diagnosis, and identifies the underlying cause of obstruction.
• Bowel obstructions are divided into large and small bowel obstructions.
• Clinical features include colicky abdominal pain, vomiting, abdominal distension, and absolute constipation.
• For large bowel obstructions, there is absolute constipation.
• For small bowel obstructions, the symptoms typically begin with vomiting.

Large Bowel Obstruction (LBO)

• Not as common as small bowel obstructions.
• Requires quick diagnosis and treatment.
• If colon increases in size, the risk of bowel perforation increases in turn.
• Perforation happens at the obstruction site, or more proximally due to secondary ischaemic change.
• Dilation of the caecum (>9cm) and >6cm for the rest of the colon is abnormal.
• The presentation includes abdominal pain, distension, failure of passage of gas and stool.
• Common causes include diverticular strictures and rectal cancer.
• There may be a soft tissue density evident at the level of the obstruction.
• Obstruction may not always be present, as there may be gas in the rectum

Pseudo-obstruction

• Pseudo-obstruction differs from bowel obstruction.
• Colonic Pseudo-obstruction Is a functional abnormality of the bowel with similar clinical features to a true obstruction, but without any mechanical cause.
• It can lead to bowel necrosis and perforation, potentially causing generalized peritonitis and death.
• It occurs more in the elderly population, those with systemic medical conditions, or those who take certain drugs.

Small Bowel Obstruction

• Adhesions secondary to intra-abdominal surgery, hernias, tumors, and Crohn's disease are the most common causes.
• Dilatation >3cm of the small bowel is abnormal; the longer the dilated segment, the more likely it is a genuine obstruction.
• Abdominal radiographs are 50–60% sensitive for small bowel obstruction. Radiographs have dilated loops of small bowel proximal to the obstruction.
• There are predominantly central dilated loops.
• Valvulae conniventes should be visible, along with the presence of >3cm dilation.
• Fluid levels are only visible if the study is erect but the "string-of-pearls sign" may be visible.
• A gasless abdomen happens when the gas within the small bowel shifts due to vomiting, NGT placement, and obstruction.
• The string of pearls (or beads) sign can be seen on erect/decubitus images and CT scans in patients with small bowel obstruction; a row of small gas bubbles in the abdomen representing pockets of gas along the superior wall of the small bowel trapped between the valvulae conniventes.
• Valvulae conniventes are mucosal folds of the small intestine, starting with the second part of the duodenum.

Normal vs Small Bowel Obstruction

• A normal small bowel meal shows the rugal folds in the stomach and the valvulae conniventes.
• Abdominal films demonstrate why the abdomen is distended.
• Multiple loops of gas-filled small bowel happen in a predominantly central distribution.

Ileus

• Ileus means an aperistaltic bowel and is not caused by obstruction.
• The phenomenon is common after abdominal surgery, but the radiological features can be similar to those of bowel obstruction.

Volvulus

• Volvulus is the twisting of the bowel; a cause of obstruction with radio graph characteristics.
• The two most common types of bowel twisting are sigmoid volvulus and caecal volvulus.
• The sigmoid colon is more prone to twisting than other segments of the large bowel because it is "mobile" because it is on its own mesentery that rises from a fixed point in the left iliac fossa (LIF).
• The coffee bean sign marks a sigmoid volvulus.

Toxic Megacolon

• A life-threatening condition characterized by dilation of the large bowel without obstruction in the context of acute bowel inflammation.
• It may result from inflammatory bowel disease, such as ulcerative colitis, and other causes of colitis

Radiology - Air in the Liver

• Pneumobilia: air in the biliary tree; shown as a radiolucent area located centrally within the liver.
• Portal Venous Gas: gas in the portal venous system of the liver.
• Radiolucent areas happen around the periphery of the liver.
• Almost always represents life-threatening intra-abdominal pathology such a bowel ischaemia or necrosis.

Radiology - Masses

• Masses are best visualised using CT.
• Masses will appear as solid areas, and may be identified through displacement of organs/structures.

Radiology - Stones

• Appear as radio-opaque areas which cause pain due to obstruction
• Renal/ureteric/bladder stones or urolithiasis are stones where 80-90% of renal tract stones are radio-opaque.
• 15% of gallstones or cholelithiasis are radio-opaque, and happen in the RUQ; with positioning confirmed using CT or US.
• Ureteric calculi or stones are those lying within the ureter from the pelvico-ureteric junction to the vesico-ureteric junction.
• classic cause of renal colic type abdominal pain, symptoms of haematuria, nausea and vomiting.
• Up to 80% of renal calculi are formed by calcium stones and calculi format due to crystal formation with calcium and uric acid supersaturate.
• A plain abdominal (KUB) film identifies large radiopaque calculi, smaller calculi and radiolucent stones may be undetected.
• Obstruction and hydronephrosis are not adequately assessed.

Fluid - Ascites

• Ascites means an abnormal amount of intraperitoneal fluid that causes abdominal distension, nausea, vomiting, dyspnoea, and peripheral oedema.
• Ascitic fluid traditionally has different composition.
• Transudate: thin, low protein count, leakage from vascular system.
• Exudate: high protein count, tissue leakage due to inflammation/local cellular damage.
• The causes include hepatic cirrhosis, alcoholic hepatitis, heart failure (CCF), portal vein thrombosis, peritoneal dialysis/carcinomatosis, pancreatitis, peritonitis due to tuberculosis, ischaemic bowel, and bowel obstruction.
• Ascites is a diffusely increased density of the abdomen, with psoas muscles, liver, and spleen.
• There is medial displacement of bowel, with increased separation of small bowel loops.

Foreign Bodies

• Foreign objects are potentially visible in the abdominal area using X-rays.

Abdomen X-Ray Projections

Acute Abdomen Series

• A set of abdominal radiographs to evaluate bowel gasses and can evaluate: amount of bowel gas with distention, air-fluid levels, and pneumoperitoneum.
• A standard series includes AP supine Abdomen, PA erect Abdomen, and PA erect Chest.
• Those who cannot stand or sit upright need AP supine Abdomen, Left lateral decubitus Abdomen, and AP supine or semi-erect chest.
• AP supine abdomen XRay performed first as it provides info needed.
• The decubitus view shows air-fluid levels and intraperitoneal free gas that the erect images could not do.
• Patient must sit up for 5-10 minutes to allow gas drift towards diaphragm, and must lie on their left side to allow gas to locate along the lateral liver edge.

Common Requests

• Constipation, suspected Small Bowel Obstruction (SBO), Vomiting, RIF pain, auscultation, Obstruction ,RUQ Pain.

Patient Prep

• Positive identification of the patient.
• Identify if the patient is pregnant.
• Remove piercings, bras, pants, any metal objects or contents in pockets.
• Patients wear a hospital gown or scrubs

Technical Factors for AP and PA Abdomen X-rays

• Use 80 kVp, ~40mAs (AEC used in bucky), as short as exposure
• Minimum 100cm SID, large focal spot, grid, large detector (35x43) portrait
• Respiration through expiration with ideal separation
• Note which side
• The anatomy should show lateral margins of the abdomen, Symphysis puis, and Diaphragm

AXR in the Abdomens

• Currently in medicine, sites wish to eliminate erect/decubitus AXRs due to the high dose and the limited information acquired.
• Supine AXRs provide the majority of diagnostic information in the abdomen.
• Erect CXRs show more pressing pathologies.
• CT scans of the abdomen performed with lower doses.
• These are replacing AXR requests, IV increases diagnostic information.