Abdominal X-Ray for Medical Student OSCE
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Prepare by turning of any stray lights. Slip film into X-ray viewer. Read pt details from envelope and film
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Describe type of X-ray
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Supine / erect / decubitus (e.g. right lateral decubitus = pt lying on their right side; radiograph taken side-on)
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Unlabelled X-ray assumed to be supine: better at showing gas patterns.
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Erect films better for showing fluid levels
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Contrast used? Barium swallow, barium meal, barium follow through, barium enema.
Barium contraindicated in perforated bowel and toxic megacolon. H2O-soluble contrasts then used (e.g. Gastrografin), but these are dangerous if aspirated.
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Interpret:
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Gas pattern
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Intraluminal – ground glass / mottled often = faecal shadowing. Large bowel – more peripheral, haustra, normally <5cm diameter. Small bowel – central; valvulae conniventes; rule of 3s: <3cm diameter, wall thickness <3mm, valvulae conniventes <3mm thick; approx 3 air fluid levels per radiograph. Note excessive air; excessive dilatation – bowel obstruction + risk of perforation if large bowel >9cm / caecum >12cm. N.B. peritonitis can cause localized ileus ? seen as ‘sentinel loop of bowel’.
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Extraluminal – gas outside stomach and bowel. Pneumoperitoneum – perforation (most likely under diaphragm). Gas within bowel wall – bowel infarct - also air in portal vein. Air in pancreas – acute necrotizing pancreatitis. In biliary tree – biliary fistula, surgery. In urinary tract – entero-vesical fistula.
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Calcification of:
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Arteries – atherosclerosis
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Pancreas – chronic pancreatitis
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Gall bladder – biliary calculi – 20% radio-opaque
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Kidney and ureters – nephrocalcinosis, renal calculi – 90% radio-opaque (follow renal tract along transverse processes of lumbar vertebrae, to level of ischial spine, before it joins bladder.
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Bladder – stone, tumour
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Appendix – 15% of appendicitis
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Pelvis – calcified fibrinoids in uterus, teratomas in ovaries
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Bones – spinal scoliosis, osteoarthritis (spine and hip), Paget’s disease, fractures, spinal mets
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Soft tissue – size and position of liver, spleen, kidney (T12-L2, parallel to psoas line, about 3 vertebral bodies in length), bladder. Absent psoas muscle shadows suggest intraperitoneal disease
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Artefacts – surgical clips, IUDs, stents, filters (Greenfield filter – IVC filter)
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Differential diagnosis
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Mechanical large bowel obstruction – causes: carcinoma, diverticulitis, volvulus (often sigmoid). Bowel gas and faecal matter collects proximally: colon dilated >5cm / caecum >9cm; normally restricted to colon by ileocaecal valve, but associated small vowel dilatation in 25% due to ileocaecal valve incompetence. Erect x-ray: long but few air fluid levels
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Paralytic ileus (non-mechanical obstruction) – failure of transmission of faecal matter and gas through intestine – this is a form of large bowel obstruction. Due to reduced motility / peristalsis. Full length of large and small bowels affected, including rectum – all dilated. Absent severe colicky pain and bowel sounds
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Small bowel obstruction – causes: adhesions, incarcerated hernias, tumours, Crohn’s disease, gallstone ileus. Small bowel dilated 3-5cm. No large bowel dilatation. Several dilated loops of bowel, multiple air fluid levels with unequal heights – ‘stepladder’ appearance of erect x-ray, + ‘string of pearls’ sign – small amounts of air trapped in fluid-filled valvulae conniventes.
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Volvulus – twisting of bowel about mesentery, in sigmoid (75%) or caecum ? obstruction, possible strangulation. ‘Coffee bean’ sign on x-ray – adjacent walls of 2 limbs of dilated loop forming dense white line, which surrounds extremely dilated bowel. Beak sign: sharp pointed end to bowel, due to twisted mesentery
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Date: Fri, 22 Jan 2010 Time: 4:09 PM
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