Investigative procedures

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CHAPTER 3 Investigative procedures

Conventional radiology 28
Ultrasonography 32
Doppler ultrasound 33
Computerized tomography (CT) 34
Magnetic resonance imaging (MRI) 35
Positron emission tomography (PET) 35
Mammography 36
Radioisotope scanning 37
Endoscopy 38
Tissue diagnosis 39
Interventional radiology 40

This chapter describes various investigative procedures commonly used in surgery. The procedures are described briefly, together with their indications and possible complications.

Conventional radiology

Radiographs penetrate differentially through tissues of the body, resulting in different exposure of the silver salts in the radiograph film. On a plain radiograph, gas and fat absorb few X-rays and consequently appear dark, while bone and calcified defects are poorly penetrated and appear white or radio-opaque.

• A plain radiograph is one where no contrast medium is administered to the patient, e.g. routine CXR.
• A contrast study involves administration of a contrast medium, which outlines or delineates the structure under study, e.g. barium in GI studies or iodinated benzoic acid derivatives in arteriography.

Plain films

Chest X-ray (CXR)

• Always check the name of the film and the right and left markers.
• Make sure the whole chest and diaphragm are clearly on the film. You may need to count the ribs to exclude a cervical rib.
• Check that the trachea is central.
• Check the mediastinal width.
• Check cardiothoracic ratio. Maximum width of heart divided by maximum ‘bony’ (rib-to-rib) diameter of chest should be <50% in normal adults.
• Check vascular pattern, e.g. reduced in recent pulmonary embolus, distension of upper lobe veins in pulmonary venous hypertension.
• Check lung fields, e.g. lobar collapse, pneumonic consolidation, bronchial carcinoma, pneumothorax.
• Check bony thoracic cage, e.g. fractures, secondary deposits, notching (coarctation of aorta).
• Check soft tissues, e.g. surgical emphysema, mastectomy.
• Check for free air under the diaphragm on erect chest X-ray.

Abdominal X-ray (AXR)

Check for the following:

• Dilated hollow viscus with or without air/fluid levels, e.g. small and large bowel obstruction
• Free intraperitoneal gas (check position in which film was taken, e.g. air under the diaphragm with perforated hollow viscus)
• Abnormal gas patterns, e.g. air in biliary tree with cholecystoduodenal fistula and gallstone ileus, bladder with colovesical fistula
• Calcified calculi – kidney, ureter, bladder, gallbladder; 10% of gallbladder stones are radio-opaque and 85% of renal stones are radio-opaque
• Foreign bodies, e.g. swallowed keys, etc.; trauma, e.g. bullet wounds; carelessness, e.g. swabs
• Abnormal calcification, e.g. arteriosclerotic vessels, pancreatic calcification seen with chronic pancreatitis (rarely carcinoma of the pancreas calcifies), uterine fibroids
• Retroperitoneum, e.g. absence of psoas shadows with retroperitoneal haemorrhage, retroperitoneal gas with retroperitoneal perforation of a viscus
• Bones, e.g. bony metastases, fractures, osteoarthritis (plain radiographs of the limbs and skulls are dealt with in Chapters 4, 17 and 18).

Contrast studies

Gastrointestinal tract

Barium meal

This investigation is used less commonly now in view of the increased use of endoscopy. Barium suspension is given orally together with sodium bicarbonate tablets to give a barium/air double-contrast study. The progress of barium is checked by screening, image intensification being used to show a moving image on a TV monitor. Areas of interest are noted and radiographs taken. The patient should not have any solid food overnight but sips of water are allowed prior to the investigation. A study is useful for diagnosis of pharyngeal lesions, e.g. pharyngeal pouch; oesophageal lesions, e.g. carcinoma, reflux, achalasia; stomach, e.g. ulcers and carcinoma; duodenum, e.g. duodenal ulcer and pyloric stenosis.

Barium enema

Barium suspension is administered rectally. Rectal and lower sigmoid lesions should have first been excluded by sigmoidoscopy. Air is usually insufflated to give a double-contrast picture. Buscopan, an anticholinergic agent, may be given intravenously (i.v.) to relax the bowel during the investigation.

Strict bowel preparation is required prior to barium enema. A laxative should be administered the evening prior to the enema and the occasional rectal washout is required if there is evidence of residual faecal loading. Barium enema should not be performed within 7 days of a rectal biopsy because of the risk of perforation. The study is useful for diagnosis of bowel carcinomas, polyps, diverticular disease and inflammatory bowel disease. Fine mucosal abnormalities may be missed on barium enema and colonoscopy should now be considered the first-line investigation for large bowel lesions.

Barium follow-through or small bowel enema

Barium may be swallowed and followed through the small bowel into the colon. Alternatively, a duodenal tube may be positioned under radiographic control and barium injected into the duodenum and followed through the small bowel (a small bowel enema). This is useful for the diagnosis of Crohn’s disease and small bowel tumours.

Barium should be avoided in the following situations:

• If there is a significant risk of peritoneal leakage, e.g. assessing the integrity of an anastomosis. Barium causes an intense peritoneal irritation and adhesion formation, and water-soluble contrast media should be used in preference when checking an anastomosis, e.g. Gastrografin.
• In bowel obstruction, as the barium may rest at the site of a partial obstruction, solidify and cause a partial obstruction to become complete.

Biliary tree

Ultrasound

Ultrasound is now the first-line test for diagnosis of gallstones. It will also show a dilated biliary tree but will rarely pick up stones in the common bile duct due to the fact that the lower end of the common bile duct is likely to be obscured by gas from the transverse colon.

Magnetic resonance cholangiopancreatography (MRCP)

MRCP is now the initial imaging test of choice for biliary tree abnormalities, e.g. obstruction. It is a non-invasive method of imaging the biliary and pancreatic ducts. The technique does not require intravenous contrast material and uses specialized MRI sequences (i.e. heavily T2-weighted) to make the fluid in the ducts appear bright, while the surrounding organs and tissues are suppressed and appear dark. Heavily T2-weighted images give excellent anatomical detail. MRCP may be used as a screening examination in patients with a low or intermediate probability of choledocholithiasis, failed or incomplete ERCP, demonstrating variations in ductal anatomy, demonstrating postoperative anatomy (e.g. biliary-enteric anastomoses, sclerosing cholangitis), complications of chronic pancreatitis (e.g. ductal dilatation, strictures).

Endoscopic retrograde cholangiopancreatography (ERCP)

Contrast medium is injected retrogradely through the ampulla of Vater via a side-viewing duodenoscope. The technique is described more fully in the section on endoscopy, below.

Percutaneous transhepatic cholangiography (PTC)

This is used for diagnosis of obstructive jaundice. A long fine needle (22G Chiba) is passed percutaneously into the liver until a duct is pierced, witnessed by the aspiration of bile. Contrast is then injected to outline the biliary tree. Jaundiced patients may have clotting defects, e.g. abnormal prothrombin time (PT), and therefore a clotting screen should be carried out prior to this investigation. Vitamin K or fresh frozen plasma (FFP) should be administered i.v. if the PT is abnormal. Complications include haemorrhage, bile peritonitis, cholangitis and septicaemia. This technique however, has been largely superseded by MRCP.

Operative cholangiogram

At operation for cholecystectomy, the ducts should be checked for stones. Contrast is injected via a cannula inserted into the common bile duct via the stump of the cystic duct and radiographs are carried out or the image intensifier used. The diameter of the ducts, presence of filling defects and failure of contrast to pass into the duodenum are significant.

T-tube cholangiogram

If the common bile duct has been explored to exclude or remove stones, a latex T-tube is usually inserted. The horizontal bar of the T is in the duct and the vertical bar is brought out through the skin. Contrast is injected down the T-tube 8–10 days postoperatively to check for any residual stones, biliary leakage or stenosis prior to removal of the tube. There should be free flow of contrast medium into the duodenum and no filling defects.

Urinary tract

Intravenous urography (IVU)

Intravenous contrast is administered, which is excreted by the kidneys and eventually delineates the renal pelvis, ureters and bladder. A plain film is taken first so that any opacities seen can be compared with the films after contrast is given. It is useful for the diagnosis of obstruction, tumours, infection, congenital abnormalities and trauma. The only contraindication is allergy to the contrast medium. Caution must be exercised in diabetes mellitus, renal failure, multiple myeloma and cardiac failure.

Cystography

The patient is catheterized and the bladder filled with contrast medium. Bladder leaks, tumours, vesicoureteral reflux, and diverticulae can be diagnosed. A post-micturition film will diagnose residual urine. This technique has largely been superseded by ultrasonography.

Urethrography

A water soluble contrast medium is injected per urethram. Ruptures of the urethra, strictures or tumours may be seen.

Retrograde pyelography

This is carried out via cystoscopy by passing a ureteric catheter into each ureteric orifice. Clear views of the ureter and pelvicalyceal system are obtained. This test is used in patients with impaired renal function with poor concentration of contrast or if incomplete filling of the collecting structures is seen on IVU. The ureteric catheter may be left in situ to allow drainage of an obstructed system and for renal function tests to normalize prior to operative procedures.

Antegrade pyelography

The pelvicalyceal system of the kidney is punctured with a fine 22G needle. Contrast is injected and allows accurate assessment of the ureter and pelvicalyceal system, as well as assessing drainage.

Vascular system

Arteriography

Contrast medium is injected directly into the lumen of an artery. The catheter is usually introduced via the Seldinger wire technique into a suitable and easily accessible artery. The femoral artery at the groin is the usual portal of entry, although the brachial and axillary may be used. A careful history of allergies to contrast media needs to be ascertained. A clotting screen should be carried out prior to vascular radiology. With a catheter in situ, water soluble contrast medium is injected directly into the artery and images recorded in rapid sequences. Stenosis, thrombosis, embolism or aneurysm can be demonstrated. Complications include haemorrhage at the puncture site, dislodgement of atheromatous plaques, embolism, thrombosis.

Digital subtraction angiography (DSA)
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