Interventional radiology
Over
the last 20—30 years, interventional radiology has made an essential
contribution to patient management. The speciality has developed from
angiographic techniques, with guidewires and catheters as key ingredients. The
parallel developments in cross-sectional imaging have provided enhanced
guidance for interventional procedures and radiology has evolved from providing
purely diagnostic information to
Percutaneous
biopsy is possible for most radiologically detected abnormalities. Small lesions
immediately adjacent to major vessels or a biopsy path that traverses the colon
may be regarded as relative contraindications but the decision often depends on
local expertise. In general, the shortest route from skin to lesion is chosen if
no vital structure intervenes. Fluoroscopy usually provides suitable guidance
for biopsy of large parenchymal or peri hilar masses in the chest. CT guidance
may be necessary for small lesions. Ultrasound or CT guidance is most commonly
employed in the abdomen. Ultrasound is quick and flexible and allows the needle
path to be followed in real time without additional radiation burden to the
patient. Small lesions and lesions which cannot be adequately imaged with
ultrasound, particularly within the retroperitoneum, are more appropriately
biopsied under CT control (Fig. 2.30).
A
platelet count of less than 80 000 or an international normalised ratio (INR) of
greater than 1.3 should be corrected where possible, by the administration of
fresh frozen plasma and/or vitamin K, where appropriate, prior to biopsy. Gross
ascites should be drained prior to liver biopsy unless biopsy via a transjugular
approach is available. The choice of needles is wide. In general, an 18G
automatic spring-loaded cutting needle provides an excellent core biopsy. Larger
14G needles may be useful where architectural assessment is required in patchy
disease, e.g. cirrhosis. Cytological analysis via 22G needle is often adequate
for the diagnosis of malignancy. Accuracy rates exceed 80 per cent. Negative
biopsies may be due to faulty needle placement. Complications are unusual,
occurring in less than 2 per cent of patients and include haemorrhage,
pancreatitis, pneumothorax and occasional seeding of the needle track by tumour.
Almost
any fluid collection in the chest, abdomen or pelvis may be considered for
percutaneous catheter drainage, which has largely replaced surgery as the
treatment of choice. Initially percutaneous drainage was confined to large
superficial postoperative collections, but use has broadened to include
complex multilocular collections, multiple abscesses and collections in
difficult locations (e.g. presacral space, psoas muscle).
CT
or ultrasound is used to define a safe access route avoiding the penetration of
major vessels or bowel. Ultrasound is adequate for superficial collections and
may be preferable where an angled approach is required, e.g. subphrenic
collections (Fig. 2.31). Superficial collections, where there is little risk of
misdirection, may be safely drained via a simple one-step trochar catheter
system. More complex or
Percutaneous biliary procedures
Drainage
of an obstructed biliary system is usually achieved by ERCP.
Endoscopic cannulation of
the ampulla allows the passage of guidewires and catheters, and the majority of
strictures can be bypassed and stented by this approach. In gallstone
obstruction of the common bile duct, endoscopic stone removal can be achieved
following sphincterotomy by basket retrieval, mechanical lithotripsy or balloon
sweepage of the duct. A proportion of patients with obstructive jaundice is not
suitable for this endoscopic approach, because of previous gastric surgery,
difficulties with cannulation of the ampulla or a tight stricture which cannot
be negotiated from below In these patients, a percutaneous transhepatic approach
is required. Percutaneous transhepatic cholangiography involves puncture of an
intrahepatic bile duct with a fine needle from a right intercostal approach.
Successful visualisation of the ducts is achieved in almost all patients with
dilated ducts and over 85 per cent of patients with nondilated ducts (Fig.
2.33).
Dilated systems require drainage to reduce the risk of sepsis and relieve jaundice. A peripheral duct with a direct line of approach to the common hepatic duct is chosen for cannulation. Teflon-coated hydrophilic guidewires are particularly useful in traversing even the tightest strictures. Subsequent management depends on the nature of the obstruction demonstrated.
Options include
the following:
•
balloon dilatation;
•
simple external drainage;
•
external/internal drainage;
•
endoprosthesis — plastic or expanding metal.
Balloon
dilatation
Endo
prosthesis
The
recent introduction of self-expanding metallic prostheses means that a smaller
percutaneous track is sufficient and the stent can often be inserted immediately
without a period of external drainage. Often a percutaneous approach with
guidewire manipulation through a stricture is combined with an endoscopic
approach. The guidewire is ‘grabbed’ in the duodenum and a stent placed
endoscopically. Stent occlusion, by either bile encrustation or tumour ingrowth
or overgrowth, remains a problem, although the expanding metal stents have a
longer life span than plastic endoprostheses (Fig. 2.36).
Major
complications in these patients who generally have severe underlying disease
have been observed in 2—5
per cent of patients (death,
sepsis, haemorrhage).
Minor
complications (pain, fever, catheter blockage or leakage) occur in 20—40 per
cent of patients.
Gall bladder
drainage
Percutaneous
drainage of obstructed kidneys, percutaneous nephrostomy, is performed in
patients who are septic or in
In
a patient presenting with renal failure, it is vital not to miss the presence of
bilateral obstruction or an obstructed solitary kidney, and an ultrasound
examination is mandatory. The decision to drain the kidney is usually
straightforward, particularly in the presence of sepsis. In bilateral
obstruction, the better functioning kidney (larger, thicker parenchyma) should
be drained first to enable the uraemia and hyperkalaemia to be corrected. If
known malignant pelvic disease is resulting in bilateral obstruction, then
discussion and consideration of the likely prognosis of the underlying disease
process is advisable before proceeding. The indications for percutaneous
nephrostomy are shown in (Fig. 2.37.
Nephrostomy
tube placement may be performed under fluoroscopic or ultrasound guidance. The
aim is usually to puncture a lower pole calyx rather than a direct central
puncture which is more likely to cause vascular damage. A middle calyx approach
may be preferred if antegrade stent
• Obstructed infected kidney
• Obstructed solitary kidney with deteriorating renal function
• Obstruction with severe pain
• Obstruction with renal failure
• Pressure—flow studies — obstruction?
• Percutaneous access for stone removal or ureteric procedures,
e.g. stent insertion
placement
is contemplated. Using a flexible sheathed needle and guidewire with dilatation
of the track, final placement of a small pigtail catheter is achieved with
minimal trauma to the kidney and discomfort to the patient (Fig.
2.38). The use
of self-locking catheters reduces the risk of subsequent catheter dislodgement.
Haemorrhage is usually venous and mild, lasting for up to 24 hours. Significant
haemorrhage occurs in 1—2 per cent of patients and may occasionally require
arteriography to identify a bleeding point or false aneurysm, which may then be
treated with selective embolisation. Septic complications occur in 1—2 per
cent. They can be minimised by appropriate prophylactic and antibiotic cover and
minimising catheter/guidewire manipulation.
Ureteric
J-J pigtail stent insertion is usually approachedretrogradely by cystoscopy.
It is of value where long-term drainage is required. Indications include
calculous obstruction, often in relation to extracorporeal shock wave
lithotripsy (ESWL) which produces many small fragments which may block the
ureter; benign or malignant ureteric strictures and to allow ureteric
perforations to heal. If a retrograde approach fails then an antegrade approach
is possible. Most strictures can be traversed with modern flexible hydrophilic
guidewires.