2. Diagnostic and interventional radiology

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2. Diagnostic and interventional radiology



ALISON M. MCLEAN





Imaging


The reason for great emphasis on physical signs in the past was the absence of
confirmatory imaging techniques. Because of the facility with which these facilities
confirm or

refute a physical sign, care in their interpretation is rarely taken. Yet, it is
physical signs which may lead to a diagnosis, and the constant observation of the
patient can delineate changes that are helpful to management.





Most physical signs can

be confirmed by

ultrasonography, plain radiography,
CT or MRI.

It is important to be aware of the appropriate test. If a swelling has been
defined an ultrasound scan will usually confirm or refute the claim. It will define
whether the swelling is solid or

cystic, and whether it is aneurysmal, particularly with
the aid of Doppler imaging. Biopsy using ultrasonography or CT guidance will give
histological confirmation of the nature of the swelling (Fig. 1.9). Plain radiographs
will define bony changes and fr
actures (Fig. 1.10), and gas shadows, such as in
abdominal distension. MRI will define abnormalities in joints (Fig. 1.11) and within
the skull, whereas CT, particularly with contrast enhancement, will outline solid
organs (Fig. 1.12).

Imaging, to reach it
s full diagnostic potential, must be used correctly, and thus
requires study within each surgical discipline.

Diagnostic process

The initial surgical process is complete when a diagnosis has been obtained by
history, examination and imaging, supported by p
athology. Experience enables
correct weighting to be placed on each aspect of this process to define the correct
treatment. All pieces of the jigsaw must fit together, and when they do not, great care
must be exercised. Surgical

conditions tend to follow a

logic based on anatomy, physiology and pathology (Fig.
1.13); if that logic is transgressed, mistakes are made, and the patient may be wrongly
treated.

Before submitting a patient to surgery, the diagnosis should be exact, the patient’s
condition carefull
y assessed and physiological variables corrected as far as possible.
Any addi-tional risks should be taken into account and allowance made for them in
the surgical process.

Introduction

Accurate diagnosis is the key to good surgical practice. Over the last

two decades the
introduction and increased availability of new imaging modalities have made the
diagnostic process easier. Imaging helps to resolve the uncertainties of diagnosis
based on physical signs and clinical judgement. To achieve the optimum diagn
ostic
potential it is necessary to understand the complexities of modern imaging and to
recognise the most appropriate test to fit the clinical context. Communication between
the clinician and radiologist is vital for each to understand the clinical proble
m, and
the strengths and weaknesses of the imaging test selected. An ability to interpret
images gives a new depth of understanding of the disease process and of the nature
and timing of surgical intervention.

There is no standard approach to imaging altho
ugh some basic principles apply. It is
generally good practice to perform the simplest and least expensive test first if this
will provide the answer. For example, the plain abdominal film remains the diagnostic
cornerstone in assessing the acute abdomen;
in a patient with a clear history of biliary
colic, a simple ultrasound examination may be sufficient to determine management.
However, in a patient with a more complex clinical presentation, it may be more cost
-
effective to perform a more expensive test [
e.g. computerised tomography (CT) scan]
early in the diagnostic work
-
up as this may lead to a more confident diagnosis and
management, and potentially shorten the hospital stay. Cost
-
effectiveness requires
that more complex tests are not merely layered on
top of existing more standard
procedures. Through consultation, the best test must be determined. The selection of
the best investigation for a particular clinical context has been made more complex by
the rapid changes in existing technology. The developm
ent of spiral (helical) CT, for
example, has created new diagnostic possibilities based on the patterns of arterial and
venous blood flow providing information not previously available on older
equipment. Decision making therefore must be tailored to both
the available
technology and local expertise. It is also essential to view the imaging results in
conjunction with the clinical condition of the patient and to treat the patient rather
than the X
-
rays. In a patient with inflammatory bowel disease, for exam
ple, the extent
and severity of the abnormality demonstrated on a small bowel barium examination
may have little correlation with the patient’s clinical presentation (Fig. 2.1). In
contrast, a patient with fulminant colitis may be clinically toxic but with

only minimal
signs on the plain film before the reflex dilatation signaling toxic megacolon
develops.

There is a general increase in public awareness of the adverse effect of radiation in the
induction of cancer and genetic defects. Most of the received i
onising radiation comes
from the sun and earth’s core. However, medical radiation accounts for approximately
12 per cent of the total received by humans.



As more non
-
radiation dependent imaging techniques become more widely
available [e.g. ultrasound,

magnetic resonance imaging (MRI)], radiation hazard is an
increasingly important factor influencing the selection of investigation, particularly in
children and young people. The effective dose imparted by a CT scan, for example, is
equivalent to 400 ches
t X
-
rays (CXRs). However, this theoretical risk must be
balanced against the likely diagnostic yield of the examination in terms of benefit to
the patient. The aim must be to reduce unnecessary investigations, which not only add
needlessly to patient irrad
iation but also waste limited resources and increase waiting
times. The Royal College of Radiologists has published a very useful booklet, Making
the Best Use of a Department of Clinical Radiology (see Further reading section).
This gives guidelines for in
vestigations most likely to contribute to the clinical
diagnosis and management in particular clinical situations. It highlights the chief
causes of wasteful use of radiology (Tab. 2.1). Other factors must also be taken into
consideration when deciding on
the appropriate investigation, including the age and
condition of the patient and their ability to undergo the chosen investigation (Tab.
2.2).

Diagnostic imaging Imaging techniques

Conventional radiology


Conventional radiographs depend on the differentia
l absorption by soft tissue, bone,
gas and fat of X
-
rays passing through the body. The unabsorbed rays blacken a
photographic film, contained within light
-
sensitive screens, which is then processed to
produce the hard copy. Modern radiology involves the us
e of many technical
modifications to reduce the dose of X
-
rays to the patient. Plain X
-
rays remain the
primary diagnostic tool in the chest and abdomen, and in trauma and orthopaedics.
With careful interpretation, accurate diagnosis can be achieved and it
is vital that the
plain film is not jettisoned in favour of more complex and expensive imaging
techniques.

When X
-
rays strike a fluorescent screen, light is emitted which, by means of an
imaging intensifier, can be projected on a television screen. This is

the basis of
fluoroscopy (screening) which allows continuous monitoring of a moving process. It
also provides guidance for many interventional and angiographic procedures and for
barium investigations of the gastrointestinal tract. Barium studies remain a

standard
technique for evaluating disorders of swallowing and oesophageal function and for
the small bowel. The role of the barium meal and enema is challenged by the
expansion of endoscopy. However, there is little evidence to indicate that in the
diagno
sis of significant disease, e.g. ulcer/cancer, endoscopy is superior (Fig. 2.4).
Choice of examination depends on local expertise and availability. Endoscopy is
preferable where there is gastrointestinal bleeding (upper or lower) or inflammatory
bowel dise
ase.

Intravenous contrast contains iodine which absorbs X
-
rays by virtue of its high atomic
number. It provides arterial or venous opacification depending on the route and timing
of injection. Contrast injected intravenously is excreted rapidly by the kidn
eys which
forms the basis of the intravenous urogram(IVU) where the nephrographic (renal
parenchymal) and pelvicalyceal (collecting system) phases, ureters and bladder are
successively demonstrated and recorded over approximately 30 minutes following
contr
ast injection. The IVU remains the best method for investigating renal stones and
haematuria. No other technique can equally visualise the pelvicalyceal systems and
ureters (Fig. 2.5).




Tab 2.3 Imaging in the acute abdomen.



Imaging





Indications/signs



CXR (erect)

Gas under diaphragm



Abdomi
nal X
-
ray (AXR) (supine)

Dilated bowel/gas pattern


Gas inside/outside bowel



Obstruction?


Closed loop?


Bowel wall oedema?




IVU


Renal colic


Ureteric obstruction by stone?



Ultrasound (US)


Ascites




Cholecystitis


Abscess


Obstruction?


dilated fluid
-
filled



bowel


Focused high
-
resolution US

Diverticulitis


Appendicitis



Bowel wall thickening/abscess


CT

Severe pancreatitis


Diverticulitis



Abscess


Small bowel obstruction (high


grade
)


Bowel infarction



Focused CT

Appendicitis


Ureteric colic (if
contrast allergy)


Ultrasound

Ultrasound is inexpensive, quick, reliable and noninvasive and is an excellent initial
investigation for a wide range of clinical problems. It is technically demanding and
requires an experienced operator to maximise the poten
tial of the examination.
Despite the advances in technology, there are still problems with gas (which reflects
sound completely) and obese patients, who are often unsuitable for ultrasound. As
ultrasound is so accessible there is a tendency to overload dep
artments with requests
which may be on the margins of appropriateness. As with all investigations, clinicians
should consider whether the request for ultrasound is justified as to its likely yield and
its subsequent effect on patient management.

Ultrasound

depends on the generation of high
-
frequency sound waves, usually of
between 3 and 7 MHz, by a transducer placed on the skin. Sound is reflected by tissue
interfaces in the body and the echoes generated are picked up by the same transducer
and converted in
to an image which is then displayed in real time on a monitor. The
scope of ultrasound has increased vastly over the last decade with higher frequency
probes of diminishing size producing high
-
resolution images. The current range of
ultrasound includes pro
bes measuring only millimetres and operating at 20 MHz,
which can be introduced via a catheter into a blood vessel to image the vessel wall;
probes combined with fibre
-
optic endoscopes to visualise the gut wall at echo
endoscopy (EUS) (7.5

20MHz) (Fig. 2.6
); endoluminal probes for transvaginal and
trans
-
rectal scanning (7.5 MHz); dedicated very
-
high
-
frequency probes of up to 15
MHz for scanning the breast, other superficial structures and musculoskeletal work;
and an increasing array of specialised probes f
or abdominal scanning. Ultrasound is
the first
-
line investigation in hepatobiliary disease, suspected pancreatic, aortic and
many other intra
-
abdominal disorders (Fig. 2.7).

There is an increasing recognition of the value of intra-operative ultrasound sca
nning,
acknowledging the fact that visualisation at surgery is frequently incomplete, the
surgeon seeing only the exposed surfaces. These limitations are accentuated by the
restrictions imposed by minimally invasive and laparoscopic surgery.

Doppler ultra
sound measures the shift in frequency between transmitted and received
sound and can therefore measure blood flow. The spectral Doppler wave form and
ultrasound image are combined in duplex scanning. Colour Doppler imaging displays
flowing blood as red or
blue, depending on its direction, towards or away from the
transducer (Fig. 2.8). Power Doppler is not dependent on frequency or direction of
flow but is exquisitely sensitive to low flow and has the poten-tial to demonstrate
tissue perfusion (Fig. 2.9). C
ontrast agents have been developed based on micro
-
bubbles to enhance the Doppler effect. These techniques have revolutionised the
diagnosis of both arterial and venous vascular disease.


Computerised tomography


To create a CT scan, a thinly collimated bea
m of X
-
rays passes through an axial
‘slice’ of tissue and strikes an array of very sensitive detectors which can distinguish
very subtle differences in tissue density. By analysis of the collected data, the digital
information is translated to a greyscale
image where the attenuation value of tissues is
related to water, which is given a CT number of zero Hounsfield units (HU). Tissue
densities range from + 1000 (bone) down to

1000 (air). An observer working at a
viewing console can, by varying the range an
d centering of densities represented
(window width/level), display an image appropriate to the tissue being examined (Fig.
2.10).

In conventional CT, a series of individual scans is acquired during suspended
respiration. Helical or spiral CT involves conti
nuous rotation of the X
-
ray tube with
the beam tracing a spiral path around the patient such that a volume of tissue is
scanned. In this way, during a single breath
-
hold of up to 30 seconds, 30 cm or more
of tissue can be covered in one acquisition. Furthe
r developments have allowed
thinner collimation and stretching of the spiral to cover greater distances. The
volumetric data can then be processed to produce conventional transaxial images or
multiplanar (sagittal and coronal) and three
-
dimensional images
(Fig. 2.11). The
development of spiral scanning has greatly enhanced the diagnostic potential of CT
(Fig. 2.12). It is now possible to exploit the enhancement characteristics of tissues in
both the arterial and venous phases of imaging and this modificatio
n has opened up
the fields of CT angiography, three dimensional imaging and ‘virtual endoscopy’ of
the bronchial tree and colon (Fig. 2.13).

CT scanning is usually performed after simpler investigations such as plain films or
ultrasound. In many centres,
however, CT is often used as a first line examination in
the evaluation of abdominal trauma and severe pancreatitis. It




Reduced scan time: advantages in critically ill and children




Imaging at peak levels of contrast: arterial and venous phase




Over
comes the problem of ‘mis
-
registration’


lesion ‘missed’

because of different depth of respiration




Ability to review and reconstruct data retrospectively


improved lesion detection



Multiplanar and three
-
dimensional analysis



CT angiography



Co
mplex joints



Facial bones



‘Virtual endoscopy



Spiral pneumocolon


has a major role in cancer staging and an increasing role in ‘problem solving’ in the
chest and abdomen. Some centres advocate early CT in assessment of the acute
abdomen (vide i
n Ira). The development of the technique of CT spiral pneumocolon is
challenging the barium enema and colonoscopy in the investigation of large bowel
disorders (Fig. 2.14).



Magnetic resonance imaging


The basic principle of magnetic resonance imaging (MR
I) centres on the concept that
the nuclei of hydrogen, most prevalent in water molecules, behave like small spinning
bar magnets and align with a strong external magnetic field. When knocked out of
alignment by a radio frequency pulse, a proportion of thes
e protons rotates in phase
with each other and gradually returns to their original position, releasing small
amounts of energy which can be detected by sensitive coils placed around the patient.
The strength of the signal depends not only on the proton den
sity but on the relaxation
times, T1 and T2. T1 reflects the time taken to return to the axis of the original field
and T2 on the time the protons take to dephase. T1 images usually demonstrate
exquisite anatomical detail because of the high soft tissue di
scrimination. Most
pathological processes increase T2 relaxation times, producing a higher signal than
the surrounding normal tissue on T2
-
weighted scans.

The complexity of the imaging process is compounded by the variety of pulse
sequences available. In
general, image acquisition time is longer than CT. Respiratory
and cardiac motion degrade the image but this can be largely overcome with cardiac
and respiratory gating. Technological developments are fast and scanning times are
shortening. Intravenous gad
olinium acts as a contrast agent by reducing Ti relaxation
and enhancing lesions which then appear as areas of high signal intensity (Fig. 2.15).
Specific sequences have been developed to demonstrate flowing blood and produce
images resembling conventional

angiography. This technique of magnetic resonance
angiography (MBA) can be achieved without the risks of intravascular injection of
contrast and may ultimately replace conventional studies (Fig. 2.16). Heavily T2
-
weighted sequences which demonstrate fluid
-
filled structures as areas of very high
signal intensity have been developed to show the biliary and pancreatic ducts in
magnetic resonance cholangiopan-creatography (MRCP). It seems likely that this
technique will take over from diagnostic endoscopic ret
rograde
cholangiopancreatography (ERCP) (Fig. 2.17).

The major strength of MRI is in intracranial, spinal and musculoskeletal imaging,
where it is superior to any other imaging technique because of its high contrast
resolution and multiplanar imaging capab
ility. Cardiac MRI is firmly established and
the value of breast MRI, particularly in multifocal and recurrent cancer, is
increasingly recognised. It is currently the best investigation for staging cervical
cancer and for anorectal sepsis (Fig. 2.18).

Open

access magnets have been developed which allow interventional procedures to
be performed with MRI guidance and there is no doubt that this will revolutionise the
operating room of the future (Fig. 2.19). There is a vast potential for MRI in the
assessment

of disease in the abdomen and pelvis and undoubtedly the role of MRI
will continue to expand. However, because of the expense of the equipment and its
installation, the provision of scanners cannot keep up with the demands for scanning
time and most hospi
tals have to impose strict guidelines for access.

Radionuclide imaging

Radionuclides can be tagged to substances which concentrate selectively in certain
tissues of the body. These radio-pharmaceuticals are injected intravenously and, in
general, emit gam
ma radiation detected by a gamma camera. The emitted radiation
strikes a sodium iodide crystal which generates a small flash of light which is then
enhanced by photo
-
multiplier tubes to produce the image. Many studies employ
technetium
-
99m (99mTc) which ha
s a short half
-
life and imparts a radiation dose to
the patient which is lower than many other imaging investigations.

In general, spatial resolution is poor as the technique demonstrates physiological and
functional changes rather than anatomy (Fig. 2.20
). A standard gamma camera
provides only a two
-
dimensional display of activity. Single photon emission
computed tomography (SPECT) creates a three
-
dimensional image by means of an
array of photomultiplier tubes that surround the patient in the same way as
with CT
and MRI. This technique uses conventional radionuclides. Positron emission
tomography (PET) scanning is more sensitive, depending on the coincidence
detection of annihilation protons resulting from radionuclides that decay by positron
emission. How
ever, these studies require specially designed, dedicated and currently
expensive cameras and an in
-
hospital cyclotron to generate the radionuclide. These
scans are therefore not widely available.

Cross
-
sectional imaging techniques have replaced many radi
onuclide studies (liver
colloid scans, brain scans). Bone scanning remains a sensitive tool for detection of
bone metastases and occult fractures. Ventilation

perfusion scans are widely used to
detect pulmonary embolic disease, although contrast
-
enhanced s
piral CT of the
pulmonary vessels is challenging this role. New exciting techniques of
radiopharmaceutical labelling of monoclonal antibodies are opening up possibilities
of targeted cancer therapy and early detection of micrometastases.


Imaging in the a
cute abdomen

The term ‘acute abdomen’ encompasses many diverse entities. Imaging tests are
selected based on the likely diagnosis (Fig. 2.21). The erect CXR and supine abdomen
remain the investigation of choice where perforation or intestinal obstruction i
s
suspected (Fig.2.22 and Fig.2.23). In many patients this will provide sufficient
information to determine further management. When the diagnosis is less clear, new
imaging techniques are challenging the traditional approach. Both ultrasound and CT
may co
ntribute valuable information in inflammatory disease within the abdomen

notably in diverticulitis, appendicitis and in inflammatory bowel disease. In some
centres


particularly in the USA


the use of spiral CT as a first
-
line investigation
is being pro
moted as a cost
-
effective alternative to increase the specificity of primary
diagnosis (Fig. 2.24).

Imaging in oncology

Modern surgical treatment of tumour requires an understanding of tumour staging
systems, as in many instances this will define appropria
te management. The
development of stage
-
dependent treatment protocols involving neo
-
adjuvant
chemotherapy and preoperative radiotherapy relies on the ability to define tumour
stage accurately by imaging before surgical and pathological staging. Once a
diag
nosis of tumour has been established, often by percutaneous or endoscopic
biopsy, new imaging techniques have considerably improved the ability to define the
extent of tumour, although the pathological specimen remains the gold standard.
Many staging syste
ms are based on the TNM classification (tumour/node/metastasis).




Tumour

In most published studies, cross
-
sectional imaging techniques (CT, ultrasound, MRI)
are more accurate in staging advanced (T3, T4) than early (T1, T2) diseases and the
staging of
early disease remains a challenge. In gut tumours, endoscopic ultrasound is
more accurate than CT or MRI in staging early disease (T1 and T2) by virtue of its
ability to demonstrate the layered structure of the bowel wall and the depth of tumour
penetratio
n (Fig. 2.25). Developments in MRI may also improve staging accuracy of
early disease.


Nodes

Accurate assessment of nodal involvement remains a chal-lenge for imaging. Most
imaging techniques rely purely on size criteria to demonstrate lymph node
involve
ment with no possibility of identifying micrometastases in normal sized nodes.
A size criterion of 8

10 mm is taken but it is not usually possible to distinguish
benign reactive nodes from infiltrated nodes. This is a particular problem with
intrathoracic
neoplasms where enlarged benign reactive mediastinal nodes are
common. The echo characteristics of nodes at endoscopic ultrasound have been used
in many centres to increase the accuracy of nodal staging and nodal sampling, via
either mediastinoscopy or tra
nsmural biopsy under EUS control. New radioisotope
techniques are being developed using radiolabelled monoclonal antibodies against
tumour antigens which may increase detection of nodal involvement by demonstrating
micrometastases in nonenlarged nodes.


M
etastases

The demonstration of metastatic disease will usually signifi-cantly affect surgical
management. Modern cross
-
sectional imaging has greatly improved the detection of
metastases but occult lesions will be missed in between 10 and 30 per cent of pat
ients.
CT is the most sensitive technique for detection of lung deposits, although the
decision to perform CT will depend on the site of the primary tumour, its likelihood of
intrapulmonary spread and the effect on staging and subsequent therapy of the
dem
onstration of intrapulmonary deposits.

Ultrasound and CT are most frequently used to detect liver metastases. Contrast
-
enhanced CT can detect most lesions of greater than 1 cm, although accuracy rates of
CT vary with the technique used and range from 70 t
o 90 per cent. Recent studies
suggest that MRI may be more accurate than CT in demonstrating metastatic disease.
While enhanced CT is used in most centres for screening for liver deposits, CT AP
(CT with arterial portography), which requires contrast injec
tion via the superior
mesenteric artery, is used in many centres as the most accurate technique for staging
liver metastases if surgical resection is being considered. Preoperative identification
of the segment of the liver involved can be determined by tr
anslation of the segmental
surgical anatomy as defined by Couinaud to the cross
-
sectional CT images (Fig.
2.26).

Intraoperative ultrasound is an alternative method of staging that provides superb
high
-
resolution imaging of sub
-
centimetre liver nodules that

may not be palpable at
surgery.



Imaging in trauma

The response of the skeleton to trauma changes both with the nature and force of the
injury and with the maturity and strength of the skeleton. In children the ‘physis’ or
growth plate provides the weake
st link and therefore epiphyseal injuries or
apophyseal displacements are common. The skeleton is less brittle, resulting in
buckling of the cortex or incomplete ‘green
-
stick’ fractures. In the mature adult
skeleton the soft tissues


ligaments and muscula
r insertions are the weakest link,
and sprains and strains occur more commonly than fractures. The elderly osteopenic
skeleton is brittle and susceptible to fracture often with minimal force.

Fracture radiographs should be performed in two planes and wher
e possible should
include the adjacent joint. Most fractures are easily diagnosed but some may be subtle
and occult. Where a fracture is strongly suspected but not demonstrated, a repeat X
-
ray 5

10 days after the injury may identify the fracture line when
bone absorption
has begun. Stress fractures, either ‘fatigue fractures’ (normal bone) or ‘insufficiency
fractures’ (abnormal bone), can be difficult to diagnose. Radionuclide bone scanning
and more recently MRI are useful additional investigations if stres
s fractures are
strongly suspected. The ability of CT to scan in the axial plane, together with
excellent resolution of bony detail and the ability for multiplanar reconstruction,
makes CT valuable in assessment of fractures of the spine, foot and pelvis (
Fig. 2.27).

Severe trauma

In patients who survive the immediate injury, imaging is considered after clinical
evaluation and acute resuscitation. Acute spinal trauma is initially assessed by plain
films. In approximately 10 per cent of patients there are mu
ltiple levels of injury. If
spinal instability or spinal canal disruption is suspected, thin
-
section CT scanning
with reconstruction of the images is required. Suspected cord damage may require an
urgent MRI scan (Fig. 2.28). Evaluation of severe head, che
st and abdominal trauma
usually necessitates CT scanning after initial plain films (Fig. 2.29).



Interventional radiology

Over the last 20

30 years, interventional radiology has made an essential
contribution to patient management. The speciality has deve
loped 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 diagnos
tic
information to therapy, offering effective alternatives in the treatment of abdominal
and thoracic disorders. In some instances, interventional radiology techniques have
replaced the conventional surgical approach, removing the need for a general
anaes
thetic with consequent decreased morbidity and length of hospital stay, with
similar patient outcome. The increasing complexity and sophistication of both surgery
and available intetventional techniques requires close liaison in decision making
between the

surgeon and radiologist to choose the optimum method of treatment.



Percutaneous biopsy

Percutaneous biopsy is possible for most radiologically detected abnormalities. Small
lesions immediately adjacent to major vessels or a biopsy path that traverses th
e 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 biops
y 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 o
f 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 t
o 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 assessme
nt is required in patchy disease, e.g. cirrhosis.
Cytological analysis via 22G needle is often adequate for the diagnosis of
malig-nancy. 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.



Drainage of abscesses and fluid collections

Almost any fluid collection in the chest, abdomen or pelv
is 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
postopera-tive collections, but use has broadened to include complex m
ultilocular
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 s
uperficial collections and may be
preferable where an angled approach is required, e.g. sub-phrenic collections (Fig.
2.31). Superficial collections, where there is little risk of misdirection, may be safely
drained via a simple one
-
step trochar catheter s
ystem. More complex or deep
collections often require the more precise guidance of CT, using the needle guidewire
and catheter exchange system originally devised by Seldinger for arterial puncture
(Fig. 2.32). Diagnostic fine needle aspiration should be pe
rformed before drainage to
determine the nature and viscosity of the collection. Nonviscous fluid


ascites,
cysts, seromas, biliomas, urinomas


can be satisfactorily drained via an 8

10
French catheter. Thick, inspissated, infected material often require
s a larger bore
catheter (10

14 French) with multiple side holes and, ideally, a double lumen for
cavity irrigation. At catheter insertion, the cavity should be evacuated as completely
as possible. Saline irrigation may help to decrease the viscosity of th
e contents and
encourage drainage. Patients should be given broad
-
spectrum antibiotic cover before
and after the procedure. Following catheter placement, regular saline irrigation (10

20 ml tds) is important to maintain catheter patency. The catheter shoul
d be left in situ
for several days until drainage ceases. Continued drainage of 50 ml or more suggests
possible fistulous communication which may be confirmed by a contrast study via the
catheter. Prolonged catheter drainage over several weeks may be neces
sary in such
cases to allow fistulae to close. Successful catheter drainage of simple postoperative
collections or localised abscesses can be achieved in over 90 per cent of cases. The
cure rate for more complex collections such as pancreatic abscesses, ab
scesses caused
by leak from enteric, biliary or urinary anastomosis and thoracic empyaema is lower,
between 70 and 85per cent. The multilocular nature of many of these collections
makes complete evacuation difficult. However, in many patients percutaneous
drainage achieves palliation and allows the patient to undergo delayed, elective,
single
-
stage surgery in a more stable condition with a relatively clean operative bed.


Percutaneous biliary procedures

Drainage of an obstructed biliary system is usually ac
hieved 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, difficu
lties
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 cholangio-graphy 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. Subseq
uent 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 dilatatio
n


Over 90 per cent of benign biliary structures are post-operative, the remainder
resulting from sclerosing cholangitis or pancreatitis. If there is biliary sepsis, balloon
dilatation should not be attempted until this has been treated with antibiotics an
d a
period of external biliary drainage. A 7

9 French balloon
-
tipped catheter is placed in
the strictured segment with fluoroscopic guidance and the balloon inflated until the
‘waist’ of the balloon within the strictured segment is obliterated. Results sug
gest that
75

8 0 per cent of strictures will remain patent for at least 3 years.


External/internal drainage


The majority of biliary strictures is malignant and is due to carcinoma of the
pancreas, primary bile duct tumours, nodal enlargement at the porta

hepatis or
encroachment on the major bile ducts by hepatic metastases. Treatment is aimed at
palliation. If there is hilar obstruction, it is usually sufficient to drain only one side of
the system as drainage of 30 per cent or more of the liver parenchym
a will relieve the
obstructing symptoms. If a stricture cannot be bypassed, a catheter may be left in situ
with external biliary drainage. This will decompress the system, control the risk of
sepsis and will result in resolution of oedema such that a secon
d delayed attempt to
traverse the stricture is often successful. A percutaneous catheter is manipulated
through the obstruction, into the normal distal common duct or duodenum. Side holes
in the catheter that are located above and below the obstruction per
mit the re
-
establishment of enterohepatic circulation of bile such that the catheter may be
clamped (Fig. 2.34).

Endo prosthesis


An endoprosthesis may be placed into the bile duct to remove the inconvenience of a
catheter protruding from the skin and redu
ce the risks of infection. Percutaneous
placement of plastic endoprostheses requires a transhepatic track of 12 French or
greater, which carries an increased morbidity (Fig. 2.35).

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
guide
wire 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

5per cent of patients (death, sepsis, haemorrhage).

Minor complications (pain, fever, catheter blockage or leakage) occur in 20

40 per
ce
nt of patients.

Gall bladder drainage


Percutaneous gall bladder puncture and drainage may be beneficial in acute calculous
or acalculous cholecystitis, or gall bladder empyema in patients who are high risk for
surgery or whose medical condition is unstabl
e. The procedure is usually performed
under ultrasound guidance. A transhepatic route is advocated to reduce the risk of
biliary peritonitis, although a transperitoneal approach is acceptable as the
complication rate does not appear to be significantly inc
reased. In severely ill patients
the procedure can be performed at the bedside. Ideally, a self
-
retaining catheter with a
locking loop should be left within the gall bladder. In septic patients, recovery is
usually rapid and can be followed 2

3 weeks later

by elective cholecystectomy.
Complications are uncommon although vagal effects (bradycardia and hypotension)
do occur and may be treated with atropine and intravenous fluid. Percutaneous gall
bladder puncture and aspiration has been advocated in intensive

therapy unit (ITU)
patients who are pyrexial, without a demonstrable cause, in whom the gall bladder is
distended and contains sludge, raising the possibility of acalculous cholecystitis.
Approximately 50 per cent of such patients may improve following ga
ll bladder
drainage.


Percutaneous renal intervention

Percutaneous drainage of obstructed kidneys, percutaneous nephrostomy, is
performed in patients who are septic or in renal failure due to ureteric obstruction by
neoplasm, calculi or stricture. Other pe
rcutaneous techniques have evolved from this,
including antegrade ureteric stent placement, balloon dilatation of ureteric strictures
and the creation of a track for percutaneous stone removal (nephrolithotomy) in
patients not suitable for lithotripsy.

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 i
n
the presence of sepsis. In bilateral obstruction, the better functioning kidney (larger,
thicker parenchyma) should be drained first to enable the uraemia and hyper-kalaemia
to be corrected. If known malignant pelvic disease is resulting in bilateral obs
truction,
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


Urgent (within 12

24 ho
urs)




Obstructed infected kidney




Obstructed solitary kidney with deteriorating renal function


Priority




Obstruction with severe pain




Obstruction with renal failure


Elective




Pressure

flow studies


obstruction?




Percutaneous access for ston
e 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 dis
comfort 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 m
ay 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 approached-retrogradely by cystoscopy. It
is of value where long
-
term drainage is required. Indications include calculous
obstruction, often in relation to extr
acorporeal 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 possib
le. Most strictures can be traversed with
modern flexible hydrophilic guidewires.


Gastrointestinal Intervention


Enteric strictures

Dilatation of benign or malignant oesophageal strictures can be performed with either
endoscopic or fluoroscopic guidance.
The choice depends on local expertise but
screening during dilatation is advisable to reduce the risk of oesophageal perforation.
Balloon dilatation is achieved by the introduction of a balloon over a guidewire under
fluoroscopic guidance. Balloon dilatati
on has the advantage of providing a controlled
radial dilating force without the longitudinal shearing forces associated with
conventional oesophageal bougie dilatation, which is thought to predispose to
oesophageal rupture. Obliteration of the waist of th
e balloon with inflation can be
observed in real time and provides an indication of the likely success of the
procedure.

In patients with malignant oesophageal disease, considered incurable by surgical
intervention, oesophageal stent placement provides goo
d palliation. The use of rigid
plastic stents (Celestin or Atkinson tubes) has been gradually superseded by self
-
expanding metal stents (Fig. 2.39). Some of these are covered with plastic,
minimising tumour ingrowth and sealing any associated perforation o
r fistula.
Placement rapidly relieves symptoms, allowing the patient to return home to a
relatively normal diet. These techniques are being expanded to strictures elsewhere in
the gastrointestinal tract. Duodenal and colonic strictures have been satisfacto
rily
stented although experience is currently limited and the long
-
term prospects for such
procedures are currently unknown.


Percutaneous gastrostomy

Percutaneous gastrostomy placement provides a more comfortable alternative to long
-
term nasogastric feedi
ng in patients who are unable to maintain nutrition with oral
intake. This is usually as a result of upper aerodigestive tract malignancy or an
inability to swallow as a result of a previous cerebrovascular accident. Percutaneous
placement of gastrostomy f
eeding tubes can be achieved using either endoscopy or
fluoroscopy. The choice again largely depends on local expertise and both methods
are technically satisfactory. Fluoroscopic placement is essential in patients in whom
nasopharyngeal or oesophageal nar
rowing is such that even the smallest endoscope
cannot bypass the obstruction. The fluoroscopic technique requires insufflation of the
stomach with air or CO2 via a fine nasogastric tube. This renders it fluoroscopically
visible and distends the stomach ag
ainst the anterior abdominal wall. A puncture site
is selected over the lower body of the stomach. Following guidewire placement, the
track is dilated co
-
axially and a 12
-
French loop catheter finally positioned with a
retention loop in the stomach. Minor c
omplications include wound infection and tube
dislodgement. Peritonitis does occasionally occur which may be minimised by
gastropexy, i.e. fixation of the stomach to the anterior abdominal wall by removable
sutures (Fig. 2.40).


Interventional vascular tec
hniques



A wide range of interventional vascular techniques has developed from basic
angiographic principles and has had a profound impact on many aspects of medicine
and surgery.



Vascular therapy

By selective arterial cannulation it is possible to d
eliver a high local dose of a
chemotherapeutic agent to the feeding vessels of a tumour. This technique has been
used with success for liver turnouts, particular hepatocellular carcinoma, metastatic
colorectal cancer and ocular melanoma.

There has been a
resurgence of interest in the potential of low dose intra
-
arterial
infusion of thrombolytic agents in peripheral arterial thromboembolic occlusion. The
choice of therapy between surgical embolectomy and thrombolysis is controversial.

In patients with recu
rrent or threatened pulmonary embolisation from lower extremity
or pelvic thrombus, inferior vena caval filters may be inserted percutaneously, from
either a femoral or jugular approach to prevent the passage of a major embolus. A
femoral approach is appro
priate if the thrombus does not extend proximally into the
inferior vena cava and if the contralateral femoral and pelvic veins are patent.
Otherwise, a jugular approach is indicated, assuming the superior vena cava is patent.


Man
agement of vascular obst
ruction

Percutaneous transluminal angioplasty



This technique of balloon dilatation of a vascular stenosis, with the aim of increasing
blood flow and improving perfusion, has had a profound impact on the treatment of
vascular disease. Initially describe
d by Dotter and Judkins in 1964, the technique has
undergone many modifications and now provides a lower risk alternative treatment to
surgical bypass graft.



Indications include:




peripheral vascular disease with relatively short occlusions (10

15 c
m in length);




ischaemic heart disease with coronary artery stenosis;




hypertension or chronic renal failure with renal transplant artery stenosis;




mesenteric/coeliac artery stenosis.

The technical success rate for femoral and popliteal angio
plasty is between 85 and 95
per cent for stenoses with a 20

70 per cent patency rate at 5 years (Fig. 2.41).
Complications include local haemorrhage and haematoma, false aneurysm formation
at the puncture site, subintimal dissection and arterial perforatio
n. The incidence of
peripheral embolisation of atheromatous deposits is low, reported as between 3 and 5
per cent of cases and rarely resulting in clinically apparent ischaemia.



Vascular stenting



In 1988, Palmaz reported the use of intravascular sten
ts in atherosclerotic arterial
stenosis. The therapeutic potential of expanding metal stents in vascular disease is
great and stents are being successfully used in renal ostial stenosis, abdominal aortic
aneurysm repair, coronary artery disease and other m
ajor peripheral vessels. A major
problem of intravascular stents is their thrombogenic potential as fibrin and platelets
are deposited within the mesh of the stent. This can be inhibited by anticoagulation
and over a period of weeks endothelialisation of t
he stent occurs. It is likely that with
further technical developments, stents will be developed that will be antithrombotic,
encourage endothelialisation and inhibit neo
-
intimal hyperplasia.


Transjugular intrahepatic porto
-
systemic shunt

(TIPSS)

A par
ticular use of expanding metal stents has been in the development of TIPSS,
which involves the percutaneous creation of a communication between the portal and
hepatic venous systems for the relief of portal hypertension (Fig. 2.42). This
procedure was firs
t performed by Richter in 1988 and is now firmly established as an
alternative to surgery in patients with recurrent variceal bleeding who are resistant to
sclerotherapy or endoscopic banding. The technical success rate is over 90 per cent.
The major compl
ication is hepatic encephalopathy which can develop following the
procedure. Shunt occlusion may develop, usually as a result of intimal hyperplasia.
This may require re
-
intervention with balloon dilatation or a second stent insertion.



Therapeutic embol
isation

Deliberate vascular embolisation with the aim of occluding a vessel can be achieved
using a variety of different materials including gelatin, sponge fragments, polyvinyl
alcohol foam particles (PVA) and spiral metal coils.

Arterial embolisation

m
ay be used in the treatment of:




acute haemorrhage;




tumour therapy;




arterio
-
venous malformations;




hypersplenism;




priaprism.

Venous embolisation

is used for treatment of:




gastro
-
oesophageal varices;




testicular varicocele.



The te
chnique can be performed under local anaesthetic and requires a highly skilled
radiologist to position selectively the catheter. The technique is not without risk as
accidental embolisation of adjacent normal structures may occur. Tissue necrosis
following

the procedure may cause pain and fever due to tissue infarction and
occasionally results in abscess formation.


Further reading


Armstrong, P. and Wastie, M. (eds) (1997) Diagnostic and Interventional Radiology in
Surgical Practice, Chapman & Hall, London
.

Mueller, P. and Van Sommenberg, E. (1990) Interventional radiology in the chest and
abdomen. New England Journal of Medicine, 322, 1364

74.

Royal College of Radiologists (1998) Making the Best Use of a Department of Clinical
Radiology: Guidelines for Doc
tors, 4th edn, Royal College of Radiologists, London.

Shuman, WP. (1997) CT of blunt abdominal trauma in adults. Radiology,205, 297

306.