Download Imaging of malignant cervical lymphadenopathy.

Dentomaxillofacial Radiology (2000) 29, 133 ± 143
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REVIEW
Imaging of malignant cervical lymphadenopathy
SEJ Connor*,1 and JFC Olli€1
1
Department of Diagnostic Radiology, Queen Elizabeth Hospital, Birmingham, UK
Diagnostic imaging is superior to clinical staging in the detection of malignant cervical
lymphadenopathy, and thus helps in¯uence therapy and prognosis. The imaging modalities of
CT, MRI, US and PET each have their own diagnostic criteria, accuracy and limitations.
Newer innovations such as functional imaging, novel MRI contrast agents and FNAC are
being appraised with the aim of identifying the micrometastases which are currently
radiologically occult.
Keywords: tomography, X-ray computed; magnetic resonance imaging; lymph nodes; head
and neck neoplasms
Introduction
General principles
Identi®cation of cervical lymphadenopathy is critical to
the management and outcome of diseases that present
with malignant nodal in®ltration. Conditions such as
bacterial, viral and granulomatous infection may e€ect
the cervical lymph nodes and it is important for the
radiologist to be able to di€erentiate malignant and
benign cervical lymph nodes. Squamous cell carcinoma
(SCC) of the head and neck is the commonest tumour
of the upper aerodigestive tract and the presence of
cervical lymph node metastases in these patients is of
particular prognostic and therapeutic signi®cance, with
a single lymph node metastasis reducing survival by
one-half.1
The purpose of this article is to outline the abilities
and limitations of the current diagnostic imaging
techniques used to determine the presence of malignant nodal disease, with particular emphasis on those
used to detect nodal metastases of head and neck
squamous cell carcinomas. The individual modalities of
CT, MRI, US and PET will be covered with the
important issues of extracapsular spread and recurrent
nodal disease being discussed separately. This will be
followed by sections on the imaging features of cervical
lymphoma and non head and neck metastatic disease
and the impact of current imaging on management.
The inaccuracies in physical examination of the cervical
lymph nodes have been well documented2 and all
diagnostic imaging modalities have been shown to have
superior diagnostic accuracy.3 ± 7 This is in some part
due to visualisation of non palpable deep lymph nodes
and because some metastases in normal sized nodes
may be detected using diagnostic imaging. Furthermore, imaging studies may contribute useful prognostic
information such as extranodal spread in the case of
anatomical imaging8 ± 10 and, possibly, tumour aggressiveness in the case of functional imaging.11
Reliable comparisons of sensitivities and speci®cities
between di€erent studies and imaging modalities are
dicult, owing to di€ering study populations in terms
of primary tumour characteristics, clinical neck staging
and the use of di€ering radiological criteria. In
addition, the accuracy of imaging techniques maybe
presented in terms of predicting individual lymph node
involvement or in making the more relevant distinction
of a node positive from a node negative neck. When
interpreting the results, it must also be remembered
that the gold standard of histopathological examination will still miss some small metastases.12 The impact
of imaging on treatment planning and outcome is of
paramount importance and has generally not been
addressed.
The imaging criteria used to determine metastatic
cervical lymphadenopathy have been extensively
evaluated. Unfortunately, the most widely used
features such as nodal enlargement or shape, are only
`indirect' evidence and therefore less accurate. It is
more desirable to use `direct' criteria, that include
*Correspondence to: SEJ Connor, Department of Neuroradiology, King's
Healthcare NHS Trust, King's College Hospital, Denmark Hill, London SE5
9RS
Received 28 September 1999; accepted 14 January 2000
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
134
nodal necrosis or an heterogeneous appearance on CT
or magnetic MRI and eccentric cortical widening on
US. Recent imaging advances have concentrated on
potential di€erences in the `function' of malignant
lymph nodes as demonstrated by di€erential uptake of
radiolabelled ¯uorodeoxyglucose (FDG) positron emission tomography (PET)5,11,13 or tissue speci®c MRI
contrast media.14 Finally, the importance of accurate
pre-operative diagnosis, has led to the evaluation of
more `invasive' techniques such as US guided ®ne
needle aspirate cytology (FNAC).15
As well as predicting metastatic nodal involvement it
is important for the radiologist to communicate
accurately the location of abnormal lymph nodes to
the surgeon, since this may e€ect the planning of a
selective neck dissection. Head and neck surgeons have
adopted a simpli®ed numerical classi®cation with
major nodal groups classi®ed as levels one to six.
Details of this and other anatomical classi®cations are
well described.9,16,17
Diagnostic imaging techniques
Computed tomography
CT remains the most widely used modality for neck
imaging. The CT examination is performed in the
axial plane with contiguous sections of 3 ± 5 mm
whilst a bolus of intravenous contrast media is
administered. CT criteria for assessing lymph node
metastases are based on size, shape, the presence of
central necrosis and the appearance of a cluster of
nodes in the expected lymph drainage pathway for
the tumour.10
Use of lymph node size operates on the assumption
that the larger the lymph node, the more likely it is to
be diseased. Traditional `abnormal' values of greater
than 10 ± 15 mm16 have been challenged as the
resolution of CT scanners has improved. The most
e€ective size criteria for indicating metastatic involvement are now de®ned as minimum axial diameters in
excess of 11 mm in the jugulodigastric region and in
excess of 10 mm elsewhere.18 Using these sizes a
sensitivity of 42% and speci®city of 99% per node
were produced; however, the sensitivity increased to
89% if assessed per neck side dissected, that is 11% of
necks would have been mislabelled as N0 by CT.18 It
has recently been proposed that the cross-sectional area
of the lymph node is a more valid criterion than any
measurement of the diameter.19 However, this will still
not overcome the inadequacy of using size, since
reactive nodes may be large and 39% of clinically
occult metastases measure less than 3 mm.12
Using the additional feature of nodal shape, there is
a slight improvement in the sensitivity of CT. If a
lymph node is of `borderline' size, then a `spherical'
shape increases the likelihood of tumour involvement.10 With the use of spiral CT, it is possible to
reconstruct the image in any plane with good quality,
allowing more accurate calculation of the maximal
Dentomaxillofacial Radiology
axial and longitudinal dimensions and thus assessment
of nodal shape. One study concluded that a ratio of
maximal longitudinal to maximal axial dimension of
less than two was a more accurate criterion than
size.20
Nodal grouping in the drainage chain of a tumour
is a further indicator of metastatic disease (Figure
1). This is de®ned as three or more contiguous or
con¯uent lymph nodes, each of which has a minimal
axial diameter of 8 ± 10 mm.18 Combined with a
minimal axial dimension of 10 mm, the criterion of
nodal grouping slightly improves both sensitivity and
speci®city for malignancy.18
The most accurate CT predictor of metastasis is the
presence of central necrosis, which has been said to
have a 100% speci®city.18,20 This is seen as a central
area of low attenuation surrounded by a thick,
irregular rim of enhancement9,10 and is due to nodal
replacement of the medulla by less enhancing tumour
(Figure 2). Unfortunately, nodal necrosis is more
commonly seen in large nodes which may be
diagnosed on size criteria alone. Nodal necrosis may
be mimicked by lipid metaplasia which represents fatty
degeneration secondary to in¯ammation or irradiation.
However, this fatty change generally occurs at the
periphery of the node (Figure 3). Abscess formation
may also have a similar appearance but such
suppurative transformation is usually evident clinically.
Figure 1 Axial CT scan with intravenous contrast demonstrating
bilateral deep cervical (level two) lymph nodes. The group of left
sided lymph nodes (three of which (arrowheads) measured 8 mm in
minimum axial diameter) is indicative of malignant involvement in
this patient with an oral SCC
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
Using all these combined CT criteria, a sensitivity of
87% and speci®city of 94% per neck dissection
specimen has been achieved.18 The most recent studies
in which CT has been used to assess the status of the
cervical lymph nodes have not improved on these
results.19,21,22
Magnetic resonance imaging
Advances in MRI technology has led to its increased
use in evaluating cervical lymph nodes. Dedicated neck
surface coils, 3 ± 5 mm sections, increased matrix size
(512 line images) and a smaller ®eld of view have all
led to improvement in spatial resolution. MRI o€ers
the advantages over CT of multiplanar imaging
Figure 2 Axial CT scan with intravenous contrast demonstrating a
left-sided tongue SCC extending across the midline. There are
bilateral enlarged submandibular (level one) lymph nodes demonstrating marked necrosis
Figure 3 Axial CT scan with intravenous contrast demonstrating
lipid metaplasia (arrow) eccentrically placed in a left submandibular
(level one) lymph node which has a 6 mm minimum axial diameter
without the need for computer reconstruction, the
absence of ionizing radiation, the lack of streak artifact
as a result of ®llings and dense cortical bone and
superior contrast resolution of the tissue without the
need for intravenous contrast medium. MRI is
precluded in certain individuals with ferromagnetic
prostheses, such as older intracranial aneurysm clips
and cardiac pacemakers.
Standard protocols for MRI of the cervical lymph
nodes include a selection of T1- and fast spin echo T2weighted axial, coronal and sagittal images. The use of
fat suppressed techniques also help to increase the
contrast between lymph nodes and adjacent high signal
fat on both sequences. STIR sequences allow a
combination of T1- and T2-weighting with fat
suppression, and malignant nodes are clearly demonstrated as high signal. T1-weighted images depict
lymph nodes as being of intermediate signal intensity,
similar to muscle, whilst T2-weighted images show
them as hyperintense signal (Figure 4). Unfortunately
these signal characteristics do not di€er consistently
between normal and abnormal lymph nodes23 so these
conventional MR techniques will only allow discrimination on the basis of morphology. Hence MRI will
have the same inaccuracy as other modalities using
`indirect' morphological criteria.
The presence of internal nodal abnormality, seen on
CT as central low attenuation, can also be noted as
central hypointensity on T1-weighted and hyperintensity on T2-weighted MRI. Gadolinium enhanced T1weighted scans24 with or without fat suppression25 have
been reputed to allow more accurate detection of
central necrosis. However CT sensitivity for nodal
necrosis is 20% greater than MRI.26
Using these criteria, there were early claims of 100%
sensitivity at the cost of poor speci®city using a nodal
size of greater than 5 mm to identify nodal involvement.27 However when a more conventional upper limit
of 10 mm has been used, sensitivities of 57 ± 84% and
speci®cities of 50 ± 92% for a positive neck dissection
have been recorded.7,25,27 ± 29 Direct comparisons have
shown CT to perform better than MRI even when
using current technology.26,29 The sensitivities for level
four nodes have been shown to be particularly poor
which is probably due to breathing artifact.25
However, newer MR techniques have aimed to
overcome the inherent disadvantages of indirect
criteria, by using tissue-speci®c imaging which may
detect metastases in normal sized nodes. Both
intravenous ultrasmall superparamagnetic iron oxide
particles14 and magnetization transfer imaging30 have
been evaluated for this purpose and deserve further
investigation.
135
Ultrasound
Ultrasound assessment of cervical lymph nodes has the
bene®ts of rapidly and cheaply demonstrating all three
nodal dimensions without the need for ionizing
radiation or intravenous contrast medium. Deeper
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Malignant lymphadenopathy
SEJ Connor and JFC Olliff
136
lymph nodes, as in the retropharyngeal region cannot
be assessed by ultrasound. The optimal size to de®ne
pathological lymph nodes ultrasound are minimum
diameters of 9 mm for level two nodes and 8 mm for
the remaining levels31,32 which o€er a sensitivity of 74%
and speci®city of 78%.31 It is easy to evaluate nodal
shape by rotating the probe, and the ratio of minimal
to maximal axial diameter has been reported to be a
valuable predictor of malignancy.6,32,33 A ratio of
greater than 0.55 indicates malignancy with a
speci®city of 63% and sensitivity of 92%.6 The
improved spatial and contrast resolution of high
a
frequency ultrasound probes have allowed the internal
architecture of lymph nodes to be studied. Varying
appearances of the echogenic lymph node hilum and
the surrounding hypoechoic cortex have been shown to
be helpful in distinguishing malignant from benign
normal sized nodes33,34 (Figure 5). However, this degree
of spatial resolution is only possible with relatively
super®cial lymph nodes. The distribution of blood ¯ow
in lymph nodes has recently been evaluated using
Doppler ultrasound35,36 with areas of vascular sparing
and isolated peripheral ¯ow being suggestive of
malignancy. Newly available intravenous ultrasound
contrast media may contribute to such Doppler
assessments in the future.
The most promising contribution of US is in the
guidance of FNAC. Aspirates are obtained from any
readily visible lymph nodes, with enlarged and rounded
nodes being primarily chosen for sampling. An 18
gauge needle is rotated within the lymph node whilst
suction is applied via connecting plastic tubing. FNAC
increases the speci®city of ultrasound in detecting
lymph node metastases to 100%.15,37,38 However,
reported sensitivities remain between 50 ± 98%15,37 ± 39
and depend on whether the study population includes
patients with N0 necks, since these lymph nodes will be
smaller and more dicult to aspirate. Direct comparisons of US-guided FNAC with CT and MRI have
shown it to be the most accurate technique in staging
both the clinically metastatic and normal neck.3,39
Ultrasound is better suited than the other modalities
for guiding the nodal sampling since it can be
performed in `real time'. However, its acceptance as
an isolated investigation has been hindered by the lack
of easily interpretable hard copy images as well as its
time consuming and invasive nature. Its opponents
have also suggested that results are predominantly a
b
Figure 4 (a) T1 weighted and (b) T2 weighted sagittal MRI scans
demonstrate a large pathological deep cervical lymph node (level two/
three) which is of intermediate signal on T1 and high signal on T2
Dentomaxillofacial Radiology
Figure 5 US image of a deep cervical (level four) lymph node in a
patient with a nasopharyngeal SCC. The nodal hilum is hyperechoic
relative to the hypoechoic peripheral cortex. The increased size
(14 mm) and the eccentric cortical widening are indicators of
malignant involvement
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
re¯ection of the operator's expertise, even though
interoperator variability has been demonstrated to be
low.15 However, its imperfect sensitivity remains
problematic, particularly for the N0 neck.
Positron emission tomography
Most head and neck PET imaging is performed with
the radiolabelled glucose analogue 18FDG which has
increased uptake in viable malignant tumour due to
enhanced glycolysis. The uptake can be mapped by two
opposing detectors which are able to construct a three
dimensional representation of the tracer distribution.
The result can be expressed as a standardised uptake
value (SUV), with those values greater than two being
considered abnormal. PET scanning provides functional rather than anatomical imaging. This overcomes
some of the disadvantages of US, CT and MRI since it
does not rely on structural change but rather on the
ability to map metabolism or function. Sensitivities of
up to 90% and speci®cities of up to 94% have been
recorded for individual lymph nodes in FDG-PET
studies11,40 and direct comparisons with CT, US and
MRI have shown it to be at least as accurate.11,13,40,41
Some of the false positive results are due to uptake in
reactive or granulomatous lymph nodes.11 This
distinction between tumour and in¯ammation may
not be achievable with FDG-PET and may require the
use of other substances labelled with positron emitters
such as 11CH3 methionone.40,42 Sensitivity will be limited
by the low spatial resolution of PET. However, current
scanners can detect malignant lymph nodes less than
5 mm11,40 which would be negative on anatomical size
criteria. Sensitivity and speci®city will vary with visual
interpretation of the PET scans,43 and whilst this is
partially overcome by measuring the SUV, borderline
values still represent a problem.
Since FDG-PET is able to measure tumour
metabolism, it also o€ers the potential to evaluate
tumour proliferation rate and tumour hypoxia which
may help guide therapy.41 Tracer uptake has already
been shown to be associated with aggressive tumours
and a poor outcome.44
PET scanning is a relatively expensive modality due
to the high cost of both the scanner and the
radiopharmaceutical. However, cost e€ectiveness has
been demonstrated by contraindicating surgery in nonresectable tumours.45 More recently, conventional
gamma cameras have been adapted to image the
higher energy gamma rays of positron emitters but
these scanners have reduced sensitivity.
Although spatial resolution continues to improve on
newer PET scanners, there is not the anatomical detail,
such as bony erosion, soft tissue in®ltration and vascular
invasion, that is vital for surgical planning. The
anatomical localization of MRI may be combined with
the functional imaging of PET (Figure 6) by combining
the two images in `fusion images' or `co-registration'.46
A particularly useful role of PET is in localising
occult primary tumours in the presence of metastatic
cervical lymphadenopathy. These head and neck
tumours are frequently small and submucosal and are
therefore elusive in 3 ± 6% of patients despite
anatomical imaging, panendoscopy and biopsy of
likely primary sites.47 FDG-PET has been shown to
establish the location of primary malignancy in 47% of
patients as compared with 33% using CT and MRI.
No patients with negative PET studies subsequently
demonstrated an overt primary focus.48
137
Speci®c imaging features and tumour types
Extranodal spread and invasion of surrounding structures
The presence of tumour outside the nodal cortex is
associated with a 50% decrease in 5-year survival,
increases the risk of local recurrence by tenfold8 and
may indicate the need for postoperative radiotherapy.49
Recognition of extracapsular spread in a normal sized
node will help distinguish tumour involvement. Therefore it is a useful feature to identify on imaging.
CT ®ndings that indicate extranodal spread
include irregular nodal boundaries and in®ltration
of adjacent fat planes. These criteria are only
accurate if the patient has not had recent surgery,
radiation therapy or infection in the area.9,10
Although similar ®ndings may be evident using
MRI, CT has been shown to be more speci®c in
determining extranodal spread.24 US may detect
hypoechogenicity and loss of fat planes in surrounding tissues but its ability to detect extranodal spread
has not been fully evaluated.
Once extracapsular spread has occurred, vital
structures such as blood vessels, nerves and skull base
in the near vicinity are under threat. No current
imaging study can accurately predict carotid invasion.
If greater than 2708 circumference of the artery is in
contact with the tumour on CT (Figure 7) then there is
a strong possibility that adherent tumour will
necessitate surgical sacri®ce of the vessel.50 Greater
accuracy may be achieved with US in which the
arterial wall is normally depicted by an echogenic
band, which is lost when in®ltrated with tumour.51
Carcinomatous extension of lymph nodes into the skull
base is best seen on coronal scans. Early cortical bone
erosion is best demonstrated by CT whilst marrow
in®ltration, intracranial and dural extension is well
documented by MRI.10
Residual and recurrent nodal disease
Residual and recurrent disease may occur in the
cervical lymph nodes following treatment. Random
biopsies are often non-diagnostic and biopsy-initiated
necrosis following radiotherapy may lead to devastating complications. Thus timely non-invasive evaluation
of residual or recurrent lymph node disease would be a
great asset.
Following surgery and radiotherapy, normal anatomical structures become extensively distorted and
Dentomaxillofacial Radiology
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
138
a (i)
(ii)
(iii)
(iv)
Dentomaxillofacial Radiology
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
lymph nodes may be mimicked by haematoma, focal
scar tissue, abscesses or pseudo-aneurysm.52 As well as
limiting clinical examination, this makes anatomical
assessment with US, MR and CT dicult. In the
months following radiotherapy, there may be a general
shrinkage of metastatic nodes, but there are no
morphological features to distinguish nodes that
contain residual or recurrent tumour from these which
have been successfully treated.53 Once recurrent lymph
node involvement has been diagnosed, MR or CT is
indicated to establish the anatomical extent of disease.
There is an even greater role for functional imaging
in the post-therapy patient. Most series have looked at
primary site recurrence41,42 However, recurrence of
nodal disease has been detected with a sensitivity of
greater than 90%54 which makes it a useful ®rst step in
assessing the patient with equivocal clinical ®ndings.
None the less the shortcomings of FDG-PET in
distinguishing tumour from in¯ammation are a
particular problem following radiation or surgery
when uptake may be seen in the post-surgical bed for
at least 3 months and in areas of radionecrosis.
Pretreatment with steroids or antibiotics may reduce
the number of false positive diagnosis, but patients
with positive FDG-PET scans and negative biopsies
will remain a serious problem.
Cervical lymph node lymphoma
After squamous cell carcinoma, lymphoma is the
second most common malignancy to a€ect the
extracranial head and neck.55 Nodal non-Hodgkin's
lymphoma (NHL) is he most common manifestation
and most frequently of a large cell subtype.55 Although
there is considerable variation in the imaging appearances, a distribution of multiple bilateral lymph nodes
is suspicious for lymphoma (Figure 8). Deep cervical
chains are frequently involved55,56 but nodes in the
submental, submandibular, retropharyngeal or posterior triangle regions are more suggestive because these
are less typical drainage routes for squamous cell
carcinomas.56,58 Contrast-enhanced CT scanning reveals
homogenous, clearly delineated lymph nodes which
occasionally enhance.10 Irradiation may lead to nodal
necrosis or calci®cation.10,55 US features which are
useful in di€erentiating NHL from other metastases
include distal enhancement and lack of nodal
necrosis.57 Hodgkin's disease is more likely than NHL
to cause contiguous lymph node enlargement and
extranodal sites are less common. A high index of
suspicion for lymphoma is required in order to avoid
unnecessary surgical procedures and to prevent a vain
search for an occult primary squamous cell carcinoma.
139
Other metastatic disease
Cervical lymph nodes may also be involved by
metastatic disease other than head and neck squamous
cell carcinoma. Thyroid carcinoma, salivary gland
tumours, hypernephroma, breast carcinoma, cervical
carcinoma and lung carcinoma have all been reported
to metastasise to cervical lymph node sites.53,58 Thyroid
papillary carcinoma has already spread to the cervical
nodes in 50% of cases at presentation.59 This may
b
Figure 6 (a) 18FDG PET images demonstrating uptake in the nasopharyngeal region (axial (i) and coronal (ii)) at the site of a nasopharyngeal
primary SCC and on the left side of the neck (axial (iii) and coronal (iv)) at the site of level three malignant nodal involvement. (b) Axial post
gadolinium T1-weighted MRI image demonstrates a left sided nasopharyngeal SCC (arrow) with superior anatomical detail. (Images courtesy of
Dr P. Guest, Queen Elizabeth Hospital, Birmingham)
Dentomaxillofacial Radiology
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
140
a
b
Figure 7 Axial CT scan with intravenous contrast demonstrates a
large left deep cervical (level three) lymph node mass surrounding the
left common carotid artery (arrow) indicating that the artery may
need to be sacri®ced at surgery
Figure 9 Axial CT scans (a) and (b) with intravenous contrast
demonstrate recurrent cervical lymphadenopathy at multiple levels in
a patient who had previously undergone a total thyroidectomy for a
papillary carcinoma of the thyroid. The intense enhancement of the
right level three and four lymph nodes (arrowheads) with intravenous
contrast is characteristic of these metastases
Figure 8 STIR MRI coronal image demonstrating bulky bilateral
cervical lymph node enlargement (arrowheads) in a patient with nonHodgkin's lymphoma
produce homogenous nodes, extensive nodal necrosis
leading to the appearance of a benign cyst, intensely
contrast enhancing nodes or, rarely, high attenuation
nodes due to local haemorrhage10 (Figure 9). The
presence of thyroid protein or haematoma may
manifest as increased signal on T1-weighted MRI.10
The most common infraclavicular tumours to metasDentomaxillofacial Radiology
tasise to cervical lymph nodes are breast, lung and
renal carcinomas. The presence of supraclavicular and
inferior posterior triangle lymph node enlargement
should alert the radiologist to the possibility of an
infraclavicular tumour.53 Renal carcinoma also causes
hypervascular lymph nodes which may haemorrhage
and undergo central necrosis.10
Current impact of imaging
It is clear that the various imaging modalities o€er
unique abilities but that none are able to challenge the
gold standard of histopathological examination of the
neck dissection. The choice of imaging or whether to
perform imaging at all, depends largely on local
availability, whether and how the primary tumour is
Malignant lymphadenopathy
SEJ Connor and JFC Olliff
imaged, and the surgeon's preference in each clinical
scenario. In turn, the relevance of false positive and
false negative imaging results depend on how the nodal
disease is managed.
The management of the clinically N0 neck has been
particularly controversial. More than 25% of patients
who present with head and neck tumours and no
palpable lymph nodes have cervical lymph node
metastases. Although a discussion of the therapeutic
options60 is beyond the scope of this article, in general
prophylactic radiotherapy or surgery is widely practised if the risk of occult metastases is felt to be greater
than 20 ± 30%.8 This assessment is based on the site,
thickness, T staging, histological di€erentiation and
identi®able molecular markers of the primary
tumour.60,61 However such management will lead to
overtreatment in the majority of cases and it is argued
that elective surgery may not o€er a therapeutic
advantage over a `wait and see' policy.62,63 In
addition, radiotherapy makes subsequent clinical and
imaging assessment dicult. If the risk of occult
metastases can be suciently diminished by the
presence of normal lymph node imaging, then it may
be possible to avoid elective surgery and monitor the
lymph nodes. In order to select patients who do not
need elective surgery, a highly sensitive imaging
modality with highly sensitive criteria is more
important than speci®city since undertreatment is not
as acceptable as overtreatment. This has led to further
re®nements of the optimal size criteria31 and the use of
sensitive, but not speci®c, modalities such as PET.42
Unfortunately in the N0 neck, sensitivities are likely to
be lower due to a greater incidence of micrometastases
and therefore radiologically occult disease.12
Another way in which imaging techniques may
in¯uence disease management is in the selection of
conservative surgery for the node-positive neck.
Modi®ed radical neck dissections which preserve one
or more non-lymphatic structures or selective neck
dissections which preserve one or more lymph node
groups64 may be used in the N1- neck and preserve
function more e€ectively than the traditional radical
neck dissection. The decision as to which neck
dissection to perform depends on the risk of nodal
metastases at each level and accurate imaging should
help facilitate this decision.
Finally, imaging studies may help guide management
of the contralateral neck (the opposite side to the
primary tumour). In stage T2c or more tumours, or in
tumours at sites such as the tongue base, nasopharynx
or supraglottis, there is an increased likelihood of
bilateral nodal metastases even if there are no palpable
nodes on the contralateral side. Imaging can be used in
a similar capacity to an ipsilateral N0 neck and there
remain the same shortcomings.
141
Conclusion
We have outlined the current imaging techniques used
to evaluate malignant cervical lymphadenopathy, and
their potential in¯uence on therapy. Current imaging
improves on clinical staging but does not detect the
micrometastases, which are found in 25% of N0 neck
dissections, reliably.13 Hence, our current modalities
cannot alone dictate whether and how to operate, but
should play a signi®cant role in the multifactorial
decisions concerning treatment. Innovations such as
PET imaging, novel MRI contrast agents and FNAC
show promise and need to be reappraised continually
in the light of advancing technology. Advances in
imaging should be used alongside other non imaging
strategies in order to achieve the goal of minimal
morbidity without overtreatment.
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