Ultrasound evaluation of neck lymph nodes

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Ultrasound evaluation of neck lymph nodes
Ultrasound evaluation of neck lymph nodes
Michael Ying PhD; *Anil Ahuja FRCR; Fiona Brook PhD; *KT Wong FRCR
Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong
Kong SAR, China
*Department of Diagnostic Radiology & Organ Imaging, Prince of Wales Hospital, Shatin, New Territories, Hong
Kong SAR, China

cytology (FNAC) (98% and 95% respectively)8. It has been
Ultrasound is a useful imaging modality in the assessment of
reported that ultrasound is superior to clinical examination
cervical lymph nodes. Grey scale sonography helps to evaluate the
in the detection of cervical lymphadenopathy with a
morphology of cervical nodes, whereas power Doppler sonography
sensitivity of 96.8% and 73.3% respectively9. Ultrasound is
can be used to assess the vasculature of lymph nodes. The grey
more sensitive than computed tomography (CT) in the
scale sonographic features that help distinguish the various causes
detection of small nodes. Lymph nodes less than 5 mm in
of cervical lymphadenopathy include their size, shape, internal
diameter are difficult to detect with CT1, whereas high
architecture, and distribution; the presence of intranodal necrosis,
resolution ultrasound can detect lymph nodes as small as 2
an echogenic hilus or calcification. The presence of adjacent soft
mm in diameter10. Neo-vascularization is commonly found
tissue edema and matting of nodes are useful features to identify
in malignant lymph nodes2, 11, with this abnormal vascularity
tuberculous lymphadenitis. In power Doppler sonography, vascular
being different from that of normal lymph nodes. Power
pattern of the lymph nodes is more useful than vascular resistance
Doppler sonography has a high sensitivity in the detection
in differentiating benign from malignant cervical nodes.
of fine vessels. It provides additional information during
A good understanding of the normal lymph node anatomy,
sonographic examination of cervical nodes
scanning equipment required and the scanning technique is
by indicating the presence/absence of vascularity,
essential before pathology assessment should be commenced.
demonstrating the vascular distribution and estimating the
vascular resistance of nodal vessels.
This article reviews these topics to provide an overview for
sonography of cervical lymphadenopathy.
Cervical lymph nodes are located along the lymphatic
Keywords: Ultrasound, grey scale, Doppler, cervical lymph nodes,
channels of the neck. Each cervical lymph node has cortical
normal, abnormal
and medullary regions, and is covered by a fibrous capsule12, 13.
The cortex consists of lymphocytes which are densely packed
Evaluation of cervical lymphadenopathy is essential for
together to form spherical lymphoid follicles, whereas the
patients with head and neck carcinomas because it helps in
medulla is composed of medullary trabeculae, medullary
the assessment of prognosis and the selection of treatment1,2.
cords and medullary sinuses. The paracortex is an
In patients with head and neck carcinomas, the presence of
intermediate area between the cortex and the medulla,
a metastatic node on one side of the neck reduces the 5-year
where the lymphocytes return to the lymphatic system from
survival rate by 50%, whilst the presence of a metastatic node
the blood circulation. In the medulla of the lymph node, the
on both sides reduces the 5-year survival rate to 25 %3.
medullary trabeculae, composed of dense connective tissue
Metastatic neck nodes from head and neck carcinomas are
similar to the capsule, act as a framework extending from
site specific. It has been reported that metastatic nodes in an
the capsule and guides blood vessels and nerves to different
unexpected site indicates that the primary tumour is more
regions of the lymph node. The medullary cords and
biologically aggressive4.
medullary sinuses are composed of reticulum cells. The
The head and neck region is a common site of involvement
medullary cords contain mainly plasma cells and small
for lymphoma compared to other parts of the body, and the
lymphocytes, whilst the medullary sinuses are filled with
cervical lymph nodes are most commonly involved5.
lymph and are part of the sinus system of the lymph node12, 13.
Lymphoma of cervical lymph nodes is often difficult to
Cervical lymph nodes contain blood vessels. The main
differentiate from other metastatic cervical lymph nodes
artery enters the lymph node at the hilus, which then
clinically. As the treatment for lymphoma and metastases is
branches into arterioles. Some of the arterioles supply the
different, accurate differential diagnosis between the two
conditions is essential.
capillary bed in the medulla and some of them run along
the medullary trabeculae to the cortex where the arterioles
Tuberculous lymphadenitis is a common disease in South
further branch into capillaries and supply the lymphoid
East Asia. However, with the increasing prevalence of
follicles. The rest of the arterioles run along the trabeculae
acquired immune deficiency syndrome (AIDS) and an
and reach the capsule where they anastomose with other
associated increase in tuberculous lymphadenitis6, 7, the
incidence of tuberculous lymphadenitis is increasing
worldwide, and thus the need for early accurate diagnosis.
The venous system has a similar route as the arterial system.
The venules converge to form small veins in the cortex. The
Ultrasound plays an important role in the evaluation of
small veins run along the trabeculae of the lymph node and
cervical lymph nodes because of its high sensitivity and
reach the medulla where they further converge to form the
specificity when combined with fine-needle aspiration
main vein. The main vein leaves the lymph node at the hilus12-14.
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Ultrasound evaluation of neck lymph nodes
different imaging modalities such as computed tomography
There are about 300 lymph nodes in the neck4. The American
and magnetic resonance imaging, some lymph nodes in
Joint Committee on Cancer (AJCC) classification was
this classification may be difficult to be assessed by
developed to provide a simple and efficient way to classify
ultrasound, such as the paratracheal prelaryngeal, and
the cervical lymph nodes, and this classification is widely
upper mediastinal nodes.
used by surgeons and oncologists. The AJCC classification
In order to simplify the ultrasound examination of the neck
divides palpable cervical lymph nodes into seven levels
and to ensure that all areas of the neck are covered in a
which are based on the extent and level of cervical nodal
systematic way, Hajek et al.16 developed another classification
involvement by metastatic tumour15 (Figure 1).
for ultrasound examination of the neck which is based on
Despite the common use of the AJCC classification in
the location of the lymph nodes (Figure 2). However, one
identifying the location of lymph nodes, some common sites
should note that this classification is used to facilitate the
of nodal metastases of head and neck tumours, such as the
ultrasound examination of the neck and should not be used
parotid and retropharyngeal nodes, are not included in
for staging of carcinomas which is based on the AJCC
this classification. Since the AJCC classification is used in
Upper internal jugular chain
Submental Submandibular
Spinal accessory chain
Middle internal jugular chain
Transverse cervical chain
Lower internal jugular chain
Anterior cervical
Upper mediastinal
Figure 1 Schematic diagram of the neck showing the American Joint Committee on Cancer (AJCC) classification of cervical
lymph nodes.
Middle cervical
Lower cervical
Supraclavicular fossa
Upper cervical
Posterior triangle
Figure 2 Schematic diagram of the neck showing the classification of the cervical lymph nodes to facilitate ultrasound examination.
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Ultrasound evaluation of neck lymph nodes
When PDS is used to evaluate the vasculature of lymph
For ultrasound examinations of the neck, a linear array 7.5
nodes, it starts with adjusting the size of the colour box so
MHz transducer is the basic requirement. A transducer of
that it is large enough to cover the whole lymph node. The
higher frequency, e.g. 10 MHz, allows better resolution for
Doppler settings are then optimized as described. The
the superficial structures, however, there is a trade-off with
vascular pattern of the lymph node is assessed with the
lower penetration. Recently, broadband transducers, eg 5 to
transducer slowly sweeping from one end of the node to
12 MHz, give higher resolution images and provide
another. The vascular pattern is classified into four categories, ie
satisfactory penetration. For the assessment of deep lesions, a
• Hilar – flow signals branch radially from the hilus,
5 MHz convex transducer or a 5 to 7 MHz broadband convex
regardless of whether the signals orginate from the
transducer is occasionally used. A standoff pad is useful in
central area or from the periphery (Figure 3).
the assessment of large and superficial masses. Doppler units
• Peripheral – flow signals along the periphery of the lymph
and applications are now standard on most of the
node and have branches perforating the lymph node,
commercially available ultrasound units, and power Doppler
which are not arising from the hilar vessels (Figure 4).
sonography (PDS) is desirable for the assessment of the
• Mixed – the presence of hilar and peripheral vessels
vasculature of the small structures in the neck, such as lymph
(Figure 5).
nodes, because of its high sensitivity in detecting small vessels.
• Apparent avascular – absence of flow signal.
When PDS is used in the evaluation of the vasculature of
Spectral Doppler is used to measure the vascular resistance
cervical lymph nodes, the Doppler setting should be
(resistive index, RI; pulsatility index, PI) in the lymph node.
optimized for the detection of vessels with low blood flow:
The more prominent vessels are selected for the
• high sensitivity
measurement, and the angle of insonification is varied to
• pulsed repetition frequency (PRF) = 700 Hz
identify the prominent vessels. Measurements are obtained
• medium persistence
from the average value of three consecutive Doppler
• low wall filter
waveforms. The sample volume should be adjusted to the
• the colour gain is first increased to a level which shows
smallest value, e.g. 1 mm, and is placed in the centre of the
colour noise, and then decreased until the noise just
For ultrasound examination of cervical lymph nodes, the
patient should lie supine on the examination couch with
the shoulder supported by a pillow or triangular soft pad,
and the neck hyperextended. The examination should
begin with a transverse scan of the submental area. The
transducer is then swept laterally to one side of the neck to
the submandibular area, and the patient’s head is turned
away from the side under examination to allow free
manipulation of the transducer. The submandibular area
is examined with transverse scans along the inferior border
of the mandibular body. As some of the submandibular
nodes may reside behind the submandibular niche behind
the body of the mandible, the transducer may need to be
angled cranially to assess these lymph nodes. The
transducer is then swept laterally and superiorly along the
Figure 3 Power Doppler sonogram of a reactive lymph node
angle of the mandible, and the mandibular ramus towards
showing hilar vascularity.
the pre-auricular region to examine the parotid region.
Transverse and longitudinal scans are used to examine the
parotid nodes. The internal jugular chain nodes are divided
into upper, middle and lower cervical nodes. They are
examined with the transducer scanning transversely from
the tail of the parotid gland to the junction between the
internal jugular vein and the subclavian vein, and along
the common carotid artery and internal jugular vein. The
transducer is then moved laterally along the clavicle to the
supraclavicular fossa, where the supraclavicular nodes are
examined with transverse scans. A slight caudal angulation
is required to avoid obscuring the lymph nodes by the
clavicle. The posterior triangle nodes are examined with
transverse scans from the mastoid tip to the acromion
process along the imaginary course of spinal accessory
nerve. Longitudinal scanning is occasionally used to assess
the relationship between lymph nodes, especially when
Figure 4 Power Doppler sonogram showing a malignant node
they may be matted.
with peripheral vascularity (arrows).
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Size has been used to differentiate reactive from malignant
nodes16. Although larger nodes have a higher incidence of
malignancy, reactive lymph nodes can be as large as
malignant nodes. Moreover, metastases can be found in small
lymph nodes22. In the literature, different cut-off values of
nodal size have been reported (5mm, 8mm and 10mm)16, 22,
23. As the cut-off points of nodal size increase, the sensitivity
of the size criteria in differentiating reactive from malignant
nodes decreases whilst the specificity increases24. In our
experience, size of lymph nodes cannot be used as the sole
criterion in differential diagnosis. However, nodal size is
useful in clinical practice when the size of lymph nodes in a
patient with a known carcinoma increases on serial
ultrasound examinations, and is highly suspicious for
Figure 5 Power Doppler sonogram of a malignant node with
metastases. Moreover, progressive change of nodal size is
both hilar (arrows) and peripheral (arrowhead) vascularity.
useful to monitor the treatment response of the patients25, 26.
vessel. Angle correction should be made at 60° or less, if
blood flow velocity (peak systolic velocity, PSV; end
diastolic velocity, EDV) is to be measured. The Doppler
Malignant lymph nodes (lymphoma and metastases) tend to
gain is increased until background noise appears and then
be round with a short axis to long axis (S/L) ratio greater than
reduced until the noise is just suppressed. A low wall filter
0.5 (Figure 6), whereas normal and reactive nodes are usually
should be used and PRF is adjusted until the PSV and EDV
elliptical in shape with a S/L ratio less than 0.5 (Figure 7)2, 27-29.
can be measured and without aliasing.
Normal cervical lymph nodes are usually found in the
submandibular, parotid, upper cervical and posterior
triangle regions17. Metastatic nodes in head and neck cancers
have a specific distribution, and this typical distribution helps
with identifying neck metastases and tumour staging4, 18. In
patients with no known primary tumour, the distribution of
metastatic nodes may give a clue to identify the primary.
Moreover, cervical lymph nodes involved with non-
Hodgkin’s lymphoma and tuberculosis also have a specific
distribution19-21. Table 1 summarizes the distribution of cervical
lymph nodes in different metastatic head and neck
carcinomas, non-Hodgkin’s lymphoma and tuberculosis.
Figure 6 Longitudinal sonogram showing a round, hypoechoic
malignant submandibular node without echogenic hilus
Table 1 Distribution of cervical lymphadenopathy in different
(arrows). The arrowheads indicate the body of mandible.
Nodal group(s)
commonly involved
Oropharynx, hypopharynx,
larynx carcinomas
Jugular chain
Oral cavity carcinomas
Upper cervical
Infraclavicular carcinomas
Supraclavicular fossa
Posterior triangle
Nasopharyngeal carcinoma
Upper cervical
Posterior triangle
Papillary carcinoma of the
Internal jugular chain
Non-Hodgkin’s lymphoma
Upper cervical
Posterior triangle
Figure 7 Longitudinal sonogram of an elliptical, hypoechoic
Supraclavicular fossa
normal parotid node with an echogenic hilus (arrow), which
Posterior triangle
is continuous with the adjacent fat (arrowheads).
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It has also been reported that tuberculous nodes are often
round in shape20, 21. Although pathologic nodes are usually
round, normal submandibular and parotid nodes can also be
round in shape (95% and 59% respectively)29. Therefore, shape
of lymph nodes cannot be the sole criterion in the diagnosis.
Eccentric cortical hypertrophy is another useful feature in
identifying malignant nodes, and it correlates with focal
cortical tumour infiltration in the lymph node2.
Echogenic hilus
The echogenic hilus is mainly the result of multiple
medullary sinuses, each of which acts as an acoustic
interface, which partially reflects the ultrasound waves and
produces an echogenic structure, whilst fatty infiltration
makes the hilus more obvious2, 30, 31. On ultrasound, the
echogenic hilus appears as an hyperechoic linear structure
Figure 8 Transverse sonogram showing a metastatic node in
and is continuous with the adjacent fat (Figure 7)30-32. In the
papillary carcinoma of the thyroid, which is hyperechoic when
normal neck, about 90% of nodes with a maximum
compared to the adjacent muscle, and shows multiple,
transverse diameter greater than 5mm show an echogenic
punctuate calcifications (arrows).
hilus33, and the incidence of echogenic hilus within lymph
nodes is higher in older people34. The higher incidence of
intranodal deposition of thyroglobulin, which is produced
echogenic hilus is probably related to the increased fatty
in the primary tumour38. Therefore, when hyperechoic
deposition in lymph nodes in the elderly. Malignant lymph
nodes are detected, radiologists should also examine the
nodes usually do not show echogenic hilus (Figure 6), and
thyroid glands for any tumours.
the presence of an echogenic hilus within lymph nodes was
Lymphomatous nodes were previously found to be
previously considered as a sign of benignity10. However, it
hypoechoic with posterior enhancement, a pseudocystic
has been reported that echogenic hilus may also be found
appearance19. However, with the use of higher frequency
in malignant nodes2, 18, 21, 31, and small normal nodes may not
transducers, e.g. 5 to 12 MHz broadband transducers,
show echogenic hilus33. Therefore, the presence/absence of
lymphomatous nodes demonstrate a micronodular
echogenic hilus should not be used as the sole criterion for
echopattern (Figure 9)39. Tuberculous nodes tend to be
evaluating cervical lymphadenopathy.
hypoechoic which is related to intranodal cystic necrosis20, 21.
Nodal border
Malignant lymph nodes tend to have sharp borders, whilst
normal lymph nodes usually show unsharp borders23. Our
previous study showed that normal lymph nodes in the
upper neck (submental, submandibular, parotid and upper
cervical regions) usually have unsharp borders, but normal
posterior triangle nodes predominantly show sharp borders
(70%)29. An unsharp border is also found in tuberculous
nodes, and is related to the associated edema and
inflammation of surrounding soft tissue (periadenitis)18, 21.
The sharp border in malignant nodes is due to the fact that
tumour infiltration causes an increase in the difference in
acoustic impedance between intranodal and surrounding
tissues23. However, malignant nodes in advanced stages may
also show an ill-defined border, indicating extracapsular
spread and it reduces the survival rate for 50%35. In our
Figure 9 Sonogram with a high-resolution transducer showing
experience, nodal border is not a reliable criterion in
a lymphomatous node with micronodular echopattern
distinguishing normal from abnormal nodes in routine
clinical practice. However, the presence of ill-defined
borders in a proven metastatic node indicates extracapsular
spread and is useful in predicting patient prognosis.
Calcification within lymph nodes is uncommon, however,
metastatic cervical nodes from medullary and papillary
carcinoma of the thyroid tend to show calcification (Figure
Metastatic lymph nodes are predominantly hypoechoic
8)4, 37, 38. The calcification is usually punctuate, peripherally
when compared to the adjacent soft tissues18, 20, 21, 36, except
located and shows acoustic shadowing with a high
for metastatic nodes from papillary carcinoma of the thyroid
resolution transducer. Although metastatic nodes from
which are commonly hyperechoic (Figure 8)37. The
medullary and papillary carcinoma of the thyroid may both
hyperechogenicity of metastatic nodes in papillary
show calcification, the incidence is relatively lower in
carcinoma of the thyroid is probably related to the
medullary carcinoma of the thyroid. In addition, the
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echogenicity of the lymph nodes may help the
differentiation, as metastatic nodes from medullary
carcinoma of the thyroid are hypoechoic, whereas metastatic
nodes from papillary carcinoma of the thyroid are
hyperechoic. The relatively high incidence of calcification
in metastatic nodes from papillary carcinoma of the thyroid
makes this feature useful for the diagnosis.
Calcification may also be found in lymph nodes, including
lymphomatous and tuberculous nodes, after treatment.
However, the calcification in these nodes is usually dense
and shows acoustic shadowing.
Intranodal necrosis
Lymph nodes with intranodal necrosis, regardless of their
size, are pathologic4. Intranodal necrosis can be classified
into two types: cystic necrosis (also known as liquefaction
Figure 11 Transverse sonogram of a tuberculous node (arrows).
necrosis) and coagulation necrosis. Cystic necrosis appears
Note the adjacent soft tissues edema which appears
as an echolucent area within the lymph nodes (Figure 10),
heterogeneous and hypoechoic with loss of fascial planes
whilst coagulation necrosis is an uncommon sign and
appears as an echogenic focus within the nodes30-32.
Figure 12 Sonogram showing matting of multiple tuberculous
Figure 10 Transverse sonogram showing a metastatic node
with intranodal cystic necrosis (arrows).
a common feature in tuberculous lymphadenitis (59% -
Intranodal necrosis may be found in malignant and
64%)20, 21. The high incidence of matting in tuberculous nodes
inflammatory nodes, with cystic necrosis more common
is considered to be the result of periadenitis and adjacent
than coagulation necrosis. Cystic necrosis is common in
soft tissues edema. Since matting of lymph nodes is common
tuberculous nodes20, 21, and metastatic nodes from squamous
in tuberculous lymphadenitis, it is a useful feature to
cell carcinomas4 and papillary carcinoma of the thyroid4, 37.
differentiate tuberculosis from other diseases.
Lymphomatous nodes seldom show cystic necrosis unless
the patient has previous radiation therapy or chemotherapy,
Vascular pattern
or has advanced disease5, 40.
It has been reported that the evaluation of the vascular
pattern of normal and abnormal cervical lymph nodes is
Adjacent soft tissues edema
highly reliable, with a repeatability of 85%41. Small normal
Granulomatous and metastatic nodes can invade the
lymph nodes (maximum transverse diameter < 5 mm)
surrounding soft tissues and cause edema or induration20, 40.
usually do not show vascular signals as the blood vessels
On ultrasound, the soft tissues edema is identified by diffuse
are too small to be detected. Approximately 90% of normal
hypoechogenicity with loss of fascial planes (Figure 11). It
lymph nodes with a maximum transverse diameter greater
has been reported that adjacent soft tissues edema is
than 5 mm present with hilar vascularity33. Normal and
common in tuberculous lymphadenitis (43% - 49%)20, 21.
reactive lymph nodes usually present with hilar vascularity,
Therefore, it is a useful feature for diagnosing tuberculosis.
or may seem to be apparently avascular42-45.
However, soft tissue edema may also be found in patients
with previous radiation therapy of the neck25.
Peripheral or mixed vascularity are common in metastatic
nodes42-44, 46, 47. Therefore, the presence of peripheral vessels
in lymph nodes is highly suspicious of malignancy. The
Matting is considered as clumps of multiple abnormal nodes
peripheral vascularity in metastatic nodes is related to
with no normal intervening soft tissues (Figure 12), and it is
tumour infiltration of the lymph nodes in which the tumour
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cells produce tumour angiogenetic factor (TAF), which
sensitivities (RI, 47% - 81%; PI, 55% - 94%) and specificities
causes angiogenesis and recruitment of peripheral vessels42-
(RI, 81% - 100%; PI, 97% - 100%)43, 44, 46, 50. Our previous study
44, 46. A lymph node with a mixed vascularity is a condition
suggested that the optimum cut-off of RI and PI are 0.7 and
where angiogenesis occurs and peripheral vessels are
1.4 respectively, with a sensitivity of 86% and 80%
induced, whilst the pre-existing hilar vessels are preserved
respectively, and a specificity of 70% and 86% respectively47.
until they are destroyed by the tumour cells at a later stage43.
Unlike metastases, lymphomatous nodes tend to have mixed
Normal cervical lymph nodes are usually found in
vascularity, while pure peripheral vascularity is relatively
submandibular, parotid, upper cervical and posterior triangle
less common43, 46, 48.
regions. They are hypoechoic and predominantly elliptical
in shape, except for submandibular and parotid nodes. An
The vascular pattern of tuberculous nodes is variable, which
echogenic hilus and hilar vascularity are usually found in
simulate both benign and malignant conditions49.
lymph nodes with a maximum transverse diameter greater
Nevertheless, apparent avascularity and displaced hilar
than 5 mm.
vascularity are commonly seen in tuberculous nodes49.
Displaced hilar vascularity in tuberculous nodes is related
Cervical lymphadenopathy from various causes has a
to the high incidence of focal cystic necrosis within the lymph
specific distribution. Malignant and tuberculous nodes tend
nodes, which displaces the vessels towards the periphery
to be large, round, hypoechoic and without echogenic hilus.
(Figure 13). In lymph nodes with extensive cystic necrosis,
Metastatic nodes from papillary carcinoma of the thyroid
blood vessels are destroyed and thus they appear apparently
are usually hyperechoic and show intranodal cystic necrosis
and calcification. Mirconodular appearance is a specific
feature of lymphomatous nodes when a high resolution
transducer is used. The presence of cystic necrosis, adjacent
soft tissue edema and matting of nodes are useful features
to identify tuberculous nodes. In power Doppler
sonography, the presence of peripheral vascularity in lymph
nodes is highly suspicious of malignancy. Displaced hilar
vascularity is usually found in tuberculous lymphadenitis.
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