An IMBUS lymph node exam needs to be carefully performed and interpreted to avoid over- or under-reacting to these lumps.
Ultrasound is usually better than CT at finding and sizing lymph nodes in the neck, axilla, epitrochlear area, and groin. A general lymph node survey, whether traditional or IMBUS, has not been shown beneficial as part of a periodic physical, but has anecdotally been useful in systemically ill patients who could have an infectious, inflammatory, or neoplastic disease because an abnormal node might be biopsied to make a diagnosis. An examiner needs good technique and knowledge of lymph node anatomy to perform such a survey.
Most patients who need an IMBUS lymph node exam come to clinic after noticing a lump in the neck, armpit, or groin. If a lump is an abnormal node, a more general node survey might be done to determine if the lymphadenopathy is generalized. The differential diagnosis for generalized lymphadenopathy is different from that of localized lymphadenopathy.
The most frequent enlarged node in clinic is a neck node, the great majority of which are a reaction to head or neck infection. Yet, malignancy is the fear, which is why the size and character of nodes is evaluated carefully. In the primary care setting, initially unexplained lymphadenopathy has only about a 1% chance of malignancy, but failure of node regression over 4 weeks increases the chance of malignancy.
The neck region is divided into Anterior and Posterior triangles, based on the sternocleidomastoid muscle, as shown in the next diagram. The small Subclavian triangle shown in the image is the location of supraclavicular nodes.
The next image shows the location of lymph node groups in the neck. There are nodes superficial and deep to the sternocleidomastoid. Some nodes are near the carotid artery and internal jugular vein. For a neck survey, the probe is moved in a transverse orientation up and down the neck from medial to lateral just like a systematic palpation exam would be performed.
The axillary region has nodes on the lateral chest, high in the axilla, and on the upper, inner arm, as in the following image. A systematic survey of axillary nodes would rarely be done with IMBUS, but when a patient has noticed a lump in this general area, it is important to know where to look for additional nodes in the region.
The epitrochlear region is small and many normal patients have only very small nodes in this location. However, an enlarged node indicates either generalized lymphadenopathy or an inflammatory condition in the lower arm, which should be obvious. The following image shows the location of potential epitrochlear (supratrochlear) nodes in the groove just medial to the biceps muscle. Notice the close proximity of the node group to the basilic vein near the medial epicondyle.
Groin nodes can be inguinal, which are located near the inguinal ligament and drain the lower retro-peritoneum, pelvis, and genitals, or they can be femoral, which are located anterior and medial to the common femoral and great saphenous veins. The femoral nodes drain the leg and occasionally the genitals. The following diagram shows the inguinal and femoral node groups.
Lymph nodes are best evaluated with the linear probe and an exam type for a machine that is optimized for good detail and low Nyquist limits. All the peripheral node regions are best examined with the patient in the supine position. The view of each node should be optimized with depth and focus position so details of shape and texture can be observed. To be consistent amongst examiners and between follow up exams, the probe should be rotated to find the greatest dimension of the node, which is considered the “length”. The probe is then rotated 90 degrees to measure the “width” and “depth” of the node. These dimensions may have no relationship to the traditional parasagittal or transverse planes on the body. Color power Doppler should be applied to assess the vascularity.
It is impossible to be certain that a node is normal or abnormal (or certainly reactive versus malignant) based on any single characteristic. However, the combination of findings, integrated with the rest of the clinical story, helps the care of the patient.
Normal nodes appear the same in any of the four regions that IMBUS can evaluate. They are less than 1.0 cm (often less than 0.5 cm) in length, oval/elliptical in shape, with a hyperechoic central hilum. Color power Doppler shows only a little flow in the hilum. The periphery of the node has moderate to low echogenicity and the margins of the node should be clear and smooth. The following image is a normal neck node in an asymptomatic patient. This node measured 0.7 cm in greatest diameter.
Increased size usually prompts a node exam but size alone does not distinguish reactive from malignant nodes. Every malignant node begins small.
A node that is ≥ 1 cm in length is enlarged. In general, reactive nodes should maintain an oval/elliptical shape and should have a preserved hyperechoic hilum, but the periphery of the node may be more hypoechoic than normal. Color power Doppler flow may be increased at the hilum of a reactive node but the margins of the node should still be sharp and smooth. The following image shows a modestly enlarged node that was proven to be reactive with careful follow up.
The next node was more worrisome to the examiner. It was in the groin and had been present for over a month.
There was no obvious inflammatory focus in the leg or groin. The enlarged node was more rounded and seemed to have an irregular border. The periphery was definitely more hypoechoic than normal. Color power Doppler flow was increased in the hilum. After seeing the surgeon several weeks later with persistence of the node, FNA was performed and no malignancy was seen. Thus, differentiating reactive from malignant nodes is difficult and biopsy is sometimes needed.
Malignant nodes typically become rounded or irregularly shaped and are usually markedly hypoechoic, although a few types of tumors can create very hyperechoic nodes. Color power Doppler flow can be increased in various places in the node. The next image is a neck node proven to be lymphoma. It was a 3 cm node, and while the margin was distinct and smooth, the hilum was obliterated and the node was very hypoechoic. There was also scattered color flow throughout the node.
Here is a clip showing a large node in the neck that was a squamous cell carcinoma. This node was round without a hilum and had heterogeneous parenchyma.
The next composite image shows epitrochlear nodes ranging from normal to inflammatory and then malignant. Note that the reactive cat scratch disease node is difficult to differentiate from a malignant node. The rest of the clinical story and followup are usually necessary to separate reactive from malignant nodes.
The last case was a middle-aged woman who noticed a groin swelling. The clip shows a mass that seems to contain 3-4 nodes that are enlarged and rounded. A few nodes still have hila but the parenchyma is hypoechoic.
Here is the color Doppler (not power) of the largest node in the group. The color Doppler flow is increased at the hilum and into the parenchyma of the node.
It is impossible to know if these are reactive or malignant nodes and given the overall appearance of the group and without an obvious leg, genital, or intra-abdominal inflammation, waiting a month for regression was probably not the right approach for this patient. So, an immediate CT of the abdomen and pelvis was obtained, but this showed no pathology to explain the nodes. Only longer term follow up will differentiate reactive from malignant.
IMBUS APPROACH TO NODES
1. Each enlarged node should be measured for length, width, and depth. The other characteristics of the node should be noted, including color power Doppler flow, and the images/clips should be saved in case follow up comparison is needed.
2. A patient with a modestly enlarged node with other characteristics still appearing normal can be reassured by the extremely low likelihood that this node is malignant, particularly if the node is in the neck and the patient is younger. But, over the next month, each patient should note whether the node decreases or disappears (without vigorous palpation every day)! With a less reliable patient, a follow up visit should just be scheduled. If the node does not regress or even increases, the patient must return for re-imaging. Reactive nodes do not have to fully disappear in a month, but they should not grow, unless the inflammatory condition is continuing. A clear reduction in size over a month strongly supports a reactive node.
3. Older patients, particularly smokers, with neck nodes and an absence of recent infections in the head/neck are more worrisome for cancer. A 4 week repeat exam might be appropriate, but with any other atypical characteristic beyond size, ENT consultation without a 4-week wait, with or without a preceding CT, would be justified.
4. The larger and more abnormal a node appears, the greater the concern for malignancy. The integration of all the node findings with the rest of the clinical story will often prompt immediate ENT or surgical consultation (with or without CT imaging).
4. Multiple abnormal nodes in several locations (generalized lymphadenopathy) has a broad differential diagnosis of infectious, inflammatory, and neoplastic conditions. Integration with the rest of the clinical findings is essential, but a lymph node biopsy may contribute to the diagnosis and IMBUS can help identify the best node to biopsy.