Indocyanine green (ICG) lymphography
Table of contents
Indocyanine green lymphography enables the visualisation of superficial lymphatic vessels and allows the study of how lymph flows through a specific area of the body. It is mainly used in the specialist assessment of lymphoedema and can provide useful information when it is necessary to identify which pathways maintain lymphatic drainage or to plan specific procedures.
What is indocyanine green lymphography and what does it enable us to investigate?
The lymphatic system consists of a network of vessels and lymph nodes which, amongst other functions, helps to remove excess fluid from the tissues. This fluid, known as lymph, circulates through the lymphatic vessels before re-entering the bloodstream.
When this transport is disrupted, lymph can accumulate in the tissues and contribute to the development of lymphoedema. A physical examination allows the swelling to be identified and any changes in the limb to be assessed, but it does not always reveal where the lymph continues to circulate.
Indocyanine green lymphography, also known as fluorescence lymphography, provides this additional information. To perform the test, a small amount of indocyanine green – a fluorescent tracer – is injected under the skin and can be tracked using a special camera positioned over the area being examined.
As the tracer enters the lymphatic vessels and travels through them, the camera allows certain pathways to be observed and areas where its distribution is altered to be identified. In this way, the test combines information on the visible anatomy of the vessels with information on lymphatic flow in that region.
Its scope is primarily superficial. Vessels situated at greater depth or covered by a greater thickness of tissue may lie beyond the camera’s detection range. Consequently, the examination does not provide a complete map of the entire lymphatic system, but rather a detailed assessment of the vessels accessible to this technique.
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Our team can advise you on the test and the most appropriate care pathway.
When it can provide useful information
Indocyanine green lymphography is included in the assessment when understanding superficial lymphatic drainage can help answer a specific clinical question.
In people with secondary lymphoedema, for example following certain surgical procedures or cancer treatments, the images can show which pathways are still transporting lymph and in which areas there are abnormalities in its distribution. It may also be used in some cases of primary lymphoedema, associated with abnormalities in the development or function of the lymphatic system.
Not everyone with lymphoedema requires this examination. The assessment begins with symptoms, medical history and a clinical examination. Lymphography is added when the images it provides can supplement this information, help to better characterise the drainage pattern or provide relevant data to inform decisions on the next steps.
One of its most characteristic applications arises when certain lymphatic microsurgical techniques are being assessed. Some procedures require the identification of vessels that still retain the ability to transport lymph. Being able to identify their course prior to the operation can help the surgeon plan the areas in which they might work.
Undergoing the test does not, however, mean that a person requires surgery. The decision depends on the type and progression of the lymphoedema, the condition of the tissues, the symptoms, the treatments already undertaken and the overall specialist assessment.
Monitoring the progress of the marker allows us to identify superficial pathways where lymphatic flow is maintained and areas where its distribution changes. This information complements the findings of the physical examination.
How to prepare and how the test is carried out
Preparation depends on the purpose of the examination and whether the lymphography is carried out on its own or in conjunction with another procedure. The unit will provide specific instructions regarding food, drink, medication and compression garments, as these guidelines may vary depending on the protocol.
Before the scan, it is important to report any previous reactions to indocyanine green or any of its components, as well as any allergies and thyroid conditions that may be relevant. You should also mention if you are pregnant or might be pregnant, if you are breastfeeding, your regular medication and any treatments you are using for lymphoedema.
If you are wearing a compression sleeve, stocking or other compression garment, the team will advise you when to remove it and when it can be worn again. You must not stop taking any medication or alter your treatment on your own initiative.
You should also inform the team if you are due to have a thyroid test involving radioactive iodine, as certain indocyanine green preparations may temporarily interfere with this specific type of test.
At the start of the scan, the team examines the area to be studied and selects the points where the tracer will be administered. After cleaning the skin, one or more small superficial injections are given. When examining the arms or legs, these may be administered into the hand, foot or other selected sites, depending on the lymphatic pathway to be observed.
The injections may cause a prick, a stinging sensation or brief discomfort. The camera is then positioned over the area being examined and the observation begins. The camera remains outside the body and detects the fluorescence of the tracer as it enters the lymphatic vessels and travels through them.
Depending on the aim of the examination, photographs or video sequences may be recorded. When the images are to be used to plan a procedure, certain pathways may be marked on the skin to facilitate their subsequent identification.
At certain points, the team may ask you to make small movements or perform specific manoeuvres to observe how the tracer’s movement changes. Once indocyanine green has been administered, it is not necessary to perform a new puncture each time an image is taken: the same area can be observed again as time passes.
The tracer takes time to travel through the lymphatic vessels. This is why the scan may involve alternating periods of observation and waiting, which allow us to monitor how it progresses and how its distribution changes.
Duration, recovery and aftercare
There is no standard duration for all scans. The time taken depends on the size of the area being examined, the speed at which the tracer moves, and whether it is necessary to take further images after a waiting period.
When lymphography is carried out as a standalone outpatient test, it does not usually require a specific recovery period. If it forms part of a surgical procedure or other intervention, the post-procedure instructions will also depend on that context.
A slight greenish discolouration may remain at the injection sites, but this will gradually fade. Post-procedure recommendations depend on the preparation used. Certain formulations require these areas to be temporarily protected from direct sunlight and ultraviolet radiation; therefore, the specific instructions provided by the medical team must be followed.
What the images show and how they are interpreted
The specialist does not interpret a single photograph in isolation. They observe how the tracer begins to move, which pathways can be followed and how its distribution changes over time.
In some areas, relatively well-defined lines can be identified, corresponding to vessels through which the tracer follows a visible path. These pathways indicate that superficial lymphatic transport is present in that region under the conditions in which the study is carried out.
In other areas, the image may take on a different appearance. The tracer may be distributed across a more extensive network of small vessels in the skin rather than following only well-defined linear pathways. This pattern is known as dermal reflux and may occur when lymphatic drainage is impaired.
The significance of these images does not depend solely on their appearance. The location of the lymphoedema, the characteristics of the tissues, the progression of symptoms, previous treatments and the clinical question that prompted the examination are also taken into account. Therefore, a particular pattern does not automatically correspond to a specific stage of the disease, nor does it, on its own, determine the treatment the person requires.
Nor is it always possible to trace all the vessels present in the area. A weak signal or the absence of a visible pathway may be related to impaired transport, but it may also be due to the depth of the vessel, the thickness of the tissues, the site where the tracer was administered, or the conditions under which the examination was carried out.
Failure to visualise a vessel, therefore, does not prove that it does not exist. If the images do not provide a sufficient answer to the clinical question, the team may review the study, obtain further observations or use another technique that provides different information about the lymphatic system.
When the examination forms part of the planning for a surgical procedure, the identified pathways can help to identify the areas requiring a more precise assessment. The image, however, does not in itself establish the surgical indication nor does it allow for an individual prediction of the outcome of an operation.
Indocyanine green acts solely as a tracer. Its administration provides information about the lymphatic system, but it does not repair the vessels nor does it, in itself, constitute a treatment for lymphoedema.
Limitations of indocyanine green lymphography
The main limitation of this technique is the depth at which images can be obtained. The camera primarily examines vessels close to the surface, whilst deeper structures may lie beyond its reach.
The result also depends on how the scan is performed. Factors such as the site and depth of the injections, the time elapsed since the tracer was administered, the manoeuvres performed and the characteristics of the equipment all have an influence.
Furthermore, the protocols and classifications used to describe the images are not entirely standardised. Consequently, two studies carried out using different procedures cannot always be directly compared.
A scan showing no visible abnormalities does not rule out all diseases of the lymphatic system, just as an abnormal pattern does not necessarily explain all the components of a swelling. The value of the test lies in adding information to the clinical assessment, not in replacing it.
Risks and special circumstances
The most common side effects are related to the small injections and may include a pricking sensation, stinging or local tenderness.
As with any medicine, indocyanine green may cause hypersensitivity reactions. Serious reactions are rare, but they justify the contrast agent being administered under medical supervision and in a setting equipped to deal with them.
A previous reaction to indocyanine green or any of its components may preclude its use. Some preparations contain iodides and therefore require specific precautions in certain thyroid conditions. The team will review the patient’s medical history before administering the contrast agent.
Pregnancy, the possibility of pregnancy and breastfeeding must be disclosed before the examination. During pregnancy, the use of the contrast agent requires an individual assessment of the need for the test and the available alternatives. During breastfeeding, the recommendations specific to the particular preparation used must be followed.
After the test, a slight greenish discolouration at the injection sites may persist for a while; this does not in itself indicate a complication.
Seek immediate medical attention if you experience difficulty breathing, swelling of the lips, tongue or face, severe dizziness or a feeling of faintness. You should also contact the centre if pain at the injection sites gradually increases or if you develop spreading redness, significant warmth or a fever.
ICG lymphography and other tests of the lymphatic system
There is no single examination capable of answering all questions about the lymphatic system. The choice depends on the information the medical team needs to obtain.
Indocyanine green lymphography is particularly useful for visualising vessels close to the surface and locating specific pathways. Lymphoscintigraphy, on the other hand, is a nuclear medicine procedure that allows the study of how a radiopharmaceutical is transported through the lymphatic system and how it progresses towards specific lymph nodes.
Magnetic resonance lymphography can provide information on tissues and structures located deeper within the body. Ultrasound, including Doppler ultrasound, can be useful when it is necessary to examine tissues or assess whether a venous disorder is contributing to the swelling.
These techniques are not equivalent, nor do they necessarily compete with one another. Each addresses different questions and can be used complementarily within the same diagnostic process.
Professionals involved
At the Publio Cordón Memorial Hospital, specialist care for lymphoedema is provided by the Advanced Breast Reconstruction and Lymphoedema Unit, which forms part of the Department of Plastic and Reconstructive Surgery.
The unit is headed by Dr Jaume Masià Ayala, and his team includes Dr José María Lasso and Dr Gemma Pons.
The specialist team assesses whether an examination of superficial lymphatic drainage can provide relevant information and how this should be integrated with the physical examination, the patient’s symptoms and the specific aim of the assessment.
Lymphography thus forms part of a broader diagnostic and therapeutic process. The images can help to better understand how the drainage system functions or to plan certain procedures, but clinical decisions are made taking into account each individual’s overall situation.
Medical information for general guidance
This factsheet aims to help you understand what indocyanine green lymphography is, what the medical team needs to assess, how the examination is carried out and what the images obtained might mean.
At Publio Cordón Memorial Hospital, we promote accurate, understandable and useful medical information, linked to scientific research and outreach.
The indication for the test, the contrast medium used, the preparation required, precautions, aftercare and the interpretation of the results must be tailored to each individual’s clinical situation and the relevant clinical protocol.