Diagnostics
Watching the flow
The role of lymphangiography By Elliott Weiss and Moira Stilwell raditionally, the diagnosis of lymphedema has been purely clinical, based on the clinical history and the findings on physical examination. Sometimes one is born with lymphedema (e.g., Milroy’s Disease), or it develops during the teenage years (e.g., Meige Disease), or later in life, (e.g., Lymphedema Tarda). It can also be seen in combination with other congenital conditions. In other cases, lymphedema occurs secondary to conditions such as malignancies (cancer) or infections (most commonly filariasis), among many others. Originally this condition was considered to be due to a ‘blockage’ or other forms of lymphatic flow malfunction, limiting the transport of lymphatic fluid. With each new medical imaging technology, our understanding of lymphedema evolves. With the advent of X-ray technology, the use of medical imaging allowed for investigations of the lymphatic system, primarily using a technique called lymphangiography with the procedure called a lymphangiogram. Started in 1952, the original version of this test involved injecting a dye under the skin to map out the lymphatic vessels. It was a very painful technique, using standard X-ray technology, but it was considered the gold standard of imaging and viewing lymphatic flow over the next 40 years. During that time, nuclear medicine technology developed in parallel with traditional X-rays. Improvements in technology, safety and comfort, led to it replacing the traditional lymphangiogram. In the past, both methods
were seen as binary tests; either you had normal lymphatic flow or not. Nuclear medicine technology has become more sophisticated and is used to diagnose, measure and stage this condition. It is now used to follow the course of disease before and after treatment.
visualization of lymphatic flow over time. The images may be obtained at various time intervals. This allows for an understanding of the lymphatic flow through the lymphatic vessels. Sentinel node biopsies such as in breast cancer management, use this technology
What is a nuclear medicine lymphangiogram, also known as a lymphangio-scintographic scan (LSG)? A LSG involves an injection of a sterile medical grade tracer under the skin, typically sub-dermally or subcutaneously. The tracer, which is tagged with a radioisotope such as technetium-99m (99mTc), is picked up by the lymphatic system and normally travels up the lymphatic vessels to the lymph nodes. A scanning device called a gamma-ray detector measures the radioactive tracer, as it is moves up the limb. The intensity and distribution of 99mTc is tracked and produces an outline of the lymphatic vessels, although typically it is measured in the superficial lymphatic system. This technology is considered to be a functional imaging modality as it allows for
to stage patients with a known malignancy before surgery. What was initially used as a static (yes-no) technology is now able to follow lymphatic flow in real time. This allows physicians and surgeons to have a much better understanding of lymphatic function and assist in decision-making.
Photo: centraloregonradiology.com
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Dr. Elliott Weiss, MD FRCPC is a specialist in Physical Medicine & Rehabilitation who is primarily based out of Providence Healthcare in Vancouver. Dr. Weiss has been involved in the care of patients with lymphedema for over thirty years. Dr. Moira Stilwell, MD FRCPC is a Radiologist and Nuclear Medicine physician. She practises Nuclear Medicine in Vancouver, British Columbia. Drs. Erin Brown, Kathryn Issac and Weiss have established a provincial lymphedema clinic at Vancouver General Hospital.
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What are the risks of LSG? There are three main concerns regarding a nuclear medicine lymphoscintigraphy: • t he effects of radiation • the possibility of infection •w hether the procedure might make lymphedema worse Radiation exposure is very low. Normally, the tracer passes from the lymphatics into the blood supply, then very quickly to the kidneys and the bladder. That is why the bladder is often visible in these scans. As well, 99mTc has a short half-life (six hours) and it is nearly completely decayed within a day, without any known long-term effects. A sterile technique is used to minimize the risk of infection. Allergic reactions are rare. People with a medical/contrast dye allergy are generally not allergic to this particular agent. Summer 2021
How is lymphatic flow assessed using LSG? In a LSG, lymphatic flow is assessed based on the uptake of tracer from the injected area up the limb, which is usually compared to the other side. The assessment criteria include: • Lymph node uptake, typically in the groin or axilla (armpit) • Dermal backflow, as it applies to the appearance of stagnant tracer, which has difficulty travelling up a limb • Collateral lymphatic flow, if the lymphatics are not functioning normally • Appearance of the main lymphatic circulation • The speed of clearance of the radioisotope from the site of injection A normal LSG will demonstrate efficient
passage of the tracer through the limb from the injection site upward. With lymphedema, the tracer may move more slowly up the limb or there may be no movement. There may be dermal backflow with a specific pattern on imaging. In the case of primary lymphedema, LSG is the best investigative tool to establish this diagnosis. LSG can demonstrate intact lymphatic flow and pathways, which allow for transport or document abnormal or no flow. The role for LSG in secondary lymphedema is similar to the primary case. It allows for visualization of the damaged lymphatic system, including the lymphatic response to surgery or radiotherapy. In the past 25 years, the role of surgical management of lymphedema has evolved. Lymphangiography has played an important role during this time in that it assists in surgical planning and the evaluation of outcomes following surgical procedures such as lymphatico-venous anastomosis and lymph node transfers.
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It is unlikely a LSG will make lymphedema worse as the tracer is picked up by the usual lymphatic circulation. In a person with lymphedema, it may take longer for the tracer to leave the body but as noted above, it decays very quickly, even if it takes longer to pass through the body.
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angiograms demonstrate different conditions and the health of the lymphatics. It also has value in post-operative management. Our understanding of conditions affecting the lymphatic system has evolved over the past 70 years, in good part due to evolving medical imaging technologies. The future looks very promising with emerging imaging technologies improving our understanding of disorders of the lymphatic system. These new approaches will continue to provide guidance and direction regarding treatments and interventions for the patient with lymphedema. LP As previously noted, the results following a LSG provide quantitative and qualitative information, which will assist the physician/ surgeon in advising the best management for lymphedema. Therapists performing lymphatic massage may also find the imaging results to be of value, as these results can provide valuable information regarding the distribution of lymphatic drainage and flow in an affected limb. What’s new in lymphatic imaging? Improvements in nuclear medicine scanning are beginning to be more accessible. This includes improvements with digital imaging. Newer
radioisotopes may offer better imaging quality. Positron Emission Tomography (PET) lymphangiogram technology may eventually replace or complement more traditional techniques. Fusion technologies such as the combination of Magnetic Resonance Imaging (MRI) with a lymphangiogram are emerging trends. MRI-lymphangiography offers a new level of imaging of the lymphatics not seen before. Finally, the use of indocyanine green (ICG) lymphangiography allows for clinicians to view the superficial lymphatics at the bedside without radiation exposure. It allows for staging of disease severity and assists in pre-operative assessment. ICG lymph-
A full set of references can be found at www.lymphedemapathways.ca
Editor’s Note: Despite advances in medical imaging for lymphedema, this technology is used mainly by surgeons and specialists assessing primary lymphedema. At this time it is not in widespread use in clinical practice, where diagnosis continues to rely primarily on clinical history and physical findings.
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