Lymphatic Imaging (PDE Video Fluoroscopy)

General Surgery

What is PDE video fluoroscopy?

PDE (Photo Dynamic Eye) video fluoroscopy is an imaging tool which visualises the lymphatic system and gives us a real time picture of the lymphatic vessels and lymph nodes to see how they are functioning.

PDE video fluoroscopy uses Indocyanine green (ICG) dye which is injected into the web spaces between your toes or fingers. ICG is a water-soluble dye that fluoresces when exposed to near-infrared (NIR) light.

Video fluroscopy has been used for many years in medicine for different purposes and more recently it has proved to be an important modality in lymphatic imaging.

A small amount of local anaesthetic is injected into the webspace before the ICG, to ensure it is as pain free as possible. The ICG is taken up by the lymphatics and a special infrared camera (PDE) is used to follow the dye as it progresses up the limb. It can therefore be used to map lymphatic function and provide important information regarding the lymphatics as well as monitoring for any new changes in those patients at risk of developing lymphoedema following lymph node surgery for breast, gynaecological and skin cancer.

The imaging also gives a road map of the lymphatics which can be used to guide lymphoedema nurses or physiotherapists about the best direction to massage excess fluid out of the limb as part of lymphoedema management.

What does a normal scan look like?

Normally, ICG is rapidly absorbed into the lymphatic system and transported up the lymphatic vessels to the lymph nodes in the armpit or groin. We can assess how quickly the ICG is absorbed and moved up the limb. As the PDE is real time imaging, we can observe the vessels contracting and pushing the dye towards the lymph nodes (peristalsis). A scan showing normal function shows the linear lymphatics with good progression of dye can be seen here.

What does the scan look like in lymphoedema?

There are 2 types of lymphoedema:

Primary lymphoedema is a problem caused by failure of the lymphatics to develop. It can present at birth or in early or late adulthood.
Secondary lymphoedema is more common and caused by damage to or removal of lymphatics as part of the treatment for cancer.

In secondary lymphoedema, there is a blockage to the normal flow of lymphatic fluid out of the limb. This leads to an increase in pressure within the lymphatic channels as they are unable to drain via the normal route. The increased pressure means that the fluid flows backwards into the microscopic lymphatic vessels that collect lymph fluid from the skin. The lymph fluid then leaks into the skin, which is called dermal backflow. This dermal backflow can be seen on the scan. As the lymphoedema worsens different characteristic patterns can be detected and recognised.

Early dermal re-routing is called ‘splash back’, but as the lymphoedema progresses it evolves into a more severe starburst pattern. In very severe lymphoedema, the dye collects throughout the skin and subcutaneous tissue, leading to a diffuse pattern.

In primary lymphoedema, the PDE picture varies depending on the type of primary lymphoedema. Some forms of primary lymphoedema are caused by absence of parts of the lymphatic system or lymph nodes, and therefore the ICG lymphography results are like secondary lymphoedema.

In other forms of primary lymphoedema there are abnormal or absent lymphatic channels. This is seen as severely delayed uptake and transport of the ICG or even totally absent uptake and transport.

How safe is ICG video fluoroscopy?

ICG has a robust safety profile as it is metabolised by the liver and does not rely on good kidney function to clear it. It can therefore be used in patients with renal impairment. Allergic reactions to ICG are very rare even with high doses and no episodes of allergic reactions have ever been reported following the low dose subcutaneous injections used for ICG lymphography.

There is a very small risk of introducing infection by giving injections into the arm or leg affected by lymphoedema, but this is unlikely as sterile needles and antiseptic skin preparation are used routinely. Antibiotics will be used in the unlikely event an infection occurs.

ICG lymphography does not involve exposure to radiation like lymphoscintigraphy. The dye has a green colour and may leave a small green patch of skin, like a bruise, for a few days following the test. After ICG lymphography, you can resume normal activities straight away, for example, it is fine for you to drive yourself home.

What happens when I attend for PDE imaging?

On the day of the appointment, we will go through the procedure with you including all known risks and complications. You will have plenty of opportunity to ask any questions and if you are happy to proceed then we will ask you to sign a consent form.

I will then inject the dye into the hands or feet, and we ask you to complete a questionnaire about your symptoms which we repeat every time you have a scan to monitor your progress. We will also take measurements of your limbs to monitor the limb volume.

We need to give the dye approximately 30 minutes to move up your limb and then we can perform the imaging with a handheld camera. You will be able to see the images yourself on the monitor. Once I have the report of the PDE, I will contact you with an explanation of the results for your information. If the scan is abnormal then I will arrange a follow up appointment to discuss this further in more detail.