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Background
For effective lymphatic function, lymph must be absorbed from the interstitium and transported into the valved peripheral collecting channels and lymph nodes to the cisterna chyli, where it then transits to the thoracic duct. Aberrations in this process can lead to lymphedema, (LED), the accumulation of lymphatic fluid in soft tissues due to impaired lymphatic drainage, resulting in inflammatory changes, fat hypertrophy, and fibrosis. LED affects approximately 1 in 30 people worldwide and has significant consequences on patients’ quality of life. In primary LED, anatomic or developmental aberrations cause lymphatic system malformation, while in secondary LED, external factors such as malignancy or infection disrupt a normally developed lymphatic system. There are many available methods for imaging primary and secondary LED, including lymphoscintigraphy, MR/CT, and transpedal or intranodal lymphangiography (IL), each with their associated pros and cons. For instance, lymphoscintigraphy has been considered the reference standard for LED and tracks the path of a radiotracer in the affected limb but is limited by low image resolution. Transpedal and IL are interventional radiology (IR) methods that provide detailed images of lymphatic vessels as well as the opportunity for intervention, with intranodal lymphangiography as the less invasive option. However, IL is a relatively new technique, and there are limited data on the patterns of anatomic details it provides in LED. The purpose of this exhibit is to review intranodal lymphangiography findings across patients with primary LED. We focus on patients with primary LED, because there is a lack of existing studies that evaluate the anatomic lymphatic aberrations of primary LED.

Educational Goals / Teaching Points
The goals of this exhibit are to briefly review the methodology of in IL, and to present the IL findings that occur in primary LED, with an emphasis on patterns seen across multiple patients. We draw our data from a unique cohort of primary lymphedema patients who have also undergone lymphoscintigraphy and/or MRI. As such, we present our findings in reference to the additional information that intranodal lymphangiography provides.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
We performed IL via ultrasound-guided injection of groin lymph nodes with lipiodol to visualize lymphatic channels in patients with primary LED. Common IL findings included: a paucity of groin lymph nodes/abnormal lymph node morphology, delayed flow to the thoracic duct, cross-over emptying of the lymphatic channels to the contralateral side, and lymphovenous shunting. Compared to lymphoscintigraphy or MRI, IL gave added resolution and detail of the lymphatic anatomy, particularly for adjacent anatomic landmarks and vasculature.

Conclusion
IL is an imaging method for LED that can combine resolution of anatomic detail with potential intervention. It is particularly relevant in cases of primary LED, where the developmental abnormalities of the lymphatic channels are unclear. In this exhibit we describe the methodology of IL and present the common findings seen in primary LED.