Current and Developing Lymphatic Imaging Approaches for Elucidation of Functional Mechanisms and Disease Progression

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TL;DR

This review summarizes current and emerging lymphatic imaging techniques, including lymphoscintigraphy, MR lymphangiography, near-infrared fluorescence (NIRF) imaging, and photoacoustic imaging, highlighting their roles in understanding lymphatic function, diagnosing lymphedema, and guiding cancer sentinel lymph node mapping. Key findings include that lymphoscintigraphy remains the gold standard for lymphedema diagnosis with sensitivity up to 96% and specificity 100%, while newer modalities like NIRF with ICG offer improved spatial resolution but are depth-limited. The clinical significance lies in how multimodal imaging and nanoparticle-based contrast agents are advancing lymphatic research and improving patient outcomes in lymphedema and cancer.

Full summary

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**Background:** The lymphatic system plays critical roles in fluid homeostasis, immune surveillance, and lipid absorption, yet its study has historically lagged behind other body systems. Dysfunction contributes to diseases such as lymphedema, cancer metastasis, autoimmune disorders, and obesity. Imaging techniques are essential for elucidating lymphatic anatomy, physiology, and pathology. This narrative review discusses current and developing lymphatic imaging approaches, their applications in understanding fundamental mechanisms, diagnosing and staging lymphedema, mapping sentinel lymph nodes in cancer, and exploring roles in other disease states.

**Methods:** The authors conducted a narrative review of the literature, summarizing key studies on lymphatic imaging modalities including lymphoscintigraphy, near-infrared fluorescence (NIRF) lymphangiography, MR lymphangiography, ultrasound, photoacoustic imaging, intravital microscopy (especially multiphoton microscopy), and nanoparticle-based multimodal imaging. They also discuss sentinel lymph node mapping techniques using blue dyes, radiotracers, indocyanine green (ICG), and hybrid tracers. The review covers preclinical and clinical studies, with emphasis on diagnostic performance metrics (sensitivity, specificity) and technological advancements.

**Key Results:** - Lymphoscintigraphy remains the gold standard for lymphedema diagnosis, with studies reporting sensitivity of 92% (Gloviczki et al., 1989) and 96% (2017 study), and specificity of 100% in both. However, it has poor spatial resolution and lacks standardization. - MR lymphangiography provides superior anatomical detail but lower diagnostic performance: a 2014 study found sensitivity 68% and specificity 91% (correlation coefficient 0.62 with lymphoscintigraphy). - Ultrasound showed 94.6% diagnostic accuracy in a 2021 study of 14 patients, correctly diagnosing lymphedema in 39 of 54 leg areas where lymphoscintigraphy failed. - NIRF imaging with ICG offers improved spatial and temporal resolution but is depth-limited to 2–4 cm. It can visualize dermal backflow and tortuous vessels. - Photoacoustic imaging visualized similar numbers of lymphatic vessels as lymphoscintigraphy in lymphedema staging. - For sentinel lymph node mapping, blue dye (isosulfan blue) had 88% sensitivity and 100% specificity in a 1994 study (Giuliano et al.). ICG identified 100% of nodes vs. 88.3% for methylene blue in a 2017 study (P=0.006). A 2018 trial found ICG identified 215/220 nodes vs. 172/220 for radiotracer, with 100% detection when combined. - Nanoparticle-based multimodal imaging (e.g., 124I-cRGDY-PEG-C dots) achieved 0% false-negative rate and 90% concordance with Tc-99m sulfur colloid in a clinical trial of 24 melanoma patients. - Intravital microscopy revealed meningeal lymphatic vessels draining cerebrospinal fluid (Louveau et al., 2015) and their role in neuroinflammation (EAE model). - Lymphatic dysfunction is linked to obesity, atherosclerosis, myocardial infarction, and Alzheimer's disease via imaging studies in animal models.

**Clinical Implications:** Lymphatic imaging is crucial for accurate diagnosis and staging of lymphedema, guiding surgical treatments like lymphaticovenous anastomosis, and improving sentinel lymph node biopsy to reduce iatrogenic lymphedema. Emerging techniques such as NIRF, photoacoustic imaging, and multimodal nanoparticles offer enhanced resolution and functional information, potentially improving early detection and personalized treatment. The discovery of meningeal lymphatics opens new avenues for neurological disorders. Continued development and validation of these imaging tools are needed to translate preclinical findings into clinical practice and improve patient outcomes across a wide range of diseases.