Residency · Residency · Nuclear Medicine
Lymphoscintigraphy for Lymphedema
Introduction
Lymphoscintigraphy is the gold standard nuclear medicine technique for evaluating lymphatic function and diagnosing lymphedema. By injecting Tc-99m sulfur colloid or Tc-99m tilmanocept intradermally in the affected extremity, lymphatic transport can be visualized and quantified. The study differentiates primary from secondary lymphedema, identifies lymphatic obstruction patterns, and guides treatment decisions including surgery and physiotherapy.
Pathophysiology of Lymphedema
Classification
Primary lymphedema results from congenital or hereditary lymphatic malformation. Congenital forms (Milroy disease) are present at birth. Lymphedema praecox, the most common primary form, appears at puberty. Lymphedema tarda presents after age 35. Secondary lymphedema is an acquired disruption of lymphatic drainage caused by surgical lymph node dissection (particularly axillary or inguinal), radiation therapy, infection (filariasis is the leading cause worldwide), malignant infiltration of lymphatics or nodes, or trauma and chronic venous insufficiency.
Clinical Significance
Lymphedema affects an estimated 250 million people worldwide. Post-breast cancer treatment lymphedema occurs in 20-30% of patients after axillary dissection. Progressive swelling leads to skin changes, fibrosis, and recurrent infections. Early diagnosis enables timely intervention and improved outcomes.
Radiopharmaceutical and Technique
Injection
Tc-99m sulfur colloid (filtered or unfiltered) is the most common agent. It is injected intradermally in the first or second web space of the hand (for upper extremity evaluation) or foot (for lower extremity evaluation). The administered activity is 18.5-37 MBq (0.5-1 mCi) per injection site in a volume of 0.1-0.2 mL. Bilateral injection is performed to allow comparison between the symptomatic and contralateral normal extremity. Gentle massage or exercise of the injected extremity promotes lymphatic flow.
Imaging Protocol
Dynamic imaging of the extremity begins immediately after injection. Serial whole-body or regional images are obtained at 30 minutes, 1 hour, and 2-3 hours. Anterior and posterior views of the extremities and regional lymph node basins are acquired. Delayed images up to 4-6 hours are obtained if transit is slow or nodes are not visualized. Quantitative analysis includes time to lymph node visualization and calculation of a transport index.
Normal Findings
Normal lymphoscintigraphy demonstrates rapid transit from the injection site through lymphatic channels to regional nodes. For the upper extremity, epitrochlear and axillary lymph nodes are visualized within 30-60 minutes. For the lower extremity, popliteal and inguinal nodes appear within the same timeframe. The appearance should be symmetric between paired extremities, with well-defined lymphatic channels and discrete nodal uptake. Liver uptake indicates systemic absorption of radiotracer and is a normal finding.
Abnormal Findings
Primary Lymphedema Patterns
Primary lymphedema may present as aplasia (absent lymphatic channels and nodes), hypoplasia (reduced number or caliber of channels), or, less commonly, hyperplasia (dilated, tortuous channels). Delayed or absent nodal visualization and dermal backflow -- diffuse dermal activity indicating lymphatic reflux -- are characteristic findings.
Secondary Lymphedema Patterns
Secondary lymphedema typically shows asymmetric delayed transit on the affected side, visualization of collateral lymphatic pathways, obstruction at the level of the nodal basin, and dermal backflow distal to the obstruction. Cross-over drainage to contralateral lymph nodes may occur in some cases.
| Finding | Normal | Primary Lymphedema | Secondary Lymphedema |
|---|---|---|---|
| Lymphatic channels | Well-defined | Absent/hypoplastic | May show collaterals |
| Nodal visualization | <30–60 min | Delayed or absent | Delayed; obstruction at basin level |
| Dermal backflow | Absent | Present (distal) | Present (distal to obstruction) |
| Symmetry | Symmetric | Variable (often bilateral) | Asymmetric (affected side delayed) |
| Contralateral cross-over | Absent | Rare | May be present |
Quantitative Parameters
The transport index is a composite score incorporating transit time, distribution pattern, and nodal uptake. Normal transit time to regional nodes is less than 30-60 minutes. Delayed transit is defined as greater than 60 minutes. Absent nodal visualization on delayed imaging is highly abnormal.
Clinical Applications
Differential Diagnosis of Extremity Swelling
Lymphoscintigraphy reliably distinguishes lymphedema from venous edema, lipedema, and myxedema. Venous edema typically shows normal or even accelerated lymphatic transport. Lipedema produces symmetric fat deposition with normal lymphatic function. Combined lymphatic-venous insufficiency may produce mixed patterns.
Surgical Planning
The study guides selection for lymphovenous anastomosis (LVA) or vascularized lymph node transfer by identifying functional lymphatic channels suitable for microsurgical anastomosis. It maps collateral drainage pathways and can assess post-surgical improvement in lymphatic transport.
Treatment Monitoring
Baseline studies before initiating complete decongestive therapy (CDT) allow objective documentation of subsequent improvement. Follow-up studies track changes in transport parameters and evaluate the efficacy of pneumatic compression therapy and surgical interventions.
Advanced Techniques
SPECT/CT Lymphoscintigraphy
SPECT/CT improves anatomic correlation of lymphatic channels and nodes, better localizes the level of obstruction, distinguishes deep from superficial lymphatic systems, and is particularly useful in complex anatomy such as trunk or genital lymphedema.
ICG Lymphangiography
Indocyanine green near-infrared fluorescence imaging provides real-time visualization of superficial lymphatic channels and complements radionuclide lymphoscintigraphy. It is primarily used intraoperatively for LVA planning but has limited depth penetration of only 1-2 cm.
MR Lymphangiography
Non-contrast and contrast-enhanced MRI techniques offer superior soft tissue characterization without radiation exposure. MR lymphangiography has an emerging role in surgical planning and anatomic mapping.
Clinical Pearls
Dermal backflow (diffuse dermal radiotracer activity) is the hallmark lymphoscintigraphic finding of lymphedema, indicating lymphatic overload and reflux into the dermal lymphatic plexus. Bilateral injection and imaging are essential for comparison, as the contralateral normal extremity serves as an internal control for transit time and nodal uptake. Lymphoscintigraphy reliably distinguishes lymphedema from lipedema and venous edema, which is critical because these conditions require entirely different management approaches. Quantitative transport indices and transit times provide objective parameters for documenting disease severity and monitoring treatment response over time.
References
- Dalia RM, et al. "Qualitative and Quantitative Radionuclide Lymphoscintigraphy: Practice Guideline." J Nucl Med Technol. 2014;42(1):4-11.
- Hassanein AH, et al. "Lymphoscintigraphy for the Diagnosis and Management of Lymphedema." Plast Reconstr Surg. 2017;140(5):735e-743e.
- Pappalardo M, et al. "Lymphoscintigraphy for the Diagnosis and Planning of Microsurgical Treatment of Lymphedema." J Surg Oncol. 2018;117(4):706-714.
- Executive Committee of the ISL. "The Diagnosis and Treatment of Peripheral Lymphedema: 2020 Consensus Document of the International Society of Lymphology." Lymphology. 2020;53(1):3-19.