Sentinel Lymph Node and Lymphoscintigraphy
Report template: Lymphoscintigraphy and sentinel lymph node (breast, melanoma)
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Learning objectives and modules3 modules · about 2 h 5 min
Learning objectives
After this chapter you will be able to:
- Explain lymphatic transport and the effect of particle size on radiocolloid kinetics.
- Explain the sentinel lymph node concept, injection techniques and imaging protocol in breast cancer and melanoma.
- Interpret the findings of lymphoedema on lymphoscintigraphy.
- Describe the characteristics of the gamma probe and apply the criteria for identifying the sentinel node during surgery.
Modules
The chapter is divided into study modules without changing the order of the text: read, watch the animations, then answer the questions linked to those headings.
- Module 122.1 Lymphoscintigraphy Technique (Tc-99m Nanocolloid)35 min · 2 animations · 14 questionsAnswer the questions →
- Module 222.2–22.3 Sentinel Lymph Node Biopsy (Breast, Melanoma) · Assessment of Lymphoedema55 min · 29 questionsAnswer the questions →
- Module 322.4 Use of the Gamma Probe · Key Points for the Board35 min · 2 animations · 11 questionsAnswer the questions →
Times are estimates: 130 words per minute, 3 min per animation, 1.5 min per question.
MOST FREQUENTLY ASKED IN THIS CHAPTER
22.1 Lymphoscintigraphy Technique (Tc-99m Nanocolloid)14 questions
Basic Principles
Lymphoscintigraphy is a nuclear medicine method used to image lymphatic drainage pathways and regional lymph nodes. Its main purpose is to identify the first lymph node reached by lymphatic drainage from the primary tumour (sentinel lymph node – SLN).
Sentinel Lymph Node (SLN) Concept:
→ The first lymph node reached by lymphatic drainage from the primary tumour.
→ More distal lymph nodes are very probably also negative → unnecessary radical lymph node dissection can be avoided → morbidity falls.
Left: radiocolloid particles entering lymphatic capillaries from the injection site, carried by two channels to two SLNs, retained by macrophages, with unretained particles passing to 2nd echelon nodes. Right: activity distribution, and the size range of the selected radiopharmaceutical with injection-site, SLN and 2nd echelon curves over time.
The SLN is the first node reached by each lymphatic channel; smaller particles travel faster but are retained less, and the ideal size is 10-100 nm.
Source: concept and size ranges from book 22.1-22.2; lymphatic capillary and node anatomy OpenStax A&P 2e §21.1, StatPearls; macrophage phagocytosis Bergqvist et al., J Nucl Med 2001. Kinetic values representative.
How to use: a single click on the drawing pauses and resumes; in the second step ↑ ↓ or the buttons below change the radiopharmaceutical (particle size); ← → change steps.
Figure 22.1: Sentinel lymph node concept: the node first reached by each lymphatic channel is an SLN; subsequent nodes are considered 2nd echelon (schematic).
Radiopharmaceuticals
Tc-99m Labelled Colloids:
For the radiopharmaceuticals used in lymphoscintigraphy, lymphatic transport rate and lymph node retention vary with particle size.
| Radiopharmaceutical | Particle Size | Feature | Region of Use |
|---|---|---|---|
| Tc-99m Sulphur Colloid (unfiltered) | 100-1000 nm | Large particle → slow transport, good retention | Common in the USA |
| Tc-99m Sulphur Colloid (filtered) | 15-50 nm (0.1 μm filter) or 50-220 nm (0.22 μm filter) | Reduced by filtration → faster transport | SLN mapping in the USA |
| Tc-99m Nanocolloid (Nanocoll) | 5-80 nm (mean ~20 nm) | Small particle → fast transport | Common in Europe |
| Tc-99m Tilmanocept (Lymphoseek) | ~7 nm (molecular) | Binds the mannose receptor (CD206) | FDA approved, fast and specific |
| Tc-99m Antimony Trisulphide | 3-30 nm | Very small → very fast transport | Australia, Canada |
| Tc-99m Rhenium Sulphide | 50-200 nm | Medium size | Europe (some countries) |
| Tc-99m Phytate | Variable | Also used for liver/spleen scintigraphy | Some Asian countries |
Particle Size and Clinical Significance:
→ Lymphatic transport becomes faster but SLN retention falls (more pass-through to 2nd echelon nodes).
→ Transport slows but retention increases.
→ Specific binding to the mannose receptor (CD206) → fast transport + high retention → receptor-based mechanism (not passive filtration).
Left: radiocolloid particles entering lymphatic capillaries from the injection site, carried by two channels to two SLNs, retained by macrophages, with unretained particles passing to 2nd echelon nodes. Right: activity distribution, and the size range of the selected radiopharmaceutical with injection-site, SLN and 2nd echelon curves over time.
The SLN is the first node reached by each lymphatic channel; smaller particles travel faster but are retained less, and the ideal size is 10-100 nm.
Source: concept and size ranges from book 22.1-22.2; lymphatic capillary and node anatomy OpenStax A&P 2e §21.1, StatPearls; macrophage phagocytosis Bergqvist et al., J Nucl Med 2001. Kinetic values representative.
How to use: a single click on the drawing pauses and resumes; in the second step ↑ ↓ or the buttons below change the radiopharmaceutical (particle size); ← → change steps.
Figure 22.2: Particle size ranges of lymphoscintigraphy radiopharmaceuticals and the transport–retention balance.
Tc-99m Tilmanocept (Lymphoseek)
Injection Techniques
Breast Cancer:
Melanoma:
→ All breast quadrants drain to the subareolar plexus → independent of tumour location → technically easy, with a high SLN detection rate.
→ The radiopharmaceutical may be trapped within the tumour → lymphatic transport falls → the SLN may not be detected.
Figure 22.3: Injection techniques in breast cancer: subareolar, peritumoral, intradermal and subdermal injection sites (schematic).
Imaging Protocol
Dynamic Imaging:
Static Imaging:
SPECT/CT:
Skin Marking:
Imaging Findings
Normal Lymphoscintigraphy:
SLN Identification Criteria:
Unexpected Drainage Patterns:
EANM Interpretation Criteria:
→ Inform the surgeon → internal mammary SLN biopsy is discussed (technically difficult, clinical significance debated).
→ The drainage pattern is unpredictable → drainage to more than one basin is possible → without lymphoscintigraphy it is impossible to know which basin to biopsy.
22.2 Sentinel Lymph Node Biopsy (Breast, Melanoma)21 questions
SLN Biopsy in Breast Cancer
Indications:
Contraindications:
Dual-Tracer Technique:
The highest detection rate in SLN biopsy is achieved with the combination of radiocolloid + blue dye.
Side Effects of Blue Dye:
→ Artefact → blue dye affects light absorption → not true hypoxia.
→ Risk of serotonin syndrome → contraindicated.
ACOSOG Z0011 Trial:
Management According to SLN Biopsy Results:
| SLN Status | Management |
|---|---|
| SLN negative | No ALND needed → follow-up |
| SLN micrometastasis (0.2-2 mm) | ALND usually not needed |
| SLN macrometastasis (>2 mm), 1-2 nodes | ALND may not be needed if ACOSOG Z0011 criteria are met |
| SLN macrometastasis, ≥3 nodes | ALND recommended |
| SLN isolated tumour cells (<0.2 mm) | No ALND needed |
SLN Biopsy in Melanoma
Indications:
Importance of SLN Biopsy in Melanoma:
Critical Role of Lymphoscintigraphy in Melanoma:
Injection and Imaging in Melanoma:
→ ≥0.8 mm (or <0.8 mm + adverse prognostic factors).
→ CLND vs observation in SLN-positive melanoma → no difference in melanoma-specific survival → ultrasound surveillance may be preferred to CLND.
Figure 22.4: Unpredictable drainage to multiple basins and an in-transit node in truncal melanoma (schematic).
SLN Biopsy in Other Tumours
Vulvar Cancer:
Cervical Cancer:
Head and Neck Cancer (Oral Cavity):
Merkel Cell Carcinoma:
Endometrial Cancer:
Penile Cancer:
EANM Injection Techniques (Other Tumours):
22.3 Assessment of Lymphoedema8 questions
Assessment of Lymphoedema with Lymphoscintigraphy
Lymphoedema is accumulation of interstitial fluid due to insufficiency of the lymphatic system. Lymphoscintigraphy is the gold-standard imaging method for assessing lymphatic function.
Indications:
Technique:
Normal Findings:
Pathological Findings:
| Finding | Meaning |
|---|---|
| Delayed transport | Prolonged transit time of lymphatic channels |
| Asymmetric lymph node uptake | Unilateral lymphatic obstruction |
| Dermal backflow | Lymphatic obstruction → retrograde flow into dermal lymphatics → most specific finding |
| No lymphatic channels seen | Severe lymphatic damage/aplasia |
| Reduced/absent lymph node uptake | Lymph node damage or surgical removal |
| Collateral lymphatic channels | Alternative routes bypassing the obstruction |
| Absence of liver uptake | Severe lymphatic insufficiency |
→ Dermal backflow → because of lymphatic obstruction the radiocolloid spreads retrogradely into dermal lymphatics → diffuse, reticular pattern.
→ Normal lymphatic drainage → lymph has reached the venous system → taken up by the hepatic RES.
Primary vs Secondary Lymphoedema
Primary Lymphoedema:
Secondary Lymphoedema:
Figure 22.5: Normal, secondary lymphoedema (dermal backflow) and primary lymphoedema (aplasia) patterns on lower limb lymphoscintigraphy (schematic).
Quantitative Lymphoscintigraphy
EANM Semi-Quantitative Lymphoscintigraphy (Lower Limb):
22.4 Use of the Gamma Probe11 questions
Gamma Probe (Handheld Detector)
Definition and Structure:
The gamma probe is a handheld, portable radiation detector used intraoperatively to detect radiolabelled tissues (especially the SLN).
Components:
Left: a section of the gamma probe (crystal, shield, light detector, readout), scanning over the skin, and ex vivo node counting. Right: detector comparison, count profiles by position for narrow and wide collimation, and node counts with the 10% threshold.
Narrow collimation and side shielding give the probe its directional sensitivity; every node with ≥10% of the highest ex vivo count is an SLN.
Source: probe structure, detector comparison and the 10% rule from book 22.5; ex vivo counts are the book's example values. Scanning curves from a representative angular response model.
How to use: a single click on the drawing pauses and resumes; ↑ ↓ or the buttons below change the detector crystal in the first step and the acceptance angle in the second; ← → change steps.
Figure 22.6: Gamma probe structure and the effect of collimation angle on directional sensitivity (schematic).
Detector Types:
| Detector | Advantage | Disadvantage |
|---|---|---|
| NaI(Tl) | High sensitivity, widespread | Large size, affected by moisture |
| CsI(Tl) | Compact, robust | Moderate energy resolution |
| CZT | Excellent energy resolution, compact, works at room temperature | High cost |
Intraoperative SLN Detection
Technique:
1. SLN location is determined by preoperative lymphoscintigraphy 2. In the operating theatre the SLN position is confirmed through the skin with the gamma probe 3. Incision is made → the probe guides towards the SLN 4. "Hot spot" → the point with the highest count rate 5. The SLN is removed → ex vivo counting is performed (confirming it is the SLN) 6. Residual activity check → activity remaining in the SLN bed is measured
SLN Acceptance Criteria (10% Rule):
→ 10% rule → all nodes with counts ≥10% of the highest count are accepted as SLNs.
→ To confirm that the removed node is truly an SLN + to check residual activity in the SLN bed.
Left: a section of the gamma probe (crystal, shield, light detector, readout), scanning over the skin, and ex vivo node counting. Right: detector comparison, count profiles by position for narrow and wide collimation, and node counts with the 10% threshold.
Narrow collimation and side shielding give the probe its directional sensitivity; every node with ≥10% of the highest ex vivo count is an SLN.
Source: probe structure, detector comparison and the 10% rule from book 22.5; ex vivo counts are the book's example values. Scanning curves from a representative angular response model.
How to use: a single click on the drawing pauses and resumes; ↑ ↓ or the buttons below change the detector crystal in the first step and the acceptance angle in the second; ← → change steps.
Figure 22.7: 10% rule: nodes giving ≥10% of the highest ex vivo count are accepted as SLNs (example values).
Shine-Through Artefact
Figure 22.8: Shine-through artefact and its solutions: masking with a lead shield and delayed imaging (schematic).
Radioguided Surgery with the Gamma Probe – Other Applications
Radioguided Occult Lesion Localisation (ROLL):
SNOLL (Sentinel Node and Occult Lesion Localisation):
Radioguided Parathyroidectomy:
Radioguided Seed Localisation (RSL):
→ Radioguided Occult Lesion Localisation → marking non-palpable breast lesions with a radioactive agent and removing them under gamma probe guidance.
→ Combination of ROLL + SLN biopsy in a single session.
→ I-125 (low energy, long half-life).
Gamma Probe Quality Control
Daily Checks:
Performance Parameters:
Optical Imaging and Hybrid Tracer-Guided Surgery
Key Points for the Board
SLN Concept:
Radiopharmaceuticals – Particle Size:
Injection Techniques:
Blue Dye Key Points:
Landmark Trials:
Melanoma SLN Biopsy:
Intraoperative Rules:
Shine-Through Artefact:
Lymphoedema Lymphoscintigraphy:
Radioguided Surgery Techniques:
Gamma Probe Detectors:
SLN Biopsy – Other Tumours:
Additional Notes from EANM Guidelines:
Current guidelines on this chapter's topics
The latest guidelines and consensus documents on the procedures covered in this chapter (official EANM index and primary sources, November 2026). Comparison of the text with these versions is in progress; consult the guideline itself for details.
- 2018The EANM practical guidelines for sentinel lymph node localisation in oral cavity squamous cell carcinoma (opens in a new tab)
- 2015EANM practice guidelines for lymphoscintigraphy and sentinel lymph node biopsy in melanoma (opens in a new tab)
- 2013EANM/SNMMI practice guideline for lymphoscintigraphy and sentinel node localization in breast cancer (opens in a new tab)
- 2013The EANM clinical and technical guidelines for lymphoscintigraphy and sentinel node localization in gynaecological cancers (opens in a new tab)
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