What is the preferred method of injection, intradermal or subdermal, for sentinel lymph node dissection in patients, particularly those with a history of cancer such as breast cancer or melanoma?

Intradermal Injection is Superior to Subdermal Injection for Sentinel Lymph Node Mapping

For sentinel lymph node biopsy in breast cancer and melanoma, intradermal injection of radiotracer is the preferred technique over subdermal injection, offering significantly higher detection rates (100% vs 92.7%), superior lymphoscintigraphy visualization (96.7% vs 37%), and higher sentinel node-to-background radiotracer ratios (193:1 vs 41:1), while maintaining equivalent false-negative rates. 1, 2

Evidence-Based Rationale

Detection Performance

• Intradermal injection achieves near-perfect sentinel node identification (99.4-100% success rate) compared to subdermal injection (92.5-92.7% success rate), representing a statistically significant improvement (p=0.048). 1, 2

• The higher radiotracer uptake with intradermal injection creates a more favorable signal-to-noise ratio, facilitating intraoperative identification with gamma probe guidance. 2

• Lymphoscintigraphy visualization is dramatically superior with intradermal technique (96.7% vs 37%), which is critical for preoperative surgical planning and identifying aberrant drainage patterns. 1

Safety and Accuracy Profile

• False-negative rates remain acceptably low and equivalent between both techniques (≤5-10%), meeting the threshold established by ASCO guidelines for sentinel node biopsy in early-stage breast cancer. 3, 2

• Both intradermal and subdermal approaches successfully identify all sentinel nodes harboring metastatic disease when dual-tracer technique (radiocolloid plus blue dye) is employed. 4

Technical Considerations by Cancer Type

Breast Cancer

• The National Comprehensive Cancer Network acknowledges multiple acceptable injection routes (peritumoral, subareolar, or subdermal), but emphasizes that only peritumoral injections reliably map to internal mammary lymph nodes when this information is clinically relevant. 3

• Subareolar and intradermal injections exploit the shared lymphatic pathways between subdermal and intraparenchymal breast lymphatics, with 87% concordance between techniques. 4

• For multicentric breast tumors, intradermal or subareolar injection is specifically advantageous because it identifies the sentinel node(s) draining the entire breast rather than a single tumor focus. 3

Melanoma and Oral/Oropharyngeal Cancers

• The European Association of Nuclear Medicine established intradermal injection as the foundational technique when Morton et al. first described sentinel node mapping for melanoma in 1992, followed by peritumoral intradermal radiotracer injection by Alex et al. in 1993. 3

• For oral cavity and oropharyngeal squamous cell carcinoma, the European Association of Nuclear Medicine emphasizes that sentinel nodes need not be anatomically closest to the tumor, and multiple sentinel nodes may drain a single primary tumor—a pattern best identified through intradermal injection with preoperative lymphoscintigraphy. 5

Critical Pitfalls to Avoid

• Do not use subdermal injection when internal mammary node mapping is required—only peritumoral injection provides reliable drainage visualization to internal mammary basins in breast cancer. 3

• Avoid intradermal injection in patients with gross lymphatic involvement or clinically positive nodes, as distorted lymphatic architecture leads to aberrant drainage patterns and false sentinel node identification. 5

• For hypopharynx and supraglottic larynx tumors, the close proximity of primary tumor to first-echelon nodes creates "shine-through" effects that obscure true sentinel node location regardless of injection technique—sentinel node biopsy remains investigational for these subsites. 5

Practical Implementation Algorithm

For standard breast cancer and melanoma cases:

• Use intradermal radiotracer injection (preferred) combined with peritumoral blue dye injection for optimal dual-tracer identification. 1, 2
• Inject 0.5-1.0 mCi of Tc-99m radiocolloid intradermally over the tumor site or periareolar region 2-4 hours before surgery. 1
• Perform preoperative lymphoscintigraphy to confirm sentinel node visualization and identify drainage patterns. 1

For breast cancer requiring internal mammary assessment:

• Switch to peritumoral injection technique specifically to map internal mammary drainage. 3

For multicentric breast tumors:

• Use subareolar or intradermal injection to identify sentinel nodes draining the entire breast. 3