Introduction

Breast cancer remains the most common malignancy affecting women worldwide, representing a major health concern due to its prevalence and associated morbidity and mortality. Early diagnosis, accurate staging, and precise treatment planning are critical components of successful breast cancer management. Central to these aspects is the evaluation of axillary lymph nodes, particularly the sentinel lymph node (SLN), which is the first node in the axillary basin receiving lymphatic drainage from a primary breast tumor. Traditionally assessed through invasive surgical procedures, the incorporation of ultrasound imaging has revolutionized sentinel lymph node evaluation, significantly impacting diagnostic accuracy and treatment strategies.

Breast Cancer Overview and Sentinel Lymph Node Concept

Breast cancer diagnosis involves determining tumor characteristics, histologic subtype, and, critically, axillary lymph node involvement. The presence or absence of metastatic disease in axillary lymph nodes substantially influences prognosis and treatment decisions, highlighting the sentinel lymph node concept:

-Sentinel Lymph Node (SLN): Defined as the first node to receive lymphatic drainage from a primary tumor, acting as a representative marker for the presence of regional metastasis.
-Identification and evaluation of SLN are crucial for staging, prognosis estimation, and therapeutic planning.

Traditional Methods for Sentinel Lymph Node Assessment

Historically, SLN evaluation involved surgical lymph node biopsy with radioactive tracers (Tc-99m labeled sulfur colloid) and blue dye injections. The main limitations of these methods include:

-Invasive nature: Surgical risks, such as infection, lymphedema, seroma formation, and nerve injury.
-Limited preoperative information: No pre-surgical imaging data available to inform intraoperative decision-making.
-Procedure-related morbidity: Higher rates of complications associated with traditional axillary lymph node dissection.

Role of Ultrasound in Sentinel Lymph Node Evaluation

Ultrasound imaging has emerged as a valuable adjunct or alternative to traditional sentinel node biopsies. Its advantages include:

Technique and Protocol

-High-frequency ultrasound probes (7.5–15 MHz) used for enhanced spatial resolution.
-Standardized protocol involves systematic scanning of axillary lymph nodes, noting node morphology, cortical thickness, vascularity, and echogenicity.
-Ultrasound-guided fine-needle aspiration biopsy (FNAB) or core biopsy performed if nodes appear suspicious.

Diagnostic Criteria for Sentinel Lymph Node Involvement on Ultrasound

-Morphological changes: Enlarged nodes, loss of normal fatty hilum, rounded rather than oval shape.
-Cortical thickness: Nodes with cortical thickness >3 mm typically warrant biopsy due to high likelihood of malignancy.
-Abnormal vascularization patterns detected via Doppler imaging, indicative of metastatic involvement.

Clinical Accuracy and Diagnostic Performance. Multiple studies have demonstrated ultrasound’s effectiveness:

-Sensitivity: ranges from 50–87%.
-Specificity: consistently above 80–95%.
-Negative predictive value (NPV): crucially high, facilitating avoidance of unnecessary axillary surgery in clinically negative cases.

Clinical Impact and Advantages of Ultrasound-based SLN Assessment. Ultrasound in SLN evaluation offers multiple clinical advantages:

Reduced Invasiveness and Improved Patient Outcomes

-Preoperative identification and biopsy allow selective surgical approaches.
-Decreased need for extensive lymph node dissection, lowering morbidity (lymphedema, chronic pain, reduced arm function).

Enhanced Preoperative Treatment Planning.

-Accurate detection of metastatic nodes preoperatively can lead to tailored therapeutic decisions, including neoadjuvant chemotherapy regimens.
-Allows surgeons to optimize surgical approaches, minimizing unnecessary procedures.

Cost-Effectiveness and Healthcare Efficiency

-Reduction in surgical biopsies and shorter hospitalization times significantly lower healthcare costs.
-Streamlined clinical workflow, improving patient management efficiency.

Ultrasound Limitations and Complementary Modalities

Despite its clinical advantages, ultrasound evaluation has inherent limitations:

Operator Dependency

-Diagnostic accuracy heavily depends on operator expertise and experience.
-Variability in interpretation may affect reproducibility.

Limited Visualization in Certain Patient Populations

-Reduced accuracy in obese patients due to imaging depth limitations.
-Limited performance in assessing deeper or medially located lymph nodes.

Complementary Modalities

-MRI and contrast-enhanced ultrasound (CEUS) may supplement traditional ultrasound to improve accuracy.
-Combined imaging approaches may increase detection rates of occult metastases.

Emerging Technologies and Future Directions

Contrast-Enhanced Ultrasound (CEUS)

-Microbubble contrast agents enhance nodal characterization.
-Early studies suggest increased sensitivity in identifying metastatic lymph nodes compared to traditional ultrasound.

Elastography Ultrasound

-Evaluates tissue stiffness, potentially differentiating metastatic from benign lymph nodes due to increased tissue stiffness in malignancy.
-Promising early evidence supports its use as a complementary diagnostic technique.

Artificial Intelligence (AI) Integration

-Machine learning algorithms applied to ultrasound images, providing automated, objective interpretation of sentinel lymph node status.
-Potential to mitigate variability due to operator experience, enhancing diagnostic consistency.

Clinical Guidelines and Recommendations

Current major oncology guidelines (ASCO, NCCN, ESMO) support ultrasound evaluation as part of standard clinical practice for breast cancer staging:

-Recommended initial imaging modality for patients presenting with breast cancer, particularly for axillary staging.
-Suggest complementary use of FNAB or core biopsy for ultrasound-detected suspicious nodes.

May 2025