Introduction
Sentinel lymph node biopsy (SLNB) is primarily used in the head and neck for malignant melanoma and squamous cell carcinoma (SCC) of the oral cavity. The technique is employed to help the surgeon understand the pathologic status of a clinically N0 neck. Multiple prospective randomized trials for melanoma have failed to demonstrate a survival benefit for elective neck dissection in the N0 patient. Similarly, no clear survival benefit exists for patients with SCC. Nevertheless, cervical metastasis remains the most important prognostic factor in patients with cancer of the head and neck. As the thickness of the primary cancer increases, so does the risk for cervical metastasis. Traditionally, patients with primary lesions felt to have a more than 20% risk of nodal metastasis would undergo an elective neck dissection. Lesions of lower risk could employ a “watchful waiting” approach. In this lower risk group, SLNB provides a minimally invasive technique to help surgeons better understand the status of the neck while sparing these patients the morbidity of an elective neck dissection. If the SLNB reveals lymph node metastasis, a selective neck dissection is subsequently performed clearing the neck levels at greatest risk for metastasis.
The most important randomized control trial examining malignant melanoma was the 2006 Multicenter Selective Lymphadenectomy Trial (MSLT-1), which was updated again in 2014. MSLT-1 failed to establish a survival benefit for intermediate-risk patients stratified to observation versus SLNB with immediate lymphadenectomy for positive nodes. This lack of survival benefit emphasizes the point that the purpose of the SLNB is to deliver prognostic information, provide regional control, and guide additional therapy. From this perspective, SLNB is extremely effective since the most important prognostic factor in survival from melanoma is the status of the sentinel node, and SLNB has a negative predictive value of 96%.
Similar to melanoma, neck dissection for oral cavity SCC (OCSCCa) has no proven survival benefit. SLNB is useful when the indication to perform elective neck dissection is unclear. The largest study concerning this group is the American College of Surgeons Oncology Group (ACOSOG) study from 2010 which also revealed a negative predictive value of 94% to 96% for T1 to T2 lesions after examining 106 SLNBs. Of note, lesions less than 6 mm were excluded.
The use of SLNB is also being examined in other cutaneous malignancies (i.e., SCC and Merkel cell carcinoma) in addition to other sites in the upper aerodigestive tract (i.e., nasopharynx, oropharynx, and larynx). At this point, the evidence supporting these techniques is still being collected. Similarly, SLNB is being used to determine whether a cancer approaching the midline has unilateral or bilateral drainage pathways to help inform the extent of the neck dissection. Some investigators are also studying SLNB’s utility in predicting lymphatic drainage in patients with recurrent cancer. These are areas of active research. We will therefore focus on primary malignant melanoma and oral cavity SCC for the remainder of the chapter.
Key Operative Learning Points
- 1.
SLNB should only be offered to patients who have a clinically N0 neck with malignant melanoma of the head and neck stage 1b or greater.
- 2.
SLNB can also be used for patients who have OCSCCa with T1 to T2 lesions who are clinically N0.
- 3.
SLNB provides prognostic information and determines the need for additional neck dissection and potentially adjuvant therapy.
- 4.
SLNB has approximately 96% negative predictive value in both melanoma and oral cavity SCC.
- 5.
Patients who undergo subsequent neck dissection for a positive SLNB have no benefit in overall survival but benefit from reduced regional recurrence.
- 6.
Sentinel lymph nodes are removed until the remaining count on the gamma probe has reduced 90% from the original value.
- 7.
Thinner sectioning of the sentinel lymph node (SLN) and immunohistochemical testing for cancer markers differentiate this technique from routine lymph node evaluation. Immunohistochemistry (IHC) for S-100 and melan-A (MART-1) are used for melanoma and cytokeratin used for SCCa.
- 8.
Patients should be counseled on the possible need to undergo two operations.
- 9.
Optimal injection requires a comfortable patient, especially for oral cavity lesions.
- 10.
Avoid injection of local anesthetic in the immediate vicinity of the tumor.
- 11.
Accurate injection of radiocolloid into the dermal lymphatics is crucial.
- 12.
Avoid “shine through” artifact by properly injecting the primary tumor, resecting the primary tumor first, and creating adequate exposure to direct the gamma probe at the lymph nodes but away from the primary site.
Preoperative PERIOD
History
- 1.
All patients with cancer of the head and neck should undergo a complete history and physical examination.
- 2.
Patients with malignant melanoma will typically describe a cutaneous lesion that is changing in size, shape, or color. The lesion can also be pruritic, while at later stages it may bleed and become painful. A history of sun exposure, sunburns, prior skin biopsies, prior skin cancers, occupation, and family history also should be sought.
- 3.
Patients with OCSCCa will typically report a lesion in the mouth that has persisted or is slowly growing over time. The lesion can become painful and cause bleeding. A history of dysarthria, dysphagia, odynophagia, ill-fitting dentures, and weight loss should be sought. Importantly, tobacco (smoking and chewing) and alcohol use should be discussed.
Physical Examination
- 1.
Primary malignant melanoma should be evaluated for the “ABCDE” checklist. Lesions of concern are a symmetric, have b order irregularity, c olor variation, and a d iameter of greater than 6 mm, and be e volving over time.
- 2.
Patients with malignant melanoma require a full body cutaneous examination searching for second primary lesions. Great care must be taken when examining the patient’s scalp as hair can make identifying additional lesions difficult.
- 3.
The pinna should be carefully examined along with palpation of the parotid gland and neck.
- 4.
Evaluation of facial nerve function is important for primary cancers at risk of draining to the parotid lymph node basin.
- 5.
For OCSCCa, complete evaluation of the upper aerodigestive tract mucosa is imperative, including flexible fiberoptic laryngoscopy, as many patients will be at risk for second primary lesions given the high incidence of smoking and alcohol use in this patient population.
- 6.
Palpation of the primary lesion can give a sense of the depth of the cancer. For a lesion of the tongue, one should assess mobility. Additionally, attention should be paid to the function of the mental, lingual, and hypoglossal nerves.
- 7.
Oral opening should also be assessed, as trismus is not only indicative of invasion into the pterygoid muscles but also makes performing injection of the radiotracer into the primary difficult.
- 8.
All patients should have their neck palpated to search for cervical lymph node metastasis.
Imaging
- 1.
Patients with malignant melanoma and SCC of the head and neck will undergo a computed tomography (CT) scan of the neck with contrast to evaluate for cervical lymph node metastasis. The CT scan will also give information on the degree of invasion for larger primary cancers.
- 2.
The metastatic evaluation for malignant melanoma and SCC is dictated by the stage of the primary tumor. Patients who are candidates for SLNB are clinically N0. Stage 1 patients do not require any chest imaging. Stage 2 and 3 patients should undergo optional chest imaging.
- 3.
Chest radiograph is preferred for melanoma, and chest CT scan should be considered with OCSCCa patients with a prior history of smoking. Lastly, patients who have stage 3 melanoma can get an optional lactate dehydrogenase level.
- 4.
Lymphoscintigraphy during the SLNB procedure will be discussed below.
Indications
- 1.
For malignant melanoma, SLNB has proven to be the most sensitive and specific tool for identification of occult cervical metastasis with a negative predictive value of approximately 96%.
- 2.
SLNB is currently recommended for all patients with melanoma with a primary tumor that is >1 mm thick and a clinically N0 neck.
- 3.
The National Comprehensive Cancer Network (NCCN) additionally recommends offering SLNB to stage 1b patients (≤1 mm thick with ulceration or mitotic rate ≥1 per mm 2 ).
- 4.
The NCCN notes that one can consider a SLNB in T1a patients (tumor <1 mm without ulceration and low mitotic rate) with other negative prognostic factors like young age, angiolymphatic invasion, or deep positive margins.
- 5.
For OCSCCa, the indications are slightly less clear. Traditionally, most cancers of the oral cavity would warrant an elective neck dissection. Patients with only superficially invasive lesions might have their neck observed.
- 6.
The ideal lesion for SLNB is a T1 to T2 with intermediate thickness (2–4 mm). Cancers with invasion into deeper structures are better served with elective neck dissection.
Contraindications
- 1.
SLNB is only offered to patients who are clinically N0. Therefore, the presence of clinically positive lymphadenopathy is an absolute contraindication to the procedure.
- 2.
OCSCCa with advanced-stage primary cancer (T3 to T4 lesions) carries a high enough risk of occult lymph node metastasis that elective neck dissection is more appropriate than SLNB. Additionally, the patient should have adequate oral opening, and the cancer should be in a location that is easily accessible for injection of the radiotracer.
Preoperative Preparation
- 1.
Clinical staging should be completed, and indications for the procedure must be validated prior to the surgery.
- 2.
Preoperative check must be made to ensure that the required instrumentation is available prior to surgery, especially ensuring coordination with the nuclear medicine team.
Operative Period
Anesthesia
- 1.
SLNB can be performed under monitored anesthesia care (MAC) or general anesthesia.
- 2.
Patients with OCSCCa are better served with general anesthesia, as resection of the primary is easier with the patient intubated.
Perioperative Antibiotic Prophylaxis
- 1.
Antibiotic protocols vary by institution. SLNB is a clean procedure; therefore antibiotic prophylaxis is not required. At our institution, skin flora is routinely covered with Cefazolin.
Positioning
- 1.
The patient is positioned supine with a horizontally oriented shoulder roll.
Monitoring
- 1.
The surgeon can consider the use of facial nerve monitoring for lesions in the parotid gland. We do not routinely use facial nerve monitoring when performing SLNB.
Instruments and Equipment to Have Available
- 1.
Handheld gamma probe
- 2.
Technetium 99 ( 99 T)
- 3.
Methylene blue
Key Anatomic Landmarks
- 1.
Understanding the natural flow of lymph throughout the head and neck is critical for planning surgical interventions. The location of the primary cancer dictates the cervical nodal basins at greatest risk for metastasis. While these relationships are not directly involved with performing an SLNB, they do help surgeons predict the location of the sentinel node and inform the extent of the therapeutic neck dissection, if necessary.
- 2.
The surgeon can draw an imaginary coronal plane through the external auditory canal. For primary cancers of the facial skin, ear, and scalp, lesions arising anterior to this plane typically drain through the parotid lymph nodes then down to jugular lymphatic chain.
- 3.
More inferiorly and anteriorly located lesions (i.e., the chin) can drain through the facial and submandibular lymph nodes, avoiding the parotid.
- 4.
Lesions posterior to this coronal plan will drain to the postauricular, occipital, and posterior triangle lymphatics.
- 5.
Surgeons should be comfortable performing the resection and reconstruction of cutaneous lesions in anatomically high-risk areas (i.e., near the lips and eyelids).
- 6.
For OCSCCa, the lymphatics at greatest risk are the facial, submental, and submandibular lymph nodes, which then drain to the jugular chain.
- 7.
Understanding the surgical anatomy of the parotid and neck is critical to avoiding morbidity when performing SLNB. Approximately 25% to 30% of head and neck melanomas drain through the parotid bed.
- 8.
When sentinel lymph nodes are detected in the parotid, the surgeon can safely remove the nodes without performing a superficial parotidectomy because these nodes typically lie within the superficial lobe of the gland. However, the surgeon should always be aware of the proximity of the facial nerve and be prepared to perform a superficial parotidectomy if necessary.
- 9.
Facial nerve monitoring can be considered as an adjunct tool in this setting.
- 10.
For sentinel nodes that are present in the neck, great care must be taken to preserve the spinal accessory nerve as well as the other critical neurovascular structures typically saved in a selective neck dissection.
Prerequisite Skills
- 1.
Surgeons should be experienced in performing the resection and reconstruction of cutaneous lesions in anatomically high-risk areas (i.e., near the lips and eyelids).
- 2.
Surgeons should be experienced in performing superficial parotidectomy with preservation of the facial nerve, if required.
- 3.
Surgeons should be experienced in performing the selective neck dissection if the sentinel node is found to be positive.
Operative Risks
- 1.
SLNB is a safe procedure with a complication rate of less than 1%.
- 2.
Injury to the facial nerve and spinal accessory nerve are both potential risks of the procedure depending on the location of the sentinel node.
- 3.
Morbidity from the resection of the primary tumor is also an important consideration. As mentioned previously, the surgeon should feel comfortable with resection and reconstruction of the primary tumor site.
Surgical Technique
- 1.
Effective collaboration with nuclear medicine physicians is essential in performing effective SLNB.
- 2.
Prior to the operating room, the patient is brought to the nuclear medicine suite, and the primary tumor site is injected with radiotracer.
- 3.
Lymphoscintigraphy is subsequently performed, and the first node to which the tracer flows is defined as the sentinel lymph node. This site is marked on the patient’s skin.
- 4.
Lymphoscintigraphy can also be fused with a CT scan for increased spatial localization.
- 5.
The injection typically takes place the morning of the procedure but can also be done the night prior. The ideal time delay is not defined, but we prefer to perform the operation within 4 hours of the injection.
- 6.
99 T is the only available radiocolloid in the United States, but others can be obtained in Europe. 99 T is available in filtered and unfiltered forms. The unfiltered form is preferred, as it does not flow downstream as quickly. While this decreases the likelihood of finding multiple sentinel nodes, it does result in increased “shine through” artifact, which is when residual tracer at the primary site interferes with readings around the nodal basin. “Shine through” artifact is a more pronounced concern with oral cavity lesions than melanoma.
- 7.
The operating room staff is exposed to a minimal amount of radiation during these cases. The dose is sufficiently low to not require any special precautions; however, team members, especially those who may be pregnant, should be notified.
- 8.
Injection of the radiotracer is performed at the primary site in an awake patient. The use of anesthesia with endoscopic guidance is only required for pharyngeal, laryngeal, and sinonasal tumors, which are still under investigation.
- 9.
A narrow needle (25 g) is used to inject 4 to 5 mL of 99 T with a circumferential or four-quadrant technique into the underlying dermis for melanoma ( Fig. 62.1 ).
