Sentinel Lymph Node Biopsy in a Young Child With Thick Cutaneous Melanoma

The presence or absence of lymph node metastases is the most significant prognostic factor for survival and recurrence in malignant melanoma. Lymph node disease decreases the 5-year survival by 40% to 50%. The number of metastatic nodes and whether nodal metastases are clinically occult or apparent are independent predictors of survival.[1] Sentinel lymph node (SLN) mapping was developed in the early 1990s as a relatively noninvasive method of staging the draining lymph node basins from primary melanoma. The process helps to select patients who may benefit from a lymph node dissection and systemic therapy. The majority of SLN mapping studies in melanoma have included few children[2,3] and few patients with thick lesions (≥ 4 mm).[4-6] The Bisseck/Shen/ Pranikoff article raises the following questions regarding SLN mapping: What are the success rates and safety of lymphatic mapping in the head and neck region? Is SLN mapping justified in the management of primary melanomas with a tumor thickness ≥ 4 mm? Melanoma in Children
Melanoma in children accounts for 0.3% to 4% of all new cases of melanoma in the United States each year. It rarely occurs before puberty and is responsible for 1% to 3% of pediatric malignancies. Risk factors include the presence of giant congenital nevi, transplacental spread of maternal melanoma, and xeroderma pigmentosa.[7] There is no clear evidence that melanoma is more aggressive in children. Spitz nevi are more common in children than in adults and preferentially involve the head and neck. They may be hard to distinguish from melanoma with Spitz-like features. The biologic behavior of atypical spitzoid melanocytic lesions has not been elucidated. Su et al reported their experience with SLN biopsy in 18 patients with problematic spitzoid melanocytic lesions.[ 8] Of these patients, 11 were less than 18 years of age; 6 of the 11 (54.5%) had SLN metastases and underwent a completion lymphadenectomy. SLN Mapping in Thick Melanomas
The use of SLN mapping and biopsy in the management of thick melanomas (≥4 mm) has been questioned because of the perceived poor prognosis. These lesions are believed to be associated with a high incidence of occult regional and distant metastases.[ 9] No prospective randomized trials have demonstrated a survival benefit for patients with thick melanomas who underwent routine elective lymph node dissection. A recent review by Kim et al of 120 patients with thick melanomas found that nodal status was an independent predictor of survival.[10] Nodal status was found to be the strongest predictor of survival in three recent reviews involving patients with melanomas ≥ 4 mm thick treated by SLN biopsy.[4-6] In the Emory experience of 114 patients with thick melanomas, the 3-year overall survival for SLN-negative patients was 82% and for SLN-positive patients, 57% (P = .006, Figure 1).[4] Head and Neck Melanoma
Most series of lymphatic mapping studies have concentrated on melanomas of the trunk and extremities rather than of the head and neck. The head and neck has a rich and unpredictable lymphatic system, and excisional biopsy in this area can be technically challenging. The region contains over one-third of the body's lymph nodes. O'Brien et al found a 34% discordance between the clinical prediction of lymphatic drainage and the lymphoscintographic findings in 97 cases of head and neck melanoma.[11] In 33% of cases, there was drainage to the lymph nodes within the parotid gland. Several problems are associated with SLN mapping in the head and neck region. Background radiation from the primary injection site can incorporate the SLN, making localization at preoperative lymphoscintigraphy difficult. Lesions on the cheek can obscure parotid drainage, and lesions of the neck can shadow drainage to the internal jugular nodes. Lower doses of radioactivity are used in the head and neck region to compensate for these events. The technetium-99m sulfur(Drug information on sulfur) colloid used for mapping is absorbed by the salivary glands, thus increasing the background radiation in the parotid nodal bed. Sentinel lymph nodes in the parotid gland tend to be small, which makes intraoperative localization more difficult without the use of blue dye. There is also concern that the facial nerve can be injured during the process. Ollila et al reviewed their experience with parotid SLN mapping in 39 patients.[12] The SLNs were successfully identified in 37 patients (94.9%), and one case of temporary facial nerve paresis was reported. Despite these limitations, many authors have reported a high rate of success with SLN mapping in the head and neck region.[13-19] Conclusions
A very small percentage of melanoma cases in the United States occur in children. The indications for SLN mapping in children should be the same as for adult patients. The head and neck region is associated with several limitations to successful SLN mapping, which can be overcome with a knowledgeable nuclear medicine department and surgical experience. The SLN status of patients with thick melanomas (≥ 4 mm) is the strongest predictor of survival and should be determined routinely.