Is the retropharyngeal lymph node the first echelon node for carcinoma tonsil? Prospective evaluation and literature review

Abstract

Tonsil cancer being predominantly treated by non-surgical means, there is a paucity of data on lymph nodal drainage pathways and histo-pathologically confirmed metastatic rates. This study assesses the retropharyngeal lymph node (RPLN) in N0 squamous cell carcinoma tonsil as a possible first echelon node and a site for occult metastasis. Prospective study involving treatment naïve N0 carcinoma tonsil treated by primary surgery and adjuvant treatment from June 2017 to March 2019. In-vivo lymph nodal drainage patterns were assessed by sentinel node mapping by preoperative SPECT-CT and intra-operative hand-held Gamma probe. All patients had a subsequent Level I–III/IV sampling neck dissection supplemented with RPLN dissection. Histological evaluation of sentinel nodes and RPLN involved step-serial sectioning and pan-cytokeratin immunohistochemistry. A comprehensive literature review was performed with keywords “retropharyngeal lymph node”, “oropharynx”, “tonsil”, “squamous cell carcinoma” to determine the incidence of RPLN positivity in previously published series. Sentinel node was successfully identified by SPECT-CT in all 17 patients (ipsilateral level 2a-13/17, 2b-1/17, 3-1/17; bilateral 2a-1/17; isolated contralateral retropharyngeal node-1/17). 8/17 had occult neck metastasis. In no patient was an ipsilateral RPLN identified as the sentinel node. Histological sampling did not indicate metastatic tumor in the RPLN in any patient (0/17). A systematic literature review further confirmed that RPLN metastasis in oropharyngeal cancer is noted only in the presence of pN\u2009+\u2009disease at other neck levels, and isolated RPLN metastasis is extremely rare (1.2%). The ipsilateral RPLN is not identified either as the first echelon node or as a site of occult metastatic disease in N0 tonsil cancer. CTRI/2019/06/019551.