Role of methylene blue dye in sentinel node biopsy in N0 oral cavity squamous cell carcinoma

Presence of neck nodes in cases of head neck squamous cell cancers is an adverse prognostic factor. Elective neck dissection is traditionally recommended along with primary disease resection. Sentinel lymph node (SLN) is the first draining node. Sentinel lymph node biopsy (SNB) is a minimally invasive technique to identify occult nodal metastasis in early HNSCC.

The objective of this study is to determine the identification rate of SNB using methylene blue dye (MBD) in N0 neck of Oral Squamous cell carcinoma (OSCC) and estimating specificity, sensitivity, negative predictive value and positive predictive value of SNB with frozen section (FS) analysis and in comparison to post-operative histopathological examination (HPE). It is a cross-sectional study conducted at a tertiary care centre, Lucknow, India. 21 patients of N0 OSCC from January 2019 to May 2020, were included. All patients underwent peritumoral injection with MBD. Sentinel nodes were harvested and sent for FS. Depending on FS findings, appropriate neck dissection was performed.

SLN was identified at level Ib and II in 19 patients (90.47%). The sensitivity, specificity, PPV and NPV in identifying SLN using MBD versus FS were 100.00%, 11.11%, 15.79% and 100.00% respectively. Whereas, SLN using MBD versus HPE specimens were 100.00%, 10.52%, 10.52% and 100.00% respectively.

Despite having 100% sensitivity, MBD alone has poor specificity. With this poor discriminatory power, it is unlikely to be employed as a diagnostic test alone. It is recommended to rely on per-operative FS for taking decision as far as extent of neck dissection in N0 neck is concerned.