IntroductionClinical staging of patients with oral squamous cell carcinoma (OSCC) is crucial for the choice of treatment. Computed tomography (CT) and/or magnetic resonance imaging (MRI) are typically recommended and used for staging of the cervical lymph nodes (LNs). Although ultrasonography (US) is a non-expensive, accessible and non-ionising imaging modality this method is not consistently used.This study aimed to investigate if addition of US of patients classified as clinically LN negative (cN0) by CT and/or MRI, increases the detection of LN metastases. Also, we aimed to identify which of the sonographic characteristics: echogenicity, border, shape, appearance of hilum and nodal blood-flow pattern best detect metastases in this patient group.MethodFifty-one patients with OSCC classified as cN0 by CT/MRI were consecutively included and prospectively examined with US prior to sentinel node biopsy or selective neck dissection. Localisation, size and sonographic characteristics were registered for each LN and compared with the pathological findings. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for different size measurements and sonographic characteristics.ResultsWe found that short axial diameter was the best size criterion for detection of metastases. However, the sonographic characteristics were better predictors than size and the presence at least four of the sonographic characteristics: hypo-echoic or heterogeneous appearance; irregular border; spherical shape; absence of nodal hilum; and peripheral nodal blood-flow resulted in a sensitivity of 43.8; specificity 91.4; PPV 70.0; and NPV 78.0. The number of patients with occult metastases decreased from 16 out of 51 (31%) to nine out of 51 (18%). Three patients (6%) were over-staged by US.ConclusionThe addition of US to the clinical work-up of patients with cN0 OSCC increases the detection of metastases, thus US potentially reduces the number of patients requiring a secondary neck surgery after sentinel node biopsy.