The influence of body mass index on the diagnostic performance of pre-operative staging ultrasound in papillary thyroid carcinoma

Objective The aim of this study was to investigate the diagnostic performance of pre-operative staging ultrasound (US) according to body mass index (BMI) in patients with papillary thyroid carcinoma (PTC) Patients and methods This retrospective study included 625 patients with PTC who underwent pre-operative staging US and surgical excision at a referral centre between December 2012 and April 2013. Four experienced radiologists prospectively evaluated the extent of primary tumours, multifocality and the presence of lymph node metastasis. Patients were grouped according to BMI (normal <25; overweight 25 ≤ and <30; obese ≥30, or nonobese <30; obese ≥30 kg/m²). Diagnostic performances of pre-operative staging US (sensitivity, specificity, positive predictive value, negative predictive value and accuracy) were compared according to BMI based on pathologic findings of surgical specimens. Results Pre-operative staging US in the obese group (BMI ≥30 kg/m²) showed a significantly lower negative predictive value and accuracy in the detection of central lymph node metastasis (P = 0·010 and P = 0·025, respectively) than in the nonobese (BMI <30 kg/m²) group. However, there were no significant differences in the diagnostic performance of pre-operative staging US for extrathyroidal extension, bilateral multifocality and lateral lymph node metastasis in analyses using the two (nonobese vs obese) and three BMI (normal vs overweight vs obese) groups, respectively. Conclusion Obesity (BMI ≥30 kg/m²) may affect the pre-operative US staging of central lymph node metastasis in patients with PTC.