Effect of ultrasound transmission gel on ultrasound-guided fine needle aspiration cytological specimens of thyroid

Abstract

To investigate prospectively the diagnostic impact of ultrasound coupling gel on thyroid specimens obtained under ultrasound guidance. Patients presenting for ultrasound-guided fine needle aspiration (USG-FNA) of the thyroid were invited to participate in the study. Four specimens per nodule were collected: two using chlorhexdine wash and two using sterile, colourless ultrasound gel as couplant according to routine protocol. All slides were analysed in a blinded fashion by two senior cytologists for the presence or absence of ultrasound gel-induced artefacts. The presence of gel-induced artefacts between the two groups was analyzed using Pearson's chi-square test. Kappa statistics were used to measure the inter-rater agreement between the cytologists. Twenty thyroid nodules comprising 80 specimen slides were collected. On slides collected with gel, cytological artefacts were detected in 60-65% of cases compared with 10-15% of cases without gel (P<0.001). The inter-rater agreement between the two observers was very good (κ=0.84). Two of the 14 patients required repeat FNA due to non-diagnostic cytology results caused by inadequate sampling and gel-induced artefacts. Clinical cytopathologists, radiologists and sonographers should be aware of the potential for ultrasound gel to cause significant artefacts on cytological specimens. Our findings suggest that staff involved in USG-FNA cytology should remove the gel carefully before taking the aspirate.