Preoperative diagnostic algorithm of primary thyroid lymphoma using ultrasound, aspiration cytology, and flow cytometry.

The aims of this report were to clarify the diagnostic significance of ultrasound (US), fine needle aspiration cytology (FNAC), and flow cytometry for primary thyroid lymphoma, and to establish a preoperative diagnostic algorithm of primary thyroid lymphoma. We retrospectively examined US, FNAC, and flow cytometry in 43 patients with benign lymphoproliferative lesions and 32 patients with primary thyroid lymphoma, who underwent US, FNAC, and flow cytometry at Kuma Hospital between May 2012 and December 2015. Primary thyroid lymphomas included 27 mucosa-associated lymphoid tissue lymphomas, 4 diffuse large B-cell lymphomas, and 1 follicular lymphoma. Flow cytometry had the highest specificity (88.4%) and sensitivity (75.0%). The specificity of US was the lowest (32.6%). Both the positive predictive value (90.5%) and negative predictive value (94.7%) were the highest for FNAC. A scoring system was defined as follows: US, low suspicion 0, intermediate suspicion 1, and high suspicion 2; FNAC, benign 0, undetermined 1, malignant 2; and flow cytometry, 0.33< κ/λ ratio <3 0, κ/λ ratio ≤0.33 2, and κ/λ ratio ≥3 2. We propose that a score ≥4 indicates the need for thyroid resection for diagnosing primary thyroid lymphoma. In such a situation, the case of diffuse large B-cell lymphoma, which was aggressive, was not excluded. Approximately one-fifth of mucosa-associated lymphoid tissue lymphomas may be overlooked, but the patients could be followed up with because of an indolent course.