Primary thyroid lymphoma: CT findings of a rare malignant tumor with pathologic correlations

Background: To investigate the CT features of primary thyroid lymphoma (PTL). Methods: Clinical features and CT findings of 35 PTL cases were retrospectively analyzed. This series included 24 females (68.6%) and 11 males (31.4%). The median age was 65 years (range: 23-84 years). PTL cases were divided into type-1A (single nodule), type-1B (multiple nodules), and type-2 (diffused type). The clinical and imaging characteristics of PTL were assessed. Results: All cases were Non-Hodgkin lymphoma (NHL). Hashimoto's thyroiditis was verified pathologically in 23 patients. Two cases were type-1A, two cases were type-1B, and 31 cases were type-2. Type-1 PTL presented as one or multiple well defined nodules without calcification and necrosis, with homogeneous iso- or slightly low-attenuation relative to the sternocleidomastoid muscle on contrast enhanced CT. Type-2 PTL presented as a diffused lesion, also with homogeneous iso- or slightly low-attenuation relative to the sternocleidomastoid muscle, and mostly was enhanced to moderate extent on contrast-enhanced CT. In type-2 cases, calcification and necrosis were detected in four and five patients respectively. Type-1 PTL did not show invasive features, but type-2 PTL tended to invade adjacent structures (n=20, 57.1%). Conclusions: PTL can present as two types based on CT feature. Type-1 appear as a nodule or multiple nodules with homogeneous isodensity to muscle, type-2 tend to be a mass with homogeneous isodensity to muscle, which is likely to demonstrate invasive feature.