Thyroid lymphoma is a very rare malignant disease and is primarily encountered in elderly individuals, more commonly women, who suffer from Hashimoto's thyroiditis. A rapidly developing mass in the neck, accompanied by fever and constitutional symptoms in some cases, is the typical clinical presentation. Ultrasonography followed by a biopsy of the lesion is necessary to confirm the diagnosis.
Primary thyroid lymphoma (PTL) is very rarely encountered in clinical practice, as it comprises less than 5% of all malignancies that arise from this organ   . Lymphomas that develop in the thyroid are almost always of B-cell origin, the most common being diffuse large B-cell lymphoma (DLBCL) and mucosa-associated lymphoid tissue (MALT) lymphoma, while follicular lymphoma, small lymphocytic lymphoma, Burkitt's lymphoma and Hodgkin's lymphoma are other recognized forms  . PTL is principally diagnosed in the sixth and seventh decades of life, and a significant predilection toward female gender has been established    . Furthermore, a markedly higher number of PTLs are diagnosed in patients with preexisting Hashimoto's thyroiditis, implying its important role in the pathogenesis of PTL    . An enlarging painless mass in the neck, seen in almost 70% of cases, is the main clinical manifestation of PTL, and the mass can compress the adjacent structures in the neck, resulting in dysphagia, dyspnea, stridor, and hoarseness in 30-50% of patients   . In addition, constitutional symptoms of fever, weight loss, and night sweats, which are typical for B-cell lymphomas, may be present as well but are reported in only 10% of individuals  .
Many reports have emphasized the benefit of early recognition of PTL, primarily because therapy is quite effective in its earlier stages    . However, studies have shown that up to 36 months may pass from the onset of symptoms to the diagnosis, which markedly affects survival rates and treatment outcomes     . For this reason, a meticulous clinical workup must be performed in order to obtain enough evidence to raise clinical suspicion toward PTL. Firstly, patients should be asked about the course and progression of symptoms, whereas a detailed physical examination of the neck can result in palpation of a hard and smooth-surfaced mass . If a mass is palpated, immediate employment of imaging techniques, such as ultrasonography (US), is necessary, and a hypoechoic homogeneous mass with an enhanced posterior echoes is highly suggestive of PTL  . Based on US findings, PTL is further divided into nodular (unilateral and pseudocystic changes), diffuse (bilateral and possessing indistinct borders) and mixed, which shows multiple patchy lesions . Because the diagnosis is not conclusive without a histopathological examination, a biopsy of the lesion, most commonly in the form of fine-needle aspiration (although core-incision and open biopsy are mentioned as possible methods as well), is the vital step in workup . Not only does it confirm the diagnosis, but it also helps in determining the stage of the tumor, together with computed tomography (CT) and other imaging modalities     . Based on the extent of tumor involvement and its dissemination, PTL is classified into :