Lymphoma is a cancer primarily of the lymph nodes and there are two main types - Hodgkin's disease and Non-Hodgkin's disease. Hodgkin's rarely involves the thyroid but non-Hodgkin's disease accounts for 3% of all thyroid cancers.Primary thyroidNon-Hodgkin lymphoma(PTNHL)typically occurs in older aged women.Unlike the more common causes of thyroid cancer, radiation is not a factor in the disease. Longstanding Hashimoto's thyroiditis is a common predisposing cause.There are 3common types ofPTHNL .These are a marginal zone B-cell lymphoma type of mucosa associated lymphoid tissue(MALTOMA), a diffuse large B-cell lymphoma type(DLBL) and a mixed type (MZL-DLBL). The MZL type is composed of mainly small lymphoid cells with interspersed large lymphoid cells while the DLBL type has just large lymphoid cells.
The diagnosis is not difficult when large highly atypical lymphoid cells are seen. The main diagnostic problem is when the lesion consists solely of small lymphoid cells.In such circumstances the identification as lymphoma and not as Hashimoto's thyroditis is near impossible without special staining methods(immunocytochemistry).