The great majority of primary thyroid lymphomas are B cell lymphomas which are associated with Epstein-Barr Virus (EBV) and Hashimotos thyroiditis [4
]. Extranodal low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) type occurs in the gastrointestinal tract, salivary gland, thyroid, orbit, lung, and breast [6
]. MALT type lymphoma is a distinct subgroup of non-Hodgkins lymphoma with particular clinicopathologic behaviors. This type of lymphoma tends to appear in patients with a history of autoimmune disease or chronic inflammatory disorders. The preceding lymphoid disorders are usually the Sjögrens syndrome, Hashimoto's thyroiditis, and interstitial lymphoid pneumonia in the salivary glands, the thyroid or lung respectively. Lymphoma initially arise from the marginal zone localized around the reactive follicles and secondarily invade epithelial tissue to form the characteristic lymphoepithelial lesion [7
]. Patients with gastrointestinal MALT lymphoma generally present with localized disease. These patients have long survival rates. Recurrences may rarely appear in the same organs or in other extranodal sites. Nongastrointestinal MALT lymphoma patients have also a similar disease characteristics.
The role of surgery in the treatment of stage I non-Hodgkins lymphoma is not well defined . Patients may be treated with surgery or radiotherapy if the disease is localized, or with chemotherapy if it is disseminated . The treatment of thyroid lymphoma usually includes thyroidectomy followed by adjuvant therapy in cases with extrathyroid involvement. Primary thyroid lymphoma should be distinguished from systemic lymphoma with thyroid involvement, a somewhat unusual event .
An important diagnostic finding is the packing of follicular lumen by lymphoid cells, a feature usually not present in thyroiditis. The differential diagnosis includes the small cell variant of medullary carcinoma and insular carcinoma, which may require the use of immunohistochemistry. A very high proportion of the primary thyroid lymphomas arise in a background of lymphocytic or Hashimotos thyroiditis, this association representing the pathogenetic link between immunoproliferative and autoimmune diseases. The tumor is usually restricted to the thyroid, but also may spread to the soft tissues by direct extension, or may involve the regional nodes. The prognosis is better for intrathyroid tumors than for those that have extended beyond the thyroid capsule and for large cell lymphomas than for immunoblastic lymphomas. It is also not uncommon for the recurrence to be located in the gastrointestinal tract.
As a conclusion, lymphoma of thyroid is uncommon. The prognosis for localized thyroid lymphoma is excellent. Chemotherapy/radiotherapy regimens have proven to be very effective for most thyroid lymphomas. In the present case there was no relapse observed after a 6-month follow-up.