Primary thyroid lymphoma

Clinical History

A 42-year-old patient was referred to the endocrinologist following the appearance of a recent, non-tender, painless, fast-growing lump in the neck. The patient underwent a neck ultrasound, a chest RX, an helical contrast-enhanced CT and finally, a cytological sample test.

Imaging Findings

A woman with an unremakable medical history was referred by her GP to the endocrinologist following the appearance of a recent non-tender, painless, fast-growing lump in the neck, especially on the left side. Blood chemistry tests were normal. The patient underwent a neck ultrasound (Fig.1a,b) which confirmed the severe thyroid swelling especially in the left lobe. The thyroid parenchyma was found to be widespread and unhomogeneous but without evidence of focal lesions on the US scan, and with a poor peripheral vasculature at colour-Doppler (Fig. 1c). A chest RX showed a rough expansive process (4 x 7 x 8 cm in diameter) occupying the right superior-lateral mediastinum, compressing the right superior lung lobe and displacing the trachea (Fig. 2). The helical contrast-enhanced CT scan did not reveal a clear enhancement of the mass, which extended from the level of the oropharynx to the tracheal carina, occupying the deep cervical zone, the upper opening of the thorax, the superior and middle mediastinum, with a severe caliber reduction of the esophagus and the aerial tract (Fig. 3–5). The patient finally underwent a cytological sample test, to evaluate the suspicion of a thyroid lymphoma. The cytological sample (Fig. 6) test showed that the thyroid parenchyma was diffusely replaced by a dense, lymphoproliferative infiltrate, composed of atypical diffuse large cells with round to oval nuclei, clumped chromatin and nucleoli.

Discussion

Thyroid lymphomas are uncommon, accounting for only 2% to 5% of all thyroid malignancies. It can be divided into non-Hodgkin’s lymphomas (NHL) of B and T cell type, and Hodgkin’s lymphomas. They are almost exclusively derived from the B cells of mucosa-associated lymphatic tissue. Although NHL occurs as an extranodal disease in 25% to 50% of patients, fewer than 2% to 3% of the cases originate in the thyroid gland. More commonly, in 10% of patients it is seen as a manifestation of a primary lymphoma arising elsewhere, also involving the thyroid gland. Elderly women are most commonly affected, the disease arising in association with chronic lymphocytic thyroiditis (Hashimoto’s disease) in 40% to 80% of cases. We report the case of a 42-year-old woman with primary thyroid lymphoma without a history of Hashimoto’s thyroiditis. Histologically, thyroid NHL is generally a poorly differentiated lesion. These lymphomas remain localized for an extended period of time. In the thyroid, a gland normally devoid of lymphocytic tissue, an increased risk of lymphoma has been associated with chronic autoimmune thyroiditis (Hashimoto’s disease), which may provide the lymphocytic substrate required for NHL to arise. Thyroid lymphomas have attracted the attention of investigators because of their putative origin from active lymphoid cells in autoimmune thyroiditis, i.e., Hashimoto’s thyroiditis or chronic lymphocytic thyroiditis. The most striking clinical feature in this patient’s presentation was a rapid, nontender enlargement of the thyroid, which is a characteristic feature of thyroid lymphomas. By contrast, compression symptoms like hoarseness, dysphagia, or dyspnea, seen in up to 30% of the patients, were absent. Of note are also the patient’s age and sex, because most thyroid lymphomas are seen in the elderly, with a peak incidence in the seventh decade, and the female/male ratio ranges from 4:1 to 8:1. Imaging demonstrates the thyroidal of the growing neck lump, and shows its exact extension and anatomic relations, but not its specific nature. A neck US is a first-line, fast test, that easily provides important information about thyroid pertinency and its extension and relations at least with the carotids and jugular veins. A large, rapidly swelling nontender painless mass involving both thyroid lobes is more likely to be observed in Basedow’s disease and Hashimoto's thyroiditis than in malignancies. The diagnosis of Basedow’s disease is quite easy, due to its pathognomonic manifestations (thyrotoxicosis, ophthalmopathy, myxedema and high serum FT3-FT4 levels with a suppressed TSH levels), even in aged subjects, who may be missed cases. ECD shows a rich parenchymal vasculature in Basedow’s thyroid (thyroid hell). Hashimoto's thyroiditis seldom shows a gland swelling, as rapid and severe as in this case, so lymphoma must be suspected. Epithelial thyroid malignancies, such as anaplastic carcinoma and undifferentiated papillary carcinoma may cause a lateral neck lump, but they also have a nodular pattern on US. Thyroid lymphomas are infrequent tumors and should be suspected in patients with non-tender, painless, fast-growing lumps of the whole gland without a nodular or hypervascular pattern and other pathognomonic manifestations. The definitive differential diagnosis remains cytological, especially when Hashimoto's thyroiditis is suspected to have evolved to a lymphoma.

Differential Diagnosis List

Final Diagnosis

Primary poorly differentiated thyroid non-Hodgkin’s lymphoma.

URL:	https://www.eurorad.org/case/3279
DOI:	10.1594/EURORAD/CASE.3279
ISSN:	1563-4086