Mesenchymal Tumours
Primary mesenchymal tumours of the thyroid are extremely rare. We can cite smooth muscle tumours such as leiomyomas, leiomyosarcomas, and solitary fibrous tumours. Leiomyoma is a benign neoplasia, typical of women, which shows histological and immunophenotypical features of the smooth muscles and which can be cured, generally by complete surgical removal or by lobectomy. Leiomyosarcoma is a typical neoplasia of older patients, with no gender predilection. On gross examination, it usually appears as a large mass with infiltrative behaviour. On light microscopy pleomorphism, mitosis, atypical mitosis, coagulative necrosis can be found. Primary leiomyosarcoma of the thyroid is a very rare malignant neoplasia and its diagnosis can be made also after the exclusion of secondarism from other sites.
Primitive solitary fibrous tumour of the thyroid is a very rare mesenchymal neoplasia, for which only few cases have been reported. Solitary fibrous tumour shows prevalent fibroblastic differentiation. Some tumours can present focal or extended myofibroblastic differentiation that is generally benign.
Vascular Tumours
Vascular primitive thyroid tumours are rare and include haemangioma, lymphangioma, and angiosarcoma. In particular, the angiosarcoma is a rare and aggressive lesion representing less than 4% of thyroid lesions, with a geographical predilection of Alpine regions of Italy and of Europe. Its behaviour is similar to anaplastic carcinoma with rapid fatal outcome.
Lymphomas
Primitive thyroid lymphomas are rare neoplasms, accounting for less than 5% of all malignant thyroid tumours. They include a heterogeneous group of lesions and originate from B lymphocytes. The most frequent histotypes are large B- cell lymphomas as well as the extranodal marginal zone B- cell lymphomas of mucosa- associated lymphoid tissue (MALT), with its variants. The aetiology of primary thyroid lymphomas is strictly linked to chronic lymphocytic thyroiditis. Clinically, primitive thyroid lymphomas occur in females with mean age 60– 65 years, but they can potentially arise at any age (14– 90 years). They can pre sent different sizes, from very small to large masses with compression symptoms including pain, dysphagia, dyspnoea, coughing. Differential diagnosis must exclude secondarisms from diffuse lymphomas.
