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Int J Clin Exp Pathol 2012;5(2):143-151

Original Article
Follicular thyroid adenoma dominated by spindle cells: report of two unusual cases and
literature review

Abbas Agaimy, Thomas Hahn, Josef Schroeder, Afaf Elhag

Institute of Pathology, University Hospital, 91054 Erlangen, Germany; Department of Surgery, Waldkrankenhaus, 91054 Erlangen, Germany;
Institute of Pathology, University Hospital, 93053 Regensburg, Germany; Histopathology Department, Scarborough Hospital, North Yorkshire,
YO12 6QL, UK.

Received February 1, 2012; accepted February 9, 2012; Epub February 12, 2012; published February 28, 2012

Abstract: Primary spindle cell neoplasms of the thyroid gland are quite rare. They encompass a heterogeneous group of benign and malignant
lesions of mesenchymal and epithelial origin. We herein describe two unusual follicular thyroid adenomas dominated by spindle cells with
occasional areas of colloid-forming follicular differentiation. The tumors affected a 77-year woman and a 70-year old man; both had a
long-history of monoclonal gammopathy of unknown significance (MGUS). One tumor presented as a large cold thyroid nodule and the other
was an autopsy finding. The tumors were predominantly composed of fibroblast-like spindled cells. One case showed prominent
meningioma-like concentric perivascular arrangement and contained cytoplasmic melanin-like pigment. Stromal hyalinization was a prominent
feature of both. By immunohistochemistry, the spindled cells expressed vimentin, pankeratin (KL1), thyroglobulin and TTF1 consistent with a
follicular differentiation. They did not stain with calcitonin, CEA and other lineage-specific mesenchymal, neuroendocrine and melanocytic
markers. There was no evidence of metastasis at autopsy (case 2) or at last follow-up 2 years after surgery (case 1). These cases
demonstrate the diversity of follicular thyroid neoplasms and the unusual occurrence of extensive spindle cell metaplasia. These uncommon
lesions need to be distinguished from spindle cell medullary carcinoma, paucicellular spindle cell anaplastic carcinoma, spindle cell foci in
papillary and follicular carcinoma, solitary fibrous tumor and other rare benign and malignant mesenchymal lesions.

Keywords: Spindle cell neoplasm, thyroid, follicular adenoma, TTF1, pigmented

Address all correspondence to:
Abbas Agaimy, MD,
Pathologisches Institut
Universitätsklinikum Erlangen
Krankenhausstraße 8-10
91054 Erlangen
Tel: +49-9131-85-22288
Fax: +49-9131-85-24745
Email: abbas.agaimy@uk-erlangen.de