Images in Endocrine Pathology: Spindle Cell Lesion of the Thyroid Gland Esther Diana Rossi & Maurizio Martini & Nicola Cingolani & Renzo Ranaldi & Guido Fadda Published online: 8 February 2012 # Springer Science+Business Media, LLC 2012 Case History A 51-year-old man with a 5-cm left hypoechoic thyroid nodule underwent a total thyroidectomy. The patient did not refer a previous thyroid FNAB. The surgical specimen was fixed in 10% buffered formaldehyde, embedded in paraffin and the 5-mm-thick sections were stained with Hematoxylin–Eosin for the histological examination. Immunostains for several antibodies (see below) were carried out on microtomic sections using the labeled streptavidin–biotin–peroxidase complex. The tissues were incubated with commercial monoclo- nal antibodies diluted 1:100, after a prior microwave antigen retrieval (3-min passages in citrate buffer; pH 6.0). For molecular genetic analysis, genomic DNA was extracted from both the paraffin-embedded tumor and the residual thyroid tissue using the QIAamp DNA mini KIT (Qiagen, Hilden, Germany). A direct sequencing of the BRAF gene to identify the V600E mutation was performed. What is Your Diagnosis? Figure Composite (from 1 to 6) Pathologic Diagnosis Spindle cell encapsulated papillary carcinoma with focal invasion of tumor capsule. The lesion is a well circumscribed–encapsulated spindle cell neoplasm showing the distinctive nuclear features of a papillary thyroid carcinoma. Some areas with a trabecular pattern of growth were present. Focally, neoplastic nests resulted in a capsular invasion but a clear-cut evidence of either vascular invasion or extra-glandular extension cannot be detected (Fig. 1). The predominant pattern shows the typical nuclear features of a papillary carcinoma with nuclear clarifica- tion and elongated eosinophilic cytoplasms (Fig. 2). The immunohistochemical profile revealed a strong positivity of the neoplastic cells for thyroglobulin (Fig. 3), TTF-1 (Fig. 4), membranous HBME-1 (Fig. 5), cytoplasmic galectin-3 (Fig. 6) and cytokeratins and a negativity for calcitonin, CD34, chromogranin A, synaptophysin, S-100, monoclonal CEA, and p53. The Ki-67 labeling index was lower than 5%. No evidence of multifocality was seen. The analysis of the BRAF V600E locus resulted in a wild-type genotype. Comment Thyroid neoplasms exhibiting a pure spindle cell pattern are very uncommon. The spectrum of lesions showing a promi- nent spindle cell component encompasses both hyperplastic E. D. Rossi : M. Martini : G. Fadda (*) Division of Anatomic Pathology and Histology, Universita’ Cattolica Sacro Cuore, Agostino Gemelli School of Medicine, Rome, Italy e-mail: guidofadda@rm.unicatt.it N. Cingolani : R. Ranaldi Division of Anatomic Pathology, Hospital of Macerata, Macerata, Italy Endocr Pathol (2012) 23:132–134 DOI 10.1007/s12022-012-9193-z