Medullary thyroid carcinoma, small cell variant, as a diagnostic challenge on fine needle aspiration: a case report.
BACKGROUND
The small cell variant of medullary thyroid carcinoma (SCV-MTC) is a very unusual tumor that carries a poor prognosis. This tumor type closely resembles small cell pulmonary neuroendocrine carcinoma or lymphoma.


METHODS
A 43-year-old woman had a palpable mass on the right side of her neck. A fine needle aspiration biopsy (FNAB) revealed a hypercellular lesion composed mainly of isolated, small, round cells with salt-and-pepper chromatin interspersed with inconspicuous deposits of fluffy acellular material. A diagnosis of "malignant tumor, consistent with small cell carcinoma, metastasis not excluded" was rendered during the on-site rapid cytologic examination. Immunostaining showed a few isolated cells reactive for calcitonin, intense and diffuse immunoreactivity for carcinoembryonic antigen, dotlike positivity for chromogranin and cytokeratin, and negativity for thyroglobulin. Congo-red staining was positive in the acellular deposit, consistent with SCV-MTC. Subsequent total thyroidectomy confirmed this diagnosis.


CONCLUSIONS
The wide range of cytomorphologic features of MTC can be misleading on FNAB and can be a diagnostic challenge. Congo-red staining and immunoreactivity for calcitonin can be negative in this variant. Consequently, salt-and-pepper chromatin, Congo-red staining and a panel of antibodies comprising calcitonin, carcinoembryonic antigen, chromogranin, cytokeratin, leukocyte common antigen and thyroglobulin are mandatory for the correct diagnosis.
Department of Pathology, University Hospital and Faculty of Medicine, Geneva, Switzerland.
Stephane
S
Yerly
Frederic
F
Triponez
Patrick
P
Meyer
Neeta
N
Kumar
Massimo
M
Bongiovanni
D000328:Adult; D044963:Biopsy, Fine-Needle; D018276:Carcinoma, Medullary / Q000175:diagnosis* / Q000473:pathology* / Q000601:surgery; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D013961:Thyroid Gland / Q000473:pathology*; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000473:pathology* / Q000601:surgery