Clinical features :
Female patient, 35 years old. Solitary nodule, left lobe. Serum calcitonin : 625 ng/L (normal <10)

Gross features :
Firm, 2,5 cm left thyroid nodule, situated in the upper third, well circumscribed but not encapsulated

Microscopy :
Solid proliferation, lobular or trabecular pattern (fig A and fig B).
		fig. A
		fig. B
Some normal follicles are entrapped within the tumor (fig C). Tumoral cells are either fusiform either round, with finely granular eosinophilic cytoplasm.
		fig. C
Nuclei are round, oval with coarse chromatin and small nucleolus. Moderate anisocaryosis (fig D) and unfrequent mitosis. The stroma is fibrous moderately abundant, without amyloid deposits.
		fig. D
Immunohistochemical profile : tumoral cells are positive with anti- Cacitonin antibody (fig E) and CEA, negative with Thyroglobulin. No C cell hyperplasia (CCH) was found surrounding the tumoral nodule and in the controlateral lobe ; 2 /45 lymph nodes contain metastasis (left site of central lymph node dissection), without capsular disruption.
		fig. E

Diagnosis :
Medullary thyroid carcinoma, intra-thyroid, stage pT2 N1, sporadic form

Comments :
Medullary thyroid carcinoma without amyloid stroma can be seen in about 25 % of cases, often in early tumor. Others atypical forms include : papillary, glandular, pseudo-follicular pattern.
Anti-Chromogranine positivity can oriented the diagnosis but the confirmation of MCT requires absolutely the positivity with Calcitonin for the differential diagnosis with other neuro-endocrine tumor originating from bronchial site, thymus..
Others differential diagnosis include follicular tumor with trabecular pattern, oncocytic cytology.
The diagnosis in frozen section during surgery is sometimes difficult but can be helped by the situation in the upper third of the lobe. The ideal situation is the diagnostic in the pre-operative time by FNA and elevated seric Calcitonin level .
This tumor shows the histologic characteristics of a sporadic form : unilaterality and absence of CCH around the tumor AND in the controlateral lobe.
The study of the C cell population in the 2 lobes is very important and should be clearly mentioned in the histological report
The prognosis of medullary carcinoma is related to pathologic stage and quality of initial surgery.

References :

FRANC B., CAILLOU B.
Le cancer médullaire de la thyroïde : définitions morphologiques et immunohistochimiques. Le rôle du pathologiste en 1987.
Ann. Endocrinol. - 1988 - vol. 49 - p. 22-33.

FRANC B, MODIGLIANI E .
Le carcinome médullaire de la thyroïde : évolution des concepts
Arch Anat Cytol Path 1998, 46 (1-2), 100-111

PAPOTTI M, SAMBATARO D, PECCHIONI C, BUSSOLATI G
The pathology of medullary carcinoma of the thyroid : review of the litterature and personal experience on 62 cases
Endocrinol Pathol., 1996 ; 7 : 1-20