RESIDENT CASE STUDIES

Week 6 May 26 - May 30, 2003: Case 2   

Table of Contents | List of Diagnoses | Case 1 | Case 2 | Case 3 | Case 4

28 year old male with a 4.5cm thyroid mass that is well-circumscribed, yellow-tan in color with a focal area of hemorrhage located in the superior pole of the right lobe of the thyroid

Discussion: 
Medullary thyroid carcinoma (MTC) is a malignancy of the parafollicular C cells of the thyroid gland. MTC is a neuroendocrine tumor.¹ 

MTC may be circumscribed, but is more likely to be freely infiltrating into surrounding tissue. The tumor cells are arranged in nests separated by stroma. The cells are round to oval, or may be spindle shaped. There is focal pleomorphism. Binucleated or multinucleated cells are common.The nuclei are uniform with a low N:C ratio.Mitoses can be seen, but are not prominent.The stroma contains amyloid, although this feature is not necessary for the diagnosis. Calcifications in the area of the amyloid are also common.Medullary thyroid carcinoma commonly invades lymphatics and veins. 

The differential diagnosis depends on the pattern that is seen.A pseudopapillary pattern may be present due to shrinkage artifact and may resemble papillary thyroid carcinoma.The follicular variant resembles follicular thyroid carcinoma. MTC, however, will stain positive for calcitonin and negative for thyroglobulin, while papillary and follicular carcinomas stain negative for calcitonin and positive for thryoglobulin. A small cell pattern can also be seen which resembles small cell carcinoma.If the tumor appears poorly differentiated it may resemble anaplastic thyroid carcinoma. Small cell and anaplastic thyroid carcinomas are calcitonin negative do not contain amyloid in the stroma. 

MTC has positive immunoreactivity for calcitonin, chromogranin, synaptophysin, histaminase and neuron specific enolase as well as CK and CEA. Calcitonin is not only a marker, but is indicative of tumor size and prognosis.¹ Moreover the presence of calcitonin receptors in MTC could have a role in the proliferation of this tumor.Amyloid may be positive within the stroma. 

Of note, medullary thyroid carcinoma represents less than 10% of all thyroid cancers. Most are sporadic; however, approximately 10-20% are familial. It has been associated with a mutation in the RET oncogene on chromosome 10. The familial form is autosomal dominant and may be associated with MENIIa or MENIIb syndromes.  

MTC can metastasize to the lymph nodes. Scollo et al. noted that: 1) lymph node metastases occur early in the course of MTC; 2) contralateral lymph node metastases were observed even in patients with small thyroid tumor; 3) the number of lymph node metastases was predictive of biological cure after surgery.²

References:

¹Cohen R, Quidville V, Bihan H. Medullary thyroid carcinoma and hormones. Ann Med Interne (Paris) 2003 Mar;154(2):109-16.

²Scollo C, Baudin E, Travagli JP, et al. Rationale for central and bilateral lymph node dissection in sporadic and hereditary medullary thyroid cancer. J Clin Endocrinol Metab 2003 May;88(5):2070-5.