Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from the parafollicular C cells of the thyroid, accounting for approximately 3-5% of all thyroid cancers. C cells secrete calcitonin; therefore, serum calcitonin level serves as both a diagnostic and surveillance biomarker. Approximately 75% of cases are sporadic and 25% are hereditary (MEN2A, MEN2B, familial MTC). Hereditary forms tend to be bilateral and multifocal. Histologically, amyloid deposition is characteristic and leads to coarse calcifications. The tumor spreads via lymphatic and hematogenous routes; at diagnosis, approximately 50% of patients have cervical lymph node metastases. Unlike papillary and follicular carcinoma, MTC does not respond to radioactive iodine therapy, making early surgical treatment critical. RET proto-oncogene mutation analysis is the gold standard for screening hereditary forms.
Age Range
30-60
Peak Age
45
Gender
Equal
Prevalence
Rare
MTC originates from the parafollicular C cells of the thyroid. These cells are neural crest-derived and produce calcitonin. RET proto-oncogene mutations (particularly in hereditary forms) lead to uncontrolled proliferation of C cells. Tumor cells secrete calcitonin and calcitonin gene-related peptide (CGRP), which are amyloid precursors; extracellular accumulation of these proteins forms amyloid deposits. Amyloid deposition causes dense fibrous tissue and dystrophic calcification in the stroma — this forms the pathophysiological basis for the coarse, irregular calcifications seen on ultrasonography. Amyloid and fibrous tissue also contribute to the solid, hypoechoic ultrasound appearance of the tumor; the dense stroma absorbs sound waves more effectively. Unlike follicular cells, C cells do not concentrate iodine — therefore the tumor appears as a cold nodule on scintigraphy and does not respond to radioactive iodine therapy. The tumor's rich vascularity causes prominent enhancement on contrast-enhanced imaging, while calcifications are detected as high-density foci on CT.
Coarse, irregular calcifications within a solid hypoechoic thyroid nodule — the ultrasonographic correlate of dystrophic calcification due to amyloid deposition. Combined with elevated serum calcitonin level (>100 pg/mL), this is a highly specific combination for medullary thyroid carcinoma. Unlike the microcalcifications of papillary carcinoma, MTC calcifications are larger, irregular, and produce prominent acoustic shadowing.
Solid, markedly hypoechoic nodule with coarse, dense, irregular calcifications. Unlike the microcalcifications in papillary carcinoma, these calcifications are larger (>2 mm), have irregular margins, and produce acoustic shadowing. The nodule is generally homogeneous or mildly heterogeneous with markedly hypoechoic appearance. Intranodular coarse calcifications represent the ultrasonographic correlate of amyloid deposition and dystrophic calcification.
Report Sentence
A ... mm markedly hypoechoic solid nodule is seen in the [right/left] thyroid lobe, containing coarse dense calcifications with posterior acoustic shadowing; medullary thyroid carcinoma should be primarily considered.
The nodule's anteroposterior diameter exceeds its transverse diameter (taller-than-wide shape). This finding carries 3 points in ACR TI-RADS v2017 and increases malignancy suspicion. In MTC, it particularly reflects aggressive growth pattern — the tumor grows infiltratively perpendicular to tissue planes.
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The nodule demonstrates a taller-than-wide configuration (AP diameter > transverse diameter), which increases malignancy suspicion according to ACR TI-RADS.
Prominent intranodular hypervascularity on color or power Doppler. The vascular pattern is predominantly central/intranodular type — intranodular flow dominates over perinodular vascularity. This finding reflects the tumor's rich neovascularity. High flow velocities and low resistive index (RI) are typical for carcinomas.
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Color Doppler examination demonstrates prominent intranodular hypervascularity with central vascular pattern, favoring malignancy.
Dense, coarse calcifications within the thyroid nodule on non-contrast CT. Calcifications are typically centrally or peripherally located, with irregular margins and high density (>100 HU). In some cases, extensive calcification covering a large portion of the nodule may be seen. Coarse calcifications are morphologically distinct from the microcalcifications due to psammoma bodies in papillary carcinoma — calcifications in MTC are dystrophic calcifications due to amyloid deposition.
Report Sentence
A ... mm solid lesion containing coarse calcifications is seen in the [right/left] thyroid lobe; the calcification pattern is consistent with dystrophic calcification due to amyloid deposition, and medullary thyroid carcinoma should be considered in the differential diagnosis.
Prominently enhancing thyroid nodule with ipsilateral or bilateral cervical lymphadenopathy on contrast-enhanced CT. Enhancing lymph nodes are seen especially in the central compartment (Level VI) and lateral neck (Level II-V). Metastatic lymph nodes frequently contain cystic/necrotic components and calcifications — this finding is highly characteristic of MTC metastasis. Simultaneous calcification in the primary tumor and metastatic lymph nodes is a distinguishing feature of MTC.
Report Sentence
A prominently enhancing solid thyroid nodule is seen with ipsilateral central compartment (Level VI) and lateral neck (Level II-V) pathological lymph nodes containing calcifications, consistent with medullary thyroid carcinoma and nodal metastases.
The nodule shows intermediate-to-low signal intensity on T2-weighted images. Amyloid deposition and dense fibrous stroma reduce free water content, causing T2 signal decrease. Calcifications appear as signal voids on T2. This finding helps differentiate from T2 hyperintense simple cysts and colloid nodules.
Report Sentence
The thyroid nodule shows intermediate-to-low signal intensity on T2-weighted sequences, consistent with amyloid deposition and fibrous stroma; focal signal voids correspond to intranodular calcifications.
The thyroid nodule appears cold (nonfunctional) on Tc-99m pertechnetate or I-123 scintigraphy — shows no radiopharmaceutical uptake. Unlike follicular cells, C cells do not express the sodium-iodide symporter (NIS), therefore cannot concentrate iodine or pertechnetate. The appearance of MTC as a cold nodule also indicates it will not respond to radioactive iodine therapy.
Report Sentence
A cold nodule with no radiopharmaceutical uptake is present on Tc-99m pertechnetate scintigraphy in the [right/left] thyroid lobe, correlating with the palpable abnormality; considering C-cell origin, serum calcitonin level should be evaluated.
Criteria
Comprises 75% of cases. No RET germline mutation. Usually unilateral, unifocal. Age at diagnosis typically 40-60 years.
Distinct Features
Unilateral, solitary nodule. Advanced stage at diagnosis more common. No family history of MEN2. No association with pheochromocytoma or hyperparathyroidism.
Criteria
RET proto-oncogene mutation (codon 634 most common). MTC + pheochromocytoma (50%) + primary hyperparathyroidism (20-30%). Autosomal dominant inheritance.
Distinct Features
Bilateral and multifocal nodules. Earlier age at diagnosis (20-30 years). C-cell hyperplasia accompanies as preneoplastic precursor lesion. Pheochromocytoma should be investigated in both adrenal glands — plasma metanephrine must be measured before any biopsy.
Criteria
RET proto-oncogene mutation (codon 918, M918T). MTC + pheochromocytoma + mucosal neuromas + marfanoid habitus. Hyperparathyroidism usually absent. Most aggressive hereditary form.
Distinct Features
Aggressive MTC develops at very early age (<10 years). Mucosal neuromas of lips and tongue, intestinal ganglioneuromatosis, marfanoid body proportions. Prophylactic thyroidectomy recommended in first years of life. On imaging, bilateral, rapidly growing nodules with extensive extrathyroidal extension.
Criteria
RET mutation present but only MTC develops — no pheochromocytoma or hyperparathyroidism. Defined by MTC in at least 2 first-degree relatives or absence of other MEN2 components.
Distinct Features
Most indolent hereditary form. Age at diagnosis typically 40-50 years. Bilateral and multifocal but slower course than MEN2A/B. Prognosis better than sporadic and MEN2A.
Distinguishing Feature
Papillary carcinoma features predominantly microcalcifications (psammoma bodies, <1 mm, without acoustic shadowing), while MTC characteristically shows coarse calcifications (amyloid, >2 mm, with acoustic shadowing). Elevated calcitonin supports MTC; elevated thyroglobulin suggests papillary carcinoma.
Distinguishing Feature
Follicular carcinoma typically appears as a well-defined, isoechoic-hypoechoic solid nodule with thick halo; calcification is rare. MTC shows more prominent coarse calcifications and irregular margins. Calcitonin level is normal in follicular carcinoma. Follicular carcinoma metastasizes hematogenously (bone, lung), while MTC primarily shows lymphatic spread.
Distinguishing Feature
Anaplastic carcinoma grows very rapidly (<6 months), shows extensive extrathyroidal invasion (trachea, esophagus, vessels), and typically presents as a large mass in patients >60 years. MTC has a slower course, coarse calcifications are prominent, and elevated serum calcitonin is distinguishing. Necrosis and locally aggressive invasion are more dominant in anaplastic carcinoma.
Distinguishing Feature
Colloid nodule is typically iso-hyperechoic, well-defined, with spongiform pattern and comet-tail artifacts, representing a benign nodule. MTC is markedly hypoechoic with coarse calcifications and irregular margins. Calcitonin is normal in colloid nodules and increased vascularity on Doppler is not expected.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralUrgent referral to endocrine surgery is required for MTC diagnosis. Total thyroidectomy with central compartment lymph node dissection forms the cornerstone of treatment. Pheochromocytoma must be excluded preoperatively (plasma metanephrine) — if present, adrenalectomy is performed first. Calcitonin and CEA are postoperative surveillance markers. RET mutation analysis should be performed in all MTC patients; if positive, family screening is mandatory. Radioactive iodine therapy is ineffective. Tyrosine kinase inhibitors (vandetanib, cabozantinib) are used in advanced disease.
Medullary thyroid carcinoma arises from C cells and does not respond to RAI therapy. Treatment is total thyroidectomy + central lymph node dissection. Calcitonin and CEA are follow-up markers. RET mutation should be screened in all patients and family screening done in hereditary forms.