الفهرس 
Anatomy of the Thyroid GlandOnly 14 pages are availabe for public view
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Abstract
The thyroid gland plays a critical role in the regulation of several metabolic functions including cardiac rate and output, lipid catabolism, and skeletal growth, as well as oxygen and heat production. It is shield-shaped and situated with its upper margin near the oblique line on the thyroid cartilage and its lower margin at the level of the fourth or fifth tracheal cartilage.
Thyroid nodules are common and comprise benign nodule as, adenomas, colloid cysts, multinodular goiter, and malignant tumors. The main pathologic types of thyroid nodules carcinoma are papillary, follicular, medullary, and anaplastic. Risk factors for thyroid carcinoma include age of less than 20 years or more than 60 years, a history of neck irradiation, and a family history of thyroid cancer.
US for thyroid nodules is the most sensitive diagnostic modality for making the diagnosis of thyroid carcinoma and this modality provides valuable guidance to perform an aspiration biopsy and follow-up.
On the US of thyroid nodule, the findings for a suspicious malignant nodule include a taller than- wide shape, a spiculated or microlobulated margin, marked hypoechogenicity, microcalcifications and macrocalcifications.
Although, Direct tumor invasion of adjacent soft tissue and metastases to lymph nodes are highly specific signs of thyroid malignancy. The major ultrasound criteria of LN malignancy include cystic appearance, hyperechoic punctuations, absence of a hilum, and peripheral vascularization. Presence of at least one of the malignant US findings suggests the presence of a malignancy.
US and Doppler Findings of Thyroid nodules
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Ultrasonographic evaluation by means of power Doppler is helpful in the screening of thyroid nodules at high risk for malignancy. The power Doppler analysis of the nodules produced 5 vascular patterns: I, absence of signal blood flow; II, exclusively perinodular blood flow; III, perinodular > central blood flow; IV, central blood flow > perinodular blood flow; V, exclusively central blood flow.
Malignant thyroid nodules predominantly had central vascularization, whereas benign nodules predominantly had peripheral vascularization. Also an absence of signal blood flow only in benign lesions.
Power Doppler and RI have a diagnostic sensitivity and specificity of 92.3% and 88%, respectively, in the detection of malignant nodules.
The 3D and contrast enhanced ultrasound are new modalities techniques which play an important role in the studies of thyroid nodules and help in the differentiation between malignant and benign nodules.