Tuesday, August 04, 2009

Role of ultrasound in recurrent thyroid disease

Introduction:
Number of patients undergo total thyroidectomy for malignant lesions of thyroid. Recurrences can be identified easily and accurately by performing ultrasound examination of the thyroid bed area in the neck. The widespread availability of ultrasound guided fine needle aspiration cytology has added to the diagnostic armamentorium. Even after performing total thryroidectomy, recurrences are common in thyroid malignancies.

Role of ultrasound neck in post operative evaluation of thyroid cancer patients:
1. To identify tumor recurrence
2. To perform fine needle aspiration cytology

Usually sonographic evaluation is performed in post thyroidectomy patients using a high frequency probe 10 - 15 MHz. Since thyroid is absent in these patients, a valuable landmark in the neck is lost to the sonologist. Moreover the normal anatomy is also distorted. Hence it is imperative that in the absence of thyroid tissue, imaging should be performed in two planes i.e. transverse and longitudinal. Any visible mass in the thyroid bed should be considered to be a recurrent mass unless proved otherwise.
In the postthyroidectomy patient, the carotid artery and jugular vien slide medially into the space previously occupied by thyroid gland. The right carotid artery ideally is pulled medially and lies immediatly adjacent to the trachea, whereas the left carotid is at the lateral edge of oesophagus.

Recurrence in thyroid bed is typically seen as:
1. Round and hypoechoic mass situated between carotid and trachea
2. May have well defined margins
3. Microcalcifications may be seen within the mass
4. Abnormal vascularity
5. Loss of normal echogenic hilum seen in normal lymph nodes

Abnormal internal jugular chain of nodes should be searched on both sides.

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