IMAGE OF THE WEEK 2015
IMAGE 04 - 27 JULY 2015
Figure 1: CT coronal section through the neck showing the presence of a large thyroid mass involving both lobes and compressing on the trachea. there is a also intrathoracic involvement with substernal extension. (Click on image to enlarge)
Figure 2: CT transverse section of the same patient showing the enlarged thyroid gland with narrowing of the tracheal from external compression and a calcified structure in the substance of the left thyroid lobe. (Click on image to enlarge)
A goitre is an enlarged thyroid gland (Figure 1). Worldwide, iodine deficiency represents the most common cause. The vast majority of goitres are benign. Clinically, goitres can be euthyroid, hyperthyroid or hypothyroid.
Thyroid cancers can also develop from goitres, which occur due to reduced thyroid hormone production secondary to iodine deficiency, immunological or biochemical causes.
Hyperthyroidism indicates an overactive thyroid gland leading to the release of excessive circulating thyroid hormones. The most common cause is Graves disease. Hypothyroidism reflects lowered thyroid gland activity, and iodine deficiency remains the most common cause worldwide. However, Hashimoto’s thyroiditis is the most common cause in the first world. Management for hyperthyroidism typically includes the antithyroid drugs carbimazole, methimazole and/or propylthiouracil or radioiodine. Subtotal thyroidectomies can also be considered, although risks include hypoparathyroidism and laryngeal nerve palsies. Hypothyroidism is generally treated with thyroxine replacement.
Generally, the diagnosis for hyperthyroid/hypothyroid conditions involve TSH assays and circulating thyroid hormone (T3 and T4) levels. Additional tests include; TSH receptor antibody levels, thyroglobulin and thyroid peroxidase (TPO) autoantibody levels for Graves disease and Hashimoto’s disease.
Figure 3: CT saggital section of the same patient at the level of the neck showing a grossly enlarge gigantic thyroid mass, occupying the entire neck and extending into the chest. The neck is clinically enlarged with a large mass. (Click on image to enlarge)
An examination of the thyroid gland and cervical lymph nodes should be part of the clinical assessment. Any palpable thyroid lump should be investigated with fine-needle aspiration cytology (FNAC) to rule out malignancy.
Ultrasound is most useful for distinguishing solitary nodules from multinodular nodules and to determine tumour composition. Increased vascularity, echogenicity and calcifications on ultrasound are potential indicators of malignancy. Ultrasound is also used to evaluate the cervical lymph nodes. It is also used to aid image guided FNAC of nodules.
Radionuclide imaging is the most effective imaging modality for the investigation of thyroid nodules. ‘Cold’ nodules do not uptake radioisotopes, and are more likely to be malignant. ‘Hot’ nodules uptake radioisotopes, and are less likely to be malignant. However, there are no specific features that can indicate or rule out malignancy definitively. Its availability, cost and study time may be prohibitive.
CT or MRI is indicated when clinical findings suggest invasion beyond the thyroid capsule, suggested by voice hoarseness, stridor, dysphagia, vocal cord palsies or lesional fixation (Figure 2).
CT is also used to evaluate nodal involvement and retrosternal extension for surgical planning (Figure 1 and 3). Generally, non-contrast imaging is preferred as iodinised contrast uptake can reduce thyroid radioiodine uptake and thus ablation.
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Images and text contributed by
Dr Ian Bickle, Department of Radiology,RIPAS Hospital and Christopher Yii Bong, medical student.
All images are copyrighted and property of RIPAS Hospital.