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The evaluation and management of thyroid masses remains an area of controversy. Thyroid ultrasonography has established itself as a popular and useful tool in the evaluation and management of thyroid disorders yet alone it cannot give fully detailed information for diagnoses and proper management of thyroid diseases (1). Advanced ultrasound techniques in thyroid imaging have not only fascinated the radiologists but also attracted the surgeons and endocrinologists who are using these techniques in their daily clinical and operative practice. The role of thyroid scintigraphy, on the other hand, in the initial evaluation of the thyroid nodule has been questioned by several investigators (2). However, thyroid scanning remain critical for the determination of autonomously functioning thyroid tissue (3). Scintigraphy is usually done with one of the radioisotopes of iodine or technetium. There are minor but potentially significant differences in the handling of these two radiopharmaceuticals by thyroid follicular cells. Normal thyroid follicular cells will trap both technetate and radioiodine (4). However, only radioiodine is organized to the tyrosine residues of thyroglobulin and stored in the colloid space (5). Most investigators would agree that the routine use of thyroid ultrasound for the evaluation of thyroid nodules is not cost effective (5). Nonetheless, ultrasonography provides considerably more anatomic (but not functional) detail than thyroid scintigraphy or computerized tomography and it has an important role in certain situations. The high-resolution 10 MHz transducers are able to resolve thyroid cysts that measure only 2 mm, and solid lesions as small as 4mm in size (6).
The introduction of high resolution thyroid ultrasonography provides for anatomic definition that is clearly superior to thyroid scintigraphy. However, radionuclide imaging of the thyroid remains critical for determining the functional status of abnormal thyroid tissue (6). While aspiration, ultrasound, and scintigraphy all have appropriate indications, utility, and limitations, no single test or group of tests substitutes for careful clinical assessment and follow up. This is because the sonographic features of these processes may be similar but they have different biochemical profile and clinical presentations (7).
This study aims to assess the sonographic and radionuclide scintigraphy findings of patients presenting with thyroid mass at Muhimbili National Hospital (MNH).

1.1.1 Anatomy of the thyroid gland
Thyroid is a butterfly shaped gland that sits low on the front of the neck. It lies below the Adam’s apple, along the front of the windpipe. It has two lobes, connected by a bridge (isthmus) in the middle. When the thyroid gland is its normal size, it cannot be felt by palpation. The gland is brownish-red in color and is rich with blood vessels. Nerves important for voice quality also pass through the thyroid gland and also secretes several hormones, collectively known as thyroid hormones. The main hormone is thyroxine, also known as T4. Thyroid hormones act throughout the body, influencing metabolism, growth and development, and body temperature. During infancy and childhood, adequate thyroid hormone is crucial for brain development. The C cells in the thyroid gland make calcitonin. This hormone plays a small role in keeping a healthy level of calcium in the body. Four or more tiny parathyroid glands are on the back of the thyroid. These glands make parathyroid hormone which plays a significant role in helping the body maintain a healthy level of calcium.
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1.1.2 Thyroid mass
A thyroid mass (a swelling in the neck) is usually due to an enlargement of thyroid gland which is also known as goiter. Nodules are lumps in the thyroid gland. These lumps normally present as midline swelling, anterior neck swelling, or lateral lumps if only one lobe is involved. A thyroid nodule may be a lump in an otherwise normal thyroid gland. However, goiters may consist of many nodules (multi-nodular goiter) and solitary nodules may exist within goiter. Nodules may be cystic, colloid, hyperplastic, adenomatous or cancerous (8) (9).

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1.1.3 Risk factors
• Women are affected more than men by 7:1
• Goiters and thyroid lumps are more common in areas of low iodine consumption. This is less likely in countries where iodine is added to table salt.
• Conversely, excessive consumption of iodine (found in seaweed) can cause goiters.
• Malignancy is more common where benign thyroid disease has existed.
• The risk of malignancy in a thyroid nodule is higher under the age of 20 and over the age of 70.
• Thyroid nodules and cancers are more common after exposure to radiation. This includes therapeutic radiotherapy, and exposure to radiation following events such as those in Hiroshima and Chernobyl.
• Smoking increases the risk of nodular goiter.
• Family history.
• Medication such as amiodarone and lithium.
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