Radiology Quiz Case: Diagnosis Diagnosis: Papillary thyroid carcinoma with metastatic extension to the thyroglossal tract associated with previous Hashimoto thyroiditis

Thyroid malignancies are rare, accounting for 0.5 to 1.0% of the deaths that occur as a result of malignant disease. In the United Kingdom, the incidence is 4 per 100000 per annum. More than 90% of thyroid malignancies are well-differentiated adenocarcinomas, with papillary carcinoma accounting for 80% of these. Papillary thyroid carcinomas have a 4:1 predominance in women, with the peak incidence between the third and fifth decades of life. Although the majority of these tumors present as a solitary thyroid nodule, they have a propensity for lymphatic spread in 50% of cases at presentation and are often multicentric (30%-50%). Only 5% of patients develop distant metastasis. The relationship between Hashimoto thyroiditis and papillary carcinoma has been a contentious issue since its initial description. Singh et al describe a rate of Hashimoto thyroiditis that is 2.77 higher in patients with papillary carcinoma than in the general population. However, the presence of Hashimoto thyroiditis does not affect the diagnostic approach or outcome, and may even confer a survival benefit, which may be a reflection of the increased prevalence of Hashimoto thyroiditis in young, otherwise healthy women. Malignant transformation within the thyroglossal tract is rare, occurring in only 1% of cases. The most common histologic type in this site is papillary adenocarcinoma, although follicular carcinoma may also be seen. The origin of these malignant neoplasms within the thyroglossal tract remains controversial. It is possible that papillary carcinoma arises de novo in the thyroglossal tract (thyroid follicles are found in the walls of a cyst in 7% of patients). It is also possible that the thyroglossal tract is the route of spread of carcinoma from the gland. In our case, this is the most likely possibility The differential diagnosis of midline neck masses includes congenital, inflammatory, infective, and neoplastic masses. A congenital midline mass is most likely to be a thyroglossal duct cyst, is most frequently observed in patients 20 to 30 years of age, and has a malefemale ratio of 1.0:1.5. The possibility of neoplasia was suspected in our patient because of the progressive enlargement of the mass and the presence of psammoma bodies on fine-needle aspiration cytology, both of which are characteristic of papillary carcinoma. The presence of enlarged cervical lymphadenopathy also increased the possibility of malignancy. It is estimated that up to 8% of the population may have nodular thyroid disease. Thyroid malignancies, however, are rare, and identifying the patients with malignant thyroid disease requires detailed investigation. Clinical evaluation includes the identification of risk factors, including previous neck irradiation, age, sex, family history, characteristics of the nodule (eg, size, consistency, and fixation), presence of enlarged lymph nodes, pressure symptoms, and hoarseness. Thyroid function tests are mandatory, although it is unusual for thyroid cancer to cause abnormalities in thyroid function. Despite being operator dependent, ultrasound-guided fineneedle aspiration cytology is probably the most accurate and cost-effective method of differentiating benign from malignant nodules, with accuracy rates approaching 95%. Thyroid scintigraphy can be used to assess nodules with suspicious findings on fine-needle aspiration cytology. The risk of malignancy in a palpable solitary nodule is between 5% and 10%, and the risk increases to 20% if the nodule is cold or warm and decreases to less than 1% if it is truly hot. Computed tomography provides vital anatomical information, with its main role in the evaluation of extracapsular disease and nodal, tracheal, laryngeal, and superior mediastinal involvement. In this case, the preoperative computed tomographic scan showed a mixed-attenuation soft tissue nodule measuring 3.0 2.0 2.5 cm that extended from 1 cm below the hyoid bone anterior to the thyroid cartilage (Figure 2). The nodule appeared almost continuous, with a nodule of similar size in the isthmus of the thyroid gland (Figure 3). Both lobes of the thyroid gland showed mixed attenuation and appeared slightly enlarged. There were 2 other soft tissue masses that exhibited mixed attenuation, one on each side of the neck (Figure 4). On the left side, the mass appeared within the lower pole of the thyroid gland, whereas on the right side, the mass was separate from the thyroid gland, a finding that is consistent with the level III and IV nodes on the right side in which metastatic deposits were found on histologic examination. Both of these lesions contained calcification. Malignant transformation within the thyroglossal tract is rather rare, occurring in only 1% of cases. The most common histological type in this site is papillary adenocarcinoma, although follicular carcinoma may also be seen. The differential diagnosis of midline neck masses includes congenital, inflammatory, infective, and neoplastic masses. A congenital midline mass, which is most likely due to a thyroglossal duct cyst, is most frequently observed in patients who are 20 to 30 years old, and it has a male-female ratio of 1.0 to 1.5. The possibility of neoplasia was suspected in our patient because of the progressive enlargement of the mass and the presence of psammoma bodies on fine-needle aspiration cytology, both of which are characteristic of papillary carcinoma. The presence of enlarged cervical lymphadenopathy also increases the possibility of malignancy. The origin of these malignant neoplasms within the thyroglossal tract remains controversial. It is possible that papillary carcinoma arises de novo in the thyroglossal tract, as thyroid follicles are found in the walls of a cyst in 7% of patients. However, it is also possible that the thyroglossal tract is the route of spread of carcinoma from the gland. In our case, this theory was the most likely possibility, as there was carcinoma within the right lobe of the thyroid gland and metastatic spread in the cervical lymph nodes.