Anaplastic thyroid carcinoma: computed tomographic differentiation from other thyroid masses

Anaplastic thyroid carcinoma is rare but is one of the most aggressive malignancies. Therefore, accurate diagnosis is important in order to provide appropriate therapy.

To establish useful computed tomographic (CT) criteria for differentiating anaplastic carcinoma from other thyroid masses.

The CT scans of nine patients with anaplastic carcinomas were retrospectively reviewed and compared with those of 32 patients with papillary carcinomas (n = 12) or benign lesions (n = 20) exceeding a maximum diameter of 2.0 cm. Image analysis was performed according to the following CT parameters: size, margin (well defined or ill defined), composition (cystic, mixed, or solid), mean attenuation value, ratio of attenuation of the mass to that of the adjacent muscle (M/m attenuation ratio), necrosis (present or absent), and calcification (stippled, nodular, or absent) of the thyroid mass; and tumor-spreading patterns including the presence of surrounding normal thyroid tissue in the involved lobe, involvement of the contralateral thyroid lobe, extension into the adjacent structures, and cervical lymphadenopathy.

Anaplastic carcinomas appeared as large (average 4.6 cm), solid (100%), and ill-defined (88.9%) masses accompanied by necrosis (100%), nodular calcification (44.4%), direct invasion into the adjacent organs (55.6%), and cervical lymph node involvement (77.8%). Tumor necrosis was the most valuable parameter in differentiating anaplastic carcinomas from other thyroid masses. Patient age (>70 years) and low attenuation value on postcontrast scan (attenuation value <100 HU, or M/m attenuation ratio <1.3) are also helpful predictors for anaplastic carcinoma.

If a patient is older than 70 years of age and has a large necrotic thyroid mass of low attenuation, anaplastic carcinoma should be included in the differential diagnosis.