Anaplastic thyroid carcinoma (ATC) accounts for only 1–2% of all thyroid cancers.

It is a very aggressive, highly malignant tumor that is most commonly seen in older people. The peak incidence of ATC is the seventh decade of life and more than two thirds of all ATC affects people over the age of 65 years.

Women are more commonly affected than men, approximately 1.5:1.

Clinical findings: a rapidly growing mass with tightness in the neck, dysphagia, hoarseness, dyspnea, neck pain, sore throat, and cough. Examination of the neck usually reveals a fixed, large, firm mass [1].

ATC can be seen in several contexts: (1) a patient with DTC whose disease suddenly becomes fulminant after an interval of several years; (2) a patient with a longstanding goiter that suddenly grows at a rapid rate; (3) a patient without previous thyroid disease who develops a rapidly growing neck mass; (4) a patient whose pathological sections reveal a focus of ATC in the thyroid specimen; and (5) a patient with widespread metastases whose biopsy of an accessible metastasis suggests an ATC. In a retrospective analysis of 84 patients with ATC by Aldinger et al., 21% had a history of differentiated thyroid cancer, 37% had a longstanding goiter with sudden rapid growth, 30% had no previous thyroid disease, and 6% had widespread metastatic disease. 93% patients were presented with stage III and stage IV disease. A 5-year survival rate was only 7.1% with a mean survival period of 6.2 months from the time of diagnosis and 11.8 months from the time of onset of symptoms [2].

In a cohort of 38 patients with ATC, systemic metastases were present in 46% of ATC patients at presentation, and 68% ATC of patients had metastases diagnosed during the course of their illness [3].

In another retrospective cohort of 39 ATC patients, 82% died during the follow-up period of up to 10 years, 75% of these patients had distant metastases to the lung, bone, mediastinum, and peritoneum at the time of diagnosis [4].

In a cohort of 516 patients by Kebebew et al., 8% of patients had intrathyroidal tumors, 38% had extrathyroidal tumors and/or lymph node invasion, and 43% had distant metastasis. The average tumor size was 6.4 cm (range, 1–15 cm). Age at diagnosis of ATC is a strong predictor of prognosis. There was a 28% difference in mortality between patients <60 year and those >60 years. They also reported a 45% difference in mortality at 1-year follow-up between patients who had distant metastasis and patients who had intrathyroidal ATC only [5].

In a cohort of 18 cases of ATC (17 have US scan) by Suh et al., the most common US features included (Figs. 17.1aa and 17.2aa): solid mass (11 of 17, 64.7%), irregular margin (15 of 17, 88.2%), presence of cervical lymph node involvement (13 of 17, 76.4%), wider-than-tall shape (12 of 17, 70.5%), marked hypoechogenicity (9 of 17, 52.9%), and internal calcification (9 of 17, 52.9%). However, except for lymph node involvement, US findings for each group were not statistically different from other types of aggressive thyroid cancer. A correct diagnosis of ATC by initial US-FNAB was made in 9 of 18 (50%) of the cases [6].

On computed tomography of nine patients, ATC appeared as: large size (average 4.6 cm), solid of 100%, and ill-defined of ≈89%, masses accompanied by necrosis of 100%, nodular calcification of ≈44%, direct invasion into the adjacent organs of ≈56%, and cervical lymph nodes involvement of ≈78% [7].

Considering the limitations of US evaluation in studying larger masses, CT or MR are more useful to obtain information on the extent and location of tumor necrosis, site of calcification in the tumor, and detecting lymph node metastases. It helps to lower false negative diagnosis by appreciating indication sites for FNAB. However, when ATC is clinically suspected, US-guided FNAB is initially performed and CT or MRI is performed after diagnosis [8].