Ectopic thyroid is the most common anomaly of thyroid histogenesis and can develop along the thyroglossal duct tract. However, it can also present, although less frequently, in the mediastinum, lymph nodes, tracheal or oesophageal wall. Ectopic thyroid is susceptible to the same diseases that affect the thyroid gland, but malignant transformation is rare.2
For example, only 1% of endothoracic goitres present as ectopic or autonomous goitre and usually there is no parenchymal connection with the thyroid gland.3
In addition, most patients with retrosternal goitres have a cervical mass and experience dyspnoea, dysphonia, dysphagia, pericardial effusion and superior vena cava syndrome.4
The peak incidence of anaplastic carcinoma occurs in old age around the seventh decade; more than 60% of cases involve patients 65 years and older.5
Anaplastic thyroid carcinoma can present as a long-standing differentiated carcinoma that suddenly becomes fulminant after an interval of several years. In a retrospective study of 84 patients with anaplastic carcinoma, 21% had been diagnosed with differentiated thyroid carcinoma, and 37% reported having a goitre that was dormant for a long time and then underwent a sudden burst in growth.6
In the present case, the origin of the anaplastic tumour on the ectopic gland is clearly shown to be from a previous papillary carcinoma. Unfortunately, anaplastic carcinoma is associated with a very poor patient prognosis as it is one of the most aggressive thyroid cancers.7
Metastatic spread is common in anaplastic tumours with 75% of patients already having distant metastases detected at the time of diagnosis. Frequently these tumours metastasise to the lungs, bones, mediastinum and peritoneum.8
In this case, the patient did not have detectable metastases. Advanced age, male gender and dyspnoea at the time of diagnosis are associated with a worse prognosis.9
The presence of leucocytosis and eosinophilia in the patient's peripheral blood was of relevant clinical interest in this case especially in the absence of detectable infection. In fact, previous studies have reported the occurrence of thyroid carcinoma concomitant with leukemoid reaction and hypereosinophilia, but none was located in an ectopic mass.10
Moreover, the haematopoietic growth factors produced by tumoural tissue can cause eosinophilia and neutrophilia associated with non-lymphohaematopoietic malignant diseases, such as differentiated thyroid carcinoma11–13
and anaplastic carcinoma.10 14–17
Furthermore, paraneoplastic leucocytosis is usually associated with granulocyte-colony-stimulating factor-producing tumours such as anaplastic thyroid carcinoma.15
Therefore, the present case was unique in its presentation of leucocytosis and hypereosinophilia as a manifestation of anaplastic carcinoma in an ectopic thyroid.
- This rare condition must be included in the differential diagnostic of leucocytosis and hypereosinophilia especially when infection and bone marrow proliferative diseases are ruled out.
- An ectopic thyroid should be followed for the possibility of neoplastic transformation.
- Ectopic goitre without thyroid involvement is rare.