We present, to our knowledge, the first instance of cerebellar metastasis of papillary thyroid carcinoma prior to the identification of primary thyroid papillary carcinoma. Prior cases of brain metastasis from occult carcinoma measuring (< 3 mm) were recently published [12, 13]. In this report, the patient presented with neurological symptoms initially, but the thyroid primary was identified at the time [12, 13]. In both of these reports, the site of the metastasis was the occipital lobes. Brain metastases are rare (0.15 – 1.3% of all metastatic thyroid carcinoma) [4]. Although several brain metastasis have been reported, (Additional file 1) the primary thyroid carcinoma was diagnosed at the time of the brain metastasis [5–11, 14, 15].
The most common sites for distant metastasis of PTC are the lungs, followed by the bone [3], and rarely to the skin, liver and brain [2–17]. The literature review showed a reported case of metastasis to each of the following sites: breast, parotid, adrenal, pituitary, kidney, porta hepatis, the orbit, the sphenoid sinus, pancreas and the skeletal muscles.
Several investigators have attempted to determine the risk factors for distant metastases which include male gender, advanced age, histologic grade, extrathyroidal invasion at initial examination, and completeness of surgical resection of the primary tumor [1, 16].
Chiu A C et al, [18] reported 47 instances of brain metastases from thyroid cancer (32 of them with differentiated carcinoma), that were presented at M.D Anderson Cancer Center between March 1944 through September 1995. In that study, 68% were identified during the subsequent course of disease, 23% discovered at autopsy, and only 15% as a primary clinical feature at initial presentation. The median survival was 4.7 months once the brain metastases were diagnosed, with a disease-specific mortality rate of 78%. A solitary lesion with complete surgical resection was found to be associated with a better prognosis.
Misaki T et al [17] reported nine cases of differentiated thyroid carcinoma that metastasized to the brain; seven of them were PTC. They noticed that the median survival time for patients after discovery of brain metastases is 9.4 months. None of the brain lesions showed significant uptake of radioactive iodine, probably due to the blood brain barrier. It was recommended that CT scan or MRI should be performed for any patient with suspicious neurological symptoms. For therapy they recommended radiosurgery as alternative for surgical removal, although they used it for only 2 patients.
Radioiodine scan may not be reliable to detect brain metastasis from PTC [16, 17]; however, a high serum thyroglobulin level may be helpful but not specific [16, 17], as it is usually high in all metastatic disease.
Surgery, radiotherapy, and radioactive iodine therapy have been used with varying results for treatment of brain metastases from papillary thyroid carcinoma. The best therapeutic option seems to be resection, followed by radioactive iodine therapy [4], although there is no clearly defined protocol concerning the management of intracranial metastases [4].
Retrospectively, the cause of the patient's hoarseness of voice was the invasion of the recurrent laryngeal nerve by the PTC. Approaching a patient with brain metastases should involve the thyroid gland and the possibility of brain metastases from PTC during the course of follow-up should be kept in mind.
