CASE STUDY
A 58-year old male presented to our institution with a 3-month history of progressive generalised weakness. He had been previously well and had no prior history of radiation exposure, nor a family history of thyroid cancer. On examination he had a firm, immobile nodule in the right lobe of the thyroid, flaccid paralysis of his upper limbs and spastic paraparesis in the lower limbs, with a T4 sensory level and preservation of bowel and bladder function. The patient was clinically and biochemically euthyroid, with a thyroid-stimulating hormone level of 0.66 mIU/L (0.27–4.2 mIU/L).
Magnetic resonance imaging of the neck showed a mixed density mass with areas of necrosis and calcification, arising from the right lobe of the thyroid gland (Figure 1A). The mass measured 40 mm × 56 mm × 33 mm. It was well circumscribed; however, it extended posteriorly into the vertebral space and attenuated the proximal cervical oesophagus. There was a complete destruction of the C7 vertebral body with a partial destruction of C5 and C6 and invasion into the spinal canal. Similar lesions were noted in the lumbar and sacral spine as well as the pelvis.
(A) MRI of the cervical spine showing mass (arrow) arising from right lobe of thyroid extending posteriorly into vertebral space causing a destruction of C5, 6 and 7 vertebrae and (B) microscopy showing fibroconnective tissues infiltrated by variably sized, colloid-containing thyroid follicles showing no nuclear features of papillary thyroid carcinoma
Biopsy of the mass revealed follicular thyroid carcinoma with an infiltration of fibrous tissues by follicles containing colloid materials (Figure 1B). Biopsy of the sacral mass also contained thyroid follicles proving metastatic disease. Due to the instability of the cervical spine as a result of extensive tumour invasion, the mass was deemed inoperable and the patient was referred to for palliation. He demised shortly thereafter.
DISCUSSION
Follicular thyroid cancer is the second most common variant of thyroid cancer and is associated with a higher mortality than papillary thyroid carcinoma.(1) It spreads primarily via the haematogenous route mainly to bone and the lung.(1) Although more aggressive than PTC, cervical cord compression due to local invasion of differentiated thyroid cancer is exceedingly rare. Common sites for an extrathyroidal extension of differentiated thyroid cancer include the trachea, oesophagus and recurrent laryngeal nerve.(2) To our knowledge, less than five cases of contiguous spread to the cervical spine have been reported in the literature.(3,4) These patients generally presented with clinical features of spinal cord compression (3,4) while one patient presented with a cervical radiculopathy.(3) Most patients with spinal cord compression did not survive.(3) Magnetic resonance imaging is an important diagnostic modality to differentiate local invasion from bony metastases to the cervical spine.(3)
Factors associated with a higher mortality include older age at presentation, distant metastases and tumour sizes above 40 mm.(5,6) In general, differentiated thyroid cancer is associated with a good prognosis, particularly if diagnosed early.(2,5) However, we believe that the delayed presentation and extent of local invasion at presentation in this case were the key factors leading to the poor outcome.