Magnetic resonance imaging findings of a presumptive calcitonin‐negative neuroendocrine canine thyroid tumour with suspected metastasis to the cervical vertebral canal and intracranial extension

Abstract A 6‐year‐old Portuguese water dog presented with progressive tetraparesis. Magnetic resonance imaging revealed a left thyroid gland mass and a large, left‐sided, extradural mass in the cranial cervical vertebral canal extending into the caudal cranial fossa. Both masses were heterogeneously hyperintense on short tau inversion recovery, T2‐ and T1‐weighted images, with moderate to marked contrast enhancement. Ultrasound showed the thyroid mass as hypoechoic and heterogeneous, while the extradural spinal mass was mildly heterogeneous, of medium echogenicity, and hyperechoic to the spinal cord. Fine needle aspiration cytology showed evidence of a thyroid carcinoma with metastasis to the cervical spine. Immunocytochemistry of both masses was negative for thyroglobulin and calcitonin. The thyroid mass was positive for chromogranin A but negative for synaptophysin. The final diagnosis was a calcitonin‐negative primary neuroendocrine tumour of the thyroid gland. This is the first clinical report of a metastatic thyroid gland carcinoma in the cervical spine of a dog documented by magnetic resonance imaging.