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Cervical CT, soft tissue window

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On CT images of the neck, both thyroid glands are normal in size, shape, and architecture. There is a large (~6.5cm) poorly marginated soft tissue density mass arising ventral to the common pharynx. The mass can not be visually separated from the base of the tongue or the hyoid apparatus, and appears to extend into the ventral wall of the pharynx. There is partial destruction of the bones of the hyoid apparatus. There is moderate contrast enhancement present throughout the mass. There is no lymphadenopathy in the region imaged. On the post-contrast images, there is also focal contrast enhancement along the falx cerebri in the region of the olfactory bulb.

(No followup on the brain lesion at this time)

Diagnosis

Ectopic thyroid follicular carcinoma.

Discussion

The neoplasm has features consistent with derivation from follicular cells. It is infiltrative in into connective tissue stroma. However, it is not known whether this is stroma that is internal to the mass and the mass is still contained by a connective tissue capsule or if this is infiltration occurring external to the original thyroid capsule. Endocrine tumors in general have a propensity to invade local vasculature and in the case of thyroid carcinomas, there may be spread to the thoracic cavity via blood vessels prior to involvement of the regional lymph node.

Rossi F, Caleri E, Bacci B, Drees R, Groth A, Hammond G, et al. Computed tomographic features of basihyoid ectopic thyroid carcinoma in dogs. Vet Radiol Ultrasound. 2013 Jun 23.