Ultrasound (US), CT, MRI, and physical examination findings were compared for evaluation of canine thyroid carcinoma. There were 3 objectives: 1) identify CT and MRI features in canine thyroid carcinoma; 2) compare the sensitivities of US, CT, and MRI in diagnosing thyroid carcinoma; and 3) compare physical examination and radiologic findings in the evaluation of regional lymphadenopathy and local invasion of the thyroid mass. Diagnosis was ultimately confirmed with histology.

Characteristics of the masses examined included origin, size, degree of vascularization, capsule disruption, local tissue invasion, and lymphadenopathy. With MRI, thyroid carcinomas appeared hyperintense compared with surrounding muscle; on CT, thyroid carcinomas showed a lower attenuation value than did normal thyroid tissue; mineralization and fluid pockets within masses were common as well. The most common presenting clinical signs were respiratory and included coughing, dyspnea, gagging, and stertor/stridor.

MRI had the highest sensitivity (93%) and CT the highest specificity (100%) in diagnosing thyroid carcinoma. In this study, MRI was preferred for diagnosing and staging thyroid carcinoma. US had the lowest sensitivity and specificity but was useful as an initial screening tool. Palpation was not accurate in determining local tissue invasion.

Commentary
Masses in the neck of dogs may arise from multiple tissues (eg, mandibular/retropharyngeal lymph nodes, salivary glands, thyroid/parathyroid glands, esophagus, trachea, hyoid apparatus). Not all cervical masses are caused by neoplasia; for example, cervical masses may represent abscesses or hematomas. Although this study focused on a specific tumor type (thyroid carcinoma), it demonstrated the difficulty of identifying the exact organ of origin and local extension of large cervical masses, particularly with US. Accurate identification and mass histopathology significantly impact surgical or medical options and prognosis. When presented with a cervical mass, referral should be considered for cross-­‐sectional imaging (eg, CT, MRI) or consultation with a diagnostic imaging specialist.—Ajay Sharma, BVSc, MVSc, DVM, DACVR

Source
Comparison between clinical, ultrasound, CT, MRI, and pathology findings in dogs presented for suspected thyroid carcinoma. Taeymans O, Penninck DG, Peters RM. VET RADIOL ULTRASOUND 54:61-70, 2013.