Patient Information

Age: 10 years

Gender: Spayed Female

Breed: Mixed Breed Canine

Weight: 39 pounds

History

Patient was presented for ultrasound of the neck due to weight loss, changes in hair coat, a palpable neck mass, and an elevated T4 (7.5ug/dL; RR 0.8-3.5Ug/dL) with otherwise normal CBC/chemistry. The neck mass had been previously aspirated by the referring veterinarian a few years prior when it was about 1cm. Cytology is reported to have come back as a lipoma/fatty tissue at that time.

Cervical ultrasound

The left thyroid is not specifically identified. There is a large (3.0x4.1cm sagittal; 3.0x3.8cm transverse) hyperechoic heterogenous cavitated mass in the left neck that is highly vascular.

The right thyroid gland is normal in size, shape, and echogenicity. (Right Thyroid - 3.1x0.5cm)

The cranial most parathyroid gland is mildly enlarged - 1.8x4.5mm. The caudal most parathyroid is normal in size - 1.8x3.1mm

All other structures within the neck were within normal limits

Imaging

Differentials

Neck mass - the findings are moderate - Ddx: thyroid neoplasia (carcinoma vs. adenocarcinoma vs. adenoma vs. granuloma vs. cyst) vs. lymphadenopathy vs. other neoplasia

Right Parathyroid Enlargement - the findings are mild - DDx: normal for this patient (suspected) vs. diffuse hyperplasia vs. adenoma vs. adenomatous hyperplasia vs. adenocarcinoma (Normal Parathyroid Size = 2-3mm; Parathyroid Neoplasia > 4mm (mean of 7mm); Parathyroid Hyperplasia > 2mm < 4mm (range 3-6mm))

Additional Diagnostics/Recommendations

Right parathyroid gland enlargement is very mild and could be normal for this patient. Recommend screening total and ionized calcium level +/- PTH levels. If hyperparathyroidism is clinically suspected, right parathyroidectomy could be considered.

Cytology

Ultrasound guided aspirates of the neck mass were obtained for cytology and submitted to Eastern Vet Path for analysis. Unfortunately, the aspirates were inconclusive due to low cellularity, however the slides consisted of a lightly proteinaceous background, scattered red blood cells, and scattered free nuclei, and were therefore not suggestive of a lipoma. Re-aspiration or biopsy with histopathology was recommended.

CT, Surgery, and Biopsy with Histopathology

The patient was referred first for oncology consultation where a cervical CT was performed and a cystic mass was confirmed to be thyroid in origin. She was then referred to a specialty veterinary facility for surgery where a left thyroidectomy was performed. The mass was submitted for histopathology and confirmed thyroid carcinoma without angiolymphatic invasion.

Outcome

The patient is doing well following surgery and remains asymptomatic. As expected following thyroidectomy for a functional tumor, she is experiencing hypothyroidism and is currently on a tapering course of Levothyroxine.

Discussion

Though cytology was inconclusive for this case, a thyroid carcinoma was suspected based on the patient’s clinical signs, lab work, and the sonographic appearance of the mass. Thyroid carcinomas are typically large, heterogeneous, and moderately to strongly vascularized as was the case in this patient. Unfortunately they do not always exfoliate well or samples are hemodiluted due their large blood supply and cytology is not always rewarding, however referral for additional diagnostics and surgery could still be confidently recommended in this case based on other evidence.

Sonographer: Meredith Adams DVM

Special thanks to Midlothian Animal Clinic and Eastern Vet Path for their collaboration on this case!