- 5–year–old female spayed golden retriever that presented for further evaluation of a ventral cervical mass with a duration of two weeks. Prior to this, she was noticed to be panting heavily on walks, had exaggerated swallowing and more recently, intermittent gagging.
- Bloodwork was obtained prior to presentation to our clinic. It revealed a mild hypoalbuminemia (26) [reference interval; 27-39 g/L], and a mild hyperglobulinemia (47) [reference interval; 24-40 g/L] as the main significant findings.
- Physical examination revealed moderate pyrexia (40°C) and a 4cmx5cm multilobulated, firm, moveable cervical mass immediately dorsal in proximity to the normal thyroid gland.
View the five CT video clips of the neck and thorax thorax below; then make your diagnosis:
Head/Neck and Thorax:
- Centered on the hyoid apparatus at the base of the tongue there is a large, soft tissue attenuating, moderately heterogeneously contrast enhancing mass that causes lysis of the ceratohyoid, basihyoid, and thyrohyoid bones. The margins of the mass are poorly defined with similar heterogeneous contrast enhancing lesions seen in the ventral subcutaneous tissues adjacent to the hyoid apparatus and laryngeal region.
- The medial retropharyngeal lymph nodes are moderately enlarged, with irregular margins and non-uniform contrast enhancement.
- In the dorsal aspect of the right caudal lung lobe there is an irregularly marginated soft tissue density mass that has mild contrast enhancement.
- Multiple other small (<5mm) irregular soft tissue dense nodules are present in the remainder of the lungs.
- The tracheobronchial lymph node is moderately enlarged.
- A small enhancing nodule is in the caudal aspect of the left lateral liver lobe
- Multifocally in the skin on the dorsal aspect of the neck and cranial thorax there are a few soft tissue density nodules.
- Extensive aggressive mass centered on the hyoid apparatus. Primary differentials at the time was neoplasia with basihyoid ectopic thyroid carcinoma, adenocarcinoma, or squamous cell carcinoma being considered. Infectious etiologies (e.g., abscess or fungal granuloma) were considered less likely.
- Right caudal lung lobe mass. Differentials at the time included metastatic lesion from ventral neck mass, concurrent primary pulmonary neoplasia such as bronchogenic carcinoma, pulmonary abscess or fungal granuloma (e.g., blastomycosis).
- Multifocal small irregular pulmonary nodules. Differentials at the time included metastasis from the ventral neck mass or right caudal lung lobe mass or infectious disease (e.g., pneumonia)
- Mild-moderate medial retropharyngeal and tracheobronchial lymphadenopathy. Differentials at the time included neoplastic metastasis or reactive lymphadenitis.
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Solitary hepatic nodule. Differentials at the time included nodular hyperplasia, a hemangioma, hepatoma, or malignant neoplasia (Hepatocellular carcinoma, Hemangiosarcoma).
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Nonspecific multifocal subcutaneous nodules.
Diagnosis:
Fine needle aspirates of the cervical mass and the medial retropharyngeal lymph nodes were obtained.
Cytology results from all samples revealed marked suppurative inflammation with Blastomycoses sp. infection.
Discussion:
Blastomycosis (Blastomyces dermatitidis) is a saprophytic yeast organism endemic to North America in areas surrounding the Ohio and Mississippi River valleys and the Great Lakes. (1) Young, large breed, intact male dogs are over-represented, specifically Labrador Retrievers, Golden Retrievers and Doberman Pinchers. (2,3) Multiple involvement of different organ systems is common, particularly the CNS, bone and lymphatic systems, eye, and skin. (4,5)
This clinical presentation of Blastomycosis was unique in that the ventral cervical mass was masquerading as a possible basihyoid ectopic thyroid carcinoma. CT features of basihyoid ectopic thyroid carcinomas have been described as oval to bi-lobed masses centered on the basihyoid bone with associated bone lysis, highly vascularized capsules with central poorly contrast enhancing areas. (6) Tumor metastases to the retropharyngeal lymph nodes and lung have also been reported with basihyoid ectopic thyroid carcinomas. (6)
After approximately 4 months of Itraconazole therapy, the ventral cervical mass was no longer palpable and the pulmonary nodule was no longer visible on thoracic radiographs. After approximately 7 months of Itraconazole therapy, the patient’s urine Blastomycosis antigen test was negative and medical therapy was discontinued.
Blastomycosis should be considered as a differential diagnoses in patients from endemic areas with CT-imaging findings of soft tissue dense mass centered over the hyoid apparatus.
References:
1.Epidemiologic and Ecologic Features of Blastomycosis: A Review. Kaitlin Benedict, Monika Roy, Tom Chiller, Jeffrey P. Davis
2. Evaluation of risk factors for blastomycosis in dogs: 857 cases (1980-1990) D.G. Rudmann, B.R. Coolman, C.M. Perez, et al. J Am Vet Med Assoc, 201 (1992), pp. 1754-1759
3. Blastomycosis in dogs: 115 cases (1980-1995) K.A. Arceneaux, J. Taboada, G. Hosgood. J Am Vet Med Assoc, 213 (1998), pp. 658-664
4. Brömel C, Sykes JE. Epidemiology, diagnosis, and treatment of blastomycosis in dogs and cats. Clin Tech Small Anim Pract 2005;20:233–239
5.Kerl ME. Update on canine and feline fungal diseases. Vet Clin North Am Small Anim Pract 2003;33:721–747.
6.Computed Tomographic Features of Basihyoid Ectopic Thyroid Carcinoma in Dogs. F Rossi, E Caleri, B Bacci, R. Drees, A. Groth, G. Hammond, M. Vignoli, T. Schwartz. Vet Radiol Ultrasound, 23 Jun 2013.