Cystic thyroid carcinoma (superior mediastinal mass)

Case contributed by Michael P Hartung
Diagnosis certain


Neck mass.

Patient Data

Age: 80
Gender: Male

Complex solid and cystic mass inferior to the right thyroid lobe extending into the superior mediastinum. Most of the mass is cystic, with enhancing solid soft tissue along the posterior aspect. Few fine calcifications along the posterior aspect. The mass abuts the proximal esophagus and trachea. 


Specimen: A-B - Right thyroid cyst (malignant appearing)

Clinical History: Thyroid nodule.

Operation/Procedure: Right thyroid lobectomy and isthmusectomy

Diagnoses: Sclerosing fibrous lesion with atypical follicular cells suspicious for neoplasm.

Addendum: This case was sent out for consultation to Dr. X. Dr. X favors a diagnosis of “Carcinoma, favor poorly differentiated of thyroid origin”

Case Discussion

This is a great case to ponder the differential diagnosis for a superior mediastinal mass. The mass closely approximates the lower right thyroid gland, but it is not completely clear that it arises from it. However, when you consider the differential diagnosis for a solid and cystic mass extending into the superior mediastinum, there are not many options. It is not in the location you would expect for a germ cell or thymic tumor. It does not look like lymphoma, and there is no adenopathy elsewhere. Finally, a cystic nodal metastasis from head and neck tumor would be possible, but unlikely in the absence of other cervical chain nodal mets.  

The trouble in this case was it previously had a BENIGN biopsy. This can almost be expected, given that the only enhancing soft tissue is located quite deep and posterior in the mass, and the biopsy yield was understandably very low yield and mostly cystic. However, one of the jobs of the radiologist in this case is to insist that the chances of malignancy are quite high, and that a repeated biopsy with special targeting of the vascular soft tissue or surgical excision is indicated. It was not until surgical excision (and second pathologic opinion) that a confident diagnosis of poorly differential thyroid carcinoma was made. 

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