Solitary fibrous tumor of the perithyroid soft tissue. Report of a case simulating a thyroid nodule.

A case of solitary fibrous tumor (SFT) of the perithyroidal soft tissue is reported. Due to its proximity to the upper aspect of the right thyroid lobe, its slow growth and its ultrasound features, the tumor was confused with a thyroid nodule. Two fine needle aspirations (FNA) gave only scant non diagnostic material. For these and cosmetic reasons together with the fact that ultrasound exam detected two solid nodules in the left lobe, a thyroidectomy was decided. Examination of the surgical specimen showed a nodule that was well demarcated and, although entirely extrathyroidal, bulged from the thyroid profile in a niche of the upper medial aspect of the right lobe. On histologic, immunohistochemical, and ultrastructural examination the tumor fulfilled the criteria for a diagnosis of solitary fibrous tumor. Thus, SFT must be considered in the differential diagnosis of suspected thyroid nodules mainly when FNA gives only scanty non diagnostic material which is unusual in thyroid hyperplastic nodules.