Plexiform Fibrohistiocytic Tumor Presenting as a Central Neck Mass Clinically Mimicking a Thyroglossal Duct Cyst: An Unusual Case Reported with Histo-cytopathologic Correlation and a Review of the Cytopathology Literature.

We present the case of an uncommon example of a plexiform fibrohistiocytic tumor (PFHT) occurring in the anterior central neck region of a 40 year-old female with previous subtotal thyroidectomy. The tumor clinically mimics a complicated thyroglossal duct cyst. On fine needle aspiration cytology, the tumor was composed of sheets of bland spindle cells and nests of plump histiocytoid cells in vaguely whorled arrangements. Occasional multinucleated giant cells were also identified. The excised specimen showed an irregular, highly infiltrative subcutaneous tumor arranged in a nodular/plexiform pattern concentrated to the center of the tumor mass. In addition, the tumor contained numerous tongue-like extensions composed of variably cellular, fibroblastic/fibromatosis-like areas. These fibroblastic/fibromatosis-like extensions reached far from the epicenter of the tumor and were associated with scattered small plexiform nodules of histiocytic cells. These tongue-like extensions multifocally involved the surgical margins. The fibroblastic and histiocytoid cells showed diffuse smooth muscle actin (SMA) expression. The multinucleated giant cells and also the histiocytoid proliferation were positive for CD68. This case illustrates an uncommon both anatomical and demographic manifestation of PFHT and also characterize the fine needle aspiration cytologic features in this tumor, which previously have been reported in a few cases.