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

Abstract

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.

Keywords: Fine needle aspiration cytology; Neck; Plexiform fibrohistiocytic tumor; Thyroglossal duct cyst.

Fig. 1

a Smear showed vaguely whorled clusters of plump histiocytoid cells (x400). b Loose sheet of plump histiocytoid cells and dispersed singly occurring spindle cells with long tapering cytoplasm (x200). c Osteoclastic type multinucleated giant cell (x400). d Low power magnification of the tumor with a nodular to plexiform arrangement separated by dense collagenous stroma. (a, c–HC, b–PAP)

Fig. 2

a Low power magnification of a poorly circumscribed tumor in the subcutaneous fat with radiating fibroblastic extensions from the center of the mass to the surgical margin (H&E). b Center of the tumor with nodular arrangement of tumor cells (H&E x100). c Fascicles of fibroblastic-type spindle cells with longer tapering cytoplasmic processes (H&E x200). d Osteoclastic type multinucleated giant cells admixed with histiocytoid cells (H&E x400). e SMA staining in spindle and histiocytoid cells but absent in the multinucleated giant cells (x400). f CD68 staining in multinucleated giant cells and histiocytoid cells (x400)