Background Solitary fibrous tumor (SFT) is a ubiquitous mesenchymal neoplasm but it rarely occurs in the parotid gland. The histological features are variable, with the majority having spindle cell morphology and non-specific branching (staghorn) ecstatic vascular pattern. SFT ranges from benign to overtly malignant. Dedifferentiation within SFTs represents an abrupt transition from a well-differentiated component to a high-grade area, the latter most often including poorly differentiated epithelioid/round cell or high-grade spindle cell morphology. To the best of our knowledge, dedifferentiated SFT in the parotid gland has not been previously reported. Case presentation A 33-year-old woman presented with a soft tissue tumor in the right parotid gland that had been present for 6 months. Fine needle aspiration (FNA) cytology indicated epithelioid morphology in the dedifferentiated component of the tumor, along with metachromatic myxoid matrix. The tumor was initially interpreted as a salivary gland neoplasm of uncertain malignant potential (SUMP).Right partial parotidectomy was performed, and microscopic examination of the resected specimen revealed a malignant spindle cell tumor with a central epithelioid/anaplastic component. The tumor cells were diffusely positive for CD34, STAT-6 and FLI-1, and negative for pan-cytokeratin, CAM5.2, p63, S100 protein, CD31, SMA, and calponin.ERG and Ki67 immunostaining showed an accentuated nuclear staining pattern in the central dedifferentiated area. There was no overexpression of p53 or p16. The patient is currently undergoing regular follow-up and is 11 months postresection with no evidence of recurrence or distant metastasis. Conclusions Unlike the typical spindle cell morphology of conventional SFTs, malignant SFTs can show areas of dedifferentiation mimicking an epithelial neoplasm. FNA of dedifferentiated SFTs of the parotid gland may show, a combination of atypical epithelioid cells and metachromatic myxoid/collagenous matrix, which is a less emphasized cytological feature of SFT and may lead to misdiagnosis as a more common parotid gland epithelial neoplasm.

Background F-18 Fluorodeoxyglucose positron emission tomography with computed tomography (FDG PET/CT) is a powerful tool in oral cancer. However, the oral cavity is a small cavity with complex components. An invasive cancer or post-therapy change frequently cause difficulty in interpretation. In this study, we established a tongue depressor (TD)-assisted FDG PET/CT protocol to solve this problem. Methods We enrolled 264 patients with oral cancers. Early and delayed images were acquired in each FDG PET/CT examination. A wooden tongue depressor was placed either between buccal mucosa and teeth or between tongue border and teeth in delayed image. TD placed delayed image was compared with early images to analyze the extent of tumor. The discrimination ratio (DR) of the tumor was calculated as: (images that can clearly distinguish features /all images) × 100%. Results In tongue cancer group, the DR of the tumors were 26.1% on early images and 99.3% on TD placed delayed images (p < 0.001). In buccal cancer group, the DR of the tumors were 10.9% on early images and 98.2% on TD placed delayed images (p < 0.001). Conclusions The TD-assisted FDG PET/CT protocol is patient-friendly and effective in analyzing the tumor when evaluating oral cancer.