Primary intraosseous squamous cell carcinoma (PIOSCC) is a rare malignant tumor originating from remnants of odontogenic epithelium within the central jaw bone. The majority of the PIOSCC cases are diagnosed incidentally on histological findings while a potential malignancy wasn\'t necessarily determined at first on initial investigations. The diagnosis of PIOSCC is challenging and relies on ruling out other types of carcinomas, including metastatic tumors from other primary sites. It is essential for the physician to detect potential clinicoradiologic \"red flags\" for an early diagnosis and appropriate treatment. In this article, we present an unusual case of PIOSCC discovered on a cyst-like lesion with pathological fracture and review the current literature to identify the potential warning features.

BACKGROUND: As a new entity included in the 4th edition of the WHO classification of tumours of soft tissue and bone in 2013, hybrid peripheral nerve sheath tumours are benign composite neoplasms that demonstrate features of more than one type of nerve sheath tumour, with a wide age distribution and a predilection for superficial location. Those involving deep sites are relatively rare. To the best of our knowledge, only one case of primary intraosseous hybrid peripheral nerve sheath tumours has been documented. In this article, we report another case of hybrid peripheral nerve sheath tumours occurring in bone with different clinical, radiological and pathological features from those in the previously reported cases.
METHODS: A 28-year-old female presented with a painful nodule in the right tibia. Radiological examination revealed an oval eccentric osteolytic lesion in the proximal tibia. Histologically, the circumscribed but unencapsulated lesion demonstrated biphasic cellular differentiation. Bland, small epithelioid cells arranged in clusters in the myxoid or collagenous stroma and inconspicuous spindle cells scattered in the hypercellular areas were suggested to originate from Schwann cells according to the detection of S100. Both the elongated spindle cells with thin, wavy nuclei and the spindle cells in fascicular or storiform pattern in hypercellular areas showed a positive immunoreaction for epithelial membrane antigen, indicating perineurial differentiation. Based on histological and immunochemical examinations, the patient was diagnosed with hybrid epithelioid schwannoma/perineurioma. The lesion was resected and has not recurred for 8 months since resection.
CONCLUSIONS: The present case is the second primary intraosseous hybrid peripheral nerve sheath tumour to be reported. This is also the first reported intraosseous tumour composed of epithelioid schwannoma and perineurioma with hypercellularity, indicating diverse involvement sites and a wide range of histological features among hybrid peripheral nerve sheath tumours. Awareness of such diversity is critical for accurate diagnoses. The morphological overlap with other spindle and epithelioid cell neoplasms, especially pure peripheral nerve sheath tumours, requires that immunochemical and molecular examinations be used as objective tools to provide the necessary information for a differential diagnosis.

Central odontogenic fibroma (COF) is an uncommon tumor that accounts for 0.1% of all odontogenic tumors; it has been defined as a benign neoplasm of the jaw. Clinically, the lesion grows slowly and leads to cortical expansion. Radiologically, the most common finding is multilocular radiolucency. The lesions are associated with the crown of an unerupted molar, premolar, or incisor tooth and in some cases, with root resorption or displacement. Histologically, the lesion is characterized by mature collagen fibers and numerous fibroblasts. COF responds well to surgical enucleation with no tendency for malignancy or recurrence. We report a case of a 15-year-old female patient presented with painless swelling of the left side of the maxilla since her childhood. Radiographs revealed an expanding ill-defined radiolucency with a displacement of the adjacent tooth. The impacted tooth was pushed posteriorly. The lesion was removed surgically. There were no postoperative complications.