Abstract
Primitive neuroectodermal tumours (PNETs) are aggressive undifferentiated tumours that occur mainly in the central nervous system (CNS). Reviewing the literature, only six cases of primary PNET of the mandible have been reported. These rare tumours are usually overlooked in clinical practice. An 18-year-old woman who presented with dental caries and left cheek swelling was initially diagnosed with facial cellulitis, but the swelling persisted despite adequate intravenous antibiotic therapy. Subsequent ultrasound and MR examinations revealed a tumour originating from the left mandibular ramus. The ultrasonography-guided percutaneous core needle biopsy confirmed the diagnosis of peripheral PNET. The radiographic features of mandibular PNETs are similar to those of PNETs in other regions, except for haemorrhage, necrosis and calcification. In addition, this is the first reported case with sonographic and MR images of this rare tumour, and the first case that was diagnosed based on the ultrasonography-guided percutaneous core needle biopsy. Using these image characteristics, mandibular PNETs can be diagnosed more accurately.