Imaging of the parapharyngeal space: anatomy and pathology.

A multitude of histologic neoplasms occur within the boundaries of the parapharyngeal space. Contrast enhanced computed tomography and recently MRI have greatly enhanced the preoperative diagnosis of parapharyngeal space tumors. MRI is currently the modality of choice in evaluating masses originating in the parapharyngeal space or masses from adjacent spaces which grow into the parapharyngeal space. Gadolinium DTPA enhanced MRI of head and neck tumors is helpful for demonstrating neoplastic involvement of paranasal sinus, perineural tumor extension, or intracranial extension of neoplasms. Parapharyngeal space tumors are equally demonstrated by unenhanced MRI. The majority of tumors involving the parapharyngeal space are from the deep portion of the parotid gland or from minor salivary glands, and the majority of these tumors are benign mixed tumors. Based on the CT appearance and enhancement characteristics, it is difficult to accurately distinguish a minor salivary gland tumor from a neurogenic tumor. MR tissue signal characteristics alone cannot be reliably utilized in making this distinction. Internal carotid artery displacement remains the most reliable distinguishing feature. Minor salivary gland tumors will displace the internal carotid artery posterior and lateral, whereas neurogenic tumors will displace the internal carotid artery anterior and medial.