Parapharyngeal space schwanomma :MRI

• The parapharyngeal space is often described to be a deep potential neck space shaped as an inverted pyramid. 
• The base of the pyramid is at the skull base, and the apex is at the greater cornu of the hyoid bone. Clinically, the parapharyngeal space should be considered in two compartments: pre-styloid compartment and poststyloid compartment. 
• This patient showed well-defined, iso- to hyper-intense mass with heterogenous areas of enhancement in the left parapharyngeal space in the poststyloid compartment, displacing the major vessels and compressing the oropharyngeal airway.
• Of all the parapharyngeal space tumors, 70–80 % are benign, and 20–30 % are malignant. 
• Most PPS tumors are of salivary or neurogenic origin. 
• The schwannoma is the most common neural tumor found in the PPS. The vagus nerve is reported to be the origin for 50 % of parapharyngeal space schwannomas, and the cervical sympathetic chain is the next common source.  On most occasions, separation of the IJV and ICA is useful to distinguish vagal and sympathetic chain schwannomas.
• Metastatic lymph nodes, paragangliomas, and vagal schwannomas are the usual differential diagnoses to be considered. 
• Metastatic lymph nodes are often multiple, with a known primary, making the diagnosis easy However, a solitary metastatic node from an unknown primary cancer may be difficult to differentiate from a schwannoma in the absence of periadenitis or extranodal extension of disease. 
• Paragangliomas show early arterial enhancement on CT; they are hypervascular lesions (while schwannomas are hypovascular) and show certain characteristic MR imaging appearances like scattered flow voids (“salt and pepper” appearance), that usually enable the appropriate diagnosis