Schwannomas are encapsulated tumors that arise from nerve sheath cells. They are characterized by an eccentric growth pattern, compressing rather than infiltrating the nerve. In approximately 25% of the cases, they are located in the head and neck region and their behavior is benign.1 Malignant transformation occurs extremely infrequently.2 Preoperative diagnosis of these tumors is complicated. On ultrasonography, King et al3 suspect a schwannoma when the mass is solitary, oval, and hypoechoic and there is no echogenic hilum but there is posterior enhancement. They admit, however, that the latter characteristic can easily cause schwannomas to be confused with cystic lesions, as schwannomas may also contain cystic areas. Differentiating schwannomas from neurofibromas is difficult as well, because neurofibromas show the same ultrasonographic features. King and colleagues were able to identify the associated nerve in only 5 of 8 cases.
Radiology Quiz Case 1—Diagnosis. Arch Otolaryngol Head Neck Surg. 2007;133(8):836. doi:10.1001/archotol.133.8.836