Sonographic Features and Diagnosis of Peripheral Schwannomas.

BACKGROUND: To determine the sonographic features of peripheral schwannomas.

METHODS: This retrospective study included 54 cases of schwannoma in 51 patients. Ultrasonography (US) and MRI were performed in all patients. The US features of each tumor were analyzed and compared with pathologic findings. The US target sign was compared with the MRI findings.

RESULTS: On US, 53 of the 54 schwannomas had a regular shape and clear margins, and one had an irregular shape. Thirty-seven of the 54 schwannomas were categorized as solid, 16 as cystic and solid, and one as entirely cystic; distal sound enhancement was associated with 47 schwannomas. The target sign was seen in 24, the rat tail sign in 28, the vessel accompanying sign in 22, and the split fat sign in 5. The entering and exiting nerves were situated centrally in 9 and eccentrically in 19 schwannomas. Vascularity on color Doppler imaging using a 0 to III scale was graded 0 in 4 schwannomas, I in 10, II in 26, and III in 14. Twenty-four target signs were detected in 54 schwannomas by US, and 28 were detected by MRI. There was good agreement between the target signs noted on US and those seen on MRI (κ = 0.631, p < 0.001).

CONCLUSIONS: The sonographic diagnosis of peripheral schwannomas is feasible and reliable. The target sign is a prominent US feature in peripheral schwannomas, comparable to that observed with MRI. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:127-133, 2017.