Nerve sheath tumor of extremities: analysis of split-fat sign and entering and exiting nerve sign

Objective To explore the relationship between split-fat sign and entering and exiting nerve sign on MRI in nerve sheath tumors (NSTs) of extremities. Methods The MRI data of 141 patients with benign soft tissue NSTs of extremities confirmed by operation and pathology from January 2014 to July 2018 in the Second Hospital of Zhejiang University School of Medicine were retrospectively analyzed. The patients were divided into intramuscular and intermuscular groups according to the location of the tumors. The split-fat sign and entering and exiting nerve sign in the two groups were compared using χ2 test. Results There were 152 NSTs in 141 patients, including 41 intramuscular NSTs and 111 intermuscular NSTs. There were 48 split-fat sign and 14 entering and exiting nerve sign in intramuscular NSTs, while 9 split-fat sign and 190 entering and exiting nerve sign in intermuscular NSTs. Statistical analysis showed that there were statistically significant differences in split-fat sign (χ2=55.545, P<0.001) and entering and exiting nerve sign (χ2=26.969, P<0.001) between the two groups. Conclusion The split-fat sign mostly appeared in intramuscular NSTs, and the entering and exiting nerve sign mostly appeared in intermuscular NSTs. Key words: Neurilemmoma; Magnetic resonance imaging; Split-fat sign; Entering and exiting nerve sign