Differentiating focal periphyseal edema zone and physeal bar using a novel quantitative analysis on knee MRI: A pilot study.

Abstract

The magnetic resonance imaging (MRI) appearance of focal periphyseal edema (FOPE) zone mimics that of a physeal injury, and differentiating it from a physeal bar is vital.The purpose of this study was to investigate whether quantitative analysis of percentage signal difference at the site of abnormal and normal physis on MRI has a role in differentiatingFOPEzone and physeal bar. A retrospective review of knee MRI reports for patients under the age of 16 years carried out over the last 10 years was performed to search for cases where a diagnosis of FOPE or physeal bar was reported on MRI and confirmed clinically or with follow up imaging. The average signal intensity was calculated using multiple small region of interest circles, and the mean percentage signal difference was calculated at both the abnormal and normal sites. A total of 213 patients with an age range of 1-15 years underwent knee MRI scans and there were 14 (eight male, six female) FOPE lesions and 17 (seven male, 10 female) physeal bars. There was more than 50% (P < 0.001) mean signal difference on the gradient echo (GRE) sequence at the site of the physeal bar compared with adjacent normal physis, versus about 10% (P < 0.001) mean signal difference in the FOPE lesion. On the short tau inversion recovery (STIR) sequence, the mean signal difference was around 30% in physeal bar and less than 10% in FOPE lesions.An optimal cut-off value of ≥35% yielded 100% sensitivity and specificity for GRE. Addition of calculation of percentage signal difference on GRE and STIR sequences to standard imaging features can increase diagnostic confidence of differentiating FOPE zone from physeal bar.