Objective: Inadvertent lumbar facet joint injection during an interlaminar epidural steroid injection (ESI) is rare when using the loss-of-resistance technique. The pattern of contrast material on the lateral view can mimic that of a successful ESI. The purpose of this study is to illustrate the imaging features of this event.
Materials and methods: From 2001 to 2009, 6,631 interlaminar lumbar ESIs were performed. Cases in which facet joint injection was recognized by the radiologist were identified by a text search of the report for the term "facet" and corroborated by review of the case images and the patients' medical records.
Results: Forty-two positive events were identified. Imaging features are characteristic and include sigmoid-shaped area of contrast material projecting over the posterior elements on the lateral view and an ovoid area of contrast material projecting over the facet joints on the anteroposterior (AP) view. Thirty-one out of 42 events were recognized by the operator during the procedure. In 17 cases, the final images documented the appropriate location of the needle tip within the epidural space. In 9 cases, simultaneous epidural and facet joint injection occurred. In 16 cases, epidural contrast material was not documented.
Conclusion: Lumbar facet joint injection has a characteristic appearance and can be distinguished from epidural injection. However, since this event can simulate the appearance of a successful ESI, it may be unrecognized during the procedure. Therefore, the true incidence is likely higher than that suggested by this study. Recognizing the imaging features of this event permits the operator to further manipulate the needle tip and increase the success rate of ESIs.