BACKGROUND: Contralateral contrast medium spreading at very low volumes during a transforaminal epidural injection is rarely seen.

CASE REPORT: A 52-year-old woman with left L4 radicular pain and an L4–L5 broad-based protrusion underwent a left L4 transforaminal epidural steroid injection. After negative aspiration, injecting 0.5 mL of nonionic contrast medium outlined the left L4 root and crossed the midline; an additional 0.5 mL reproduced bilateral periradicular contrast medium spread. A therapeutic injection (1 mL 0.5% bupivacaine, 1 mL (40 mg) triamcinolone, and 2 mL saline; 4 mL total injectate) was administered. At one month postinjection, her pain improved from a Numeric Rating Scale score of 8 to 2. There were no complications.

CONCLUSION: Bilateral opacification observed with only 1 mL may reflect patient-specific anatomical variations, including potential midline ventral epidural fenestrations related to the Hoffmann ligament or peridural membrane variability.

KEYWORDS: Hoffmann ligaments, Transforaminal epidural steroid injection, contralateral periradicular spread, lumbar radiculopathy