DIAGRAMMATIC ANALYSIS OF SUBARACHNOID CONTRAST SPREAD IN THE CONTRALATERAL OBLIQUE VIEW: A TECHNICAL REPORT

Interlaminar epidural steroid injections are commonly used in clinical practice for the relief of low back pain. Reliable deposition of medication in the epidural space is important in producing significant results. Pathological conditions, including vertebral osteoarthritis, degenerative disc disease, and spinal stenosis, are frequently treated with epidural steroid injections. Associated degenerative features such as ligamentum flavum hypertrophy, facet joint hypertrophy, and osteophyte formation can lead to significant alterations in the anatomy of the epidural space. Epidurograms, prior to steroid injection, aid the physician in identifying the epidural space, as a false loss of resistance can occur. Extradural, subdural, intradural, and subarachnoid contrast spread has been demonstrated in the anteroposterior and lateral views; but, has not previously been demonstrated in the contralateral oblique (CLO) view. This technical report is the first to demonstrate concomitant epidural and subarachnoid spread in the contralateral oblique view after inadvertent low volume subarachnoid injection, as might happen in clinical practice. In this technical report, we demonstrate both epidural and subarachnoid contrast spread in the contralateral oblique view and compare it to the anteroposterior view. In an oblique view, epidural contrast spread is observed to approximate the ventral margin of the superior aspect of the lamina while subarachnoid contrast spread has a distinct demarcation at the ventral laminar margin. In an anteroposterior view, epidural spread is confirmed by spread of the dye along the nerve roots and beyond the margins of the pedicles. The CLO view provides an accurate and consistent visualization of the epidural space; irrespective of the obliquity, epidural contrast is observed to approximate the ventral margin of the superior aspect of the lamina. In the CLO view, if contrast spread does not approximate the lamina, then intrathecal injection must be considered. Key words: Epidural steroid injection, epidurogram, epidural spread, subarachnoid injection, intrathecal spread, fluoroscopy, contralateral oblique view