Retrodural space of Okada

The retrodural space of Okada is a wishbone-shaped potential space which links the facet joints to each other at a single level across the midline, and thus acts as a potential pathway for the spread of injected material (contrast, air, steroid, local anesthetic) as well as infection.

Gross anatomy

The location of this potential space is extradural and dorsal to the ligamentum flavum, in the interlaminar space, and allows further communication with adjacent spaces including the interspinous space (adventitial interspinous bursa formation also known as Baastrup disease), neural exit foramina and paraspinal musculature . It can also communicate with the epidural space through a space between the ligamentum flavum .

The space runs horizontally, is confined to one level, and spans approximately 5 mm craniocaudally .

Extension from one level to an adjacent level is possible in the setting of a pars defect . In such cases, the majority of superior and inferior facets communicate with the pars defect between them (94% and 63% respectively) .

Radiographic features

Fluoroscopy and CT

The retrodural space of Okada is not visible on conventional radiography unless contrast or air has been injected during facet joint injection. In such cases contrast may be seen extending from one facet to the contralateral facet, or in the setting of pars defects, from the facet joint up to the facet joint above .

It has been reported as discernible in up to 80% of cervical arthrograms .

MRI

In the absence of an intervention or pathology, the retrodural space of Okada is not readily visualized.

In the presence of inflammation or infection, fluid may be seen extending from one facet joint to the contralateral facet joint as a region of heterogeneous increased T2 signal with or without contrast enhancement. Involvement of the adjacent musculature and interspinous adventitial bursa may also be seen .

History and etymology

It was first described in 1981 by Dr Kikuzo Okada  in the cervical spine.