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 anaesthetic) as well as infection.
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 1-2. It can also communicate with the epidural space through a space between the ligamentum flavum 2.
The space runs horizontally, is confined to one level, and spans approximately 5 mm craniocaudally 2.
Extension from one level to an adjacent level is possible in the setting of a pars defect 1,2. In such cases, the majority of superior and inferior facets communicate with the pars defect between them (94% and 63% respectively) 4.
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 1.
It has been reported as discernible in up to 80% of cervical arthrograms 3.
In the absence of an intervention or pathology, the retrodural space of Okada is not readily visualised.
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 2.
History and etymology
It was first described in 1981 by Dr Kikuzo Okada 3 in the cervical spine.
- 1. Murthy NS, Maus TP, Aprill C. The retrodural space of Okada. AJR Am J Roentgenol. 2011;196 (6): W784-9. doi:10.2214/AJR.10.5751 - Pubmed citation
- 2. Lehman VT, Murthy NS, Diehn FE et-al. The posterior ligamentous complex inflammatory syndrome: spread of fluid and inflammation in the retrodural space of Okada. Clin Radiol. 2015;70 (5): 528-535. doi:10.1016/j.crad.2014.12.009 - Pubmed citation
- 3. Okada K. Studies on the cervical facet joints using arthrography of the cervical facet joint (author's transl). Nippon Seikeigeka Gakkai Zasshi. 1982;55 (6): 563-80. Pubmed citation
- 4. Shipley JA, Beukes CA. The nature of the spondylolytic defect. Demonstration of a communicating synovial pseudarthrosis in the pars interarticularis. J Bone Joint Surg Br. 1998;80 (4): 662-4. Pubmed citation
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