The posterior ligamentous complex inflammatory syndrome: spread of fluid and inflammation in the retrodural space of Okada.

The retrodural space of Okada is situated dorsal to the ligamentum flavum in the interlaminar space, and provides communication between contralateral facet joints. MRI will often demonstrate heterogeneous signal abnormality with contrast enhancement in this space and several communicating compartments of the posterior ligamentous complex: bilateral facet joints, adventitial interspinous bursae, or retrodural cysts penetrating the ligamentum flavum. Pars interarticularis defects are frequently present. This imaging pattern may be associated with axial low back pain and/or radicular pain. Recognition of this pattern at MRI has distinct implications for image interpretation, unifying prior reports of involvement of individual components of the posterior ligamentous complex. Its recognition will also affect planning for therapeutic interventional pain procedures. We refer to this constellation of imaging and clinical findings as posterior ligamentous complex inflammatory syndrome (PLCIS).