Epidural Contrast Patterns and Clinical Implications: An Educational Review

PURPOSE OF REVIEW

The purpose of this educational review is to describe the contrast spread patterns that indicate accurate needle placement in the epidural space and spread patterns associated with erroneous needle insertion.

RECENT FINDINGS

Epidural injections are minimally invasive and commonly used for patients with acute and chronic back pain that does not respond to conservative management. Imaging with contrast is frequently used during this procedure to improve accuracy and reduce adverse events. Contrast spread patterns are an important tool that can help identify where the needle is placed and whether the placement is accurate. Despite this, there may be discrepancies in the interpretation of spread patterns which ultimately reduce the utility of contrast. Inaccurate needle placement may result in intrathecal/subarachnoid, subdural, fascial, or retrodural space of Okada injections. The correct interpretation of contrast spread patterns on imaging is crucial for confirming accurate epidural needle placement. Furthermore, understanding contrast patterns of improper needle placement can prevent adverse events that result from injection outside of the epidural space.

Cervical Radiculopathy Focus on Characteristics and Differential Diagnosis

Cervical radiculopathy is characterized by neurological dysfunction caused by compression and inflammation of the spinal nerves or nerve roots of the cervical spine. It mainly presents with neck and arm pain, sensory loss, motor dysfunction, and reflex changes according to the dermatomal distribution. The most common causes of cervical radiculopathy are cervical disc herniation and cervical spondylosis. It is important to find the exact symptomatic segment and distinguish between conditions that may mimic certain cervical radicular compression syndromes through meticulous physical examinations and precise reading of radiographs. Non-surgical treatments are recommended as an initial management. Surgery is applicable to patients with intractable or persistent pain despite sufficient conservative management or with severe or progressive neurological deficits. Cervical radiculopathy is treated surgically by anterior and/or posterior approaches. The appropriate choice of surgical treatment should be individualized, considering the patient’s main pathophysiology, specific clinical symptoms and radiographic findings thoroughly.

Incidence of Unintentional Flow of Contrast into the Facet Joints During Fluoroscopy-Guided Cervical Interlaminar Epidural Injections: A Retrospective Cohort Study

OBJECTIVE

We sometimes encounter unintentional flow of contrast into the facet joints during cervical interlaminar epidural injection, which leads to false-positive epidural injection. The purposes of this study were to evaluate the rate of facet flow of contrast and to investigate various factors associated with injection into the space of Okada during fluoroscopy-guided cervical interlaminar epidural injection.

SETTING AND SUBJECTS

Images from consecutive cases of fluoroscopy-guided cervical interlaminar epidural injection performed at a single institution between July 2015 and July 2018 were obtained and reviewed.

METHODS

Cases of epidural injection were classified as either facet flow or no facet flow. Multivariate logistic regression was used to identify the predictive factors of unintended injection into the Okada space.

RESULTS

A total of 2,006 cases were included. Intra-articular flow was identified in 6.0% of cases (121/2,006). All cases of flow of contrast into the facet joints were recognized, and appropriate epidurograms were obtained during the procedures. The highest rate of unintended facet flow of the contrast (10.1%, 44/436) occurred at C5-6. Cervical interlaminar epidural injection at C5-6 and above (adjusted odds ratio [aOR] = 1.929, P = 0.001) and the paramidline approach for epidural injection (aOR = 2.427, P < 0.001) were associated with injection into the space of Okada.

CONCLUSIONS

We detected injection into the space of Okada during fluoroscopy-guided cervical interlaminar epidural injection in 6.0% of procedures. Cervical interlaminar epidural injection at C5-6 and above and the paramidline approach for epidural injection were positive predictors of unintentional facet flow of the contrast.

Case series of fluoroscopic findings and 3D reconstruction of human spinal MRIs of the space of Okada

OBJECTIVE

To better understand the unexpected spread of contrast medium observed by conventional fluoroscopic X-ray images during standard neuraxial techniques used in the treatment of pain. The support of 3D reconstruction of MRI images of structures within the lumbar spine was used to better understand the space of Okada.

METHODS

Lumbar facet joint and epidural corticosteroid injections in five patients under fluoroscopic guidance with loss of resistance to air or saline to identify the facet joints or epidural space. Next, in a retrospective study, the authors examined the retrodural space of Okada and the neighboring tissues with 3D reconstruction of spinal MRIs of seven patients without any demonstrable spinal pathology to better understand the characteristics of the space of Okada.

RESULTS

Contrast medium spread to the ipsilateral and contralateral sides was observed in five patients. The contralateral spread was thought to be through the retrodural space of Okada, which is a potential space between the anterior surface of the vertebral lamina and the posterior surface of the ligamentum flavum. It facilitates communication between the contralateral articular facet joints of the spine.

CONCLUSIONS

This study provides new evidence for the existence of the space of Okada where an unexpected contralateral spread occurred following facet joint and attempted epidural injection. The 3D reconstructions of MRIs may help us better understand the nature of the retrodural space of Okada and its clinical implications.

The retrodural space of Okada and its relevance to CT guided intervention

The spinal epidural and posterior ligamentous complex spaces are important anatomic regions which are the target of various radiologic procedures in the cervical, thoracic and lumbar spine for the purpose of analgesia and anaesthesia. Given the frequency with which procedures are performed in and around the epidural space, a sound understanding of the associated anatomy is paramount to ensure the safety and efficacy of procedural intervention.

Cross-sectional CT Assessment of the Extent of Injectate Spread at CT Fluoroscopy-guided Cervical Epidural Interlaminar Steroid Injections

Background Previous studies analyzed contrast agent spread during cervical interlaminar epidural steroid injections (CILESIs) by using planar fluoroscopy and reported wide variance of the rate of spread to the ventral epidural space (VES). Cross-sectional CT allows for direct viewing of contrast agent in the VES, providing improved spread assessment and thereby informing needle placement decisions when targeting pain generators. Purpose To determine the extent of injectate spread at CT fluoroscopy-guided CILESI, with particular attention to the VES and bilateral neuroforamina, by using cross-sectional CT. Materials and Methods This study reviewed 83 consecutive CT fluoroscopy-guided CILESIs at which a postprocedural cervical spine CT was performed (June 2016 to December 2017). All procedures used the same injectate (2 mL corticosteroid, 3 mL contrast agent). Postprocedural CT scans were reviewed for the presence of contrast within the VES, dorsal epidural space, ipsilateral neuroforamen, and contralateral neuroforamen in every cervical interlaminar level. Descriptive data are presented as frequencies or means. McNemar tests or hierarchical logistic models were used to assess associations between covariates and contrast agent spread to particular locations. Results The study cohort included 73 individual patients (59% women; 43 of 73) (mean patient age, 57.6 years ± 11.5 [standard deviation]). Mean number of levels of cranial spread were 0.6 level for VES, 1.9 levels for contralateral neuroforamen, 2.1 levels for ipsilateral neuroforamen, and 3 levels for dorsal epidural space. No VES spread in any level was found with 35% (29 of 83) of injections. VES spread was more likely to occur in the level of needle placement (43%; 36 of 83) than in other interlaminar levels (19.5%; 97 of 498; P < .001). Spread was more likely to occur in the neuroforamen ipsilateral to the needle approach compared with contralateral (P < .001). Conclusion Cervical interlaminar epidural steroid injections have injectate spreads with a mean of less than one level cranially in the ventral epidural space (VES) and approximately two levels in the neuroforamen. VES spread occurs more frequently at the level of needle placement and within the ipsilateral neuroforamen. © RSNA, 2019.