Severity of foraminal lumbar stenosis and the relation to clinical symptoms and response to periradicular infiltration - introduction of the "melting sign"

Abstract

BACKGROUND CONTEXT: Nerve root compression causing symptomatic radiculopathy can occur within the intervertebral foramen. Sagittal MRI sequences are reliable in detection of nerve root contact to intraforaminal disc material, but a clinically relevant classification of degree of contact is lacking.
PURPOSE: To investigate a potential relation of amount of contact between intraforaminal disc material and nerve root to clinical findings and response after periradicular corticosteroid infiltration.
STUDY DESIGN: Post hoc analysis of a prospective cohort.
PATIENT SAMPLE: Patients who underwent CT-guided periradicular corticosteroid infiltration (L1 - L5) at our institution (01/2014 - 05/2016) were included.
OUTCOME MEASURES: The medical records and radiographic imaging were reviewed.
METHODS: T2-weighted MR images of the lumbar spine of patients with single level symptomatic radiculopathy with (responders, n=28) or without (non-responders, n=14) pain relief after periradicular infiltration with corticosteroids were measured and compared by two independent readers to determine the amount of intraforaminal nerve root contact with the intervertebral disc ("melting" of the T2-hypointense signal). Pain relief was defined with a pain level decrease of >50% on a visual analogue scale and lack of pain relief with a pain level decrease of <25%, respectively. The amount of T2-hypointensity melting of disc and nerve root was categorized to 0%, 1-25%, and over 25%. Nothing to disclose.
RESULTS: Reader one identified 0% T2-melting in none of the responders, 1-25% melting in 13 (46.4%) patients, 26-50% in 15 (53.6%) of the 28 patients with pain relief after periradicular corticosteroid infiltration (responders) with a mean amount of T2-melting of 5.9±2.1mm. Whereas the non-responder group had 0% T2-melting in 2 (14.3%) patients, 1 - 25% T2-melting in 11 (78.6%) patients and 26 - 50% in 1 (7.1%) patient with a mean amount of T2-melting of 2.6±1.9mm (p<0.05). Reader two identified 0% T2-melting in none, 1-25% T2-melting in 15 (53.6%) patients and 26-50% in (46.4%) 13 of the 28 responders, with mean amount of 6.3±1.9mm. In the non-responder group 0% T2-melting was seen in 3 (21.4%) patients, 1 - 25% T2-melting in 10 (71.4%) patients and 26 - 50% in 1 (7.1%) patient with a mean amount of T2-melting of 2.7±1.9mm (p<0.05). None of the MR images showed T2-melting in over 50 percent of the circumference of the intraforaminal nerve root. A T2-melting of >25% had a high specificity of 93% but a sensitivity of 50%, thus a positive likelihood ratio of 7.5, to identify those with a pain relief of more than 50% after infiltration.
CONCLUSION: The amount of T2-melting of disc material and nerve root on sagittal MRI (>25%) predicts the amount of pain relief by periradicular infiltration in patients with intraforaminal nerve root irritation.