An Anatomic Shape Guide to MRI Lumbar Foraminal Stenosis

Presented at SMISS Annual Forum 2018
By G Grady McBride MD
With Arvind Kulkarni ,

Disclosures: G Grady McBride MD None Arvind Kulkarni None,

Introduction:

Accurate determination of the severity of lumbar foraminal stenosis is very important for surgeons employing MIS techniques to plan the proper corrective surgery for many degenerative and other spinal conditions. Currently radiologists use a variety of rating methods that are inconsistent and poorly correlate with clinical findings.

Aims/Objectives:

This study was designed to develop a new grading system to evaluate lumbar foraminal stenosis based on the anatomic shape of the lumbar foramen. Current grading systems i.e. mild, moderate, and severe frequently utilized by radiologists do not seem to reflect accurately anatomic abnormalities in the foramen that could explain radicular symptoms.

Methods:

Five grades were developed to evaluate lumbar foraminal stenosis based on simple anatomic shape of the pedicle based on sagittal MRI images. Alterations of the anatomic shape are believed to correlate more closely with radicular symptoms. Grade I refers to the normal oval shape of the foramen. Grade 2 refers to slight narrowing of the lower half of the oval but probably causes only mild impingement. Grade 3 refers to further narrowing of the lower half of the oval where the foramin overall shape has the appearance of a “tennis racket” and likely causes moderate impingement on the exiting nerve root. Grade 4 refers to preservation of the top or “head portion” of the “tennis racket” but complete loss of the handle portion of the “tennis racket” so that it is either non-existent or a narrowed to very thin line and likely causing severe impingement. Grade 5 refers to reduced size of the “tennis racket” head or it’s complete obliteration also reflecting severe impingement. Three experienced spine surgeons reviewed 120 foramina from L3-4 to L5-S1 in 20 MRI studies of symptomatic patients and the foramina were ranked from Class 1 to 5 and interobserver agreement was analyzed.

Results:

Interobserver agreement was 100% for Grade 1, 95% for Grade 2, 92% for Grade 3 and 4, and 90% for Grade 5. Correlation to the symptomatic level and laterality of the radicular pain was 85% and 82%.

Conclusions:

The new classification system for foraminal stenosis based on anatomic shape appears to demonstrate a high correlation between observers and help explain clinically relevant symptoms.