Devoted to diagnostic and interventional spine imaging and therapeutics


L5 Nerve Sign. Applying The Lessons of Peripheral Neurography to the Conventional Lumbar MRI Scan 2006

General Spine

Phil R Chapman, MD, Non ASSR Member
William D Keyes, MD, ASSR Member
James W Taylor, DO, Non ASSR Member

Scientific Paper


At our institution, the conventional MRI lumbar spine includes stacked axial T1 and T2 images that extend into the upper pelvis to the S1 or S2 level. This allows for rapid identification and evaluation of the L5 nerves lying ventral to the sacral ala.

We have noticed that many patients have neurographic features suggesting intrinsic nerve pathology: nerve root enlargement, T2 hyperintensity, and fascicular distortion. We sought to correlate these MRI findings with patient symptoms and determine potential significance in terms of diagnosis, treatment, and prognosis.

Methods & Materials

The L5 nerve sign was randomly identified in 37 patients over the course of 3 years. Two senior Neuroradiologists and 1 Neuroradiology Fellow reviewed all available preceding and subsequent imaging studies including MRI, CT, CT Myelography and sacral plexus neurography studies. The finding of an enlarged, hyperintense, or distorted L5 nerve was correlated with the presence of an L5 radiculopathy by patient questionnaire, patient interview, or referring physician diagnosis. Chronicity of symptoms prior to imaging was established. EMG studies were included for correlation when available. Follow up MRI studies were present in the majority of patients. The patients had a variety of treatments ranging from conservative therapy to surgery. Correlation with outcomes was performed based on medical records and patient interviews/questionnaires.


37 patients showed relative T2 hyperintensity, enlargement, or architectural distortion of a unilateral L5 nerve on conventional T1/T2 weighted axial MRI. The majority of patients had severe L5-S1 neuroforaminal stenosis with impingement of the L5 nerve. The site of impingement was occasionally related to lateral spinal stenosis at the L4-5 level. 37 of 37 patients had concordant L5 radicular symptoms as their chief complaint or as part of the total pain syndrome. 23 patients had additional follow up images ranging from 1-10 years with an average of 1.5 years. At follow up all 23 patients continued to exhibit the L5 nerve root sign, regardless of treatment. In no case did the abnormal nerve improve or resolve. The majority of these patients continued to have persistent or intermittent L5 radicular pain.


The L5 nerve sign is shown to be easily and quickly evaluated on conventional MRI that includes axial images through S1. Our findings indicated that there is a strong correlation with L5 nerve root T2 hyperintensity, enlargement, and fascicular distortion to symptomatology. We believe that this sign is the result of chronic, severe, or repetitive L5 impingement. The presence of the L5 nerve root sign implies permanent intrinsic pathology and may predict symptoms that will be resistant to treatment.


There are no finacial disclosures to make. All studies were performed through Inland Imaging, PS either at one of its outpatient imaging centers, or through one of its partner hosipitals, Holy Family Hospital or Sacred Heart Hospital in Spokane, Washington.