Diffusion-weighted MR Neurography for the Preoperative Assessment of Nerve Root Anomaly in Minimally Invasive Spine Surgery

Presented at SMISS Annual Forum 2018
By Yukihiro Nakagawa MD, PhD
With Amit Jhala MS DNB,

Disclosures: Yukihiro Nakagawa MD, PhD None Amit Jhala MS DNB None,

Introduction:

In minimally invasive spine surgery (MISS), small skin incision and limited exposure is, making it difficult to observe the whole nerve structure. Therefore, obtaining anatomical information of nerve root before surgery is important in avoiding iatrogenic nerve root injury especially in MISS.

Aims/Objectives:

To evaluate diffusion-weighted MR neurography (DW-MRN) for visualizing the lumbosacral nerve root and for the preoperative assessment of nerve root anomalies (NRA).

Methods:

194 patients with lumbar lesion (101 male and 93 female, mean 66.1yrs) underwent MRI using DW-MRN. Images were reviewed by two spine surgeons. Incidence, levels, type of NRA were investigated. Neidre and, Kadish and Simmons classification were used.

Results:

Total 18 NRA cases (9 male and 9 female) were detected. Incidence of NRA 9.1%. As for laterality, there were 8 right side, 8 left side and 1 double left side, and 1 both side. There were 1 case in L1-L2 vertebral level, 2 in L2-L3, 3 in L3-L4, 1 in L4, 2 in L4-L5, 4 in L5-S1, 1 in L5, 2 in S1-S2, 1 in S2-S3 and 3 in S3- S4. According to Neidre classification, there were 6 cases in type 1A, 8 in type 1B, 2 in type 3, 4 in unclassifiable. And there were 4 cases in type IIa, 1 in type IIb, 2 in type IIc, 11 in type IId, 1 in type III, and 1 in unclassifiable by Kadish and Simmonds classification.

Conclusions:

In previous reports, the incidence of NRA by autopsy is 8.5 to 30%, while the incidence by diagnostic imaging is 1.9 to 4%, there is dissociation between the diagnostic rates of both. That is, it means that there is a certain percentage of what is missed without diagnosing NRA. It is likely to lead to iatrogenic injury, NRA should be diagnosed by preoperative screening. In DW-MRN, the frequency of occurrence of NRA is as high as 9%, which is about 10 times incidence of NRA in MISS surgery in our department previously reported. Pitfalls include image distortion due to deformity and severe nerve compression, low quality of diffusion images. However, it is expected that diagnostic accuracy can be further improved by using other modality of MRI in combination.