MR Micro-Neurography and a Segmentation Protocol Applied to Diabetic Neuropathy

Abstract

The aim of this study was to assess with MRI morphometric ultrastructural changes in nerves affected by diabetic peripheral neuropathy (DPN). We used an MR micro-neurography imaging protocol and a semiautomated technique of tissue segmentation to visualize and measure the volume of internal nerve components, such as the epineurium and nerve fascicles. The tibial nerves of 16 patients affected by DPN and of 15 healthy volunteers were imaged. Nerves volume (NV), fascicles volume (FV), fascicles to nerve ratio (FNR), and nerves cross-sectional areas (CSA) were obtained. In patients with DPN the NV was increased and the FNR was decreased, as a result of an increase of the epineurium (FNR in diabetic neuropathy 0,665; in controls 0,699, p = 0,040). CSA was increased in subjects with DPN (12,84 mm² versus 10,22 mm², p = 0,003). The FV was increased in patients with moderate to severe DPN. We have demonstrated structural changes occurring in nerves affected by DPN, which otherwise are assessable only with an invasive biopsy. MR micro-neurography appears to be suitable for the study of microscopic changes in tibial nerves of diabetic patients.

Figure 1

(A) Ankle, axial plane. Sequence: 3D SPGR IDEAL-water image. (B) Neurovascular bundle with the tibial nerve. Sequence: TSE T1 weighted. The nerve fascicles appear dark over a brighter background, corresponding to the epineurial fat. (C) Sequence: 3D SPGR-water image. The fascicles appear bright over a dark background corresponding to the epineurium. The perineurium can be seen surrounding some of the fascicles (see Figure 2).

Figure 2

(A) Tibial nerve right above the level of the tibial malleolus, axial plane. Sequence: 3D SPGR IDEAL-water image. Voxel size is about 120 × 140 × 2000 μm. (B) Diagram of the internal nerve aspect that is visualized. Arrowheads: two fascicles surrounded by the perineurium. Dark areas: epineurium. A: posterior tibial artery. V: posterior tibial veins.

Figure 3

Tibial nerve with chronic degenerative changes (left (A, B)) compared with a volunteer (right (C, D)). The patient was in the group of the moderate/severe DPN and suffered from chronic pain and severe motor impairment. (A, C) Sequence: TSE T1. (B, D) Sequence: IDEAL-WATER. There is a visual increase of the interfascicular tissue (epineurium), while the fascicles appear reduced in number and area. Increase of fat and fibrous tissue within the epineurium is common in chronic stage of diabetic neuropathy.

Figure 4

Data comparison graph for FNR in subjects with diabetic neuropathy (indicated with “diabetes”) and controls (indicated with “normal”). There is a significant difference between the two populations. For more details see Table 2.