Is diffusion tensor imaging useful in the assessment of the sciatic nerve and its pathologies? Our clinical experience

Abstract

Objective: To evaluate the usefulness of diffusion tensor imaging (DTI) in the clinical setting as a complementary tool to conventional MRI in the study and assessment of the sciatic nerve and its pathologies.

Methods: 17 patients diagnosed with different types of sciatic neuropathy and 10 healthy controls underwent a conventional MRI and a DTI study in a 3-T MR scanner (Achieva(®) 3-T X-Series; Philips Healthcare, Netherlands).

Results: In the control group, we were able to track and visualize the common sciatic nerve and its main branches from hip to foot. In the patient group, the affected sciatic nerves presented statistically significant lower fractional anisotropy values and higher apparent diffusion coefficient values when compared with controls, suggesting nerve damage. In all cases, DTI offered complementary information for diagnosis and/or confirmation of the suspected pathology. When compared with conventional MRI, DTI showed higher sensitivity for nerve damage detection.

Conclusion: DTI offers a significant improvement and an important complement to visualize the sciatic nerve and its main branches. In patients with sciatic nerve pathology DTI allows to a better detection and characterization of the nerve damage.

Advances in knowledge: DTI enables in vivo dissection of the sciatic nerve white matter fibres; its use offers a significant improvement and complement to conventional MRI.

Figure 1.

Normal appearing tractography results merged with T₂ weighted imaging, in axial and coronal views of the common sciatic nerve in the pelvis and thigh in a healthy 24-year-old female (a–c), and distal level of the thigh (d, e) in a healthy 37-year-old female where peroneal and tibial branches are shown. Nerve colour is based on the orientation diffusion tensor imaging colour code.

Figure 2.

Normal appearing tractography in a healthy 37-year-old female merged with T₂ weighted imaging in axial plane at the lower limb. Tibial branches (tibial and sural nerves) (a), peroneal branches (deep and superficial) (b), medial plantar (c) and sural (d) nerves, medial and lateral plantar nerves as well as some of its branches (e), and the digital nerves (f). Nerve colours are based on the orientation diffusion tensor imaging colour code.

Figure 3.

Patient 17. A 47-year-old male with left lower limb Schwanoma located posterior to the lateral condyle of the femur (see white arrows). (a) T₁ weighted imaging (T1WI) showing the MRI appearance of tibial and peroneal nerves (red arrows) in the axial plane above the lesion. The lesion was hypointense in T1WI (b) and hyperintense on T₂ weighted imaging (c, d) and fat-saturated proton density–weighted images with spectral adiabatic inversion recovery sequence (PD-SPAIR) (h, f). Tractography results merged with axial T₁ weighted image (e), and axial PD-SPAIR (f) showed the existence of wrapping fibres from the sural cutaneous branch forming the tumour capsule (g). The external popliteal nerve was undamaged. Nerve colours have been changed to improve visualization.

Figure 4.

Patient 9. A 41-year-old male diagnosed with intraneural perineurioma of the left common sciatic nerve. After resection, the patient referred only mild sensory loss in the lower limb that affected the dorsal part of the feet and toes, and the distal lateral leg. Axial PD-SPAIR weighted images showing the lesion before surgery (a) and 12 months after surgery (f). Axial T₁ weighted images after contrast injection showing the location of the lesion before surgery (b) and 12 months after surgery (g, e). The lesional area presented an ill-defined contrast enhancement secondary to post-surgical changes. Post-surgical coronal T₁ weighted imaging (T1WI) turbo spin echo (TSE) (c) and short tau inversion recovery TSE (d) images; arrows point to the lesional area. (j–l) Tractography results performed 12 months after surgery merged with T₁ weighted images, in the axial and coronal views, showed the existence of an area with a lack of healthy myelin at the location of the surgery. This area was not observed in the T₁ weighted and T₂ weighted images (h, i). Nerve colour has been changed for better visualization, and arrows point to the lesion area.

Figure 5.

Patient 16.A 45-year-old male with a clinical history of three different left ankle sprains during the period of 2 years. Physical examination showed a positive Tinel's sign, suggesting nerve entrapment. The nerve conduction study of the left tibial nerve did not show pathological findings in both sensitive and motor branches. Axial T₁ weighted (a), T₂ weighted (b) and PD-SPAIR (c) images showed an area of fibrosis at the medial malleolus (white arrows) caused by chronic sprains, in a medial impingement syndrome. Illustration of tractography results merged with T₂ weighted imaging in the axial plane (d), PD-SPAIR in the coronal plane (e, f) and T₁ weighted imaging in the sagittal plane (d, f) showed the region of the nerve entrapment (white arrows) which was related to the fibrosis area (a–c). The red arrows show the location of the tibial nerve. Nerve colour has been changed for better perception.

Figure 6.

Patient 4. A 32-year-old female diagnosed with pyriformis syndrome. Axial short tau inversion recovery (STIR) (a), T₁ weighted image (b), T₂ weighted image (c) and STIR images (f) suggested inflammation in the right common sciatic nerve. Tractography of both sciatic nerves merged with T₁ weighted imaging in the coronal view (d, e) showed an increase in the size of the right sciatic nerve in the area related to inflammation observed in the MRI study (white arrows). Nerve colours are displayed according to the orientation diffusion tensor imaging colour code.

Figure 7.

Patient 5. A 56-year-old male who suffered a traumatic lesion affecting the left peroneal nerve 6 months earlier. Physical exploration revealed left common peroneal nerve paralysis. Electroneurography (ENG) showed a partial severe lesion in the left peroneal nerve probably at the level of the fibular head. Coronal and axial T₂ weighted imaging (a, b), PD-SPAIR (e), short tau inversion recovery turbo spin echo (f) and T₁ weighted imaging (d) of the left lower limb showed MRI changes in the tibialis anterior, extensor digitorum longus and peroneus muscles, secondary to muscle atrophy and fatty replacement (white arrows). Tractography results of the peroneal nerve branches (deep and superficial) merged with T₁ weighted image in the axial and coronal views showed the area of the nerve damage at the head of the fibula which matched with the ENG results. The red arrows show peroneal nerve.

Figure 8.

Patient 12. A 57-year-old male diagnosed with liver disease in 2010 and hepatic transplant in 2013. 4 months after initiation of the immunosuppressive therapy with tracolimus, the patient started with progressive weakness in both lower limbs. Electromyogram/electroneurography results revealed multiple mononeuropathy in acute/subacute phase affecting both sciatic nerves at the peroneal branch with conduction blocks. The common sciatic nerve, peroneal and tibial branches presented a normal appearance in the T₁ weighted imaging turbo spin echo (TSE) and T₂ weighted imaging (T2WI) TSE (a, b, red arrows). T2WI showed a bilateral hyperintensity affecting both anterior tibialis and peroneus brevis muscles (c, white arrows). Tractography results showed the existence of a patched myelin damage affecting both sciatic nerves (d). Both peroneal branches were absent in the tractography results (e, f). Red arrows point to peroneal and tibial branches.