Incremental value of magnetic resonance neurography of Lumbosacral plexus over non-contributory lumbar spine magnetic resonance imaging in radiculopathy: A prospective study

AIM: To test the incremental value of 3T magnetic resonance neurography(MRN) in a series of unilateral radiculopathy patients with non-contributory magnetic resonance imaging(MRI).METHODS: Ten subjects(3 men,7 women; mean age54 year and range 22-74 year) with unilateral lumbar radiculopathy and with previous non-contributory lumbar spine MRI underwent lumbosacral(LS) plexus MRN over a period of one year. Lumbar spine MRI performed as part of the MRN LS protocol as well as bilateral L4-S1 nerves,sciatic,femoral and lateral femoral cutaneous nerves were evaluated in each subject for neuropathy findings on both anatomic(nerve signal,course and caliber alterations) and diffusion tensor imaging(DTI)tensor maps(nerve signal and caliber alterations).Minimum fractional anisotropy(FA) and mean apparent diffusion coeffcient(ADC) of L4-S2 nerve roots,sciatic and femoral nerves were recorded.RESULTS: All anatomic studies and 80% of DTI imaging received a good-excellent imaging quality grading. In a blinded evaluation,all 10 examinations demonstrated neural and/or neuromuscular abnormality corresponding to the site of radiculopathy. A number of contributory neuropathy findings including double crush syndrome were observed. On DTI tensor maps,nerve signal and caliber alterations were more conspicuous. Although individual differences were observed among neuropathic appearing nerve(lower FA and increased ADC) as compared to its contralateral counterpart,there were no significant mean differences on statistical comparison of LS plexus nerves,femoral and sciatic nerves(P > 0.05).CONCLUSION: MRN of LS plexus is useful modality for the evaluation of patients with non-contributory MRI of lumbar spine as it can incrementally delineate the etiology and provide direct objective and non-invasive evidence of neuromuscular pathology.

3T magnetic resonance neurography of pudendal nerve with cadaveric dissection correlation

AIM: To evaluate the pudendal nerve segments that could be identified on magnetic resonance neurography(MRN) before and after surgical marking of different nerve segments.METHODS: The hypothesis for this study was that pudendal nerve and its branches would be more easily seen after the surgical nerve marking. Institutional board approval was obtained. One male and one female cadaver pelvis were obtained from the anatomy board and were scanned using 3 Tesla MRI scanner using MR neurography sequences. All possible pudendal nerve branches were identified. The cadavers were then sent to the autopsy lab and were surgically dissected by a peripheral nerve surgeon and an anatomist to identify the pudendal nerve branches. Radiological markers were placed along the course of the pudendal nerve and its branches. The cadavers were then closed and rescanned using the same MRN protocol as the premarking scan. The remaining pudendal nerve branches were attempted to be identified using the radiological markers. All scans were read by an experienced musculoskeletal radiologist.RESULTS: The pre-marking MR Neurography scans clearly showed the pudendal nerve at its exit from the lumbosacral plexus in the sciatic notch, at the level of the ischial spine and in the Alcock's Canal in both cadavers. Additionally, the right hemorrhoidal branch could be identified in the male pelvis cadaver. The perineal and distal genital branches could not be identified. On post-marking scans, the markers were used as identifiable structures. The location of the perineal branch, the hemorroidal branch and the dorsal nerve to penis(in male cadaver)/clitoris(in female cadaver) could be seen. However, the visualization of these branches was suboptimal. The contralateral corresponding nerves were poorly seen despite marking on the surgical side. The nerve was best seen on axial T1W and T2W SPAIR images. The proximal segment could be seen well on 3D DW PSIF sequence. T2W SPACE was not very useful in visualization of this small nerve or its branches.CONCLUSION: Proximal pudendal nerve is easily seen on MR neurography, however it is not possible to identify distal branches of the pudendal nerve even after surgical marking.