Eric H. Williams

High resolution imaging of tunnels by magnetic resonance neurography

Peripheral nerves often traverse confined fibro-osseous and fibro-muscular tunnels in the extremities, where they are particularly vulnerable to entrapment and compressive neuropathy. This gives rise to various tunnel syndromes, characterized by distinct patterns of muscular weakness and sensory deficits. This article focuses on several upper and lower extremity tunnels, in which direct visualization of the normal and abnormal nerve in question is possible with high resolution 3T MR neurography (MRN). MRN can also serve as a useful adjunct to clinical and electrophysiologic exams by discriminating adhesive lesions (perineural scar) from compressive lesions (such as tumor, ganglion, hypertrophic callous, or anomalous muscles) responsible for symptoms, thereby guiding appropriate treatment.

3-T High-Resolution MR Neurography of Sciatic Neuropathy

OBJECTIVE The sciatic nerve may normally exhibit mild T2 hyperintensity in MR neurography (MRN) images, rendering assessment of sciatic neuropathy difficult. The purpose of this case-control study was to evaluate whether a quantitative and qualitative analysis of the sciatic nerves and regional skeletal muscles increases the accuracy of MRN in detecting sciatic neuropathy. MATERIALS AND METHODS We retrospectively reviewed the MRN studies of the pelvis and thighs of 34 subjects (12 men and 22 women; mean [± SD] age, 50 ± 15 years), of which 17 had a final diagnosis of sciatic neuropathy according to electrodiagnostic or surgical confirmation, and 17 had no evidence of sciatic neuropathy and served as control subjects. On each side, the sciatic nerves were evaluated for signal intensity (SI), size, course, and fascicular shape, whereas the regional skeletal muscles were evaluated for edema, fatty replacement, and atrophy. In addition, the nerve-to-vessel SI ratio was registered for each side at the same time and 8 months later. RESULTS The sciatic nerves of the abnormal sides exhibited higher nerve-to-vessel SI ratios and higher incidences of T2 hyperintensity, enlargement, and abnormal fascicular shape compared to the nerves of the normal sides. The regional muscles of the abnormal sides demonstrated a higher grade of fatty infiltration and higher frequencies of edema and atrophy. A cutoff value of nerve-to-vessel SI ratio of 0.89 exhibited high sensitivity and specificity in predicting sciatic neuropathy. Calculation of the nerve-to-vessel SI ratio demonstrated excellent inter- and intraobserver reliability. CONCLUSION Both qualitative and quantitative criteria should be used to suggest the MRN diagnosis of sciatic neuropathy.

Tibial nerve decompression in patients with tarsal tunnel syndrome: pressures in the tarsal, medial plantar, and lateral plantar tunnels.

Background: The anatomical basis for the surgical techniques used to treat tarsal tunnel syndrome is not well studied. The authors sought to evaluate their hypotheses that (1) pronation and pronation with plantar flexion of the intact foot would have higher pressures than the intact foot in other positions; (2) decompression surgery would significantly lower the pressure in all three tunnels in all foot positions, and roof incision plus septum excision would lower the pressure further in some positions; and (3) the pressures in symptomatic patients would be significantly higher than those in an analogous cadaver study. Methods: In 10 patients with tarsal tunnel syndrome, the authors intraoperatively measured pressures in the tarsal, medial plantar, and lateral plantar tunnels in multiple foot positions before and after excision of the tunnel roofs and intertunnel septum. Results: The authors found that (1) pronation and plantar flexion significantly increased pressures in the medial and lateral plantar tunnels, to levels sufficient to cause chronic nerve compression; (2) tunnel release and septum excision significantly decreased those pressures; and (3) compared with cadaver pressures, patients had similar tarsal tunnel pressures but higher lateral plantar tunnel pressures in some positions. Conclusions: Many surgeons operating on patients with tarsal tunnel syndrome do not decompress the respective medial plantar and lateral plantar nerves and excise the septum. The authors’ study validates the hypotheses that patients who are clinically suspected of having chronic compression of the tibial nerve and its branches at the ankle have higher tunnel pressures and that releasing these structures decreases the pressures.

High-Resolution MR Neurography: Evaluation Before Repeat Tarsal Tunnel Surgery

OBJECTIVE The purpose of this study was to retrospectively determine the accuracy of high-resolution MR neurography (MRN) in presurgical evaluation before repeat tarsal tunnel surgery. MATERIALS AND METHODS Ten MRN studies of nine patients (one man, eight women; mean age, 44.4 years; range, 23-67 years) who had been referred to a peripheral nerve specialist because of persistent symptoms after tarsal tunnel release were reviewed. The MRN findings studied included presence and location of focal fibrosis, presence or absence of nerve abnormality, location of nerve abnormality, and presence of neuroma formation and regional muscle denervation. The diagnostic accuracy of MRN in detection of posterior tibial nerve, medial plantar nerve, and lateral plantar nerve injury was calculated with clinical and intraoperative findings as the reference standards. RESULTS Nine of 10 MRN studies (90%) had findings of nerve reentrapment related to focal fibrosis. Injured nerves were reliably visualized with MRN in all patients. MRN had a sensitivity of 77% for posterior tibial nerve, 100% for medial plantar nerve, and 100% for lateral plantar nerve injury, and the overall accuracy was 86%. The sensitivity of MRN was 91% for the presence of focal fibrosis affecting the three nerves and 67% for neuroma detection. Regional muscle denervation was better evaluated on MRN studies than at surgery. Smaller (1-3 mm) abnormal cutaneous nerve branches were better seen at surgery. CONCLUSION MRN yields accurate morphologic information about the location and extent of nerve injury after failed tarsal tunnel release and facilitates preoperative diagnosis.

The application of three-dimensional diffusion-weighted PSIF technique in peripheral nerve imaging of the distal extremities

To evaluate whether the addition of the three‐dimensional diffusion‐weighted reversed fast imaging with steady state free precession (3D DW‐PSIF) sequence improves the identification of peripheral nerves in the distal extremities.

High-resolution 3-T MR neurography of peroneal neuropathy

The common peroneal nerve (CPN), a major terminal branch of the sciatic nerve, can be subject to a variety of pathologies, which may affect the nerve at any level from the lumbar plexus to its distal branches. Although the diagnosis of peripheral neuropathy is traditionally based on a patient’s clinical findings and electrodiagnostic tests, magnetic resonance neurography (MRN) is gaining an increasing role in the definition of the type, site, and extent of peripheral nerve disorders. Current high-field MR scanners enable high-resolution and excellent soft-tissue contrast imaging of peripheral nerves. In the lower extremities, MR neurography has been employed in the demonstration of the anatomy and pathology of the CPN, as well as in the detection of associated secondary muscle denervation changes. This article reviews the normal appearance of the CPN as well as typical pathologies and abnormal findings at 3.0-T MR neurography of the lower extremity.

Anatomic site for proximal tibial nerve compression: a cadaver study.

Primary compression of the tibial nerve beneath the fibromuscular sling of the origin of the soleus muscle is rarely discussed in the literature. To evaluate the location and characteristics of the soleal fibromuscular sling and its relationship to the tibial nerve, 36 cadaver limbs were dissected. The leg length, location of soleal fibromuscular sling, presence of a thickened fibrous band at the soleal sling, and narrowing in the tibial nerve were recorded. The average leg length was 47.8 cm (SD ± 4.16). The fibromuscular soleal sling was 9.3 cm (SD ± 1.44) distal to the medial tibial plateau. Although 56% (20/36) of specimens had a fibrous band, only 8% (3/36) demonstrated a focal narrowing directly under this fascial sling. This study demonstrates that the fibromuscular sling of the soleus muscle may act as a potential compression site of the tibial nerve. These findings offer insight and potential hope for those patients who have persistent plantar numbness after tarsal tunnel decompression and for those patients with plantar numbness who also have weakness of toe flexion.

High-resolution 3T MR neurography of suprascapular neuropathy.

RATIONALE AND OBJECTIVES The purpose of this study was to illustrate the imaging findings on high-resolution 3T magnetic resonance neurography (MRN) in patients with suprascapular nerve (SSN) neuropathy. MATERIALS AND METHODS From 3T MRN examinations performed for brachial plexus evaluation in 51 patients over a 3-year period, 15 patients with final diagnosis of suprascapular neuropathy were recruited. The diagnosis was confirmed by electrodiagnostic studies (EDS), clinical, and/or surgical follow-up examinations. Studies performed for the evaluation of tumor, neurofibromatosis, or known diffuse polyneuropathy were excluded. RESULTS Two cases were excluded due to suboptimal imaging related to motion degradation and poor signal-to-noise ratio. MRN depicted asymmetric enlargement and/or abnormal T2 hyperintensity of C5 nerve root (10/13 cases), C6 nerve root (10/13 cases), both C5 and C6 nerve roots (7/13 cases), upper trunk (11/13 cases) and SSN (11/13 cases), and other brachial plexus segments involvement (4/13 cases). MR findings of denervation changes in the ipsilateral supraspinatus and infraspinatus muscles were detected in 12/13 cases. In all seven cases where contrast-enhanced images were available, MRN demonstrated enhancement of the denervated muscles but did not provide any additional information regarding the nerve abnormality. None of the MRN studies revealed a mass lesion along the course of the SSN. CONCLUSION 3T MRN is a valuable diagnostic tool in clinically suspected cases of suprascapular neuropathy, because it can directly demonstrate the nerve abnormality, as well as secondary muscle denervation changes. The reader should be aware that brachial plexopathy may coexist in patients with clinical diagnosis of SSN neuropathy.

MR Neurography Findings of Soleal Sling Entrapment

OBJECTIVE The ever-increasing use of higher field strength (3 T) scanners and novel pulse sequences with improved spatial resolution and signal-to-noise ratio have rendered MR neurography (MRN) a valuable technique in the assessment of peripheral neuropathies. The aim of this study is to illustrate the imaging findings of high-resolution MRN in patients who suffer from tibial nerve entrapment due to a soleal fibromuscular sling and to correlate the imaging findings with intraoperative and clinical examination results. CONCLUSION This article depicts the surgically confirmed imaging findings of high-resolution MRN in tibial nerve entrapment by the soleal sling.

Soleal sling syndrome (proximal tibial nerve compression): Results of surgical decompression

Background: Although distal tibial nerve compression is well recognized, proximal tibial nerve compression remains a rarely recognized clinical condition. This report defines the presentation, diagnosis, surgical decompression technique, and clinical outcome of neurolysis of the tibial nerve at this soleal sling compression site. Methods: Forty-nine patients with 69 proximal tibial nerves (20 bilateral) were stratified retrospectively into three groups: neuropathy (n = 10), failed tarsal tunnel syndrome (n = 25), and trauma (n = 14). Pain level, strength of the flexor hallucis longus muscle, neurosensory testing of the hallux, and subjective sensory improvement were evaluated. Each proximal tibial nerve compression was subjected to neurolysis with division of the soleal sling. Results: Results were stratified into poor, fair, good, and excellent based on the amount of pain relief and improvement in motor and sensory function. In all groups combined, there were 13 excellent (26.5 percent), 13 good (26.5 percent), 18 fair (36.7 percent), and five poor (10.2 percent) results. Results in the neuropathy group were excellent in two patients, good in three, fair in four, and poor in one (mean follow-up, 18.7 months). Results in the failed tarsal tunnel syndrome group were excellent in two, good in six, fair in 13, and poor in four patients (mean follow-up, 13.9 months). The trauma subgroup had the best outcomes: excellent in nine patients, good in four, fair in one, and poor in zero (mean follow-up, 13.4 months). Conclusion: Regardless of cause, if a proximal tibial nerve compression beneath the soleal sling is identified, neurolysis may improve pain and sensory and motor function. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.