Automated whole slide morphometry of sural nerve biopsy using machine learning.

AIM: The morphometry of sural nerve biopsies, such as fibre diameter and myelin thickness, helps us understand the underlying mechanism of peripheral neuropathies. However, in current clinical practice, only a portion of the specimen is measured manually because of its labour-intensive nature. In this study, we aimed to develop a machine learning-based application that inputs a whole slide image (WSI) of the biopsied sural nerve and automatically performs morphometric analyses. METHODS: Our application consists of three supervised learning models: (1) nerve fascicle instance segmentation, (2) myelinated fibre detection and (3) myelin sheath segmentation. We fine-tuned these models using 86 toluidine blue-stained slides from various neuropathies and developed an open-source Python library. RESULTS: Performance evaluation showed (1) a mask average precision (AP) of 0.861 for fascicle segmentation, (2) box AP of 0.711 for fibre detection and (3) a mean intersection over union (mIoU) of 0.817 for myelin segmentation. Our software identified 323,298 nerve fibres and 782 fascicles in 70 WSIs. Small and large fibre populations were objectively determined based on clustering analysis. The demyelination group had large fibres with thinner myelin sheaths and higher g-ratios than the vasculitis group. The slope of the regression line from the scatter plots of the diameters and g-ratios was higher in the demyelination group than in the vasculitis group. CONCLUSION: We developed an application that performs whole slide morphometry of human biopsy samples. Our open-source software can be used by clinicians and pathologists without specific machine learning skills, which we expect will facilitate data-driven analysis of sural nerve biopsies for a more detailed understanding of these diseases.

Granuloma, vasculitis, and demyelination in sarcoid neuropathy.

BACKGROUND: Despite the suggestion that direct compression by granuloma and ischemia resulting from vasculitis can cause nerve fiber damage, the mechanisms underlying sarcoid neuropathy have not yet been fully clarified. METHODS: We examined the clinicopathological features of sarcoid neuropathy by focusing on electrophysiological and histopathological findings of sural nerve biopsy specimens. We included 18 patients with sarcoid neuropathy who had non-caseating epithelioid cell granuloma in their sural nerve biopsy specimens. RESULTS: Although electrophysiological findings suggestive of axonal neuropathy were observed, particularly in the lower limbs, all but three patients showed ≥1 abnormalities in nerve conduction velocity or distal motor latency. Additionally, a conduction block was observed in 11 of the 16 patients for whom waveforms were assessed; five of them fulfilled motor nerve conduction criteria strongly supportive of demyelination as defined in the European Academy of Neurology/Peripheral Nerve Society (EAN/PNS) guideline for chronic inflammatory demyelinating polyneuropathy (CIDP). In most patients, sural nerve biopsy specimens revealed a mild to moderate degree of myelinated fiber loss. Fibrinoid necrosis was observed in one patient, and electron microscopy analysis revealed demyelinated axons close to granulomas in six patients. CONCLUSIONS: Patients with sarcoid neuropathy may meet the EAN/PNS electrophysiological criteria for CIDP due to the frequent presence of conduction blocks. Based on our results, in addition to the ischemic damage resulting from granulomatous inflammation, demyelination may play an important role in the mechanism underlying sarcoid neuropathy.

Long-Term Donor-Site Morbidity Following Entire Sural Nerve Harvest for Grafting.

PURPOSE: The sural nerve is the autologous nerve used most commonly for grafting. However, recent studies indicate a high rate of complications and complaints after sural nerve removal. In this prospective study, we evaluated donor-site morbidity following full-length sural nerve harvesting on long-term follow-up. METHODS: Fifty-one legs from 43 patients who underwent complete sural nerve harvesting for brachial plexus reconstruction were included in the study. After an average of 5 years, with a minimum postoperative follow-up of 12 months, sensory deficits in the leg and foot were analyzed using 2.0-g monofilaments. Regions of sensory deficit were marked with a skin marker and photographed. Over these regions of decreased sensation, we tested nociception using an eyebrow tweezer. Patients were also asked about pain, cold intolerance, pruritis, difficulties walking, and foot swelling. RESULTS: Regions most affected (84% of patients) were over the calcaneus and cuboid. However, in these regions, nociception was preserved. Regions of decreased sensation extended to the calf region in 11 of 51 legs. In 13 patients, we also observed regions of decreased sensation on the proximal leg. In five feet, the sensation was entirely preserved. No patient had any complaints about pain, cold intolerance, itchiness, difficulties walking, or foot swelling. CONCLUSION: Decreased sensation with nociception preserved was most common along the lateral side of the foot over the calcaneus and cuboid. Removing the entire sural nerve produced no long-term complaints of pain. Sural nerve use appears safe. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic II.

[Effects of free gracilis muscle flap combined with sural nerve transfer for reconstruction of digital flexion and sensory function of hand in patient with wrist electric burn].

Objective: To explore the effects of free gracilis muscle flap combined with sural nerve transfer for reconstruction of digital flexion and sensory function of hand in patient with severe wrist electric burn. Methods: A retrospective observational study was conducted. From January 2017 to December 2020, 4 patients with wrist high-voltage electric burn admitted to the Department of Burns of the First People's Hospital of Zhengzhou and 4 patients with wrist high-voltage electric burn admitted to the Department of Hand Surgery of Beijing Jishuitan Hospital met the inclusion criteria, including 6 males and 2 females, aged 12 to 52 years. They were all classified as type Ⅱ wrist high-voltage electric burns with median nerve defect. In the first stage, the wounds were repaired with free anterolateral thigh femoral myocutaneous flap. In the second stage, the free gracilis muscle flap combined with sural nerve transplantation was used to reconstruct the digital flexion and sensory function of the affected hand in 3 to 6 months after wound healing. The cut lengths of muscle flap and nerve were 32 to 38 and 28 to 36 cm, respectively. The muscle flap donor area and nerve donor area were both closed and sutured. The survival condition of gracilis muscle flap and sural nerve, the wound healing time of recipient area on forearm, the healing time of suture in muscle flap donor area and nerve donor area were observed and recorded after operation, and the recovery of donor and recipient areas was followed up. In 2 years after operation, the muscle strength of thumb and digital flexion and finger sensory function after the hand function reconstruction were evaluated with the evaluation criteria of the hand tendon and nerve repair in the trial standard for the evaluation of functions of upper limbs of Hand Surgery Society of Chinese Medical Association. Results: All the gracilis muscle flap and sural nerve survived successfully after operation. The wound healing time of recipient area on forearm was 10 to 14 days after operation, and the healing time of suture in muscle flap donor area and nerve donor area was 12 to 15 days after operation. The donor and recipient areas recovered well. In the follow-up of 2 years after operation, the muscle strength of thumb and digital flexion was evaluated as follows: 4 cases of grade 5, 3 cases of grade 4, and 1 case of grade 2; the finger sensory function was evaluated as follows: 4 cases of grade S3+, 2 cases of grade S3, and 2 cases of grade S2. Conclusions: For patients with hand dysfunction caused by severe wrist electric burn, free gracilis muscle flap combined with sural nerve transplantation can be used to reconstruct the digital flexion and sensory function of the affected hand. It is a good repair method, which does not cause great damage to thigh muscle flap donor area or calf nerve donor area.

Positional relationship between the Achilles tendon and sural nerve on ultrasound.

PURPOSE: This study sought to clarify the positional relationship between the Achilles tendon and sural nerve using ultrasound. METHODS: We studied 176 legs in 88 healthy volunteers. The positional relationship between the Achilles tendon and sural nerve at heights of 2, 4, 6, 8, 10, and 12 cm proximal from the calcaneus' proximal margin was investigated by distance and depth. Setting the X-axis (left/right) as the horizontal axis and Y-axis (depth) as the vertical axis against ultrasound images, we investigated the distance between the lateral margin of the Achilles tendon to the midpoint of the sural nerve on the X-axis. The Y-axis was split into four zones: the part behind the center of the Achilles tendon (AS), the part in front of the center of the Achilles tendon (AD), the part behind the Achilles tendon (S), and the part in front (D). We investigated the zones through which the sural nerve passed. We also studied any significant differences between the sexes and left/right legs. RESULTS: The mean distance on the X-axis was closest at 6 cm, with 1.1 ± 5.0 mm between them. The sural nerve's position on the Y-axis was such that at positions more proximal than 8 cm, the sural nerve ran through zone S in most legs and moved to zone AS through heights 2-6 cm. No parameters showed significant differences between the sexes or left/right legs. CONCLUSION: We presented the positional relationship between the Achilles tendon and sural nerve and suggested some measures to prevent nerve injury during surgery.

Sural nerve biopsy utility by masked assessment of individual histologic preparations.

BACKGROUND AND AIMS: Comprehensive study of sural nerve biopsy utility based on individual histopathologic preparations is lacking. We aimed to quantify the value of different histologic preparations in diagnosis. METHODS: One hundred consecutive sural nerves were studied by standard histological preparations plus graded teased nerve fibers (GTNF), immunohistochemistry, and epoxy-semithin morphometry. Three examiners scored the individual preparations separately by a questionnaire of neuropathic and interstitial abnormalities, masked to the biopsy number, versus a gold-standard of all preparations. Multivariate modeling was utilized to determine best approach versus the gold-standard. RESULTS: Highest confidence (range 8-9 of 10) and inter-rater reliability (99%) for fiber abnormalities came from GTNF, and interstitial abnormalities from paraffin stains (range 7-8, 99%). Vasculitic neuropathy associated with GTNF axonal degeneration (moderate to severe 79%) with OR 3.8, 95% CI (1.001-14.7), p = .04, but not significantly with the other preparations. Clinicopathologic diagnoses associated with teased fiber abnormalities in chronic inflammatory demyelinating polyradiculoneuropathy, 80% (8/10); amyloidosis, 50% (1/2); adult-onset polyglucosan disease 100% (1/1). GTNF and paraffin stains significantly correlated with fiber density determined by morphometric analysis (GTNF: OR 9.9, p < .0001, paraffin: OR 3.8, p = .03). GTNF combined with paraffin sections had highest accuracy for clinicopathologic diagnoses and fiber density with 0.86 C-stat prediction versus morphometric analysis. Pathological results lead to initiation or changes of immunotherapy in 70% (35/50; initiation n = 22, reduction n = 9, escalation n = 4) with the remaining having alternative intervention or no change. INTERPRETATION: Nerve biopsy paraffin stains combined with GTNF have highest diagnostic utility, confidence, inter-rater reliability, improving accuracy for a pathologic diagnosis aiding treatment recommendations. Immunostains and epoxy preparations are also demonstrated useful supporting consensus guidelines. This study provides class II evidence for individual nerve preparation utility.

Imaging of the peripheral nervous system in nociplastic pain: An ultrasound study in patients with fibromyalgia.

BACKGROUND AND PURPOSE: Although fibromyalgia (FM) is considered a central sensitization syndrome, studies investigating peripheral nerves in this condition are not available. The primary objective of this study is to investigate the sonographic changes (ie, increased cross-sectional area [CSA]), of peripheral nerves in patients with FM compared to healthy controls. The secondary objective is to identify potential clinical correlations associated with increased CSA in patients with FM. METHODS: In this cross-sectional observational study, consecutive female patients with FM underwent sonographic assessment using a standardized scanning protocol. The CSA of seven nerves was measured bilaterally at 11 anatomic sites by an experienced sonographer. Differences in CSA of nerves were compared with those of healthy subjects by one-way analysis of variance. Patients underwent clinimetric evaluation aimed at investigating disease severity, neuropathic pain features, depression, anxiety, fatigue, and autonomic symptoms to explore the possible correlation between CSA and clinical features. RESULTS: Forty-seven patients and 20 healthy controls were enrolled. Differences in terms of increased CSA between patients and healthy controls were identified at multiple levels, mainly at the level of the sural nerve, vagus nerve, and sixth cervical nerve root (for all, p < .001). Sonographic findings, however, did not correlate with the clinical features explored. CONCLUSIONS: Patients with FM show higher CSA of nerves than healthy subjects. The increased CSA is most evident at the sural nerve, vagus nerve, and sixth cervical nerve root. Ultrasound, a relatively easy-to-use technique, could identify morphological changes, in peripheral nervous structures in patients with FM.

The Role of the Cross Face Nerve Graft in Facial Reanimation and Endoscopic Harvest of the Sural Nerve.

Cross-face nerve grafting (CFNG) allows for spontaneous, involuntary facial movement for patients with irreversible hemifacial paralysis. This technique uses an intact contralateral facial nucleus and nerve as an input and axon source, allowing donor neural input to be routed through a nerve graft across the face. The sural nerve is well equipped for use as a nerve graft due to its length and minimal donor site morbidity. Endoscopic nerve harvest techniques allow for efficient, minimally invasive dissection that improves the integrity of the harvested nerve.

Dermal Sensory Regenerative Peripheral Nerve Interface for Reestablishing Sensory Nerve Feedback in Peripheral Afferents in the Rat.

BACKGROUND: Without meaningful, intuitive sensory feedback, even the most advanced myoelectric devices require significant cognitive demand to control. The dermal sensory regenerative peripheral nerve interface (DS-RPNI) is a biological interface designed to establish high-fidelity sensory feedback from prosthetic limbs. METHODS: DS-RPNIs were constructed in rats by securing fascicles of residual sensory peripheral nerves into autologous dermal grafts, with the objectives of confirming regeneration of sensory afferents within DS-RPNIs and establishing the reliability of afferent neural response generation with either mechanical or electrical stimulation. RESULTS: Two months after implantation, DS-RPNIs were healthy and displayed well-vascularized dermis with organized axonal collaterals throughout and no evidence of neuroma. Electrophysiologic signals were recorded proximal from DS-RPNI's sural nerve in response to both mechanical and electrical stimuli and compared with (1) full-thickness skin, (2) deepithelialized skin, and (3) transected sural nerves without DS-RPNI. Mechanical indentation of DS-RPNIs evoked compound sensory nerve action potentials (CSNAPs) that were like those evoked during indentation of full-thickness skin. CSNAP firing rates and waveform amplitudes increased in a graded fashion with increased mechanical indentation. Electrical stimuli delivered to DS-RPNIs reliably elicited CSNAPs at low current thresholds, and CSNAPs gradually increased in amplitude with increasing stimulation current. CONCLUSIONS: These findings suggest that afferent nerve fibers successfully reinnervate DS-RPNIs, and that graded stimuli applied to DS-RPNIs produce proximal sensory afferent responses similar to those evoked from normal skin. This confirmation of graded afferent signal transduction through DS-RPNI neural interfaces validate DS-RPNI's potential role of facilitating sensation in human-machine interfacing. CLINICAL RELEVANCE STATEMENT: The DS-RPNI is a novel biotic-abiotic neural interface that allows for transduction of sensory stimuli into neural signals. It is expected to advance the restoration of natural sensation and development of sensorimotor control in prosthetics.

Sural hypersensitivity after nerve transection depends on anatomical differences in the distal tibial nerve of mice and rats.

INTRODUCTION: Various mouse and rat models of neuropathic pain after nerve injury exist. Whilst some models involve a proximal nerve lesion or ligation of the sciatic trifurcation in mice and rats, others consists of a transection or ligation of distal nerves at the tibial bifurcation in mice or rats. The level of nerve cut directly affects the magnitude of hypersensitivity, and anatomical differences between mice and rats might therefore impact the development of hypersensitivity after distal tibial nerve transection as well. METHODS: The bifurcation of the distal tibial nerve into the medial and lateral plantar nerve (MPN and LPN), and the presence of anatomical differences in sural and tibial nerve distribution between mice and rat was evaluated. Sural mechanical sensitivity after transection of the MPN or whole tibial nerve was assessed using von Frey test until 8 weeks after surgery in 48 rats and 16 mice. RESULTS: The bifurcation of the tibial nerve into the MPN and LPN is situated proximal to the ankle in both mice and rats. The sural nerve joins the LPN in mice, but not in rats. A proximal communicating branch is present between the LPN and MPN in rats, but not in mice. MPN transection in mice caused hypersensitivity of the hindpaw innervated by the sural nerve, but not in rats. In rats, sural hypersensitivity only developed when both MPN and LPN were cut. CONCLUSION: Inter-species variation in nerve anatomy should be taken in consideration when performing surgery to induce plantar hypersensitivity in rodents.

Ultrasound evaluation of a new surface reference line to describe sural nerve location and safe zones to consider in posterior leg approaches.

PURPOSE: Several authors have described methods to predict the sural nerve pathway with non-proportional numerical distances, but none have proposed a person-proportional, reproducible method with anatomical references. The aim of this research is to describe ultrasonographically the distance and crossing zone between a surface reference line and the position of the sural nerve. METHODS: Descriptive cross-sectional study, performed between January and April 2022 in patients requiring foot surgery who met inclusion criteria. The sural nerve course in the posterior leg was located and marked using ultrasound. Landmarks were drawn with a straight line from the medial femoral condyle to the tip of the fibula. Four equal zones were established in the leg by subdividing the distal half of the line. This way, areas based on simple anatomical proportions for each patient were studied. The distance between the marking and the ultrasound nerve position was measured in these 4 zones, creating intersection points and safety areas. Location and distances from the sural nerve to the proposed landmarks were assessed. RESULTS: One-hundred and four lower limbs, 52 left and 52 right, assessed in 52 patients were included. The shortest median distance of the nerve passage was 2.9 mm from Point 2. The sural nerve intersection was 60/104 (57.7%) in Zone B, 21/104 (20.1%) in Zone C and 19/104 (18.3%) in Zone A. Safety zones were established. Average 80.5% of coincidence in sural nerve localization was found in the distal half of the leg, in relation to the surface reference line when comparing both legs of each patient. CONCLUSIONS: This study proposes a simple, reproducible, non-invasive and, for the first time, person-proportional method, that describes the distance and location of the main areas of intersection of the sural nerve with points and zones (risk and safe zones) determined by a line guided by superficial anatomical landmarks. Its application when surgeons plan and perform posterior leg approaches will help to avoid iatrogenic nerve injuries. LEVEL OF EVIDENCE: IV.

A New Technique of Achilles Tendon Rupture Repaired by Double Transverse Mini-incision to Avoid Sural Nerve Injury: A Consecutive Retrospective Study.

OBJECTIVE: Percutaneous suture is a classic technique used in Achilles tendon repair. However, the complication rates surrounding the sural nerve remain relatively high. Modified percutaneous repair technology can effectively avoid these complications; however, the surgical procedure is complicated. Hence, the present study was conducted to describe a redesigned repair technique for the Achilles tendon able to avoid sural nerve injury and reduce the complexity of the procedure. METHODS: Data of patients with acute primary Achilles tendon rupture at our hospital from January 2019 to May 2020 were included. Subjects with expectations for surgical scarring underwent a minimally invasive-combined percutaneous puncture technique. The surgical time, requirement for conversion to other technologies, and length of postoperative hospitalization were investigated to assess efficacy. The American Orthopedic Foot & Ankle Society (AOFAS) score and the Arner-Lindholm scale (A-L scale) were used to assess postoperative clinical outcomes (> 24 months). During the 2-year follow-up, MRI was performed to observe the healing of the Achilles tendon. In addition, subjective satisfaction with surgical scar healing was recorded. RESULTS: Twenty consecutive subjects with an average follow-up of 28.3 ± 4.5 months (range, 24-41) met the inclusion criteria. None of the 20 enrolled patients required a converted surgical approach. The mean surgical time was 26.9 ± 6.47 min (range, 20-44). None of the patients experienced dysesthesia or anesthesia around the sural nerve. No signs of postoperative infections were observed. MRI data showed that the wounds of the Achilles tendon healed completely in all the subjects. The AOFAS score increased from 55.6 ± 11.07 (range, 28-71) preoperatively to 97.8 ± 3.34 (range, 87-100) at the last follow-up. The A-L scale showed that 90% of the subjects (n = 18) presented as excellent and 10% of the subjects (n = 2) presented as good, with an excellent/good rate of 100%. Moreover, subjects' satisfaction for surgical scars was 9.1 ± 0.78 (upper limit, 10). CONCLUSIONS: The results indicate that this technique can achieve good postoperative function, a small surgical incision, and high scar satisfaction. In addition, this technique should be widely used in suturing Achilles tendon ruptures.

Sural Nerve Vertical Cross-Face Graft for Lacrimal Gland Neurotization to Improve Tear Secretion in Neurodeprivative Dry Eye.

PURPOSE: No specific interventions have been reported for the treatment of severe neurodeprivative dry eye disease owing to facial nerve palsy. We describe herein the feasibility of a novel surgical procedure to reinnervate the lacrimal gland and report the preliminary outcomes of the first series of patients who were treated accordingly. METHODS: Prospective interventional case series including consecutive patients affected by facial palsy with absolute deficiency of tear secretion who underwent lacrimal gland neurotization. A sural nerve vertical cross-face graft was used to connect the lacrimal gland with the parasympathetic branch of the lingual nerve directed to the contralateral submandibular gland. RESULTS: Lacrimal neurotization was performed uneventfully in 10 patients (4 M, 6 F; mean age 47.1 ± 17.1 years). In all cases, the procedure was combined with facial reanimation, while corneal neurotization was performed in 4 cases. One year postoperatively, mean values of a Schirmer test increased significantly compared with baseline values (7.56 ± 7.84 vs. 0 ± 0 mm/5 min; P = 0.02), while the mean daily number of instillation of tear substitutes decreased significantly (21.8 ± 4.5 vs. 7.1 ± 2.2; P = 0.009). Overall, all patients were satisfied with surgery (very satisfied: n = 7 and satisfied: n = 2). No major postoperative complications occurred. CONCLUSIONS: Vertical cross-face using a sural nerve graft to connect the lacrimal gland with the contralateral submandibular gland is a novel technique for treating patients with facial nerve palsy and severe neurodeprivative dry eye disease. This surgery both performed alone and combined with corneal neurotization is able to improve tear secretion and decrease the need for frequent instillations of tear substitutes.

Diagnostic yield of nerve biopsy in the evaluation of peripheral neuropathies.

BACKGROUND: With progress made in neurogenetics and neuroinflammation, the indications and value of nerve biopsies in the diagnostic evaluation of peripheral neuropathies are less clear. In this study, we aimed to evaluate the diagnostic yield of nerve biopsies in patients with peripheral neuropathies. METHODS: We performed a retrospective review of nerve biopsy reports from April 1998 to June 2021 of patients with peripheral neuropathies presenting to the Department of Pathology, University of Malaya Medical Centre, Kuala Lumpur, Malaysia. The diagnostic value of the biopsies was determined based on the criteria by Midroni and Bilbao as follows: contributive (essential and helpful), non-contributive and inadequate. RESULTS: A total of 107 nerve biopsies were analysed. Sixty-four (60 %) were males and the mean age was 52 years, ranging from 13 to 86 years. Ninety-four (88 %) were sural nerve biopsies; and only one patient (1 %) each had superficial peroneal and superficial radial nerve biopsy. The indications for the procedure were vasculitis (34 %), peripheral neuropathy of unknown aetiology (34 %), amyloidosis (14 %) and chronic inflammatory demyelinating polyneuropathy (10 %). In 68 (63 %) biopsies, the diagnostic value was contributive. Of these, 28 (26 %) were essential and 40 (37 %) were helpful. In contrast, 35 (33 %) biopsies were non-contributive and 4 (4 %) were inadequate. In 66 % (71/107) of cases, the nerve biopsy did not reveal a definite pathological diagnosis. However, in the remainder, a diagnosis of vasculitis (18 %, 19/107), followed by amyloidosis (10 %, 11/107) could be determined. For 32/71 biopsies with undetermined pathological diagnosis, neuropathy remained cryptogenic in 22 % (7/32) upon follow up. CONCLUSIONS: With the exception of vasculitis and amyloidosis, there is limited value in performing nerve biopsies in the evaluation of patients with peripheral neuropathy. However, this should be interpreted with caution as the number of patients with a clinical diagnosis of vasculitis and amyloidosis were relatively larger than patients with other diagnosis. Refinement and careful selection of cases are required to increase the diagnostic yield of nerve biopsy.

Anatomy of the Sural Nerve in the Posterolateral Approach to the Ankle: A Cadaveric Study.

Sural nerve injury may occur during the posterolateral approach to the ankle during fracture fixation. We aimed to map its location in a posterolateral approach in cadaveric specimens. A posterolateral approach was used in 28 cadaver legs with the incision made halfway between the medial border of the fibula and the lateral border of Achilles tendon, extending proximally from the tip of the lateral malleolus. The sural nerve was identified and the distance from the distal tip of the incision to where it crossed the incision proximally was measured. The mean distance was 3.4 ± 1.2 (range 0.5-7.0) cm. In 22 cases (78.5%), the distance from the lowest part of the incision to the inferior part of the nerve was between 2.7 and 4.5 cm. The nerve did not cross the incision in 2 cases. We have demonstrated that the sural nerve crossed the posterolateral incision between 2.7 and 4.5 cm proximal to the tip of the fibula in the majority of cases. However, there remains individual anatomical variation, and we would recommend that care should be taken to look for the nerve closer to the Achilles tendon proximally and nearer the fibula distally. We hope that this information can help surgeons plan their approach and minimize iatrogenic injury to the sural nerve.

Sural nerve: imaging anatomy and pathology.

High resolution ultrasound (US) and magnetic resonance (MR) neurography are both imaging modalities that are commonly used for assessing peripheral nerves including the sural nerve (SN). The SN is a cutaneous sensory nerve which innervates the lateral ankle and foot to the base of the fifth metatarsal. It is formed by contributing nerves from the tibial and common peroneal nerves with six patterns and multiple subtypes described in literature. In addition to the SN being a cutaneous sensory nerve, the superficial location enables the nerve to be easily biopsied and harvested for a nerve graft, as well as increasing the susceptibility to traumatic injury. As with any peripheral nerves, pathologies such as peripheral nerve sheath tumors and neuropathies can also affect the SN. By utilizing a high frequency probe in US and high-resolution MR neurography, the SN can be easily identified even with the multiple variations given the standard distal course. US and MRI are also useful in determining pathology of the SN given the specific image findings that are seen with peripheral nerves. In this review, we evaluate the normal imaging anatomy of the SN and discuss common pathologies identified on imaging.

A Cohort Study on Neuropathic Pain of the Sural Nerve-Can Neurectomy Be Considered a Valid Treatment Option?

BACKGROUND: Sural nerve neuroma is often caused by an injury during prior surgery, for example, osteosynthesis or ligament refixations at ankle level. Different surgical techniques to treat neuroma have been described. Neurectomy of an injured symptomatic sural nerve has been described as a treatment option for neuropathic pain. The aim of this study was to evaluate the outcomes of this technique to operatively treat sural nerve neuroma in our department. METHODS: From 2010 to 2020, a total of 30 consecutive patients with neuropathic pain and suspected neuroma of the sural nerve underwent sural nerve neurectomy. A medical chart review was performed to collect patient-, pain-, and treatment-specific factors. Outcomes were registered. RESULTS: After neurectomy, 22 patients (73.3%) had persisting pain. In logistic regression models evaluating the risk of persisting pain after sural nerve neurectomy, no independent predictor of higher risk of persisting pain could be identified. CONCLUSION: For sural nerve neuromas, neurectomy remains an option as the surgical morbidity is minor, but patients need to be counseled that only a fourth of those undergoing surgery will be pain-free afterward.

Clinical feature and sural biopsy study in nitrous oxide-induced peripheral neuropathy.

OBJECTIVE: The objective was to analyze the clinical characteristics and pathological characteristics of sural biopsy in nitrous oxide (N2O) -induced peripheral neuropathy. METHODS: We recruited 18 patients with N2O abuse-induced neurological disorders and reported their demographic data, clinical manifestations, laboratory examinations, and nerve conduction studies. Seven patients underwent sural nerve biopsy pathologic examination. RESULTS: All 18 patients had polyneuropathy, the nerve conduction results showed significant reductions in motor and sensory amplitudes, slowing of conduction velocities, and prolongation of latencies in most tested nerves compared to the controls. Toluidine blue staining of semi-thin sections of sural nerve biopsy showed decreased myelinated nerve fiber density, increased thin myelinated nerve fiber density, and axonal regeneration. Electron microscopy showed axonal degeneration and nerve regeneration. CONCLUSION: The main manifestations of peripheral nerve damage caused by the abuse of N2O are lower limb weakness and distal sensory disorder. The nerve conduction study results demonstrated that mixed axonal and demyelinating neuropathy was the most common type of neuropathy. Sural biopsy showed the main pathological change was chronic axonal degeneration.