Evaluation of peripheral nerve injury according to the severity of damage using 18F-FDG PET/MRI in a rat Model of sciatic nerve injury

OBJECTIVES

We ascertained that the PET scan may be a valuable imaging modality for the noninvasive, objective diagnosis of neuropathic pain caused by peripheral nerve injury through the previous study. This study aimed to assess peripheral nerve damage according to severity using18F-FDG PET/MRI of the rat sciatic nerve.

METHODS

Eighteen rats were divided into three groups: 30-second (G1), 2-minute (G2), and 5-minute (G3) crushing injuries. The severity of nerve damage was measured in the third week after the crushing injury using three methods: the paw withdrawal threshold test (RevWT), standardized uptake values on PET (SUVR), and intensity analysis on immunohistochemistry (IntR).

RESULTS

There were significant differences between G1 and G3 in both SUVR and IntR (p = 0.012 and 0.029, respectively), and no significant differences in RevWT among the three groups (p = 0.438). There was a significant difference in SUVR (p = 0.012), but no significant difference in IntR between G1 and G2 (p = 0.202). There was no significant difference between G2 and G3 in SUVR and IntR (p = 0.810 and 0.544, respectively).

DISCUSSION

Although PET did not show results consistent with those of immunohistochemistry in all respects, this study demonstrated that PET uptake tended to increase with severe nerve damage. If this research is supplemented by further experiments, PET/MRI can be used as an effective diagnostic modality.

Characterizing peroneal nerve injury clinicoradiological patterns with MRI in patients with sciatic neuropathy and foot drop after total hip replacement

OBJECTIVE

Sciatic nerve injury following total hip arthroplasty (THA) predominantly affects the peroneal division of the sciatic nerve, often causing a foot drop. This can result from a focal etiology (hardware malposition, prominent screw, or postoperative hematoma) or nonfocal/traction injury. The objective of this study was to compare the clinicoradiological features and define the extent of nerve injury resulting from these two distinct mechanisms.

METHODS

Patients who developed a postoperative foot drop within 1 year after primary or revision THA with a confirmed proximal sciatic neuropathy based on MRI or electrodiagnostic studies were retrospectively reviewed. Patients were divided into two cohorts: group 1 (focal injury), including patients with an identifiable focal structural etiology, and group 2 (nonfocal injury), including patients with a presumed traction injury. Patient demographics, clinical examinations, subsequent surgeries, electrodiagnostic study results, and MRI abnormalities were noted. The Student t-test was used to compare time to onset of foot drop and time to secondary surgery.

RESULTS

Twenty-one patients, treated by one surgeon, met inclusion criteria (8 men and 13 women; 14 primary THAs and 7 revision THAs). Group 1 had a significantly longer time from THA to the onset of foot drop, with a mean of 2 months, compared with an immediate postoperative onset in group 2 (p = 0.02). Group 1 had a consistent pattern of localized focal nerve abnormality on imaging. In contrast, the majority of patients in group 2 (n = 11) had a long, continuous segment of abnormal size and signal intensity of the nerve, while the other 3 patients had a segment of less abnormal nerve in the midthigh on imaging. All patients with a long continuous lesion had Medical Research Council grade 0 dorsiflexion prior to secondary nerve surgeries compared with 1 of 3 patients with a more normal midsegment.

CONCLUSIONS

There are distinct clinicoradiological findings in patients with sciatic injuries resulting from a focal structural etiology versus a traction injury. While there are discrete localized changes in patients with a focal etiology, those with traction injuries demonstrate a diffuse zone of abnormality within the sciatic nerve. A proposed mechanism involves anatomical tether points of the nerve acting as points of origin and propagation for traction injuries, resulting in an immediate postoperative foot drop. In contrast, patients with a focal etiology have localized imaging findings but a highly variable time to the onset of foot drop.

Diagnostic Efficacy of 18F-FDG PET/MRI in Peripheral Nerve Injury Models

The aim of this study was to evaluate the diagnostic efficacy of ¹⁸F-FDG PET/MRI in two different peripheral neuropathic pain models using the injured rat sciatic nerves. Twelve rats, with operation on left sciatic nerves, were evenly divided into three groups: sham surgery (control group), crushing injury and chronic constriction injury (CCI) (experimental groups). The nerve damage was assessed at 3 weeks postoperatively using following methods: paw withdrawal threshold values (RevWT), maximum standardized uptake values on PET/MRI images (SUVR), and counting the number of myelinated axons in proximal and distal sites of nerve injury (MAxR). The results were quantified and statistically analyzed. Compared to the control group, the crushing injury demonstrated significant differences in RevWT (p < 0.0001) and SUVR (p = 0.027) and the CCI group demonstrated significant differences in RevWT (p < 0.0001), SUVR (p = 0.001) and MAxR (p = 0.048). There were no significant differences between the two experimental groups for all assessments. Correlation analysis demonstrated that RevWT and SUVR assessments were highly correlated (r = -- 0.710, p = 0.010), and SUVR and MAxR were highly correlated (r = 0.611, p = 0.035). However, there was no significant correlation between RevWT and MAxR. The PET scan may be a valuable imaging modality to enable noninvasive, objective diagnosis of neuropathic pain caused by peripheral nerve injury. Also, MRI fused with PET may help clarify the anatomic location of soft tissue structures, including the peripheral nerves.

Division of Sacrospinous and Sacrotuberous Ligaments Expands Access Through Greater Sciatic Foramen: Anatomic Study with Application to Resection of Greater Sciatic Foramen Tumors

OBJECTIVE

Tumors of the greater sciatic foramen remain difficult to treat. They often have both intrapelvic and extrapelvic components that may limit visualization and make safe resection of the tumor difficult. Therefore the goal of the present anatomic study was to quantitate how much additional surgical working space could be gained by transection of the sacrospinous and sacrotuberous ligaments.

METHODS

Sixteen sides from 9 fresh-frozen Caucasian cadaveric torsos underwent transgluteal dissection and exposure of the greater sciatic foramen and associated liagments. With the piriformis in place, the vertical and horizontal diameters of the greater sciatic foramen were measured. Next, the sacrotuberous and sacrospinous ligaments were cut at their ischial attachments. The vertical diameter of the now confluent greater and lesser sciatic foramina (V₂) was measured.

RESULTS

The mean vertical diameter of the greater sciatic foramen (V₁) was 54.8 ± 9.7 mm. The horizontal diameter of the greater sciatic foramen had a mean of 44.3 ± 6.1 mm with a range of 30-52 mm. After transection of the sacrotuberous and sacrospinous ligaments, the vertical distance of the greater and lesser sciatic foramina (V₂) had a mean of 74.8 ± 6.8 mm with a range of 60.1-90 mm. The mean ratio of V₂ to V₁ was 1.40.

CONCLUSIONS

The vertical length of the greater sciatic foramen increased, on average, 40% after resection of the sacrotuberous and sacrospinous ligaments. The results of this study support an alternative technique for resecting large intrapelvic tumors via a transgluteal approach.

Noninvasive Measurement of Sciatic Nerve Stiffness in Patients With Chronic Low Back Related Leg Pain Using Shear Wave Elastography

OBJECTIVES

The purpose of this study was to determine whether sciatic nerve stiffness is altered in people with chronic low back-related leg pain by using shear wave elastography.

METHODS

In this cross-sectional study, the sciatic nerve shear wave velocity (ie, an index of stiffness) was measured in both legs of 16 participants (8 with unilateral low back-related leg pain and 8 healthy controls). Sciatic stiffness was measured during a passive ankle dorsiflexion motion performed at 2°/s in an isokinetic dynamometer. The ankle range of motion and passive torque, as well as muscle activity, were also measured.

RESULTS

In people with low back-related leg pain, the affected limb showed higher sciatic nerve stiffness compared to the unaffected limb (+11.3%; P = .05). However, no differences were observed between the unaffected limb of people with low back-related leg pain and the healthy controls (P = .34).

CONCLUSIONS

People with chronic low back-related leg pain have interlimb differences in sciatic nerve stiffness, as measured by a safe and noninvasive method: shear wave elastography. The changes found may be related to alterations in nerve mechanical properties, which should be confirmed by future investigations.

Sciatic neuropathy caused by a pressure ulcer: A case report

RATIONALE

Sciatic neuropathy has various causes; however, cases in which a pressure ulcer led to sciatic neuropathy have not been reported to date.

PATIENT CONCERNS

A 33-year-old woman with no pre-existing mobility problems visited our department with the chief complaint of an extensive pressure ulcer and necrosis in her right buttock. She had a medical history of being bedridden for 2 days while in a coma due to a drug overdose 2 months previously. Physical examination revealed loss of sensation and foot drop in the right foot.

DIAGNOSIS

Physical examination, magnetic resonance imaging, and nerve conduction studies were conducted; the patient was diagnosed with a common peroneal branch injury of the right sciatic nerve.

INTERVENTIONS

The necrotic tissue was debrided and sciatic nerve decompression was performed, followed by frequent dressing changes. In addition, psychiatric treatment and physical therapy were performed simultaneously.

OUTCOMES

The pressure ulcer decreased in size and healed to some extent with granulation tissue. However, gait disorders, accompanied by symptoms of sciatic neuropathy, continued. The patient was transferred to the department of gastroenterology for the treatment of toxic hepatitis, which occurred during her inpatient treatment.

LESSONS

Physicians should be aware that sciatic neuropathy may occur during the treatment of patients with a pressure ulcer who exhibit no symptoms of paraplegia or quadriplegia. To prevent neuropathy, aggressive treatment of the pressure ulcer is necessary.

Sciatic Nerve Entanglement Around a Femoral Prosthesis During Closed Reduction of a Dislocated Total Hip Prosthesis: The Role of Metal-Suppression MRI: A Case Report

CASE

A 68-year-old woman who had undergone a right total hip arthroplasty presented with a right posterior hip dislocation, and subsequently developed an ipsilateral sciatic nerve palsy after closed reduction. Magnetic resonance imaging (MRI) with metal suppression demonstrated sciatic nerve entanglement around the prosthetic femoral neck. A sciatic nerve release was performed, resulting in poor early neurologic recovery.

CONCLUSION

Sciatic nerve entanglement following closed reduction of a dislocated total hip prosthesis is a rare injury. Assessment of neurovascular status before and after reduction is imperative. We recommend prompt MRI with metal suppression in patients with acute neurologic symptoms following reduction of a dislocated hip prosthesis to evaluate for acute nerve pathology and assess the need for emergency surgery.

B-scan ultrasonographic monitoring of orthotopic xenografted plexiform neurofibroma in mice

BACKGROUND/AIM

Xenografted benign tumours in immunodeficient mice provide an in vivo model to study tumour biology and the effect of agents on tumour growth. Conventionally, these small grafts can only be monitored upon sacrificing the animals. We evaluated ultrasound biomicroscopy for monitoring such grafts in vivo.

MATERIALS AND METHODS

Small fragments (<10 mm(3)) of a plexiform neurofibroma obtained from patients with established diagnosis of neurofibromatosis type-1 (NF1) were orthotopically-xenografted onto the sciatic nerve of immunodeficient mice and monitored using a high-resolution in vivo micro-imaging system.

RESULTS

Grafts were identified in most cases and were distinguished from the surrounding inflammatory host tissues by detailed ultrasonographic signals. Graft sizes could be calculated precisely from serial scan sections and monitored during the whole course of drug treatment.

CONCLUSION

High frequency sonographic measurement is a superior non-invasive method for monitoring small grafts of slowly growing benign tumours in mice in vivo, e.g. plexiform neurofibroma, and is especially suitable for tracing the effects of drugs at multiple time-points, thus allowing a very cost-effective follow-up.

Endoscopic resection of a presacral schwannoma. Case report

Presacral tumors are rarely found in adults. Resections via open abdominal or sacral approaches have been advocated traditionally as the preferred treatment for these tumors. The endoscopic surgical technique provides direct visualization of the presacral or retroperitoneal space. The authors report on a 67-year-old man who experienced difficulty in defecation off and on for 5 weeks, and recently he had suffered indistinct pain in the lower abdomen. The abdominal computed tomography scan revealed a 5.1 x 4.2-cm, homogeneous, low-density, well-defined mass arising from the left sciatic nerve abutting the left piriformis muscle, favoring a diagnosis of benign neurogenic tumor. Endoscopically guided resection was applied, with a favorable outcome. This procedure represents a less invasive approach that may be useful for benign retroperitoneal pelvic tumors.

Persistent sciatic artery: an uncommon cause of intermittent claudication

Persistent sciatic artery (PSA) is a rarely seen variation of the lower limb vessels. Anatomically the PSA is the continuation of internal iliac arteries. It follows the sciatic nerve from the sciatic foramen to the level of the knee. We report our experience with conservative therapy in a patient with complete occlusion of a PSA. A 54-year-old man with typical symptoms of intermittent claudication on the left limb was referred to our Department. After clinical examination Doppler and duplex sonography were performed. Angiography showed bilateral PSA. On the left side the PSA was occluded. The patient received 20 intravenous courses of prostaglandin E1 for 4 weeks, followed by oral anticoagulation with phenprocoumon for life (INR: 2.5-3.5). After 3 years therapy he does not show any typical symptoms of intermittent claudication or limb ischemia. This case shows that conservative therapy may be effective. However, it has to be emphasised that this approach requires frequent clinical and duplex sonography follow-up every 3 to 6 months with oral anticoagulation.

Diagnóstico de recurrencia mediante FDG-PET en un caso clínico de schwannoma maligno

The peripheral nerve sarcoma, also called malignant schwannoma, is originally a soft tissue sarcoma. It is mainly located in the peripheral sheath nerve of the limbs and usually infiltrates the nerve fibres. We present the case of a thirty year old woman with a malignant schwannoma in her left leg sciatic nerve who had been treated on several occasions. An 18-FDG positron emission tomography was performed to evaluate the management of the patient. It showed regional recurrence, which required leg amputation. The pathological result has confirmed the PET diagnosis. PET can be a useful technique to detect recurrence for this kind of tumor, mainly in patients who have been previously radiated when the MRI is insufficient to perform a differential diagnosis between postirradiation fibrosis and tumoral recurrence, allowing for suitable therapeutic management of the patient.

Neuromuscular choristoma of the sciatic nerve. Case report

The authors report the findings of a neuromuscular choristoma of the sciatic nerve in an otherwise healthy 18-year-old man who presented with sensorimotor symptoms and deformities of the right leg and foot. Only a few cases of this rare tumor, also known as "neuromuscular hamartoma" or "benign triton tumor," have been reported in the surgical literature. The authors discuss the clinical presentation, radiological findings, pathological diagnosis, and surgical rationale for this case and review the associated literature.