Intraoperative high-resolution ultrasound and contrast-enhanced ultrasound of peripheral nerve tumors and tumorlike lesions.

The diagnostic workup and surgical therapy for peripheral nerve tumors and tumorlike lesions are challenging. Magnetic resonance imaging is the standard diagnostic tool in the preoperative workup. However, even with advanced pulse sequences such as diffusion tensor imaging for MR neurography, the ability to differentiate tumor entities based on histological features remains limited. In particular, rare tumor entities different from schwannomas and neurofibromas are difficult to anticipate before surgical exploration and histological confirmation. High-resolution ultrasound (HRU) has become another important tool in the preoperative evaluation of peripheral nerves. Ongoing software and technical developments with transducers of up to 17-18 MHz enable high spatial resolution with tissue-differentiating properties. Unfortunately, high-frequency ultrasound provides low tissue penetration. The authors developed a setting in which intraoperative HRU was used and in which the direct sterile contact between the ultrasound transducer and the surgically exposed nerve pathology was enabled to increase structural resolution and contrast. In a case-guided fashion, the authors report the sonographic characteristics of rare tumor entities shown by intraoperative HRU and contrast-enhanced ultrasound.

Intraoperative Sodium-Fluorescence Imaging in Peripheral Nerve Sheath Tumors (PNST)-A New Additional Promising Diagnostic Tool.

Background: Through the development and implementation of specific fluorophore filters to microscopes in 2012, sodium fluorescein (SF) is currently experiencing a remarkable renaissance in neurosurgery. The present study examines its intraoperative application during surgical removal of peripheral nerve sheath tumors (PNST) and metastases. Methods: This single-center study includes 10 cases of benign and malignant tumors as well as metastases of peripheral nerves (in total 11 PNST). Their surgical resections were all performed under microscope-based fluorescence with SF, which was administered intravenously (0.5-1.0 mg/kg body weight) during anesthesia induction. Microsurgical tumor removals were filmed and the collected data were retrospectively analyzed via ImageJ. Results: Microsurgical tumor preparation was possible under the usage of fluorophore filter. In seven histological confirmed schwannoma (n = 6 patients) tissue differentiation between tumor mass and not involved fascicles was statistically significant for the colors green and red. Schwannoma maximum mean for green reached 254.7 pixel and 179.4 pixel for red, whereas passing healthy fascicles revealed a maximum mean for green 94.91 and for red 120.76 pixel. One case of neurofibroma achieved lower amount of pixel. Similar to schwannoma, the two MPNST cases showed a strong homogeneous fluorescence (max. mean green 215 pixel and red 124.51) involving the whole nerve segment. Subcutaneous tumor remnants were visualized and therefore resected. Via fascicular nerve biopsy a B-cell lymphoma of the tibial nerve could be detected. SF led to variable stain intensities in single fascicles. The resected fascicle revealed a max mean green of 100.54 pixel, whereas surrounding fascicles came up with max. mean green of 63.0 pixel. Conclusions: Intraoperative SF visualization for PNST is feasible and of low risk. During resection of benign PNST, enhanced tissue differentiation between affected and not affected nerve segments is very useful. Tumor remnants can be detected safely and effectively. Its application during resection of malignant PNST is limited. Due to the infiltrative nature of those tumors, intraneural tissue differentiation is not possible. "Fluorescence-guided" biopsy can be regarded as an additional advantage in PNST surgery. Due to the encouraging experience in our institution SF was established as standard visualization tool in PNST surgery.

Sodium Fluorescein as Intraoperative Visualization Tool During Peripheral Nerve Biopsies.

OBJECTIVE: Owing to technical development of specific fluorophore filters, the neurosurgical application of sodium fluorescein (SF) has regained value in brain tumor surgery. The aim of this study was to determine the usefulness of SF during nerve biopsies. METHODS: This single-center study included 5 cases of nerve biopsies performed under microscope-based fluorescence with SF performed between March 2016 and February 2017. SF was applied intravenously (1 mg/kg body weight). After microsurgical dissection of the involved nerve segment, fluorescence-guided fascicular biopsy was performed. Selection of target fascicles was at the surgeon's discretion and took into account nerve stimulation for preservation of motor function and fluorescence intensity. Correlation to histopathologic examination was examined. Video analysis of intraoperative images comparing target fascicles with intense fluorescent response to adjacent fascicles of the same nerve segment was performed using ImageJ. RESULTS: All patients had motor or sensory deficits. Magnetic resonance imaging findings were similar, depicting long segments of gadolinium enhancement (minimum 11.7 cm). Each biopsy sample was positive resulting in diverse histopathologic results. Digital image analysis revealed a statistically significant difference of the complementary color green (P = 0.0473). CONCLUSIONS: Magnetic resonance imaging is the gold standard in diagnostic work-up of peripheral nerve disorders. Longitudinal nerve thickening with positive contrast enhancement is an unspecific magnetic resonance imaging finding. Various pathologies, such as tumors and inflammatory lesions, may cause this morphologic phenomenon. Nerve biopsies may be needed for diagnostic work-up. Intraoperative SF may help to depict the most affected fascicles and identify target fascicles for biopsy and increase diagnostic certainty of nerve biopsies.

High-resolution ultrasonography in evaluating peripheral nerve entrapment and trauma.

High-resolution ultrasonography is a noninvasive, readily applicable imaging modality, capable of depicting real-time static and dynamic morphological information concerning the peripheral nerves and their surrounding tissues. Continuous progress in ultrasonographic technology results in highly improved spatial and contrast resolution. Therefore, nerve imaging is possible to a fascicular level, and most peripheral nerves can now be depicted along their entire anatomical course. An increasing number of publications have evaluated the role of high-resolution ultrasonography in peripheral nerve diseases, especially in peripheral nerve entrapment. Ultrasonography has been shown to be a precious complementary tool for assessing peripheral nerve lesions with respect to their exact location, course, continuity, and extent in traumatic nerve lesions, and for assessing nerve entrapment and tumors. In this article, the authors discuss the basic technical considerations for using ultrasonography in peripheral nerve assessment, and some of the clinical applications are illustrated.

Sodium Fluorescein-Guided Surgery in Peripheral Nerve Sheath Tumors: First Experience in 10 Cases of Schwannoma.

BACKGROUND: The intravenous application of sodium fluorescein (SF) for brain tumor surgery goes back to the late 1940s. The development of specific fluorophore filters significantly reduced the required dosage of SF and therefore diminished possible side effects. This study investigates the application of SF in benign peripheral nerve sheath tumors (PNSTs), concentrating on its feasibility during microsurgical removal. METHODS: The single-center study includes 10 consecutive schwannoma cases operated on between September 2016 and March 2017. Inclusion criteria were defined as age ≥18 years, preoperative magnetic resonance imaging with suspicion of schwannoma, and final histopathologic confirmation of schwannoma. Exclusion criteria were a history of intolerance to SF and renal insufficiency. The microsurgical part of each surgery was video recorded, and the collected material was retrospectively analyzed. Red, green, and blue values of various regions of interest set on tumor and normal nerve of each patient were evaluated using ImageJ, an open platform for scientific image analysis. RESULTS: Digital video analysis confirmed the intraoperative impression of increased fluorescence of the tumor in contrast with normal nerve tissue. Because the color yellow is predominantly a mixture of red and green, values of these colors were significantly increased in schwannomas compared with normal nerve tissue (P = 0.0003 and P = 0.0023, respectively). CONCLUSIONS: SF reveals increased fluorescence in schwannomas compared with normal nerve tissue. Intraoperative differentiation of tumor and normal nerve tissue becomes possible using a low dose of SF (0.5-1 mg/kg). No side effects occurred. Secure microsurgical preparation is feasible during application of the YELLOW 560 nm filter.

Nerve sheath tumor surgery: case-guided discussion of ambiguous findings, appropriateness of removal, repeated surgery, and nerve repairs.

In this article the authors attempt to raise awareness of the pitfalls and controversial issues in nerve tumor surgery. In a case-guided format, examples of ambiguous findings, inappropriate tumor removal, repeated surgery, and nerve repairs are provided. The authors also discuss the need to establish a correct diagnosis preoperatively and to avoid the erroneous identification of malignant peripheral nerve sheath tumors (MPNSTs). They emphasize that not all of the principles of soft tissue sarcoma treatment protocols are applicable to MPNST. A situation of repeated surgery for supposedly malignant tumor is described, and an outline of the indications for, and an approach to, repair after lesion removal is given.

Intraoperative high-resolution ultrasound: a new technique in the management of peripheral nerve disorders.

OBJECT: Surgical treatment of nerve lesions in continuity remains difficult, even in the most experienced hands. The regenerative potential of those injuries can be evaluated by intraoperative electrophysiological studies and/or intraneural dissection. The present study examines the value of intraoperative high-frequency ultrasound as an imaging tool for decision making in the management of traumatic nerve lesions in continuity. METHODS: Intraoperative high-frequency ultrasound was applied to 19 traumatic or iatrogenic nerve lesions of differing extents. The information obtained was correlated with intraoperative electrophysiological, microsurgical intraneural dissection, and histopathological findings in resected nerve segments. RESULTS: The intraoperative application of high-resolution, high-frequency ultrasound enabled morphological examination of nerve lesions in continuity, with good image quality. The assessment of the severity of the underlying nerve injury matched perfectly with the judgment obtained from intraoperative electrophysiological studies. Both intraneural nerve dissection and neuropathological examination of the resected nerve segments confirmed the sonographic findings. In addition, intraoperative ultrasound proved to be very time efficient. CONCLUSIONS: With intraoperative ultrasound, the extent of traumatic peripheral nerve lesions can be examined morphologically for the first time. It is a promising, noninvasive method that seems capable of assessing the type (intraneural/perineural) and grade of nerve fibrosis. Therefore, in combination with intraoperative neurophysiological studies, intraoperative high-resolution ultrasound may represent a major tool for noninvasive assessment of the regenerative potential of a nerve lesion.

Surgical treatment of traumatic peroneal nerve lesions.

OBJECTIVE: In this study, we compare different surgical procedures regarding the functional outcome of traumatic peroneal nerve lesions. METHODS: In a retrospective study, 48 patients with traumatic lesions (17 iatrogenic) of the peroneal nerve were evaluated. Twenty-two patients presented with lesions in continuity displaying regenerative potential by nerve action potential recording. In these cases, surgery was restricted to either external (12/) or interfascicular neurolysis (10/). Twenty-two cases had no regenerative potential (10/) or showed discontinuity (12/) and thus were reconstructed with autologous sural nerve grafts. In four cases, a reconstructive procedure was intraoperatively abandoned as a result of the large extent of the lesion. RESULTS: Thirty-six patients with an adequate follow-up period of at least 18 months were included in this study. Among those with external neurolysis, 73% (eight out of 11) showed a good functional outcome, obviating the need for a kick-up foot brace (M >or= 4). In the interfascicular neurolysis group, 71% (five out of seven) exhibited a similar outcome. In the grafted group, however, only 28% (five out of 18) obtained a functionally useful result dependent on graft length. A graft length under 6 cm led to a functionally useful outcome in 44% of patients (four out of nine) compared with 11% (one out of nine) when the graft length was greater than or equal to 6 cm. In six patients, muscle-tendon transfers were performed, resulting in strong, useful foot lift. CONCLUSION: Peroneal nerve lesions lacking regenerative signs should be explored. A functionally useful result (M >or=4) was achieved in 72% of the patients with either external or internal neurolysis and in 28% of the patients after a nerve graft procedure. Patients in whom nerve surgery failed to reconstitute useful foot lift need to be evaluated for their suitability to undergo a tendon transfer procedure.

The influence of prophylactic vasoactive treatment on cochlear and facial nerve functions after vestibular schwannoma surgery: a prospective and open-label randomized pilot study.

OBJECTIVE: Facial nerve paresis and hearing loss are common complications after vestibular schwannoma surgery. Experiments with facial nerves of the rat and retrospectively analyzed clinical studies showed a beneficial effect of vasoactive treatment on the preservation of facial and cochlear nerve functions. This prospective and open-label randomized pilot study is the first study of a prophylactic vasoactive treatment in vestibular schwannoma surgery. METHODS: Thirty patients were randomized before surgery. One group (n = 14) received a vasoactive prophylaxis consisting of nimodipine and hydroxyethylstarch which was started the day before surgery and was continued until the seventh postoperative day. The other group (n = 16) did not receive preoperative medication. Intraoperative monitoring, including acoustic evoked potentials and continuous facial electromyelograms, was applied to all patients. However, when electrophysiological signs of a deterioration of facial or cochlear nerve function were detected in the group of patients without medication, vasoactive treatment was started immediately. Cochlear and facial nerve function were documented preoperatively, during the first 7 days postoperatively, and again after long-term observation. RESULTS: Despite the limited number of patients, our results were significant using the Fisher's exact test (small no. of patients) for a better outcome after vestibular schwannoma surgery for both hearing (P = 0.041) and facial nerve (P = 0.045) preservation in the group of patients who received a prophylactic vasoactive treatment. CONCLUSION: Prophylactic vasoactive treatment consisting of nimodipine and hydroxyethylstarch shows significantly better results concerning preservation of the facial and cochlear nerve function in vestibular schwannoma surgery. The prophylactic use is also superior to intraoperative vasoactive treatment.