Ralph W. Koenig

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.

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 Fishers 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.

Thoracic outlet syndrome in 3T MR neurography—fibrous bands causing discernible lesions of the lower brachial plexus

ObjectivesTo investigate whether targeted magnetic resonance neurography (MRN) of the brachial plexus can visualise fibrous bands compressing the brachial plexus and directly detect injury in plexus nerve fascicles.MethodsHigh-resolution MRN was employed in 30 patients with clinical suspicion of either true neurogenic thoracic outlet syndrome (TOS) or non-specific TOS. The protocol for the brachial plexus included a SPACE (3D turbo spin echo with variable flip angle) STIR (short tau inversion recovery), a sagittal-oblique T2-weighted (T2W) SPAIR (spectral adiabatic inversion recovery) and a 3D PDW (proton density weighted) SPACE. Images were evaluated for anatomical anomalies compressing the brachial plexus and for abnormal T2W signal within plexus elements. Patients with abnormal MR imaging findings underwent surgical exploration.ResultsSeven out of 30 patients were identified with unambiguous morphological correlates of TOS. These were verified by surgical exploration. Correlates included fibrous bands (n = 5) and pseudarthrosis or synostosis of ribs (n = 2). Increased T2W signal was detected within compressed plexus portion (C8 spinal nerve, inferior trunk, or medial cord) and confirmed the diagnosis.ConclusionsThe clinical suspicion of TOS can be diagnostically confirmed by MRN. Entrapment of plexus structures by subtle anatomical anomalies such as fibrous bands can be visualised and relevant compression can be confirmed by increased T2W signal of compromised plexus elements.Key Points• MR neurography (MRN) can aid the diagnosis of thoracic outlet syndrome (TOS).• Identifiable causes of TOS in MRN include fibrous bands and bony anomalies.• Increased T2W signal within brachial plexus elements indicate relevant nerve compression.• High positive predictive value allows confident and targeted indication for surgery.

Surgical treatment of traumatic peroneal nerve lesions.

OBJECTIVEIn this study, we compare different surgical procedures regarding the functional outcome of traumatic peroneal nerve lesions. METHODSIn 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. RESULTSThirty-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 ≥ 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 cm3 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 cm3. In six patients, muscle–tendon transfers were performed, resulting in strong, useful foot lift. CONCLUSIONPeroneal nerve lesions lacking regenerative signs should be explored. A functionally useful result (M ≥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.

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 Findings in Peripheral Nerve Pathologies

For many years, intraoperative B-mode ultrasound has been part of the clinical routine in cranial and spinal neurosurgery, mainly for localization and resection control [3, 4, 21, 24]. In peripheral nerve surgery, intraoperative application of ultrasound did not play any role so far, primarily because of the technical demands warranted to visualize peripheral nerves and peripheral nerve pathologies. Nowadays, as a consequence of an ongoing software and transducer development, high-frequency, high-resolution ultrasound of peripheral nerves from its first description by Fornage [9] became a highly versatile tool in the diagnostic work-up of peripheral nerve pathologies: entrapment, trauma, tumor, and neuropathies and apart from that is now routinely used during nerve surgery [13, 22].