Neurosurg Focus  Volume 39 • September 2015

neurosurgical focus Neurosurg Focus 39 (3):E4, 2015

Historically, peripheral nerve surgery has relied on landmarks and fairly extensive dissection for local-ization of both normal and pathological anatomy. Surgeons can refine anatomical localization with electro-myography and nerve conduction studies. More recently, MRI and ultrasound (US) have been used preoperatively as diagnostic adjuncts to limit the need for extensive dis-sections, particularly in cases of tumors and neuromas.4 Here, we present 5 cases in which intraoperative US was particularly helpful in localization of the pathology.

Ultrasound localization of the peripheral nerves has become commonplace in nerve blocks.11 There have been reports in the literature for some time about the use of US for preoperative diagnosis and treatment planning for pe-ripheral nerve disorders.2 As the resolution of US has im-proved greatly, its clinical use has increased. Fornage was the first to systematically examine the appearance of pe-ripheral nerves under high-resolution ultrasonography.5 A cadaveric study by Gofeld et al. demonstrated the validity of this technique.6 However, only recently has intraopera-tive US localization of peripheral nerves been reported.8

Several case studies report localization of difficult-to-find branches of peripheral nerves, whereas other case studies diagnose peripheral nerve tumors or compres-sions.3,9 The use of anatomical landmarks for the local-ization of peripheral nerves is currently standard practice.

However, the low risk and cost of intraoperative US make this an easily accessible tool to increase the accuracy and efficiency of peripheral nerve exposures (Figs. 1–4). We report here the use of intraoperative US in 5 cases.

Case SeriesCase 1: Neurofibroma of the Right Greater Occipital Nerve

A 35-year-old woman who previously underwent a craniotomy presented with a painful lump over her right occipital bone. The lesion enlarged over a period of 6 months. Intraoperative US was used to identify the lesion, which appeared to be hypoechoic, elongated, and nodular. The mass was found to be a 2 × 1–cm lesion arising from the right greater occipital nerve. The lesion was excised and the proximal end of the nerve was buried in muscle. Pathological examination revealed a neurofibroma (Fig. 1).

Case 2: Multiple Traumatic Neuromas of the Arm and Hand After a Crush Injury

A 54-year-old woman suffered a crush injury, resulting in partial amputation of her left hand 12 years prior to pre-sentation to our clinic. She previously underwent 2 resec-tions of neuroma 2–3 years after her injury. She presented to our clinic with extreme hyperalgesia, allodynia, and

AbbRevIATION US = ultrasound.subMITTed May 1, 2015.  ACCepTed June 16, 2015.INClude wHeN CITING DOI: 10.3171/2015.6.FOCUS15232.

Intraoperative ultrasound-assisted peripheral nerve surgeryClayton l. Haldeman, Md, MHs, Christopher d. baggott, Md, and Amgad s. Hanna, Md

Department of Neurological Surgery, University of Wisconsin Hospitals and Clinics, Madison, Wisconsin

Historically, peripheral nerve surgery has relied on landmarks and fairly extensive dissection for localization of both normal and pathological anatomy. High-resolution ultrasonography is a radiation-free imaging modality that can be used to directly visualize peripheral nerves and their associated pathologies prior to making an incision. It therefore helps in localization of normal and pathological anatomy, which can minimize the need for extensive exposures. The authors found intraoperative ultrasound (US) to be most useful in the management of peripheral nerve tumors and neuromas of nerve branches that are particularly small or have a deep location. This study presents the use of intraoperative US in 5 cases in an effort to illustrate some of the applications of this useful surgical adjunct.http://thejns.org/doi/abs/10.3171/2015.6.FOCUS15232Key wORds intraoperative ultrasound; peripheral nerve; neuroma; schwannoma; minimally invasive

1©AANS, 2015

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C. l. Haldeman, C. d. baggott, and A. s. Hanna

phantom limb pain. MRI done prior to surgery showed multiple neuromas in multiple peripheral nerve distribu-tions (Fig. 2). Intraoperative US was used to guide dis-section for a total of 8 neuromas. One large neuroma was identified as a hypoechoic mass arising from the anterior interosseous nerve in the forearm, which was treated with external neurolysis, fascicle splitting, and grafting, with intramuscular transposition. Two lesions were found aris-ing from the ulnar nerve near Guyon’s canal, which were also treated with external neurolysis, fascicle splitting, and grafting, followed by intramuscular transposition. Two smaller dorsal digital neuromas and 3 small volar digital neuromas were also excised.

Case 3: Medial and lateral sural NeuromasA 42-year-old man (a drummer) presented with pain,

claudication, and cramping in his right leg. He previous-ly underwent fasciotomy. Intraoperative US was used to localize 2 lesions, 1 arising from the medial sural nerve and 1 arising from the lateral sural nerve; both were hy-poechoic and showed loss of fascicular pattern. Both were treated with excision and intramuscular transposition.

Case 4: Iatrogenic Ilioinguinal Nerve InjuryA 52-year-old man had an inguinal hernia repaired

with mesh 16 years prior to presentation to our clinic. He had experienced progressive pain in the region, which had now become disabling. On physical examination, he was found to have a positive Tinel’s sign on the medial aspect of the scar and was taken to surgery. Intraoperative US was used to identify a 5-mm hypoechoic nodular mass in the area of his previous surgery and to guide dissection down to the right ilioinguinal nerve. A Prolene (Ethicon) stitch was found through the neuroma, which was treated with excision and intramuscular transposition.

Case 5: Cutaneous Nerve of Thigh schwannomaA 44-year-old man had pain in his right popliteal fos-

sa. Five years earlier, he had experienced the same pain and 2 schwannomas were removed from his right calf; a third was left behind because the prior surgeon found it “attached to a nerve.” We re-explored the area, using in-traoperative US for guidance (Fig. 3). Attached to a cuta-neous nerve was a rounded hypoechoic nodule, which was treated with excision, while preserving the parent nerve.

FIG. 1. Case 1. MR image obtained preoperatively, with a vitamin E cap-sule adjacent to the palpable lesion, did not show pathology (A). Photo-graph of the right occipital area with the lesion marked and a previous craniotomy scar visible (b). Intraoperative US images obtained prior to (C) and after (d) incision to help localize the lesion show the neuroma in longitudinal (e) and transverse (F) planes. Intraoperative images of the neuroma in situ (G) and after excision (H).

FIG. 2. Case 2. Axial T1-weighted with contrast (A) and sagittal T1-weighted (b) MR images of a neuroma (yellow arrow) of the left arm. On MRI, the neuroma was thought to arise from the median nerve. However, intraoperatively, it was found to arise from the anterior inter-osseous nerve. A longitudinal view (C) of the same neuroma as seen during intraoperative US, which is visualized as a hypoechoic mass with loss of the normal fascicular pattern. A more distal axial T1-weighted with contrast cut (d) of the forearm shows a neuroma of the ulnar nerve just deep to the extensor carpi ulnaris tendon. A longitudinal view (e) of the same neuroma as seen on intraoperative US. a = anterior; l = left; p = posterior; r = right.

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Intraoperative ultrasound-assisted peripheral nerve surgery

Pathology revealed the mass to be a schwannoma. Figure 4 shows the setup of the operating room with the US ma-chine and radiologist.

discussionMinimal-access surgery is an important aspect of to-

day’s neurosurgical practice. In the brain, intraoperative localization of small and deep lesions relies heavily on stealth MRI navigation, stereotaxy and, to a lesser ex-tent, intraoperative US. In the spine, accurate placement of pedicle screws relies on either stealth CT navigation or intraoperative fluoroscopy. Stealth navigation is only possible when there is a fixed relationship between the navigation frame and the target. This is not feasible when working on extremities, due to their high mobility (mul-tiple joints) and easy distortion of soft tissues with dissec-tion and retraction. We find intraoperative US particularly useful in the management of peripheral nerve tumors and neuromas of nerve branches that are particularly small or have a deep location. Localization by palpation or correla-tion with preoperative diagnostic studies may be adequate

in large and superficial lesions. However, surgical targets that are deep seated, multiple, and complex may not be amenable to surface localization at the time of surgery. Additionally, in cases of traumatic and iatrogenic neuro-mas, scarring can be a formidable adversary that increases operative time, extent of dissection, and frustration. The cases presented here demonstrate the use of the intraop-erative US technique.

Multiple neuromas were resected in Cases 2 and 3; in-traoperative US was helpful for incision planning, local-ization of the parent nerves, and identifying the multiple neuromas. In these cases, the use of intraoperative US immediately after resection was able to confirm resec-tion of all neuromas prior to closing. In Case 2 in par-ticular, the patient had significant allodynia and would not allow anybody to touch her hand while she was awake, which rendered preoperative localization by palpation or US impossible. Intraoperative mapping under general an-esthesia allowed accurate localization and resection of 8 neuromas. It is worth mentioning that successful surgical technique, including localization, equals good outcomes. The patient’s pain and allodynia significantly improved to the point that 3 months after surgery, she was asking about getting a prosthetic hand.

In Cases 1, 3, 4, and 5, we explored previous operative beds, dealing with abnormal planes related to postopera-tive scarring. It is for these cases that intraoperative US

FIG. 3. Case 5. Intraoperative and MR images of a man with right thigh pain. Preoperative planning of the incision using US (A). Coronal STIR (b) and T1-weighted (C) MR images along with axial STIR image (e) show an ovoid mass (yellow arrow) within the subcutaneous fat along the posterior medial right lower thigh, over the superficial aspect of the semitendinosus tendon. The mass was visualized with US (d) and excised with minimal incision (F and G). Pathological examination re-vealed the mass to be a schwannoma.

FIG. 4. Operating room setup for the use of intraoperative US. The surgeon and radiologist map the prepared operative field for pathology. Cooperation and a good working relationship between the involved teams are essential for optimal results.

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C. l. Haldeman, C. d. baggott, and A. s. Hanna

has been particularly helpful in identifying normal neuro-vascular and muscular structures, identifying pathology, and limiting the dissection necessary to perform safe and adequate surgery. In Case 4 in particular, finding the ilio-inguinal nerve (which is very small) within a mass of scar tissue without any intraoperative guidance would have been very challenging and frustrating.

From a technical standpoint, to optimize US imaging, the highest-frequency US probe possible should be used. However, high-frequency probes have less deep-tissue penetration. The choice of probe, therefore, depends on the depth of the pathology. As summarized nicely by Koenig et al., superficial lesions, such as the median nerve, should be examined with 15–18-MHz transducers, whereas deep nerves, such as the sciatic nerve or the brachial plexus, are better examined with 9–12-MHz transducers.7

The US appearance of peripheral nerves is typically dark nerve (hypoechoic) seen on a bright (hyperechoic) background.1 Often the nerve itself will have a fascicular echotexture, which can help differentiate it from tendons, which have a more fibrillar texture.10 The quality of the US machine is also key in obtaining high-resolution imaging.

One challenge to the use of intraoperative US is the availability and willingness of an experienced radiologist and/or technician to come to the operating room. This fac-tor can be mitigated as the surgeon gains familiarity with ultrasonographic appearance of nerves and lesions, as well as the technical nuances of using a US machine.

ConclusionsMinimally invasive surgical approaches are appeal-

ing to patients and surgeons. In peripheral nerve sur-gery, refining the localization of normal and pathological anatomy can minimize the need for extensive exposures, decrease incision size, improve cosmesis, decrease opera-tive time, reduce postoperative pain, and improve patient and surgeon satisfaction. We find it particularly useful when dealing with multiple lesions, small lesions, deep or difficult-to-localize nerves, and in scarred operative beds, whether from previous surgery or trauma. Similar to the emergence of electrophysiology as standard practice in peripheral nerve diagnosis and stealth navigation in local-izing deeply seated brain tumors, it is probable that the use of intraoperative US assistance will gain comparable traction.

Looking forward, neurosurgeons will benefit from a detailed understanding of the ultrasonic anatomy of the peripheral nerves and the associated pathologies. Im-provements in technology have made US increasingly use-ful as a real-time imaging modality. High-resolution US can define not only nerves and pathology, but also intra-neural anatomy. The ultrasonographic fascicular anatomy, which has become substantially more important in the era of nerve transfers, will be an element of peripheral nerve surgery that trainees and experienced surgeons alike will not be able to overlook.

The cases presented here demonstrate the situations that are particularly amenable to intraoperative US as-sistance. We have found that the low risk, low cost, and ease of intraoperative US assistance are beneficial to both surgeon and patient.

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mours. Clin Radiol 52:8–17, 1997 2. Buchberger W, Judmaier W, Birbamer G, Lener M, Schmi-

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3. Chiou HJ, Chou YH, Chiou SY, Liu JB, Chang CY: Peripher-al nerve lesions: role of high-resolution US. Radiographics 23:e15, 2003

4. Du R, Auguste KI, Chin CT, Engstrom JW, Weinstein PR: Magnetic resonance neurography for the evaluation of pe-ripheral nerve, brachial plexus, and nerve root disorders. J Neurosurg 112:362–371, 2010

5. Fornage BD: Peripheral nerves of the extremities: imaging with US. Radiology 167:179–182, 1988

6. Gofeld M, Bristow SJ, Chiu S, Kliot M: Preoperative ultra-sound-guided mapping of peripheral nerves. J Neurosurg 119:709–713, 2013

7. Koenig RW, Pedro MT, Heinen CP, Schmidt T, Richter HP, Antoniadis G, et al: High-resolution ultrasonography in eval-uating peripheral nerve entrapment and trauma. Neurosurg Focus 26(2):E13, 2009

8. Koenig RW, Schmidt TE, Heinen CP, Wirtz CR, Kretschmer T, Antoniadis G, et al: Intraoperative high-resolution ultra-sound: a new technique in the management of peripheral nerve disorders. J Neurosurg 114:514–521, 2011

9. Lee FC, Singh H, Nazarian LN, Ratliff JK: High-resolution ultrasonography in the diagnosis and intraoperative manage-ment of peripheral nerve lesions. J Neurosurg 114:206–211, 2011

10. Silvestri E, Martinoli C, Derchi LE, Bertolotto M, Chiara-mondia M, Rosenberg I: Echotexture of peripheral nerves: correlation between US and histologic findings and criteria to differentiate tendons. Radiology 197:291–296, 1995

11. Walker KJ, McGrattan K, Aas-Eng K, Smith AF: Ultrasound guidance for peripheral nerve blockade. Cochrane Database Syst Rev (4):CD006459, 2009

disclosureThe authors report no conflict of interest concerning the materi-als or methods used in this study or the findings specified in this paper.

Author ContributionsConception and design: Hanna, Haldeman. Analysis and interpre-tation of data: all authors. Drafting the article: all authors. Criti-cally revising the article: all authors. Approved the final version of the manuscript on behalf of all authors: Hanna. Administra-tive/technical/material support: Haldeman.

Correspondence Amgad S. Hanna, Department of Neurological Surgery, Uni-versity of Wisconsin Hospitals and Clinics, 600 Highland Ave., K4/822, Madison, WI 53705. email: ah2904@yahoo.com.

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