Intraoperative Ultrasound-Assisted Peripheral Nerve Surgery
Intraoperative Ultrasound-Assisted Peripheral Nerve Surgery
Minimal-access surgery is an important aspect of today's neurosurgical practice. In the brain, intraoperative localization of small and deep lesions relies heavily on stealth MRI navigation, stereotaxy and, to a lesser extent, 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 (multiple joints) and easy distortion of soft tissues with dissection 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 correlation 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 neuromas, scarring can be a formidable adversary that increases operative time, extent of dissection, and frustration. The cases presented here demonstrate the use of the intraoperative US technique.
Multiple neuromas were resected in Cases 2 and 3; intraoperative US was helpful for incision planning, localization of the parent nerves, and identifying the multiple neuromas. In these cases, the use of intraoperative US immediately after resection was able to confirm resection of all neuromas prior to closing. In Case 2 in particular, 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 anesthesia 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 postoperative scarring. It is for these cases that intraoperative US has been particularly helpful in identifying normal neurovascular and muscular structures, identifying pathology, and limiting the dissection necessary to perform safe and adequate surgery. In Case 4 in particular, finding the ilioinguinal 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.
The US appearance of peripheral nerves is typically dark nerve (hypoechoic) seen on a bright (hyperechoic) background. Often the nerve itself will have a fascicular echotexture, which can help differentiate it from tendons, which have a more fibrillar texture. 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 factor 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.
Discussion
Minimal-access surgery is an important aspect of today's neurosurgical practice. In the brain, intraoperative localization of small and deep lesions relies heavily on stealth MRI navigation, stereotaxy and, to a lesser extent, 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 (multiple joints) and easy distortion of soft tissues with dissection 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 correlation 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 neuromas, scarring can be a formidable adversary that increases operative time, extent of dissection, and frustration. The cases presented here demonstrate the use of the intraoperative US technique.
Multiple neuromas were resected in Cases 2 and 3; intraoperative US was helpful for incision planning, localization of the parent nerves, and identifying the multiple neuromas. In these cases, the use of intraoperative US immediately after resection was able to confirm resection of all neuromas prior to closing. In Case 2 in particular, 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 anesthesia 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 postoperative scarring. It is for these cases that intraoperative US has been particularly helpful in identifying normal neurovascular and muscular structures, identifying pathology, and limiting the dissection necessary to perform safe and adequate surgery. In Case 4 in particular, finding the ilioinguinal 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.
The US appearance of peripheral nerves is typically dark nerve (hypoechoic) seen on a bright (hyperechoic) background. Often the nerve itself will have a fascicular echotexture, which can help differentiate it from tendons, which have a more fibrillar texture. 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 factor 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.
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