Imaging Studies

Frequently, peripheral nerve surgery is possible without any diagnostic imaging. A combination of a thorough history and physical examination with supplementary electrodiagnostic studies is often adequate. However, in cases where a mass lesion or tumor is suspected, MRI is necessary for a preoperative anatomic definition and for a differential diagnosis. Other imaging studies such as plain-film radiographs and CT scans play a role in diagnosing associated injuries that may complicate peripheral nerve surgery. When attempting to diagnose root avulsion, a CT scan with myelography is often helpful to visualize the pseudomeningocele.¹⁶ However, even in the presence of a pseudomeningocele, the nerve rootlets may not be compromised.^38,³⁹

Timing of Surgery

Proper timing of surgery is crucial to restore neuronal function, to reverse end-organ dysfunction, and to facilitate recovery. Because neural regeneration occurs at the rate of approximately 1 inch per month, prompt reestablishment of neuronal connections is essential. In nonpenetrating, stretch, and compression injuries without evidence of transection, conservative management should be used for 3 months to allow for maximum recovery.⁴⁰

In trauma or postsurgery, evidence of vascular injuries such as diminished extremity pulses, auscultation of bruits or thrills, or large pulsatile hemorrhage warrants immediate intervention.^41,⁴² A detailed clinical evaluation with careful documentation is needed, and further angiographic investigation may be used preoperatively or intraoperatively to outline the vascular anatomy and to rule out pseudoaneurysm. If available, MRI scans may be obtained to assess adjacent neurovascular structures, and a vascular surgeon should be consulted.

Immediate surgical intervention is also warranted when the patient presents with an acute neurologic deficit. If the nerve is nonviable and transected, nerve repair should be performed. Surgical exploration of gunshot wounds and other blunt transections can be delayed for 3 weeks when there is no evidence of neurovascular compromise.⁴⁰ However, if the neurologic function deteriorates, surgery should proceed without delay.

Techniques of Nerve Repair

Functional outcomes are significantly affected by proper procedure selection, and an understanding of axonal regeneration and neurotropic factors has led to advances in the treatment of these diseases.⁴³^–⁴⁷ Tube repair^13,⁴⁸ (with silicone, collagen, and polyglycolic acid) and allograft nerve transplantation^49,⁵⁰ are under investigation for restoring nerve continuity. The neurotropic factors produced by regenerating nerves are also being investigated for use in surgery or for implantation within the tubes.

Nerve allograft transplantation may be an alternative to autograft repair, but this technique requires immunosuppression to avoid graft rejection. The indications for and relative advantages and disadvantages of commonly used techniques of nerve repair are summarized in Table 135-1.

Table 135-1 Techniques of Nerve Repair

Postoperative Management

Postoperative care is essential for improving outcomes and avoiding complications, and monitoring for wound infections and neurologic improvement is important. Postoperative complications mainly arise in the surgical area and its adjacent structures. Routine wound cleansing with hydrogen peroxide followed by an application of an antibiotic ointment can reduce bacterial infection. Early mobilization is recommended because this measure improves circulation and prevents soft tissue adhesions, and physical and occupational therapy consultations are needed. Aggressive pain management is also important to recovery. Finally, prophylactic use of anticoagulants, such as intravenous dextran, intravenous or subcutaneous heparin, or oral aspirin, may prevent thrombosis at the microsurgical region.⁵¹

Rehabilitation

After a peripheral nerve injury or surgery, physical therapy and range-of-motion exercises will optimize the recovery of motor function and minimize tethering adhesion formation. The need for long-term rehabilitation is determined on an individual basis because functional recovery depends on the type and extent of injury, the capability of the nerve to regenerate, associated medical conditions, and the patient’s motivation. The recovery process is slow and variable and may take as long as 5 years to complete. However, if functional recovery is not apparent after an appropriate rehabilitation period, other options such as arthrodesis and tendon transfers should be considered. Clearly, extensive injuries with multiple nerve lesions require a longer time to improve than isolated nerve injuries.

Complications of Peripheral Nerve Surgery

General Complications

Postoperative Wound Infections

Postoperative wound infections may occur and are particularly common in large exposures and lengthy operations. Meticulous sterile technique is the best preventative measure. In addition, preoperative prophylactic antibiotics and copious irrigation of the surgical site are recommended. The authors irrigate with a mixture of 500,000 U of polymyxin B with 50,000 U of bacitracin in 1 L of 0.9% NaCl.

To prevent infection, the dissection should be carried along intramuscular planes and along the nerve course, and wound closure should eliminate the dead spaces that can later become infected.⁵² Postoperative wound care with an antibiotic ointment and daily inspections and dressing changes is needed. Postoperative antibiotic prophylaxis is used for 24 hours but should not be necessary beyond this point unless gross contamination was present.

Once an infection is present, culture-appropriate antibiotics are necessary. Surgical exploration of the infected wound may be needed for focal infections and abscesses; however, prevention is the best measure for this complication.

Postoperative Hematoma

Clinically significant postoperative hematoma is a rare but serious entity. This lesion may act as a nidus for infection, a source of postoperative scarring, and a compressive mass. Extensive and repetitive muscle dissection often creates fistulae, fascial planes, and bleeding points that can contribute to hematoma formation. Bipolar electrocautery is recommended for hemostasis because this modality minimizes thermal injury to the adjacent neurovascular structures and soft tissues.¹⁰ Infected hematomas and adjacent tissues should be surgically excised and appropriate cultures and stains obtained.

Pulmonary complications can occur, especially if general anesthesia and lengthy operative time are necessary. These complications include atelectasis, pneumonia, pulmonary embolus, and acute respiratory distress syndrome.⁵³ Preoperative assessment of pulmonary risk factors aids in prevention, and postoperative pulmonary care assists in avoiding unnecessary complications. Specifically, pleural effusion, pneumothorax, hemothorax, and diaphragmatic paralysis can result from brachial plexus or thoracic outlet procedures. Each complication should be appropriately identified based on imaging and clinical judgment and should subsequently be treated appropriately.

Anatomic Variants

Anatomic variants of neural elements and non-neural structures are common and can be a source of iatrogenic injury (Table 135-2). These variations are usually encountered in certain areas, and a thorough knowledge of normal and aberrant anatomy is paramount.¹ For example, the nerve to the triceps commonly can arise off the dorsal spinal cord of the brachial plexus in the axilla. The subscapular nerve may arise from the posterior cord as part of a common trunk with the nerve to the subscapularis, or from the axillary nerve itself. The musculocutaneous nerve may arise from the median nerve or can be associated with the tendon of the pectoralis major muscle. Thus, when retracting, dividing, or reapproximating this tendon, the surgeon should pay close attention to preserving this nerve.

Table 135-2 Common Iatrogenic Nerve Injuries

Affected Nerve	Procedure
Spinal accessory	Lymph node biopsy
Transverse cervical or greater auricular	Lymph node biopsy
Brachial plexus	Radical neck dissection or mastectomy
Median	Carpal tunnel release or removal of ganglion
Radial	Arterial puncture or osteosynthesis
Ulnar	Removal of ganglion or wrist osteotomy
Superficial radial	Kirschner wire placement or removal of ganglion
Anterior interosseous	Internal fixation of forearm
Posterior interosseous	Osteosynthesis or cast
Sciatic	Hip arthroplasty
Femoral	Hip arthroplasty or femoral arterial graft
Genitofemoral or ilioinguinal	Hernia repair
Tibial	Injection or orthopedic procedure
Common peroneal	Surgery of the knee or removal of Baker cyst
Sural	Vein extirpation
Saphenous	Vein stripping

Complications of Surgery for Peripheral Nerve Tumors

Both benign and malignant tumors affect peripheral nerves.⁵⁴^–⁵⁷ These tumors cause motor and sensory symptoms through local mass effect with entrapment as well as compression of adjacent neurovascular structures. Before surgical excision, it is prudent to consider all tumors malignant until confirmed by pathologic examination.

Patients with peripheral nerve tumors should be referred to specialized centers that have experience with peripheral nerve lesions. In general, nerve tumors should be removed when small to decrease the incidence of complications. Biopsies are not recommended in lesions likely to be benign because this may lead to nerve damage or hemorrhage.⁵⁸

Intraoperative electrodiagnostic studies are mandatory to assess nerve viability and integrity and to determine if nerve grafting is necessary. During these studies, long-acting muscle relaxants should not be used, because these agents interfere with nerve conduction velocity and clinical findings.

Benign Peripheral Nerve Tumors

The most common benign peripheral nerve tumors are neurofibromas and schwannomas. Surgical management of schwannomas includes complete tumor excision, dissection beyond the entrapment site to release compression on adjacent structures, and minimization of postoperative edema. Using the surgical microscope, the tumor should be resected by gently separating it from the nerve bundles and neural elements with preservation of the uninvolved fascicles.

Neurofibromas can be multiple and fusiform, especially ones that arise from the nerve trunks, and surgery is needed for neurologic deterioration or intractable pain.^56,⁵⁹ Resection typically does not result in loss of neurologic function or permanent disability. However, superficial neurofibroma resection may result in a temporary decrease in cutaneous sensation.⁵⁷

Complications include infection, hematoma, and new neurologic deficits. The postoperative incision should be padded with soft wound dressings and inspected daily. Splint immobilization of the involved extremity for 1 to 2 weeks is recommended for nerve grafts to prevent stretching of the anastomosis. Postoperative pain management with appropriate pain medication minimizes discomfort. Finally, patient education is essential for proper medical care.

Malignant Peripheral Nerve Sheath Tumors

The appropriate diagnosis of malignant peripheral nerve sheath tumors is essential, and reliable clinical findings suggesting the presence of malignancy include a large tumor mass at initial presentation and rapid increase in size over a period of weeks to months.^56,⁶⁰ Initial management should include a percutaneous nerve biopsy to provide histologic evidence of malignancy, because intraoperative frozen sections are frequently unreliable.⁵⁷ Once the diagnosis is established, radical resection of these lesions is recommended, and this resection needs to extend 5 to 10 cm beyond the tumor margin in a contiguous nerve if possible.

In tumor surgery, complications frequently result from a lack of surgical experience or understanding of tumor pathology. Successful excision depends on the origin and location of the tumor, and in many cases total resection is impossible to perform without causing severe functional loss. However, amputation is seldom warranted at the time of initial surgery.

Complications of Surgery for Entrapment Neuropathies

Entrapment syndromes are a diverse group of diseases with varying surgical interventions; although most surgical procedures are routine, complications can occur and can result in serious morbidity. For this reason, the specific cause should be determined before entrapment release.

Diagnostic Pitfalls

The preoperative assessment includes a thorough history and physical and electrophysiologic studies; misinterpretation of these findings may lead to delay in therapeutic or surgical interventions.^1,^13,¹⁵ Associated medical conditions may include diabetes, hormonal diseases, connective tissue disorders, rheumatoid disease, arthritis, and metabolic deficiency. In addition, central nervous system pathologies such as syringomyelia, spinal cord lesions, and intracranial masses should be excluded before any surgical intervention.

Misinterpretation of physical signs can also lead to mismanagement. For example, the Hoffman-Tinel sign (a tingling sensation in the distribution of the median nerve over the hand) indicates axonal regeneration, but this sign may be absent in the early and late stages of nerve entrapment. Also, a negative Phalen sign may be due to a lack of pathology or to severe disruption of neural elements.

When a peripheral nerve is entrapped at more than one site such as would be present with carpal tunnel syndrome with cervical spine pathology, it is termed double crush syndrome. With this syndrome, the more distal compression is usually symptomatic. However, when the proximal compression is symptomatic, it is termed reverse double crush syndrome.

Electrodiagnostic studies are often used to confirm peripheral nerve entrapment neuropathies.^10,¹⁵ Inaccurate results may be due to anatomic variations, associated medical conditions, overlapping sensory innervation, errors in technical skill, and misinterpretation of the results. Examples of overlapping sensory innervation include the Riche-Cannieu anomaly (both branches of the median and ulnar nerves communicate) and the Martin-Gruber anastomosis (the median nerve or the anterior interosseous branch communicates with the ulnar nerve). Awareness of these pitfalls allows for correct interpretation and management.