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Excision of Peripheral Nerve Schwannoma
PROCEDURE 104
Excision of Peripheral Nerve Schwannoma Joshua M. Adkinson and Kevin C. Chung
Indications • Excision is recommended for a concerning subcutaneous lesion of the upper extremity. • Generally, patients present with a painless mass and the diagnosis is made intraoperatively. Other patients may present with a neurologic deficit, such as dysesthesia, neuropathic pain, and/or sensorimotor dysfunction.
Clinical Examination • Schwannomas are most commonly found on the volar surface of the distal extremity and typically affect the ulnar, median, or radial nerve (Fig. 104.1A and B). • Percussion over the mass may produce paresthesias in the distribution of the affected nerve. • Do not confuse a schwannoma with a ganglion cyst. These can be differentiated by the lack of a Tinel sign (tingling at the lesion or more distally when the lesion is percussed) over a ganglion cyst.
Imaging • Preoperative magnetic resonance imaging (MRI) may be useful to evaluate the lesion’s origin and relationship to surrounding structures. Peripheral nerve sheath tumors are dark on T1-weighted MRI and bright on T2-weighted MRI. Fig. 104.2A shows an axial view and Fig. 104.2B shows a coronal view of T2-weighted MRI of a posterior interosseous nerve schwannoma. • MRI findings alone are not adequate to differentiate between benign and malignant nerve tumors. Left index finger digital sensory nerve schwannoma
A
Left palm schwannoma involving the median nerve
B FIG. 104.1 A-B
897
898
PROCEDURE 104 Excision of Peripheral Nerve Schwannoma
A
B FIG. 104.2 A-B
Mesoneurium External epineurium Axon
Internal epineurium
Myelin
Perineurium
Nerve fiber
Connective tissue components
Endoneurium
A Schwannoma
B FIG. 104.3 A-B
Surgical Anatomy • A thorough understanding of upper extremity peripheral nerve anatomy is required when embarking on excision of a peripheral nerve tumor. Fig. 104.3A shows normal cross-sectional nerve topography. Fig. 104.3B shows nerve topography in the setting of a schwannoma.
Positioning • The patient is placed in the supine position on the operating table with the entire upper extremity positioned on an arm board.
PROCEDURE 104 Excision of Peripheral Nerve Schwannoma
Volar skin markings for extensile exposure of palm
899
A
B FIG. 104.4
FIG. 104.5 A-B
• General anesthesia is provided and a nonsterile tourniquet is applied on the upper arm. • The arm is prepared and draped in the standard fashion. • The limb is exsanguinated fully to permit a completely bloodless field.
Exposures • The location of the lesion will dictate the necessary exposure. A thorough understanding of the anatomy of the entire upper extremity is essential.
Procedure Step 1 • The incision is marked to extend proximal and distal to the lesion (Fig. 104.4). • The skin flaps are elevated with a no. 15 blade to expose the peripheral nerve tumor.
Step 2 • Surrounding vascular structures are identified and protected. The involved nerve is dissected proximally to distally. Fig. 104.5A shows exposure of a left index finger digital sensory nerve schwannoma. Fig. 104.5B shows exposure of a palmar schwannoma and identification and protection of neurovascular structures.
Step 3 • The schwannoma is removed from the parent nerve using microsurgical dissection. Fig. 104.6A shows microsurgical excision of a left index finger digital sensory nerve schwannoma. Fig. 104.6B shows microsurgical excision of a palmar schwannoma and identification and protection of neurovascular structures. • The tourniquet is then deflated and hemostasis is ensured. • The skin is closed using 4-0 or 5-0 nonabsorbable suture (Fig. 104.7).
Postoperative Care and Expected Outcomes • The arm is placed in a soft dressing and activities are limited for 2 weeks. Most patients will have full motor and sensory function after surgery, unless nerve resection is required for extensive involvement of small nerve branches or an interposition nerve graft is required for reconstruction.
EXPOSURES PEARLS
• The relevant imaging studies should be readily available during the procedure for review during dissection. • Ensure that microsurgical instruments are available for fine dissection. • Be prepared to address a nerve gap if a portion of the nerve requires resection (i.e., if intraoperative findings are consistent with a neurofibroma).
STEP 2 PEARLS
• The lesion can often be “shelled out” from the nerve, leaving the parent nerve fascicles intact. • If the mass is difficult to remove, it likely represents a neurofibroma. In this situation, the affected area is resected and reconstructed with a nerve graft. STEP 3 PITFALLS
Symptomatic neuromas may occur in 25% of patients who undergo intraneural dissection. As such, intraneural dissection should be avoided.
PROCEDURE 104 Excision of Peripheral Nerve Schwannoma
900
A
B FIG. 104.7
FIG. 104.6 A-B
• There is a higher risk for postoperative neurologic deficit in patients who have previously undergone biopsy or who have developed recurrent disease. • Recurrence is uncommon. See Video 104.1, Excision of Peripheral Nerve Schwannoma, on ExpertConsult.com.
EVIDENCE Kang HJ, Shin SJ, Kang ES. Schwannomas of the upper extremity. J Hand Surg Br 2000;25:604–7. This study presented the clinical characteristics, MRI features, and postoperative results of 20 schwannomas in the arms of 13 patients. Twelve tumors had a positive Tinel sign, one caused weakness of the wrist and another in the Guyon canal caused hypothenar muscle atrophy. Of the nine cases that underwent MRI preoperatively, six were correctly diagnosed as schwannomas. All masses were excised using microsurgical techniques and two transient neurologic complications occurred (Level III evidence). Phalen GS. Neurilemmomas of the forearm and hand. Clin Orthop Relat Res 1976;114:219–22. In this classic article, preoperative evaluation and surgical excision of 17 neurilemmomas were described. Six were present in the forearm and 11 were in the hand and wrist. There were five tumors in fingers, one in the thumb, three in the palm, and two in the wrist. In the forearm, three tumors involved the median nerve, two involved the ulnar nerve, and one arose from a small sensory branch of the radial nerve. The tumors are well-encapsulated and may be easily enucleated from the parent nerve. Resection of the involved nerve is seldom necessary except when small nerves are extensively involved (Level III evidence).
Excision of Peripheral Nerve Schwannoma Joshua M. Adkinson and Kevin C. Chung
Indications • Excision is recommended for a concerning subcutaneous lesion of the upper extremity. • Generally, patients present with a painless mass and the diagnosis is made intraoperatively. Other patients may present with a neurologic deficit, such as dysesthesia, neuropathic pain, and/or sensorimotor dysfunction.
Clinical Examination • Schwannomas are most commonly found on the volar surface of the distal extremity and typically affect the ulnar, median, or radial nerve (Fig. 104.1A and B). • Percussion over the mass may produce paresthesias in the distribution of the affected nerve. • Do not confuse a schwannoma with a ganglion cyst. These can be differentiated by the lack of a Tinel sign (tingling at the lesion or more distally when the lesion is percussed) over a ganglion cyst.
Imaging • Preoperative magnetic resonance imaging (MRI) may be useful to evaluate the lesion’s origin and relationship to surrounding structures. Peripheral nerve sheath tumors are dark on T1-weighted MRI and bright on T2-weighted MRI. Fig. 104.2A shows an axial view and Fig. 104.2B shows a coronal view of T2-weighted MRI of a posterior interosseous nerve schwannoma. • MRI findings alone are not adequate to differentiate between benign and malignant nerve tumors. Left index finger digital sensory nerve schwannoma
A
Left palm schwannoma involving the median nerve
B FIG. 104.1 A-B
897
898
PROCEDURE 104 Excision of Peripheral Nerve Schwannoma
A
B FIG. 104.2 A-B
Mesoneurium External epineurium Axon
Internal epineurium
Myelin
Perineurium
Nerve fiber
Connective tissue components
Endoneurium
A Schwannoma
B FIG. 104.3 A-B
Surgical Anatomy • A thorough understanding of upper extremity peripheral nerve anatomy is required when embarking on excision of a peripheral nerve tumor. Fig. 104.3A shows normal cross-sectional nerve topography. Fig. 104.3B shows nerve topography in the setting of a schwannoma.
Positioning • The patient is placed in the supine position on the operating table with the entire upper extremity positioned on an arm board.
PROCEDURE 104 Excision of Peripheral Nerve Schwannoma
Volar skin markings for extensile exposure of palm
899
A
B FIG. 104.4
FIG. 104.5 A-B
• General anesthesia is provided and a nonsterile tourniquet is applied on the upper arm. • The arm is prepared and draped in the standard fashion. • The limb is exsanguinated fully to permit a completely bloodless field.
Exposures • The location of the lesion will dictate the necessary exposure. A thorough understanding of the anatomy of the entire upper extremity is essential.
Procedure Step 1 • The incision is marked to extend proximal and distal to the lesion (Fig. 104.4). • The skin flaps are elevated with a no. 15 blade to expose the peripheral nerve tumor.
Step 2 • Surrounding vascular structures are identified and protected. The involved nerve is dissected proximally to distally. Fig. 104.5A shows exposure of a left index finger digital sensory nerve schwannoma. Fig. 104.5B shows exposure of a palmar schwannoma and identification and protection of neurovascular structures.
Step 3 • The schwannoma is removed from the parent nerve using microsurgical dissection. Fig. 104.6A shows microsurgical excision of a left index finger digital sensory nerve schwannoma. Fig. 104.6B shows microsurgical excision of a palmar schwannoma and identification and protection of neurovascular structures. • The tourniquet is then deflated and hemostasis is ensured. • The skin is closed using 4-0 or 5-0 nonabsorbable suture (Fig. 104.7).
Postoperative Care and Expected Outcomes • The arm is placed in a soft dressing and activities are limited for 2 weeks. Most patients will have full motor and sensory function after surgery, unless nerve resection is required for extensive involvement of small nerve branches or an interposition nerve graft is required for reconstruction.
EXPOSURES PEARLS
• The relevant imaging studies should be readily available during the procedure for review during dissection. • Ensure that microsurgical instruments are available for fine dissection. • Be prepared to address a nerve gap if a portion of the nerve requires resection (i.e., if intraoperative findings are consistent with a neurofibroma).
STEP 2 PEARLS
• The lesion can often be “shelled out” from the nerve, leaving the parent nerve fascicles intact. • If the mass is difficult to remove, it likely represents a neurofibroma. In this situation, the affected area is resected and reconstructed with a nerve graft. STEP 3 PITFALLS
Symptomatic neuromas may occur in 25% of patients who undergo intraneural dissection. As such, intraneural dissection should be avoided.
PROCEDURE 104 Excision of Peripheral Nerve Schwannoma
900
A
B FIG. 104.7
FIG. 104.6 A-B
• There is a higher risk for postoperative neurologic deficit in patients who have previously undergone biopsy or who have developed recurrent disease. • Recurrence is uncommon. See Video 104.1, Excision of Peripheral Nerve Schwannoma, on ExpertConsult.com.
EVIDENCE Kang HJ, Shin SJ, Kang ES. Schwannomas of the upper extremity. J Hand Surg Br 2000;25:604–7. This study presented the clinical characteristics, MRI features, and postoperative results of 20 schwannomas in the arms of 13 patients. Twelve tumors had a positive Tinel sign, one caused weakness of the wrist and another in the Guyon canal caused hypothenar muscle atrophy. Of the nine cases that underwent MRI preoperatively, six were correctly diagnosed as schwannomas. All masses were excised using microsurgical techniques and two transient neurologic complications occurred (Level III evidence). Phalen GS. Neurilemmomas of the forearm and hand. Clin Orthop Relat Res 1976;114:219–22. In this classic article, preoperative evaluation and surgical excision of 17 neurilemmomas were described. Six were present in the forearm and 11 were in the hand and wrist. There were five tumors in fingers, one in the thumb, three in the palm, and two in the wrist. In the forearm, three tumors involved the median nerve, two involved the ulnar nerve, and one arose from a small sensory branch of the radial nerve. The tumors are well-encapsulated and may be easily enucleated from the parent nerve. Resection of the involved nerve is seldom necessary except when small nerves are extensively involved (Level III evidence).