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Excision of Schwannoma from ulnar nerve

    Overview

    Learn the Excision of Schwannoma from ulnar nerve surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Excision of Schwannoma from ulnar nerve surgical procedure.
    Peripheral nerve sheath tumours are rare but the true incidence is unknown as many are asymptomatic and present as spurious findings on imaging for other pathologies. When they are large or occur at natural compression points they are more likely to be symptomatic. Small subcutaneous nerve sheath tumours may present as small lumps that are painful if touched. Most tumours fall into the benign category and are either Schwannoma or Neurofibroma subtypes. Most are solitary but both can present as multiple tumours in neurofibromatosis. Multiple Schwannomas are also a feature of a separate genetic condition Schwannomatosis in which strings of multiple tumours may arise from a single nerve trunk.

    Indications

    Small asymptomatic tumours with no adverse features on clinical examination or imaging may be clinically monitored with repeat imaging only if there is a change in size or symptom profile.
    Indications:
    In cases where there are motor and sensory abnormalities or in superficial tumours where they are susceptible to local repeated trauma consideration should be given to surgical removal.
    Each patient must be counselled specifically for their particular tumour by virtue of its location and size. Non-critical sensory nerve tumours may be removed with less morbidity than a proximal tumour in a mixed motor and sensory nerve. The patient must be aware of the risk of neurological deterioration following surgery. The deterioration my be transient from oedema but there is a risk of creating an axonotmesis type injury from intraneural dissection as well as the possible need for resection of an involved fascicle group for tumour clearance.
    Symptoms and examination:
    This tumour presented in the ulnar nerve at the mid forearm level and as such was symptomatic when the arm was resting on a table in the pronated position using a keyboard. The tumour was causing a mild degree of baseline pain and there was paraesthesiae in the ulnar cutaneous distribution and weakness of the ulnar-innervated intrinsic muscles at MRC grade 4. The tumour was diagnosed following an MRI scan 5 years previously and became progressively symptomatic. The original treating hand surgeon was reluctant to remove is due to worry about worsening the neurological function. The patient was adamant that she wanted the tumour removing. Imaging suggested a Schwannoma. There was an increase in size from 1.5 to 2.2cm on interval imaging over 3 years. A careful clinical examination should assess motor and sensory dysfunction. Tinel’s sign may be elicited at the site of the nerve tumour due to focal demyelination, axonopathy or compression.
    Investigations:
    Imaging of the tumour with MRI +/- ultrasound is mandatory prior to consideration of surgical removal. If there are any unusual features on imaging or worrying clinical presentation (nerve pain, rapidly increasing in size, recurrence at a site of previous resection, major motor or sensory dysfunction) then consideration should be given to a nerve biopsy prior to planning definitive surgical management. In uncertain cases the use of MRI spectroscopy shows promise in identifying abnormal proteins (trimethylamine) that may be associated with atypia or malignancy). Perhaps in the future these types of chemical imaging plus functional imaging (PET scanning) may provide diagnostic information sufficiently accurate to prevent open nerve biopsy. Neurophysiology is necessary when there is clinical evidence of deteriorating nerve function.
    Non-operative management:
    Tumours can be observed when there are minimal symptoms, no neuropathic pain and no sensory or motor disturbance as long as imaging is typical for a benign peripheral nerve sheath tumour.
    Alternative operative management:
    For benign tumours simple excision biopsy should suffice but the operation should be performed with great care to prevent further loss of nerve function. If there is diagnostic uncertainty and imaging is inconclusive consideration should be given to a formal open incisional biopsy of the lesion. The biopsy should include the interface with normal nerve tissue and so results in damage and scar that makes it more likely that there will be permanent neurological dysfunction after tumour resection. In simple cases with routine imaging and clinical findings we recommend a marginal excision of the tumour by way of excision biopsy to prevent these problems. It must be noted that despite these precautions there are still cases of inadvertent marginal excision of malignant tumours although these tend not to be neurofibrosarcomas but usually atypical presenting tumours such as synovial sarcoma or intra-neural Ewing’s sarcoma. Therefore it is essential that all potential surgical cases are discussed in a multidisciplinary meeting with review of imaging, clinical presentation and any previous histology or biopsy findings. The appropriate surgical procedure can then be planned. For malignant tumour resection wide margins are required with radical excision of surrounding normal tissue to ensure that the tumour is not breached. Reconstruction of the nerve in these rare cases must be planned and depends on the adjuvant therapy planned and the site of the nerve gap. Options include nerve grafting, nerve allografting, distal nerve transfers and tendon transfers.
    Contraindications:
    Surgery should not be undertaken outside of a specialist unit if there is a suspicion on imaging of malignant peripheral nerve sheath tumour. In such cases definitive management should be done by a sarcoma specialist and should involve radical excision margins with compartment excision or amputation.

    Setup

    The left arm was anaesthetised with an axillary regional local anaesthetic block. It is important for the anaesthetic team to understand that if the block is incomplete a peripheral top up must not be used and the patient should instead have a general anaesthetic without neuromuscular blockade. The reason for this is that during the procedure intra-operative nerve stimulation is used to define the fascicle anatomy and identify any important branches as the tumour is exposed. When the tumour is removed any fascicles entering the tumour can also be assessed to establish the potential for functional loss and provide a prognosis. Residual function can also be mapped in the preserved nerve.
    The limb is prepped and draped to the axilla and a sterile disposable upper arm tourniquet placed around the arm. Exsanguination is performed with elevation rather than an Esmarch bandage to reduce the risk of local trauma to the tumour and the involved nerve. This approach of delayed tourniquet elevation allows 30 minutes of nerve exposure and dissection before the onset of tourniquet induced ischaemic conduction block after which it may be necessary to deflate the tourniquet for 10-15 minutes before conduction is reliably restored.

    Operation – 1

    The arm is positioned on an arm table with a lead hand to stabilise the limb during the microscope dissection.

    The tumour is palpated and marked deep to the FCU and FDS muscles.

    The skin is opened and the subcutaneous fat dissected to the deep fascia.

    Haemostasis with bipolar cautery for superficial veins.

    The deep fascia is now exposed and a West self-retaining retractor is used to maintain exposure.

    The interval between the FCU muscle belly and the long finger flexors is developed to expose th eulnar neurovascular bundle.

    1 – Long digital flexor muscle mass
    2 – Ulnar nerve containing tumour
    3 – Ulnar artery radial to the tumour

    A Mixter is passed proximal to the tumour around the ulnar nerve between the artery and nerve. A sloop is passed through this interval enabling gentle retraction on the nerve to develop the plane between the nerve and artery.

    This is repeated at the distal end of the tumour.

    A sloop is passed around the distal end of the tumour. Care should be taken when closing the jaws of the Mixter to ensure that the posterior epineurium hasn’t been caught in the teeth.

    The nerve can now be lifted into the wound away from the ulnar artery and venae commitantes.

    Placing a small damp swab that has been unfolded behind the tumour provides a stable operating base for when the nerve is opened and minimises retraction and handling of the nerve. It also can be used to provide haemostasis and prevent tumour contamination of the surgical field.

    Now the tumour is visible within the nerve with fascicles stretched around it.

    A nerve stimulator needle can be used to map the fascicles and identify any important motor component stretched over the surface of the tumour. This allows a window of epineurium to be identified that can be exposed for access to the tumour without damaging any important fascicles.

    A longitudinal incision is made in the epineurium using a scalpel to create and epineurial window for tumour exposure. DeBakey forceps are use dto lift the curt edge of the epineurium. They cause less trauma than toothed forceps which should not be used near the nerve.

    The interval can be developed between the tumour and the fascicles of the normal ulnar nerve.

    A Watson-Cheyne is useful to gently develop the plane of dissection around the tumour capsule. The flattened end has smooth and curved edges that readily push fascicles away from the tumour.

    Deeper dissection can be performed in the same manner but sometimes there are difficult areas to visualise and a number of options are available. Care should be taken dissecting more proximally along the neck of the tumour go gain exposure (position A) as the fascicles here are distorted and attempts at intraneural plane development can result in an inadvertent section of a fascicle. I would advise either placement of a sloop around the tumour and positioning a second sloop around the normal nerve and using this technique to retract and open the plane for further dissection or as in this case use an operating microscope to examine the deep surface and identify any fascicles entering the tumour so that they can be stimulated to ascertain their function. In this case the blunt dissection of the deep surface produced a strong contraction of the FDP muscle and it was thought prudent to undertake further dissection with operating microscope assistance.

    The tumour has fascicles entering its deep surface that preclude further bliunt dissection.

    The operating microscope is positioned for operator and assistant visualisation of the nerve.

    The assistant can provide retraction on the tumour and on the normal nerve to allow the operator to examine the deep surface of the tumour.

    Using microscissors the distal neck is released by sectioning the interfascicular epineurium and allow further retraction of the fascicles away from the tumour.

    A Ragnell retractor is here placed gently between the normal nerv ean dthe tumour to allow the operator to visualise the deep surface of the tumour and identify the location of fascicles entering the tumour so that they can be stimulated to ascertain their function.

    Nerve stimulation confirms no useful motor function in the involved fascicle group which is sectioned distally and further blunt dissection with a Watson-Cheyne allows the tumour to be exposed circumferentially.

    The tumour is delivered through the epineural window and the feeding fascicle can be seen at the proximal tumour neck.

    Operation – 2

    The tumour is lying outside the epineural window and is ready for the proximal fascicle section.

    The proximal fascicle is exposed and sectioned with microscissors and the specimen is sent for routine histological assessment.

    The tumour has been removed and the normal nerve is seen without distortion or tension adjacent to the epineural window.

    Following removal of the damp swab from under the tumour. Final haemostasis achieved with bipolar diathermy. The tourniquet can be released and haemostasis confirmed if there are any concerns.

    Subcuticular wound closure is followed by steristrips to the wound edges and a bulky wool and crepe bandage. If the patient is under a general anaesthetic I would use local anaesthetic injection to the skin edges and leave a proximal nerve catheter above the operated site adjacent to the nerve. In such cases is is possible to check the motor function in the recovery room ad then deliver a local anaesthetic bolus through the catheter. The catheter can then be removed. In complex cases pre-existing neuropathic pain, sensitisation and revision surgery I consider leaving the nerve catheter in situ so that intermittent local anaesthetic boluses can be given during the first 48 hours with a background infusion via a pump to prevent catheter tip occlusion. In straightforward cases such as this the catheter can be removed immediately after the bolus snd the patient is discharged the same day.

    Post Operative

    The limb is elevated in a sling for 48 hours and the bulky dressing kept in place for 5 days.
    A wound review and replacement of the occlusive dressing can be performed at that stage.
    The patient’s pain and function should be assessed early and any deficits documented and the patient may be reassured.
    Further clinical follow up at around 6-8 weeks will demonstrate resolution of any conduction block from oedema and segmental demyelination from the intraneural dissection.
    Major deficits and a confirmatory Tinel will confirm axonopathy requiring nerve regeneration and the patient can be advised regarding the prognosis at this stage with further follow up planned as necessary.
    Histology should be available at this follow up appointment.

    Recommended Reading

    Generally the results of this type of benign tumour excision are excellent. The prognosis largely depends on the pre-operative neurological status and whether this is a primary or revision surgery. Most patients report resolution of pan and improved sensation and motor function within a few weeks of surgery. This was a Schwannoma and in such cases nerve reconstruction is usually not required and the involved fascicle can be resected because there is inbuilt redundancy in the nerve (typified by highly selective fascicle transfer for paralysis). If the fascicle was large and had a critical function that was not present on stimulation of the remaining nerve consideration should be given to reconstruction of the resected fascicle using a nerve graft. Allograft is useful in sensitised individuals to prevent creation of a secondary nerve injury site from donor nerve harvest. If there is significant trauma to the epineurium and the nerve is superficially located and was sensitise before surgery, I use a layered collagen nerve barrier warp around the nerve to provide some protection from subcutaneous scar formation.
    References:
    Guha D et al. Management of peripheral nerve sheath tumors: 17 years of experience at Toronto Western Hospital. J Neurosurg 2017 Jul 7:1-9. doi: 10.3171/2017.1.JNS162292 Epub
    Tang CY, Fung B, Fok M, Zhu J. Schwannoma in the upper limbs. Biomed Res Int 2013; 167196. doi: 10.1155/2013/167196. Epub 2013 Sep 4
    Tang CY, Fung B, Fok M, Zhu J. Schwannoma in the upper limbs. Biomed Res Int 2013; 167196. doi: 10.1155/2013/167196. Epub 2013 Sep 4
    Mansukhani SA, Butala RP, Shetty SH, Khedekar RG. Familial Schwannomatosis: A Diagnostic Challenge. J Clin Diagn Res 2017; Feb;11(2):RD01-RD03. doi: 10.7860/JCDR/2017/20929.9307. Epub 2017 Feb 1

    Reference

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