Neurosurgery notes/Tumours/Cranial and paraspinal nerve tumours

Cranial and paraspinal nerve tumours

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Tumours
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Schwannoma
Neurofibroma
Perineurioma
Hybrid nerve sheath tumour
Malignant melanotic nerve sheath tumour
Malignant peripheral nerve sheath tumour (MPNST)
Cauda equina neuroendocrine tumour
Paraganglioma (Glomus tumour)

General

  • Peripheral nerves are made up of the following cells
    • Schwann cell
      • Myelinating
      • Nonmyelinating
    • Perineural cells: forms perineurium
    • Mast cells
    • Pericytes,
    • Endothelial cells,
    • Endoneurial fibroblast-like cells: forms the endoneurim

Types of cranial and paraspinal nerve tumours

General

  • Most are sporadic
  • Inherited conditions that predispose an individual to developing PNSTs
    • NF1
    • SPS
    • Carney complex

Clinical features

  • A visible or palpable mass
    • Palpation of the mass might elicit dysesthesia or paraesthesia.
  • Pain
  • Weakness
  • Sensory alterations
  • Incidental finding on imaging studies,
  • Involvement of motor nerves
    • Might produce weakness or more commonly subtle functional impairment with fine motor tasks.
  • Autonomic dysfunction
    • Changes in texture, colour, and temperature of the skin or in the amount of sweat produced.
  • Stigmata of NF1
    • Café au lait spots
    • Neurofibromas
    • Lisch nodules
    • Optic glioma
    • Axillary/ inguinal freckling
    • Distinctive skeletal abnormalities
    • Family history
  • Any rapid increase in size or rapid symptom progression should raise the suspicion of
    • Cyst formation
    • Haemorrhage
    • Malignant transformation

Management

Conservative

  • Since benign PNSTs are usually slow growing, intervention is not warranted until symptoms appear.

Surgery

Indications

  • Pain
  • Neurologic symptoms
  • Concern for malignancy
    • Plexiform neurofibromas should be monitored closely for changes in size or development of symptoms.
  • Cosmesis
  • For histological diagnosis

Biopsy

  • Tumours with imaging findings suggestive of benign PNSTs do not require biopsy unless there are unusual clinical features.
  • Histological diagnosis should be sought when diagnostic uncertainty arises.
    • Because of the elevated risk of malignant transformation in NF1, there should be a low threshold for percutaneous biopsy when there is
      • Rapid tumour growth
      • Rapid onset of pain.
  • Technique
    • Fine-needle aspiration
    • Needle core biopsy
  • Performing the biopsy with PET/ CT stereotactic guidance should be considered in order to reduce the false negative rate of suspicious lesions.

Surgical excision of a PNST

  • Can be performed under general, regional, or local anaesthesia
  • Monitoring
    • Use of muscle relaxants must be avoided because these agents prevent intraoperative neurophysiological monitoring and stimulation.
    • A nerve stimulator is applied to help identify afascicular entry points.
    • Intraoperative EMG recordings provide feedback alerting the surgeon to overaggressive fascicle manipulation.
  • The patient is positioned to provide maximal exposure of the peripheral nerve in question.
  • The skin incision is made over the course of the nerve beginning 2– 4 cm proximal and extending 2– 4 cm distal to the tumour.
    • Dissection is performed though the subcutaneous tissues to expose the underlying lesion with meticulous haemostasis.
    • Exposure of the nerve begins within an area of normal anatomy and extends into the area of tumour.
  • Important to identify the normal proximal and distal limits of the tumour.
  • Loupe magnification or an operating microscope is often required to delineate the tumour, which may require internal neurolysis to identify the fascicles coursing over the tumour.
  • An afascicular dissection plane is established by gently elevating and separating the fascicles from the tumour capsule.
  • Debulking of the tumour with ultrasonic aspirator may facilitate dissection in very large tumours.
  • Specific tumours
      • Schwannomas
      • Most can be rolled out of their capsule and removed en bloc.
      • Non-functioning (as determined by stimulation) single fascicles seen entering and exiting a schwannoma may need to be divided to remove the tumour.
      • It is not necessary to remove the tumour capsule of schwannomas as it is not associated with tumour recurrence.
      Neurofibromas
      • In contrast, fascicles enlarged by neurofibromas are often still functioning and removal of the tumour inevitably requires sacrifice of one or more fascicles.
      • For extensive plexiform neurofibroma
        • Aim
          • Is often debulking to alleviate symptoms caused by neural compression.
        • Frozen sections should be obtained to determine if a malignancy is present.
        • Wound closure is then performed in layers with care taken not to entrap nerves in a tight compartment.
      MPNSTs with localised disease
      • Aims
        • Complete surgical extirpation with clear margins
        • This is crucial even in large, non- extremity malignant tumours, as often seen in NF1 patients, for which extensive gross total resection would be associated with significant morbidity.
        • Data supports the independent prognostic importance of complete surgical excision (Dunn et al., 2013).
        • In most cases of large (>5 cm) high-grade extremity sarcomas, adjuvant radiation is advocated to reduce local recurrence.
          • This however needs to be carefully discussed with all NF1 patients in view of the heightened risk of radiation-induced sarcoma.
          • Although there are no randomised trials examining adjuvant chemotherapy specifically in MPNST, adjuvant chemotherapy remains a consideration for motivated patients.
            • The recently reported SARC006 phase II trial conducted by the Sarcoma Alliance for Research (SARC) evaluated the role of chemotherapy with doxorubicin, ifosfamide, and etoposide in 48 locally advanced metastatic MPNST patients.
            • It revealed encouraging disease stabilization rates with responses accruing from neoadjuvant chemotherapy, that rendered subsequent local therapy feasible, in most patients with localized disease
        • Tumours of the brachial plexus
          • Represent an unusual disease, involve unfamiliar surgical territory for many neurosurgeons and hence present as a clinical challenge.
          • The management of these tumours requires not only an understanding of the complex anatomy of the brachial plexus but also an appreciation of the appropriate surgical approach to the various tumours that may be encountered.
          • Approach
            • Anterior supraclavicular approach
              • To treat tumours on most of the roots and trunks.
            • Infraclavicular approach
              • Is used for lesions involving the cords and distal plexal elements.
            • Posterior approach
              • Is utilized for
                • Tumours involving spinal nerves at the intraforaminal level, the C8- T1 roots, and the lower trunk.
                • Patients who present with residual or recurrent tumour or who have undergone radiotherapy.
  • Nerve grafting should be considered on occasions when a significant fascicle is sacrificed.
    • Donor nerve
      • Sural nerve
        • Commonly serves as the donor nerve;
      • Medial antebrachial cutaneous nerve
      • Sensory radial nerve.

DDx: Schwannoma vs Neurofibroma

Features
Schwannoma
Neurofibroma
Meningioma
Type of NF
2
1
2
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Tumour has thinned and displaced fascicles (Eccentric to the nerve)
Tumour envelope rather than displace the majority of fascicles (involves the nerve)
Origin
Schwann cells
Arachnoid cap cell
Spinal location
Axially more posterior as it comes off the sensory roots
Can arise more anterior
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Capsulated
No capsule
Capsulated
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No mucoid
Mucoid
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Histologically
Biphasic
Monophasic
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Malignant change is rare
2% malignant change
Very rare (depends on grade)
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Plexiform (unrelated to NF2)
Plexiform (in NF1)
n/a
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Affects extremities
Affects trunk
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Usually solitary
Usually multiple
Can be multiple in NF2
  • Schwannoma CAN be separated from nerve fascicles but Neurofibroma cannot (as it is interwinned within nerve fibers in the endoneurium).
  • A, Schwannoma resection.
    • The tumor causes well-circumscribed dilatation of the nerve.
    • Internal neurolysis shows that the tumor has thinned and displaced the fascicles.
    • A single small fascicle may be enveloped by tumor.
    • The fascicles surrounding the schwannoma are dissected free, the tumor capsule is opened, and the schwannoma, and any enveloped fascicles, are resected en bloc.
  • B, Neurofibroma resection.
    • Neurofibromas cause well-circumscribed nerve dilatation (similar to schwannomas).
    • However, unlike schwannomas, neurofibromas envelop, rather than displace, the majority of fascicles.
    • After internal neurolysis, the tumor is seen enveloping multiple nerve fascicles.
    • The neurofibroma and enveloped fascicles are resected en bloc.
    • Nerve grafts may be required to repair functional fascicles that were resected.
  • C, Plexiform neurofibroma debulking.
    • The plexiform neurofibroma has caused fusiform dilatation of the affected nerve.
    • Intraneurally, the tumor has enveloped many fascicles.
    • The tumor is debulked, but it cannot be fully resected.
Schwannoma Neurofibroma Plexiform neurofibroma c FIGURE 203-5 Schematic illustration of surgery for benign peripheral nerve sheath tumors. A, Schwannoma resection. The tumor causes well- circumscribed dilatation of the nerve. Internal neurolysis shows that the tumor has thinned and displaced the fascicles. A single small fascicle may be enveloped by tumor. The fascicles surrounding the schwannoma are dissected free, the tumor capsule is opened, and the schwannoma, and any enveloped fascicles, are resected en bloc. B, Neurofibroma resection. Neurofibromas cause well-circumscribed nerve dilatation (similar to schwanno- mas). However, unlike schwannomas, neurofibromas envelop, rather than displace, the majority of fascicles. After internal neurolysis, the tumor is seen enveloping multiple nerve fascicles. The neurofibroma and enveloped fascicles are resected en bloc. Nerve grafts may be required to repair functional fascicles that were resected. C, Plexiform neurofibroma debulking. The plexiform neurofibroma has caused fusiform dilatation of the affected nerve. Intraneurally, the tumor has enveloped many fascicles. The tumor is debulked, but it cannot be fully resected.
Schematic illustration of surgery for benign peripheral nerve sheath tumors.
 
Direction of extracapsular approach Schwannoma Epineural sheath Perineurium Nerve rootlets coursing over the Schwannoma Nerve rootlet from which the Schwannoma is arising OBy Dr. Arjun Antony
 
Schwannoma within nerve Schwannoma Perineurial sheath Endoneurium Nerve fibers c Proliferating cells of neurofibroma Perineurial sheath Nerve fibers Endoneurium Neurofibroma within nerve Difference between Neurofibroma & Schwannoma Definition Schwannoma CAN be separated from nerve fascicles & Neurofibroma cannot (as it is interwinned within nerve fibers in the endoneurium).
 
Schwannoma within nerve Schwannoma Perineurial sheath Endoneurium Nerve fibers c Proliferating cells of neurofibroma Perineurial sheath Nerve fibers Endoneurium Neurofibroma within nerve Difference between Neurofibroma & Schwannoma Definition Schwannoma CAN be separated from nerve fascicles & Neurofibroma cannot (as it is interwinned within nerve fibers in the endoneurium).