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INTRODUCTION

All cellular elements that comprise

a peripheral nerve (perineural cells,

Schwann cells and fi broblasts) can the-

oretically give rise to peripheral nerve

tumors (PNTs). The tumors are clas-

sifi ed as either benign or malignant,

and sub-classifi ed according to their

origin from either neural or non-neural

elements (Table 1).

HISTORY AND PHYSICAL EXAMI-

NATION

When a soft tissue mass is associated

with sensory and/or motor symptoms

supplied by a known peripheral nerve,

the suspicion of a peripheral nerve

tumor is readily apparent. Then a fo-

cused history of patient to harbor a pe-

ripheral nerve tumor (PNTs) should be

directed towards the onset, duration,

and growth alterations of the mass. A

family history of NF-1 or NF-2 or other

predisposition syndromes is of special

importance, since majority of PNTs are

linked with these syndromes. Presence

or absence of symptoms and signs

such as pain, numbness, weakness,

the overlying skin temperature and

color, fl uctuance, along with the pa-

tients general health inquiry including

immune status, pre-existing malignan-

cy are of importance in the differential

diagnosis. However, many peripheral

nerve tumors present without any neu-

rological symptoms due to their slow

growth rate or origin from a superfi cial

small sensory branch. Several features

of the examination that suggests a pe-

ripheral nerve origin

(1)

: 1. PNTs are mo-

bile perpendicular but not along the

longitudinal axis of a known peripheral

nerve. 2. Palpation or percussion (Ti-

nel's sign) of a PNT may elicit sensory

stimuli radiating along the distribution

of the nerve of origin. 3. A mass in the

presence of a patient with a genetic

predisposition such as neurofi broma-

tosis (NF) most likely represents a pe-

ripheral nerve tumor.

DIAGNOSTICS

Nerve conduction and EMG evalua-

tion are not generally performed in

the management of PNTs as they are

not diagnostic nor do they help in

the management decision. However,

Treatment of Peripheral Nerve Tumors

Julius July

, Abhijit Guha

1. Department of Neurosurgery, Medical School of Universitas Pelita Harapan, Siloam Lippo Karawaci Hospital, Tangerang, Indonesia

2. Professor, Department of Surgery; Alan & Susan Hudson Chair in Neurooncology Toronto Western Hospital, University Health Network; Co-Director,

Arthur & Sonia Labatts Brain Tumor Centre, Hospital for Sick Children's Research Institute, Univ. of Toronto, Ontario, Canada

Table 1. Peripheral Nerve Tumors Simple Classifi cation Scheme

Peripheral Nerve Tumors

Benign

Malignant

Neural Elements

Non Neural Elements

Schwanoma

Neurofi broma

Perineurioma

Etc.

Desmoid

Ganglion Cyst

Fibrolipomatous Hamartoma

Lipoma

Neuromuscular choristoma

Etc.

Pancoast Tumor

Soft Tissue sarcoma /-

carcinoma

Etc.

MPNST

Primary PN Lymphoma

Etc.

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intra-operative electrophysiology is

crucial as discussed below. Plain X-ray

and CT scans are occasionally helpful,

especially to demonstrate remodel-

ing of adjacent bony structures such

as the neural foramina. Angiography

or MR angiography is rarely required,

and restricted to large PNTs at the

base of the neck, chest or retroperi-

toneum, where close proximity and or

rarely vascular invasion may be pres-

ent. MRI is the most useful and sensi-

tive technique, often but not always

revealing the nerve of origin (Fig. 1).

It is especially useful in determining

the relationship of the mass to adja-

cent anatomical structures, which are

of relevance.

Although CT scan or MRI cannot dis-

tinguish between the various subtypes

of PNTs and determine whether a le-

sion is benign or malignant

(2,3)

, MR

imaging may be highly suggestive but

not diagnostic of the sub-type of PNT,

with elements of the history and physi-

cal examination often superior in pre-

dicting whether the lesion is benign

vs. malignant and the likely sub-type

of PNT to be present. Occasionally,

MR imaging of schwannoma demon-

strates the nerves of origin, and the

displaced passer-by fascicles around

the capsule, consistence with its typi-

cal extra-fascicular growth. In contrast,

neurofi bromas are more fusiform (ie.

spindle) or multi-nodal, suggestive of

their typical intra-fascicular growth. Of

note, a PNT in the context of an NF-1

patient will most certainly be a neuro-

fi broma vs. an NF-2 patient who likely

harbors a schwannoma. Lipomas have

the characteristic bright on T1 and T2

signal, while ganglion cysts are bright

on T2 with the origin traced to joint

capsule in proximity to the nerve.

MRI of PNTs may demonstrate het-

erogeneous enhancement, indicat-

ing intra-tumor hemorrhage, necrosis

or cystic degeneration. However, its

relationship to malignancy is poor. In

fact, there are no defi nitive radiologi-

cal features of a Malignant Peripheral

Nerve Sheath Tumor (MPNST), a di-

agnosis mainly suspected on rapid

clinical and radiological growth, pro-

gressive neurological deterioration

and most importantly pain. Use of

FDG PET scanning, a developing

technique for dynamic imaging of

glucose metabolism

(4,5)

, is of poten-

tial promise in distinguishing MPNST

from benign PNTs. Still, one should be

aware of the occasional false-negative

results with this modality

(6)

. Initial stud-

ies have shown that

FDG-PET can be

used to identify potentially malignant

transformation of a benign plexiform

neurofi broma to a MPNST. In those in-

stances where malignant transforma-

tion is probable but not yet confi rmed,

biopsy of the lesion before surgery is

essential.

Figure 1. Patient with Left median nerve schwanoma. Upper Left: T1W MRI showed a masses along the

course of left median nerve with obvious nerve origin. Upper Right: intraoperative picture showed proximal

and distal part before dissection to identify the nerve and isolated with rubber band. Lower: Identifying

the nerve and isolated with rubber band. Schwannoma always can be separated from the nerve and leave

the nerve intact.

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OPERATIVE PRINCIPLES

There are several operative principles

that are applicable for all peripheral

nerve tumors

(1)

, such as:

1) Anesthetic without neuromuscular

paralysis to allow intra-operative

nerve stimulation.

2) The limb was positioned and

draped to allow anatomical acces-

sibility and evaluation of the distal

muscles that are supplied by the

nerve of origin.

3) The incision over the tumor should

extend proximally and distally to

allow adequate exposure of the

nerve of origin at either pole of

the tumor, coursing in a curvilin-

ear fashion over fl exor/extensor

creases. If the tumor is adjacent to

a known entrapment point such as

the carpal tunnel or fi bular head at

the knee, the incision should allow

prophylactic release of the entrap-

ment point in conjunction with tu-

mor removal.

4) Magnifi cation,

intraoperative

electrophysiological monitoring

including Nerve Action Potentials

(NAP), and microneurosurgical

instruments should be ensured.

Ultrasonic aspiration is sometimes

required to internally debulk large

PNTs, which allows the tumor cap-

sule to be collapsed and facilitat-

ing subsequent dissection of the

passerby fascicles from the tumor

capsule.

5) The fi rst step of dissection in-

volves isolating of the proximal

and distal segments of the nerve

of origin from adjacent vascular

and soft tissue structures and en-

circling them in vessel loops.

6) Gross observation of the tumor

and the position of the displaced

fascicles will often reveal the un-

derlying pathology and vital to

avoid injuring the nerve during

tumor removal

(7,8,9)

. In schwan-

nomas, passerby fasicles will be

found displaced relative to the tu-

mor capsule, though they may be

quite attenuated. The routes of

these fasicles should be noted mi-

croscopically and evaluated with

electrical stimulation noting dis-

tal muscle activity. Neurofi bromas

in contrast typically do not reveal

the discrete passerby fasicles, as

nerve fasicles are encompassed

within the tumor. However, several

major fasicles may be displaced

around the bulk of the tumor and

their position in the tumor capsule

should be noted.

7) A small biopsy of the tumor from

an electrically silent region is sent

for pathological verifi cation. The

pathology in conjunction with the

gross and microscopic observa-

tion will determine the feasibility

of total removal (as in schwanno-

mas) vs. limited resection (as in

neurofi bromas, desmoids). If the

quick section pathology suggests

a neurogenic sarcoma, then we

recommend closure and manage-

ment as outlined below.

Using the principles outlined above,

the single nerve fascicle which gives

rise to the schwannoma can usually

be isolated and electrophysiologically

confi rmed to be non-conducting, and

then total removal of the tumor can be

undertaken, (Fig 1).

REFERENCES:

1. July J, Guha A. Surgical Management of benign peripheral nerve tumors. Medical Journal of Indonesia 2008;17(3): 163-8.

Levine E, Huntrakoon M, Wetzel L. Malignant-nerve sheath neoplasms in Neurofi bromatosis: Distinctions from benign tumors by using imaging techniques. Am.

J. Radiol.1987;149:1059-1064.

3. Suh J, Abenoza P, Galloway H, Everson L, Griffi ths H. Peripheral (extracranial) nerve tumors: Correlation of MR imaging and histological fi ndings. Radiology

1992;183:341-346.

4. Adler LP, Blair HF, Makley JT, Williams RP, Joyce MJ, Leisure G, Al-Kaisi N, Miraldi F. Noninvasive grading of musculoskeletal tumors using PET. J Nucl

Med.1991;32:1508-12.

Lucas JD, O'Doherty MJ, Wong JCH, Bingham JB, McKee PH, Fletcher CDM, Smith MA. Evaluation of fl uorodeoxyglucose positron emission tomography in the

management of soft tissue sarcomas. J Bone Joint Surg (Br) 1998;80-B:441-7.

Hsu CH, Lee CM, Wang FC, Fang CL. Neurofi broma with increased uptake of (F-18)-fl uoro-2- deoxy-D-Glucose interpreted as a metastatic lesion. Ann Nucl Med

2003;17:609-611.

7. Hudson A, Gentili F, Kline D. Peripheral Nerve Tumors. In: Schmidek H, Sweet W (Eds). Operative Neurosurgical Techniques. Grune & Stratton, New York 1988.

pp. 1599-1610.

8. Kline D, Hudson A. Operative Results of Major Nerve Injuries, Entrapments and Tumors. W. B. Saunders, Philadelphia. 1994.

Rosenberg A, Dick H, Botte M. Nerve Tumors. In Gilberman R (Ed.), Operative Nerve Repair and Reconstruction, J.B. Lippincott, Philadelphia,1991.

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