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Dx:Nerve Sheath Tumor

KEY FACTS

Terminology

Schwannoma: Arises from Schwann cells and displaces axons

Neurofibroma (NF): Mixture of Schwann cells and perineural cells that incorporate axons

Imaging

Well-defined unilocular radiolucency:Epicenter in symmetrically widened inferior alveolar canal

Mandible> maxilla: Usually inferior alveolar nerve

< 1-6 cm reported

Anterior lesion may mimic periapical pathology

Root divergence may be seen

MR will best characterize lesion contents

Top Differential Diagnoses

Hemangioma

Perineural tumor spread along CNV3

Simple bone cyst

Periapical rarefying osteitis

Pathology

Multiple neurofibromas associated with neurofibromatosis type 1 (NF1)

Clinical Issues

Frequently asymptomatic; pain or paresthesia; delayed eruption of teeth; cortical expansion

2nd-4th decades most common; females > males

Slow-growing benign lesion

Malignant transformation more common in plexiform NF associated with NF1

Treatment: Surgical enucleation with blunt dissection from involved nerve

Neurofibromas more likely to recur because of infiltrative growth

Genetic testing if multiple lesions present

TERMINOLOGY

Synonyms

Schwannoma: Neurilemmoma, peripheral fibroblastoma, neurinoma

Neurofibroma (NF): Neurinoma

Definitions

Benign perineural tumor arising from cells of neural sheath

Schwannoma: Arises from Schwann cells and displaces axons

Schwann cells cover myelinated nervesNeurofibroma: Mixture of Schwann cells and perineural cells that incorporate axons

Malignant peripheral nerve sheath tumor (MPNST)

Most commonly involves major nerve trunks, including brachial plexus

IMAGING

General Features

Best diagnostic clue

Well-defined unilocular radiolucency, often as epicenter in symmetrically widened mandibular canal on

panoramic viewsConcentric expansion of mandibular canalon coronal views

Location

25-48% occur in H&N: Tongue most common intraoral siteIntraosseous lesions less common than soft tissue lesions: < 1% of all bone tumors

Mandible> maxilla

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Usually associated with inferior alveolar nervePosterior > anterior

Schwannoma reported presenting as periapical lesion in posterior mandible and as unilocular radiolucency in

anterior mandible

Differentiation from odontogenic pathology may be difficult in these cases

Size

< 1-6 cm reportedSoft tissue lesions can reach larger size

MorphologyUnilocular with well-defined, often corticated borders

Some neurofibromashave been described as poorly defined

Radiographic Findings

Extraoral plain filmPanoramic imaging may show symmetric widening of mandibular canal with localized fusiform expansion

Anterior lesion will appear as isolated well-defined unilocular radiolucency and may mimic periapical

pathology orodontogenic and nonodontogenic cysts

Neurofibromas may be less well defined

Neurofibromas may produce flaring of the mandibular foramen:"Blunderbuss"foramen

Root divergence may be seen

CBCT and bone CT

Will show extent of lesion and any expansion

Coronal views best to show concentric expansion of mandibular canal

MR Findings

T1WI

Schwannoma: Intermediate signal most common

Neurofibroma: Most are homogeneous and isointense to skeletal muscle

T2WI: Hyperintense

T1WI C+Schwannoma: Homogeneous enhancement

Localized NF: Homogeneous or patchy heterogeneous enhancement; well-circumscribed fusiform mass

Imaging Recommendations

Best imaging tool: MR will best characterize lesion contents and extent

DIFFERENTIAL DIAGNOSIS

Hemangioma

Expansion of mandibular canal less symmetrical

Canal may become curved or serpiginous

Perineural Tumor Spread Along CNV3

Spread of malignant lesion through mandibular or mental foramina may cause widening of canal

Borders will be less well defined or destroyedMay see associated mass in oral cavity adjacent to involved nerve

Simple Bone Cyst

SBCs occur in similar age group

Males > females

May be difficult to differentiate from solitary neural lesion not in mandibular canal

Periapical Rarefying Osteitis

Inflammatory reaction at apex of pulpally involved tooth

Well-defined radiolucency

Tooth is nonvital

PATHOLOGY

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General Features

Etiology: Proliferation of Schwann cells and perineural cells within perineurium causing displacement and

compression of surrounding normal nerve tissue

Associated abnormalities

Multiple neurofibromas associated with neurofibromatosis type 1 (NF1)a.k.a. von Recklinghausen disease

Autosomal dominant neurocutaneous disorder with varied expressivity

2 neurofibromas (NF) or 1 plexiform NF (PNF) Caf-au-lait spots

Axillary freckling (Crowe sign)Bilateral acoustic schwannomas associated with neurofibromatosis type 2(NF2)

Autosomal dominant disorder associated with chromosome 22

May develop peripheral schwannomasand meningiomas

Staging, Grading, & Classification

Schwannomas have different origins

Soft tissue origin: Acoustic neuroma most common in H&N

May involve bone secondarily

Arising in nutrient canals: Causes enlargement of canal

Arising centrally within bone

Neurofibromas

Localized: Fusiform mass with nerve running through

Diffuse: In soft tissues, see infiltrative growth into subcutaneous fat

Plexiform: Highly characteristic of neurofibromatosis; extensive interlacing nerve tissue resembling "tangle of

worms"

Gross Pathologic & Surgical Features

Neurofibroma: Fusiform, firm, gray-white mass intermixed with nerve of origin

Schwannoma: Solid lesion more easily separated from associated nerve because of capsule

Microscopic Features

Schwannoma

EncapsulatedTypically see palisading organized fusiform cells (Antoni A); less organized (Antoni B)

Verocay bodies: Acellular eosinophilic zones

S100 strongly positive

Neurofibroma

Nonencapsulated

Mixture of Schwann cells, perineural cells, and endoneurial fibroblasts

Spindle-shaped Schwann cells with elongated or wavy nuclei

S100 positive

CLINICAL ISSUES

Presentation

Most common signs/symptoms: Frequently asymptomaticOther signs/symptoms

Pain or paresthesia

Patient may report tingling sensation

Prevention of eruption of teeth

Cortical expansion

Demographics

Age

Neurofibroma: 9-50 years

Schwannoma: 10-40 years2nd-4th decades most common

Gender

Females:males = 2:1Literature is contradictory

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EpidemiologyNeurofibroma

Frequency of oral peripheral nerve sheath tumors reported as 20-30%Schwannoma

Frequency of oral peripheral nerve sheath tumors reported as 16-22%

Natural History & PrognosisMalignant transformation more common in PNF associated with NF1

Slow-growing benign lesion

Malignant schwannoma rare in CNV

Treatment

Surgical enucleation with blunt dissection from involved nerve

Recurrence uncommon for schwannoma; neurofibromas more likely to recur because of infiltrative growth

Genetic testing if multiple lesions present

Examine patient for stigmata of NF1

DIAGNOSTIC CHECKLIST

ConsiderSolitary neurofibroma may represent "forme fruste": 1st or only manifestation of neurofibromatosis

Long-term follow-up to monitor for development of other lesions is critical