Schwann Oma

8/13/2019 Schwann Oma

1/4

Dx:Nerve Sheath Tumor

KEY FACTS

TerminologySchwannoma: 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 DiagnosesHemangioma

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 NF1Treatment: Surgical enucleation with blunt dissection from involved nerveNeurofibromas 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 axonsSchwann 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


2/4

Well-defined unilocular radiolucency, often as epicenter in symmetrically widened mandibular canal onpanoramic viewsConcentric expansion of mandibular canalon coronal views

Location25-48% occur in H&N: Tongue most common intraoral siteIntraosseous lesions less common than soft tissue lesions: < 1% of all bone tumors

Mandible> maxillaUsually associated with inferior alveolar nervePosterior > anteriorSchwannoma reported presenting as periapical lesion in posterior mandible and as unilocular radiolucency inanterior mandibleDifferentiation 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 bordersSome neurofibromashave been described as poorly defined

Radiographic FindingsExtraoral plain filmPanoramic imaging may show symmetric widening of mandibular canal with localized fusiform expansionAnterior lesion will appear as isolated well-defined unilocular radiolucency and may mimic periapicalpathology orodontogenic and nonodontogenic cystsNeurofibromas may be less well definedNeurofibromas may produce flaring of the mandibular foramen: "Blunderbuss"foramenRoot divergence may be seen

CBCT and bone CTWill show extent of lesion and any expansionCoronal views best to show concentric expansion of mandibular canal

MR Findings

T1WISchwannoma: Intermediate signal most commonNeurofibroma: Most are homogeneous and isointense to skeletal muscle

T2WI: Hyperintense

T1WI C+Schwannoma: Homogeneous enhancementLocalized 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 symmetricalCanal 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 destroyed

May see associated mass in oral cavity adjacent to involved nerve

Simple Bone Cyst


3/4

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 radiolucencyTooth is nonvital

PATHOLOGY

General Features

Etiology: Proliferation of Schwann cells and perineural cells within perineurium causing displacement andcompression of surrounding normal nerve tissue

Associated abnormalitiesMultiple neurofibromas associated with neurofibromatosis type 1 (NF1)a.k.a. von Recklinghausen diseaseAutosomal dominant neurocutaneous disorder with varied expressivity2 neurofibromas (NF) or 1 plexiform NF (PNF)Caf-au-lait spotsAxillary freckling (Crowe sign)

Bilateral acoustic schwannomas associated with neurofibromatosis type 2(NF2)Autosomal dominant disorder associated with chromosome 22May develop peripheral schwannomasand meningiomas

Staging, Grading, & Classification

Schwannomas have different originsSoft tissue origin: Acoustic neuroma most common in H&NMay involve bone secondarilyArising in nutrient canals: Causes enlargement of canalArising centrally within bone

NeurofibromasLocalized: Fusiform mass with nerve running throughDiffuse: In soft tissues, see infiltrative growth into subcutaneous fat

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

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

SchwannomaEncapsulatedTypically see palisading organized fusiform cells (Antoni A); less organized (Antoni B)Verocay bodies: Acellular eosinophilic zonesS100 strongly positive

NeurofibromaNonencapsulatedMixture of Schwann cells, perineural cells, and endoneurial fibroblastsSpindle-shaped Schwann cells with elongated or wavy nucleiS100 positive

CLINICAL ISSUES

Presentation

Most common signs/symptoms: Frequently asymptomatic


4/4

Other signs/symptomsPain or paresthesiaPatient may report tingling sensationPrevention of eruption of teethCortical expansion

DemographicsAgeNeurofibroma: 9-50 yearsSchwannoma: 10-40 years2nd-4th decades most common

GenderFemales:males = 2:1Literature is contradictory

EpidemiologyNeurofibromaFrequency of oral peripheral nerve sheath tumors reported as 20-30%SchwannomaFrequency of oral peripheral nerve sheath tumors reported as 16-22%

Natural History & Prognosis

Malignant 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 presentExamine patient for stigmata of NF1

DIAGNOSTIC CHECKLIST

Consider

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

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

Documents

Schwann Oma