palisaded encapsulated neuromas clinically manifest as solitary , firm , non - pigmented , dome - shaped nodules on the face of adult patients . palisaded encapsulated neuroma is known as a benign tumor of the facial skin , and is rarely found in the oral mucosa .
microscopically , the tumors are characterized by moderately cellular , fascicular proliferation of spindle cells that show some areas of parallel nuclei .
a bundle of nerves interposed between the schwann cells typically aggregates in palisades and is identified by s-100 protein immunohistochemical stain .
an alternate designation i.e. solitary circumscribed neuroma ( scn ) was proposed by fletcher in 1989 .
irrespective of the nomenclature , pen / scns are considered as reactive hyperplastic processes . in 2010 ,
koutlas and scheithauer considered pen / scns as relatively common true neuromas of the skin or mucosa . as a peripheral nerve sheath tumor , pen accounts for only 0.04 to 0.05% of oral biopsy specimens .
other peripheral nerve sheath tumors are neurofibroma , schwannoma ( neurilemmoma ) , mucosal neuroma associated with multiple endocrine neoplasia iii , nerve sheath myxoma and granular cell tumor . in the mouth , pen is mostly found on the hard palate and maxillary labial mucosa as a small , superficial and usually painless nodule .
the lesion is frequently diagnosed between the 5 and 7 decades of life , with equal sex predilection .
a preferred treatment for pen is conservative local surgical excision ; although gross total resection has been recently claimed to be the treatment of choice .
a 48-year - old man was referred to the oral medicine department of babol dental school , complaining of a tongue mass persisting for one year .
physical examination revealed an exophytic sessile mass measuring 0.3 0.4 cm with rubbery consistency on the anterior one - third of the dorsal surface of the tongue ( fig .
clinically , the overlying mucosa was depapillated and had increased vascularity . under the impression of a pg , excision of the mass was done and no recurrence was reported at 12 months postoperatively .
histopathological sections showed an encapsulated mass within the connective tissue , composed of interlacing fascicles of spindle cells that were consistent with schwann cells .
the nuclei , showing a parallel orientation within the fascicles , were characteristically wavy and pointed , with no significant pleomorphism or mitotic activity .
the overlying epithelium was atrophic and no rete ridges were seen ( figs . 3 and 4 ) .
giemsa special stain revealed no mast cells within the stroma , ruling out the differential diagnosis of neurofibroma .
photomicrograph showing an encapsulated proliferation of neoplastic cells ( hematoxylin and eosin staining ; original magnification 40 ) .
no evidence of malignancy is observed ( hematoxylin and eosin staining ; original magnification 400 ) .
mucosal neuroma can be distinguished histologically from other neurogenic tumors such as neurofibroma , neurilemmoma and pen .
briefly , mucosal neuroma is not encapsulated and does not have palisading nuclei ; whereas neurofibroma and pen are encapsulated .
mucosal neuromas are usually associated with the multiple endocrine neoplasia syndrome iii ( men iii ) , a rare syndrome with potentially fatal consequences such as medullary carcinoma of the thyroid .
other clinical signs of the patients with men iii can be considered in the diagnosis of oral lesions such as a mucosal neuroma . however
, when oral lesions are present in absence of other diagnostic signs , histopathological evaluation can be helpful .
the microscopic examination of the mucosal neuroma shows nerve bundles in various sizes surrounded by normal connective tissue , which are not usually seen in pen .
a traumatic neuroma is not a true tumor , yet it develops as a proliferation of neural tissue that is caused by injury to a peripheral nerve .
traumatic neuromas are usually associated with pain , ranging from pain on palpation to a constant severe pain .
these include the presence of perineural cells surrounding individual microfascicles , the greater abundance of interstitial collagen , mucoid matrix and myelin components , and the more orderly parallel arrangement of axons in traumatic neuroma .
antoni a , organized spindle cells in palisaded whorls , and antoni b , haphazardly distributed neoplastic cells , are two common patterns which are often found during histopathological examination of schwannomas .
other microscopic criteria include verocay bodies and the more definite palisading in the nuclei than that in pen .
contrary to the latter , it is extremely difficult to microscopically differentiate neurofibroma from pen , especially when an incisional biopsy has been performed .
the absence of marked fibrous capsule and the irregular arrangement of the neoplastic cells are the main differential clues seen in neurofibroma compared with pen .
the significant presence of mast cells , usually observed among tumoral cells of the neurofibroma , is also detectable using histochemical or immunohistochemical staining methods . as regezi and colleagues stated ,
pen / scn may be misdiagnosed clinically once identified somewhere in the mouth other than the palate .
this may be an obvious clinical impression since intraoral pen / scns are mostly found on the hard palate .
conversely , the tongue involvement comprises less than 8% of pen / scn cases . as for this case
, the pen resembled a pg on the dorsal surface of the tongue ( a common site for neurilemmoma and neurofibroma , but not for pen ) .
an erythematous lesion in a less commonly affected site rarely happens to be a pen . besides , the tongue is a potential site for pg .
have reported that pg is most commonly seen on the attached gingivae , tongue , lower lip and buccal mucosa .
the age of patient may be an important clinical parameter when the list of differential diagnoses of a lesion is formulated .
our patient was 48 years old , which was close to the recently reported average age for pg patients ( 52 years ) .
pyogenic granuloma usually occurs in patients older than 39 years , with equal gender distribution .
soft tissue enlargements of the oral cavity often present a diagnostic challenge because a diverse group of pathological processes can produce such lesions .
pyogenic granuloma can manifest as a painless smooth or lobulated mass with a surface that bleeds quite easily .
because of their high level of vascularity , young pgs are red , whereas older lesions are more collagenized and appear pink or normal colored .
clinically , oral pg occurs as an exophytic lesion manifesting as small , erythematous papule on a pedunculated or sometimes sessile base .
pyogenic granuloma arises in response to various stimuli such as chronic low - grade irritation , traumatic injury and hormonal factors .
however , the effect of female hormones on oral pg was questioned by bhaskar and jacoway since they found lesions both in males and females with no sex predilection .
palisaded encapsulated neuromas may be misdiagnosed clinically once they appear somewhere in the oral cavity other than the palate .
a pen arising on the dorsum of the tongue may mimic a pg with similar clinical morphology . even the patient s age may be misleading . on the other hand ,
peripheral nerve sheath tumors must therefore be included in the list of differential diagnoses for a pg - like lesion on the tongue .
 palisaded encapsulated ( solitary circumscribed ) neuromas ( pens ) are relatively common intraoral neurogenic tumors , which occur most frequently on the hard palate . 
 herein , we describe the clinicopathological characteristics of a palisaded encapsulated neuroma of the tongue . 
 this tumor was an exophytic sessile mass measuring 0.3 0.4 cm with rubbery consistency on the anterior one - third of the dorsum of the tongue . 
 the tumor was excised under the impression of a pyogenic granuloma ( pg ) . 
 no recurrence was reported at 12 months postoperatively . 
 histopathological examination showed a well - circumscribed mass that composed of interlacing fascicles of spindle cells . 
 the cells were s-100 positive . 
 the nuclei , showing parallel orientation within the fascicles , were wavy and pointed and showed no sign of mitotic activity . 
 giemsa staining revealed no mast cells within the stroma . 