palisaded encapsulated neuroma ( pen ) is a benign neural tumor , which usually presents as small , solitary , asymptomatic , firm , skin - colored , or pink papule , or nodule , almost always present on the face or close to a mucocutaneous junction .
palisaded encapsulated neuroma ( pen ) is a distinctive benign neural tumor , which usually presents as small , solitary , asymptomatic , firm , rubbery , skin - colored or pink papule or nodule , almost always present on the face or close to a mucocutaneous junction .  
it commonly occurs in middle - aged adults with female to male ratio of 1:1 .
rarely it can present with multiple lesions .   despite the fact that it is not uncommon ,
clinically , pen is most commonly confused with neurofibroma , basal cell carcinoma , nevus , or skin appendage tumor .  
pen has histological appearance between that of a neurofibroma and a schwannoma situated predominantly in the dermis .
differentiation from neurofibromas is essential , because the latter is often associated with neurofibromatosis , and has a propensity for malignant transformation .
pen has no association with neurofibromatosis or multiple endocrine neoplasia syndrome type 2b ( men 2b ) .
even after incomplete excision pen does not recur , a fact supporting a reactive rather than a neoplastic origin . here , we present a rare case of multiple cutaneous pen in a dermatomal distribution on the face not associated with neurofibromatosis or men 2b .
a 30-year - old female patient presented to us with asymptomatic skin lesions on the face of 4 years duration .
these lesions began as pinhead sized elevations and gradually grew in size to the present state . on examination , lesions were multiple , discrete , mostly multi - lobulated , flesh colored , soft to firm , papules , and nodules arranged in a curvilinear fashion on the face [ figure 1 ] starting from tip of the nose and gradually deviating to the left along the nose , left eyebrow , and forehead region along the distribution of the ophthalmic division of the trigeminal nerve .
routine blood investigations , chest x - ray , ultrasonography of the whole abdomen were normal .
skin biopsy specimen showed a tan granular surface of the base and histopathological examination revealed a normal epidermis . in the dermis
, there was a partially encapsulated , well - circumscribed nodule [ figure 2 ] composed of fascicles of small spindle cells with wavy nuclei interlaced with small slits and clefts [ figure 3 ] .
we had sent the patient to the plastic surgery out patient departmentfor excision of the lesion .
multiple , discrete , flesh colored , soft to firm , papules and nodules arranged in a curvilinear fashion on the face multiple partially encapsulated , well - circumscribed nodules in the dermis ( h and e , 40 ) fascicles of small spindle cells with wavy nuclei interlaced with small slits and clefts ( h and e , 100 ) tumor mass showing positive s-100 ( immunohistochemical staining , 100 )
pen of the skin was first described by reed et al . in 1972 .  
it is an infrequent , benign cutaneous neural tumor , clinically misdiagnosed as a neurofibroma , basal cell carcinoma , melanocytic nevus , epidermal cyst , or skin appendage tumor , with a histological appearance between that of a neurofibroma and a schwannoma .  
common differentials of papule / nodules on the face are presented in table 1 . despite the relatively high - incidence of this tumor ,
common differentials of papule / nodules on the face pen clinically presents as solitary , asymptomatic , firm , sessile , immobile , rubbery , skin - colored or pink dome - shaped papule or nodule , commonly present on the face or close to a mucocutaneous junction .  
the lesions have also been found on the trunk , shoulder , arm , oral mucosa , eyelid , and glans penis .  
it is usually found in middle - aged adults with equal incidence in both sexes .
clinically , it is difficult to differentiate pen from neurofibroma because of their similar clinical presentation ; though the lesions of pen are commonly present on the face , usually firm with absence of  buttonhole  sign ; whereas in neurofibroma the lesions are mostly present on the trunk , usually soft where  buttonhole  sign can be elicited .
they are composed of a partially encapsulated mass of schwann cells arranged in interlacing fascicles separated by small clefts , interspersed with a variable amount of tiny axons .  
although the nodular growth pattern is most frequently encountered , other types include epithelioid , plexiform , multi - nodular and fungating .  
immunohistochemical analyses reveal that tumor cells stain positively for s100 protein , collagen type iv and vimentin characteristic of schwann cell differentiation .
the capsule is composed of elongated perineural cells that stain positively for epithelial membrane antigen .  
the histological differential diagnosis for pen includes neurofibroma , schwannoma , traumatic neuroma and leiomyoma .   unlike pen ,
neurofibromas lack a capsule , contain mucopolysaccharide ground substance , and have fewer axons with myelin sheaths .  
schwannomas are typically found subcutaneously , contain antoni a and b type tissue with verocay bodies , and do not have axons .  
overall , the pen accounts for approximately 25% of all nerve sheath tumors of the dermis .
traumatic neuromas have axonal and schwann cell proliferation , however , scarring and inflammatory cells are evident as well .
leiomyomas are spindle cell tumors composed of muscle cells readily differentiated by immunohistochemistry where they are consistently positive for desmin .
so patients can be reassured that excision is curative with a minimum possibility of recurrence , which reduces unnecessary further testing or concern to search for systemic diseases or malignancy .
a similar presentation of linearly arranged papules , and nodules on the neck and forehead with diagnosis of collagenoma was reported .  
clinicians should include pen in the differential diagnosis of fleshy papules presenting on the nose and forehead for the purpose of obtaining wider recognition of the tumor , which responds well to excision .
multiple cutaneous pen in a dermatomal distribution on the face in a middle aged female is a very rare presentation .
 palisaded encapsulated neuroma ( pen ) is an infrequent benign cutaneous neural tumor , which usually presents as solitary , asymptomatic , papule or nodule , often localized on the faces , around the orifices , in middle age with no sex preponderance . 
 rarely , it can be multiple . 
 both solitary and multiple lesions are not associated with neurofibromatosis or multiple endocrine neoplasica syndrome type 2b ( men 2b ) . 
 we hereby report , a rare case of multiple cutaneous pen in a 30-year - old female who presented with multiple asymptomatic soft - to - firm papules and nodules in a dermatomal distribution on the face along the supply of the ophthalmic division of the trigeminal nerve with no signs of neurofibromatosis or men 2b . 
Introduction
Case Report
Discussion