kcm is itself very rare and distinct type of keratoacanthoma which usually occurs over extremities and scalp is unusual site for development of lesion . treatment is difficult as lesion of kcm present with large raised , rolled borders with peripheral extension . keratoacanthoma ( ka ) is a rapidly evolving tumor , composed of keratinizing squamous cells originating in pilosebaceous follicles and resolving spontaneously if left untreated . it is relatively common , especially in whites occurring in middle age while being uncommon in dark - skinned . . it presents as firm , rounded , flesh - colored or reddish papule ; with a rapid growth phase becoming 10 - 20 mm and then spontaneous healing taking place over three months . there are three rare clinical variants of solitary ka , namely giant ka , keratoacanthoma centrifugum marginatum ( kcm ) and subungual ka . in kcm , lesions are large , reaching upto 20 cms . the most common locations are dorsa of hands and legs , lesions on scalp being rare . we report a rare case of kcm occurring on the scalp which is an unusual site . a 62-year - old male , watchman by occupation presented with asymptomatic raised lesion on scalp since one year . lesion had developed de novo , as a pea sized lesion with gradual increase to cover entire vertex . cutaneous examination revealed a single , irregular , 12  15 cm , yellowish plaque on vertex of scalp with nodular surface and a central crater [ figure 1 ] . on palpation , the plaque was firm , non - tender , non - indurated and not attached to underlying structure . ultrasonography of lesion showed ill defined hypo echoic mass involving epidermis , dermis and subcutaneous tissue . a single , irregular , 12  15 cm , yellowish plaque on vertex of scalp with nodular surface and a central crater . deep punch biopsy revealed exoendophytic , globular , well circumscribed central cup shaped crater , epidermal invagination with marked hyperkeratosis and horn cyst with rich keratin filled crater imparting glassy appearance and well demarcated regular base . . marked epidermal proliferation with crater formation with horn pearls and inflammatory infiltrate at the base of the lesion was suggestive of a fully developed lesion of kcm . complete surgical excision with grafting was done successfully with dramatic improvement with no recurrence at 9 months [ figure 5 ] . exoendophytic , globular , well circumscribed central cup shaped crater , epidermal invagination with marked hyperkeratosis and horn cyst with rich keratin filled crater imparting glassy appearance and well demarcated regular base epidermis forming buttress over the pseudhorn cyst dense nodular lymphocytic infiltrate in the upper dermis surgical excision with grafting the etiology is multifactorial that includes chronic ultraviolet ray exposure , smoking , contact with chemical carcinogens like pitch , mineral oil , tar , trauma and vaccination . the role of human papilloma virus remains inconclusive but in one study , hpv type 6 and 11 were detected within the lesion . it can be localized to any region of the body but is more frequently seen on dorsum of hands and legs . progressive peripheral extension with a raised rolled - out margin and atrophy at the centre is a characteristic feature of kcm . the margin of the lesion showing multiple comedonal orifices giving rise to a cribriform pattern may represent a unique phenomenon of kcm . it is hypothesized that this typical appearance may arise as a result of sequential involvement of multiple adjacent hair follicles in a centrifugal fashion . kcm does not show tendency for spontaneous regression , a feature also seen in giant ka , which grows rapidly reaching a size of 5 cm or more and occurring commonly on nose and eyelids . kcm is differentiated from giant ka by absence of downward vertical spread and destruction of underlying tissue . nevertheless , in giant ka spontaneous involution takes place after several months , often accompanied by detachment of a large keratotic plaque . the other differential diagnoses include squamous cell carcinoma , lupus vulgaris , botryomycosis , blastomycosis - like pyoderma and pseudoepitheliomatous hyperplasia , hypertrophic lupus erythematosus , atypical mycobacterial infections , or deep fungal infections . there are reports that kcm has been treated successfully with oral retinoids ( acitretin , etretinate , or isotretinoin 0.5 - 1 mg / kg / day ) which should be given until complete clearance of lesion . surgical intervention is a preferred mode of therapy keeping in mind that a wide excision is performed to prevent subsequent recurrence . other treatment modalities successfully used include topical 5-fluorouracil , intralesional injections of interferon alpha , methotrexate , or bleomycin , or mohs micrographic surgery . in kcm , lesions are usually too large for excisional biopsy for diagnosis , but certain characteristic features like clinical behavior , appearance of lesions , histological features ( hyperkeratosis and hyperplasia ) , and cytological features ( tumor cells with eosinophilic and glassy cytoplasm , few mitoses ) help clinch the correct diagnosis . first time from india we are reporting case of kcm presenting over scalp which is successfully treated with surgical excision without any recurrence .
keratoacanthoma ( ka ) is a rapidly evolving tumor , composed of keratinizing squamous cells originating in pilosebaceous follicles and resolving spontaneously if left untreated . 
 it is relatively uncommon in dark - skinned and occurs in middle aged individuals . 
 males are three times more affected than females . 
 it presents as firm , rounded , flesh - colored or reddish papule ; with a rapid growth phase followed by spontaneous healing over three months . 
 two types of ka exist i.e. , solitary and multiple . 
 there are three rare clinical variants of solitary ka , namely giant ka , keratoacanthoma centrifugum marginatum ( kcm ) and subungual ka . in kcm , lesions are large , reaching upto 20cms . 
 there is peripheral extension with raised , rolled border and atrophy in the center . 
 there is no tendency toward spontaneous involution . 
 the most common locations are dorsa of hands and legs , lesions on scalp being rare . 
 a rare case of kcm occurring on scalp which is an unusual site is reported .