a 75-year - old male farmer presented to a primary care skin cancer practice in west australia with a 6-month history of an enlarging painless lesion on his left cheek with no history of any possible precursor lesion .
there was a past history of treatment of two separate squamous cell carcinomas in - situ , one on the forehead and the other on an ear , in the previous two years .
other comorbidities included asthma , coronary heart disease , chronic obstructive pulmonary disease and arthritis .
there was no history of nevus sebaceous and there was neither history nor clinical signs suggestive of cowden s syndrome .
examination showed a single small non - pigmented nodular lesion located on the left cheek in continuation with a small , pigmented macular lesion ( figure 1 ) .
dermatoscopy ( figure 2 ) revealed a raised pink lesion , 3.5 mm in diameter , with a radial arrangement of vessels peripherally , with centered blood vessels in the middle of the lesion , these vessels being centered in skin - colored clods .
no keratin structures ( keratin scale , white structureless areas or white circles ) were seen . at one edge of this lesion , in direct contact with it , was a heavily pigmented flat lesion , 1 mm in diameter with a pattern of pigmented lines radial , converging ( figure 2 ) .
the lesion was subjected to an excision biopsy with a 4 mm peripheral margin and submitted for dermatopathological evaluation .
dermatopathology ( figure 3 ) showed both the trichilemmoma and bcc ( basal cell carcinoma ) components .
the trichilemmoma ( figure 3 a1 and a2 ) was a well - circumscribed , sharply demarcated lesion with surface papillomatosis , horn cysts and a degree of central desmoplasia . under high power an eosinophilic mantle of thickened basement membrane , mimicking the outer root sheath of the hair follicle infundibulum , was seen .
peripheral palisading was evident adjacent to the basement membrane and extending from that there were clear cells which were banal cytologically , lacked mitosis or individual cell necrosis ( apoptosis ) and contained an abundant amount of glycogen within their cytoplasm .
the bcc component ( figure 3 b1 and b2 ) showed superficial bcc at the dermo - epidermal junction . in the high power view melanin pigment
trichilemmoma is a benign tumor derived from the external sheath cells of pilosebaceous units   and desmoplastic trichilemmoma is a rare variant , which can present clinically with features suggesting invasive malignancy .
there has been controversy as to whether trichilemmomas are actually aged warts , this belief being proposed by well - known dermatopathologist bernie ackerman   but vigorously opposed by others including marty brownstein .
basal cell carcinoma is a malignant tumor , of trichoblast differentiation but uncertain origin , although it is probably of follicular derivation , predilection for non - glabrous skin being consistent with this .
trichilemmoma has previously been reported in association with bcc in the context of lesions arising in a preexisting nevus sebaceous .
in addition , three cases of desmoplastic trichilemmoma arising in association with bcc without a preexisting nevus sebaceous have been reported .
the dermatoscopy of four trichilemmomas has been reported   with images being presented for three of them . in the first case
keratin masses ; perivascular whitish halos  . the other three were reported together , with the first two described as having a hyperkeratotic central area with peripheral erythematous radial lines , the third having a  peripheral radiated red area .  all three were then presented as depicting what the authors called a  red iris like structure . 
examination of the photographs published in fact displayed a non - pigmented lesion in each case with a radial arrangement of vessels peripherally and structureless white centrally with some centred vessels . in the case
we report , the clinician interpreted the lesion as a pigmented lesion and assessed it using the chaos and clues decision - algorithm .
the lesion was regarded as chaotic ( asymmetrical ) with the clues of an eccentric structureless ( pink ) area as well as lines radial segmental , which lead to a clear decision to do an excision biopsy .
the pathologist , as is often the case with esoteric lesions , was able to deliver the answer to which particular type of malignancy this was .
the dermatoscopic features of the trichilemmoma presented here are consistent with those published previously , with a radial pattern of vessels peripherally and centred vessels centrally .
association with a bcc is a previously reported , unusual variation , consistent with both lesions having hair - follicle derivation .
this case demonstrates the utility of using a decision algorithm in esoteric cases with the final diagnosis to be delivered by the gold standard of dermatopathology .
 a case of trichilemmoma in continuity with a pigmented basal cell carcinoma is presented with dermatoscopy and dermatopathology . 
 the distinction between the two lesions was evident dermatoscopically and was confirmed dermatopathologically . while trichilemmoma has been reported in association with basal cell carcinoma and dermatoscopy images of four previous cases of trichilemmoma have been published , no previous dermatoscopy image has been published of trichilemmoma associated with basal cell carcinoma . 