pilomatricoma also known as benign calcifying epithelioma of malherbe is an uncommon slow growing benign adnexal skin tumor , which differentiates towards the hair matrix .
, we report a case of pilomatricoma with bullous appearance in a young female which is rare , and also review the literature on bullous pilomatricoma .
a 17-year - old girl presented with a solitary reddish semi - transparent blister over her right upper arm since 3 months .
initially , the lesion started as a solid pin - head sized papule , which gradually progressed to form a semi - transparent blister with a hard nodule inside .
no history of similar lesions in the past or in family members . on examination , single 2 cm sized erythematous semi - transparent bullae with a white nodule was seen on the medial aspect of the right upper arm [ figure 1a and b ] .
on palpation , the bullae had a jelly like consistency and the nodule underneath was hard . on puncturing the lesion , it oozed a jelly like material .
( a and b ) 2 cm sized erythematous semi - transparent bullae with a white nodule inside photograph of a bouncy ball routine investigations were normal and excision biopsy was carried out [ figure 3 ] .
histopathology revealed islands of basaloid cells with central abrupt keratinization and dilated lymphatics with dermal edema [ figures 4 and 5a ] .
ghost cells ( shadow cells ) [ figure 5b ] , foreign body giant cell reaction [ figure 5c ] , and small foci of calcification were also seen [ figure 5d ] . with these findings ,
gross specimen of excised material histopathological features of excision biopsy showing islands of basaloid cells with central abrupt keratinization , shadow ( ghost ) cells , and dilated lymphatics with dermal edema ( h and e , 10 ) ( a ) basaloid cells undergoing abrupt keratinization ; ( b ) ghost cells / shadow cells ; ( c ) foreign body giant cell reaction ; ( d ) small foci of calcification ( h and e , 40 )
pilomatricoma is a benign tumor considered to be a hamartoma of the hair matrix composed of cells resembling those of the hair matrix , cortex , and inner root sheath .
it makes up around 20% of all hair follicle - related tumors and is the commonest hair follicle tumor .
majority of patients are under 20 years of age , and females are affected more often than males .
it is usually a solitary , deep dermal or subcutaneous tumor 3 - 30 mm in diameter situated on the head , neck or upper extremities .
clinical variants include , large ( giant ) , extruding or perforating lesions , ulcerative lesions , multiple eruptive cases , familial cases , superficial pilomatricoma presenting as a cutaneous horn and bullous pilomatricoma .
association with myotonic dystrophy , gardner 's syndrome , turner 's syndrome , and rubinstein taybi syndrome have been reported with pilomatricoma . however , no such associations with bullous pilomatricoma has been reported .
reports on bullous variant of pilomatricoma is sparse , and only 17 cases have been reported worldwide until date out of which only two cases are reported from india .
bullous pilomatricoma has a predilection for occurring on the shoulder and upper arm regions , predominantly in females .
it can also be found on the neck , trunk , eyelid , and scalp .
the peak age of presentation is 10 - 20 years , and mostly of sizes 1 - 3 cm .
usually presents as a solitary , flaccid , thick - walled red bullae with an underlying palpable hard nodule .
our present case is consistent with these reports . since our case resembled a bouncy ball , we would like to coin this as the  bouncy ball  sign in bullous pilomatricoma .
histopathological hallmarks of pilomatricoma are the tumor nests of basophilic cells and eosinophilic shadow cells .
bullous variant in addition to these findings , show dilated lymphatic vessels , giant cell reaction , lymphoedema , disruption of collagen fibers , dilated blood vessels , fibrous capsule , calcification , nests of transitional cells , and necrosis .
our case is consistent with these findings which showed islands of basaloid cells with central abrupt keratinization , shadow cells , dilated lymphatics with dermal edema , foreign body giant cell reaction and small foci of calcification .
it could be due to mechanical irritation , or it could be a pseudoblister since the bullae - like spaces are filled with lymphatic fluid .
another theory , suggests that the tumor cells or infiltrating inflammatory cells produce elastinolytic enzymes which disrupt the collagen fibers and destruct and dilate the lymphatic vessels , which lead to accumulation of lymph fluid in the dermis causing a bullae .
however , the widely accepted theory is that obstruction of lymphatic vessels and congestion of lymphatic fluid caused by the growth of tumor nodule causes dilatation of lymphatic vessels , leakage of lymphatic fluid , and edema in the dermis surrounding the tumor resulting in the bullous appearance .
malignant change ( pilomatricarcinoma ) is recorded in several cases , and appears to arise chiefly in large pilomatricomas that have been present for a long time .
, dermatologists should be aware of this rare variant of pilomatricoma and excision biopsy is the norm for diagnosis and treatment of this condition .
 pilomatricoma ( pilomatrixoma ) or calcifying epithelioma of malherbe , is a tumor with differentiation toward hair cells , particularly hair cortex cells . 
 it frequently presents as a firm , deep - seated nodule that is covered by normal skin . 
 bullous pilomatricoma is an unusual clinical variant . 
 reports on bullous variant of pilomatricoma is sparse , and only 17 cases have been reported world - wide until date out of which only two cases are reported from india . 
 we present a report of a 17-year - old female with a solitary reddish semi - transparent blister over her right upper arm since 3 months resembling a bouncy ball . 
 histopathology revealed tumor nests of basophilic cells and eosinophilic shadow cells , which are consistent with pilomatricoma . 