blue nevus is an acquired benign melanocytic nevus described as a blue or blue - black , firm papule , nodule or plaque - like lesion occurring on the skin and mucous membranes .
malignant blue nevus is rare , and a common blue nevus rarely needs a differential diagnosis from malignant melanoma .
although a melanocytic nevus with a satellite lesion is usually suggestive of a peripherally disseminating malignant melanoma , very few cases of blue nevus with satellite lesions have been reported thus far [ 1 , 2 , 3 , 4 , 5 , 6 ] . to our knowledge , this is the seventh case of a blue nevus with satellitosis .
a healthy 24-year - old japanese man was referred to our hospital with a blue - black skin lesion on his left forearm . as confirmed by the patient
, this lesion had developed after he accidentally pricked his forearm with a pencil 13 years earlier .
physical examination revealed a 10  7-mm , blue - black nodule with an irregular border , which was accompanied by 12-mm guttate macular satellite lesions ( fig .
dermoscopic examination showed a homogeneous , blue - white structure in the absence of any other dermoscopic structures ( fig .
an excisional biopsy was performed with the suspicion of a common blue nevus versus a malignant melanoma .
the lesion was excised with a 3-mm margin of surrounding normal skin down to the level of the superficial fascia .
we recognized a black - colored restiform structure in the dermis during the operation and added another 3-mm margin . in the histopathological examination of the excised lesion ,
nevus cells were dispersed in the dermis , and hyperpigmented , spindle - shaped melanocytes infiltrated among the collagen bundles ( fig .
there were no features suggestive of malignancy , such as cytological atypia , atypical mitoses or necrosis .
common blue nevi are usually solitary , blue - black , dome - shaped papules , and are not difficult to diagnose .
however , in a very small number of cases [ 1 , 2 , 3 , 4 , 5 , 6 ] , including our case , a blue nevus can be accompanied by satellite lesions .
this is when the physician needs to differentially diagnose it from malignant melanoma , especially the nodular type . under a dermatoscope
, a blue nevus usually shows a typical steel - blue , homogeneous coloration generated by the presence of heavily pigmented melanocytes in the dermis , in the absence of any other dermoscopic structure .
however , a recent study   showed that a wide spectrum of local dermatoscopic features ( whitish , scar - like depigmentation , dots / globules , peripheral streaks or vessels ) may also be observed in blue nevi
. in such cases , clinical and dermatoscopic distinction from a malignant melanoma may be difficult , or impossible , and surgical excision is necessary .
kang and chung   reported that nevus cells aggregated densely around the blood vessels in the main papule , and also in the satellite lesions , suggesting that nevus cells may spread along the perivascular space to manifest clinically as guttate or linear satellite lesions . in our case ,
periappendageal and perivascular concentrations of nevus cells were observed in the main papule as well as in the satellite lesions .
clinically , we recognized a black - colored restiform structure in the dermis during the operation .
these findings suggest that blue nevus cells could infiltrate along the perivascular area in the dermis and form multiple satellite lesions . in conclusion
, we suggest that a blue nevus should be considered as a differential diagnosis when a locally disseminating malignant melanoma is suspected .
 malignant blue nevus is rare , and a common blue nevus rarely needs a differential diagnosis from malignant melanoma . 
 although a melanocytic nevus with a satellite lesion is usually suggestive of a peripherally disseminating malignant melanoma , very few cases of blue nevus with satellite lesions have been reported thus far . to our knowledge , this is the seventh case of a blue nevus with satellitosis . 
 periappendageal and perivascular concentrations of the nevus cells were observed in the main papule as well as in the satellite lesions . 
 these findings suggest that blue nevus cells could infiltrate along the perivascular area in the dermis and form multiple satellite lesions . 
 blue nevus should be considered as a differential diagnosis when a locally disseminating malignant melanoma is suspected . 
Introduction
Case Presentation
Discussion