Description : Blue Nevus - Dermal-based benign melanocytic lesion.(Jaddasohn-Tieche)
There are two main types of blue nevus: cellular and common,which has been distinguished by the degree of fibrosis.
Blue lesions include blue nevus,vascular lesions-hemangioma,congenital and acquired melanocytic nevi,primary melanoma,metastatic melanoma and tattoo(traumatic or asthetic).
They can be benign or malignant lesions with differential diagnosis include blue nevi,pigmented basal cell carcinoma,combined nevus,primary or metastatic melanoma and hemangioma which involves the dermis.That is why blue lesions can be melanocytic and non melanocytic.Examiner should approach systematically when analyzing blue lesions.
Blue colour could indicate melanin in the deep dermis ,so shave biopsy of these lesions may not be appropriate.
Important differential diagnosis of blue nevus, especially cellular blue nevus is with nodular and metastatic melanoma.History of long standing nature and nil changes noted by the patient is not always reliable yet helpful to the examiner.In melanoma,subtle features as vascular pattern,remnant of pigment network,blue-white structures and combination of blue-black colouration could be seen.If in doubt,get a histopathological diagnosis because some metastatic melanomas could mimic blue nevus clinically and dermoscopically.
Example : Blue Nevus(Blue'common'Blue Nevus). Left arm. Confluent steel-blue colour with white veil all over the lesion.This blue nevus is on the left arm of a 76 year old lady.
Example : Blue nevus(Black'compound'Blue Nevus). Above the left lateral malleolus. This nevus was biopsied to rule out metastatic melanoma due to its satellite(skip macules) lesions.(Image courtesy of Dr Ian McColl)
Example: Nodular melanoma. Melanoma with blue white structures.Blue colour corresponds to melanosis in mid dermis and white colour corresponds to orthokeratosis of stratum corneum and fibrosis of papillary dermis.(Image courtesy of Dr A Cameron)
Example: Haemangioma with predominantly bluish colouration.Light blue tinge or veil indicates deep dermal involvment.This haemangioma is on the left thigh of a 46 year old man.He was concerned with the bluish appearance.Unnecessary biopsy was avoided due to the dermoscopic findings.
SPITZOID LESIONS.
Description : Lesion with starburst pattern appearance.Differential diagnosis will include atypical(Clark) nevus,Spitz nevus and melanoma.In some instances both dermoscopy and histopathology could not definitely diffentiate between spitzoid lesion and melanoma.
Sophie Spitz described these 13 cases of ‘childhood melanoma’ in 1948.Although it was regarded as benign ,one died of metastasis.
Symmetrical starburst pattern is more indicative of benign lesion while asymmetrical starburst pattern is a high risk feature of melanoma.It is still debating about the spitzoid lesions terminology and diagnostic criteria including ‘atypical spitz nevus/tumour,malignant spitz nevus and metastasizing spitz nevus.
Among the different patterns of Spitz nevi : atypical pattern with asymmetry, different colours with black,brown gray to blue pigmentation,different structures and pinpoint vessels can cause difficulty to distinguish between a benign and malignant lesion by dermoscopy alone.
Because of these findings, surgical excision is recommended for clinically atypical( large >1 cm,ulcerated,rapidly changing) spitzoid lesions of childhood and for all spitzoid lesions of adulthood.(G.Ferrara et al.)
EXAMPLE: Spitz nevus on the left calf. 3 year old girl with history of nevus appearing six months ago on the left calf.She was brought in by her mother to check her congenital nevus on the right hip.
Example: Spitz nevus with dark brown homogeneous centre and large peripheral globules.(Image courtesy of Dr Ian McColl)
Example: Atypical Spitz nevus.It is a melanoma mimic. (Image courtesy of Dr Tim Hackett)
Example : Melanoma with spitzoid features.Histopathologically rim of globules represent nests of melanocytes along the dermo-epidermal junction at the periphery of the lesion.The nests could become confluent at the periphery as the lesion progresses forming streaks and pseudopods.This is an example of a "False Negative Melanoma" or "Melanoma Simulating Spitz Nevus".Small percentage of melanomas can have a symmetrical starburst pattern.(Image courtesy of Dr Ben Cook)
INK-SPOT LENTIGO.
Description
These lesions have typical ,prominent,black,thickened pigment network over the entire lesion.Because of its dark,thickened pigmentation it can be mistaken for melanoma.They are usually less than 5 mm in diameter, situated in the sun exposed areas especially the upper trunk and in single lesion surrounded by solar lentigenes.First described by J.Bolognia in 1992 as darkly pigmented actinic lentigo which can be found in people with Celtic ancestry(skin phototype I-II) and clinically resembles melanoma in-situ.
Synonyms: acquired reticulated or reticular lentigo,reticulated black solar lentigo,reticulated melanotic macule.
Example: Ink-spot lentigo.This variant form of inkspot lentigo,if they have dark structureless centre, can be mistaken for reticular type of Clark nevus or even melanoma.In that case,it is justifiable to consider taking a biopsy of the lesion to get histopathological diagnosis.
Example: Ink-spot lentigo.Dark pigmented reticular lines without the features of melanoma.Another differential diagnosis of reticulated lentigo is Reed nevus.
