Amelanotic / hypomelanotic melanoma
Amelanotic/hypomelanotic melanomaThis glossary term has not yet been described. (AHMThis glossary term has not yet been described.) represents 2-8% of all melanomas, but its real incidence is difficultneeding much effort or skill to accomplish to estimate because at the beginning it is often misdiagnosed and/or confused with inflammatory diseases, benignis any condition that is harmless in the long run tumors and other malignantThis glossary term has not yet been described. tumors (i.e. actinic keratosisActinic keratosis (also called solar keratosis and senile keratosis; abbreviated as AK) is a pre-cancerous patch of thick, scaly, or crusty skin. These growths are more common in fair-skinned people and those who are frequently in the sun. They usually form when skin gets damaged by ultraviolet (UV) radiation from the sun or indoor tanning beds. AKs are considered potentially pre-cancerous; left untreated, they may turn into a type of cancer called squamous cell carcinoma. Untreated lesions have up to a 20% risk of progression to squamous cell carcinoma, so treatment by a dermatologist is recommended., Bowenalso known as squamous cell carcinoma in situ is a neoplastic skin disease. It can be considered as an early stage or intraepidermal form of squamous cell carcinoma. It was named after John T. Bowen’s disease, basal cell carcinomais the most common skin cancer, and one of the most common cancers in the United States. While BCC has a very low metastatic risk, this tumor can cause significant disfigurement by invading surrounding tissues, keratoacanthomaThis glossary term has not yet been described., Merkel cell carcinoma, pyogenic granulomaThis glossary term has not yet been described., haemangioma, wart, etc). Definitely, if singly evaluated, the real prevalence of amelanotic melanomatype of skin cancer in which the cells do not make melanin is very low, since many of these tumors present a residual pigmentation that can be seen mostly at the periphery and should be considered hypomelanotic rather than amelanotic. The low or absent melanin production and the presence of regressionThis glossary term has not yet been described. are the two reasons why melanomaThis glossary term has not yet been described. could be amelanotic or hypomelanotic; both these phenomena may even occur within the same lesion.
AHM has been classified in several variants:
- True amelanotic melanoma (melanoma not producing any trace of pigment)
- Hypomelanotic melanomaThis glossary term has not yet been described. (with low production of melanin that may extend to the entire lesion)
- Partially pigmented melanoma(with a pigmentation occupying less than 25% of the lesion)
- Regressive melanoma (in advanced stages of regression)
AHM often occurs in sun-exposed skin of older people and appears as a flat lesion, but more frequently as an elevated tumor, firm on palpation, and typified by rapid growth. This three characteristics (EFG: Elevation, Firmness, Growth) represent a precious clinical guide in melanomas without the classical ABCDThis glossary term has not yet been described. clinical criteriameasure of how well one variable or set of variables predicts an outcome.
By dermoscopyDermoscopy is a non invasive diagnostic method., the diagnostic cluesEvidence, in an investigation for AHM are the vascular structuresThis glossary term has not yet been described., often also difficult to detect because require a minimal pressure of the dermatoscopeThis traditionally consists of a magnifier (typically x10), a non-polarised light source, a transparent plate and a liquid medium between the instrument and the skin, and allows inspection of skin lesions unobstructed by skin surface reflections. Modern dermatoscopes dispense with the use of liquid medium and instead use polarised light to cancel out skin surface reflections. on the lesion to avoid the compression of the blood vesselsare the part of the circulatory system, and microcirculation, that transports blood throughout the human body. As general rule, six main categories of vascular morphologies can be seen in tumoral lesions: comma vesselslinear curved short vessels dermal nevi (in intradermal neviThis glossary term has not yet been described.); dotted vesselstiny pinpoint vessels flat melanocytic lesions inflammatory diseases Bowen disease (in melanocyticThis glossary term has not yet been described. lesions, especially Spitz neviThis glossary term has not yet been described. and melanoma); linear–irregular vesselsThis glossary term has not yet been described. (in melanoma and other skin malignancies); arborizing vesselsanalytic term is branched vessels; Bright red sharply in focus large or thick diameter vessels dividing into smaller vessels; BCC (in basal cell carcinoma); hairpin vessels (in keratinizing tumors, especially if surrounded by a whitish halo, and melanoma); and glomerular vesselsThis glossary term has not yet been described. (in Bowen’s disease). Moreover, also the following three specific global morphologies can be identified: crown vesselsRadial serpentine or arborizing vessels at the periphery of the lesion that radiate towards the center but do not cross the midline od the lesion. sebaceous hyperplasia surrounding a white center, strawberry patternReddish pseudo-network (erythema and wavy fine vessels) around hair follicle openings which are accentuated with a white halo appearance and milky-red areas/globulesThis glossary term has not yet been described.. (Fig.1)
The most common vascular structures in AHM are dotted vessels, linear-irregular vessels, hairpin-irregular vessels, serpentine vesselslinear irregular linear vessels with multiple bends flat BCC melanoma or a combination of them (polymorphic vessels); also milky-red areas can be frequently visualized.MorphologyThis glossary term has not yet been described. of vessels modifies during tumor growth. In fact, in early stages, the vessels often appear short and homogenous in shape, while in the advanced tumors, they appear longer and irregular. In thin melanoma (less than 0.5 mm Breslow thickness) the vessels are usually pointThis glossary term has not yet been described.-like with a rather regular arrangementThis glossary term has not yet been described.. Tumors of 0.5–2mm thickness show both point-like and hairpin vessels, again with a regular arrangement. When thickness is over 2 mm the hairpin loops are more twisted, splintered and irregularly distributed, while melanomas of more than 3 mm of thickness develop polymorphic vessels. A multicenter retrospective study from Menzies et al. evaluated several amelanotic and hypomelanotic melanomas to determine the diagnostic accuracy of various dermoscopic features. Positive predictors included blue-white veil, scar-like depigmentationArea of white that is whiter than surrounding normal skin (true scarring). It should not be confused with hypo- or depigmentation due to simple loss of melanin. Shiny white structures and blood vessels are not seen in areas of regression., multiple blue-gray dotsDots are small, round structures of less than 0.1 mm in diameter that have a red color when corresponding to blood vessels; however, when due to melanin, their color ranges from black, brown, to blue-gray depending on the depth and concentration of the melanin in the skin (Tyndall effect)., irregularly shaped depigmentation, irregular brown dots or globules, 5 to 6 colors within the same lesion and peripheral light brown structureless areas covering more than 10% of the lesion. Among vascular features, the positive predictors were predominant central vessels, milky red-areas, more than one shade of pink, and a combination of dotted and linear irregularlinear vessels with multiple bends vessels. The most significant negative predictors of melanoma were multiple (>3) milia-like cystsThis glossary term has not yet been described., the predominance of comma vessels with a regular arrangement, a symmetrical pigmentation, and regular and multiple blue-gray globules (Fig.2, 3,4,5,6,7).
ReferencesThis is material contained in a footnote or bibliography holding further information.
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