Hemorrhoid With a Melanocytic Nevus

Reasons for rarity of anal melanocytic naevi

“…Therefore, we believe that anal naevi, as sun‐shielded lesions, appear to complete their differentiation and maturation faster and earlier than those of the skin and consequently lose their cellular and behavioural characteristics and undergo involution . The absence of dysplasia in reported cases supports this assumption, indicating that these lesions were on their way towards involution but were excised before its completion …”

“…AMN are rare and our literature search for sun‐shielded melanocytic naevi, immunohistochemical and molecular studies of skin and anorectal melanocytic lesions revealed only the seven definite cases . We add three additional cases (associated with haemorrhoids) making a total of ten cases reported in the literature over the last 15 years.…”

“…Consequently, they either remain overlooked, to be discovered incidentally on histological examination of an unrelated presenting anorectal condition, or persist to complete their determined involution and undergo atrophy . Furthermore, AMN may present as coloured skin rather than pigmented lesions and as such may be missed clinically . Routine rectal examination is also essentially a palpation procedure rather than inspection; therefore naevi located at a high level in the anal canal may be missed.…”

“…Cutaneous melanocytic naevi (CMN) are common lesions and most individuals have at least one, while anal melanocytic naevi (AMN) are rare, appearing in the literature mostly as genital, perianal and perineal naevi . Only seven definite AMN are well documented in the literature …”

“…Furthermore, the density of melanocytes in the anoderm and the anal canal is similar to that of the epidermis, also implying that the development of skin and anal melanocytic lesions, and consequently, their frequencies, are supposedly indistinguishable from each other, taking into account their common neuroectodermal origin. Therefore, with these common characteristics in mind, it is arguably sound to assume that AMN are not as rare as anticipated and that their occurrence may be hidden among reports of sun‐shielded naevi . The sun‐exposed lesions appear to have attracted most clinical and research attention due to their association with melanoma, leading to sun‐shielded lesions, including AMN, escaping separate recognition and reporting.…”