Infiltrating Giant Congenital Cellular Blue Nevus Of Neck Presenting As Melanoma

摘要

Blue nevus is an uncommon pigmented lesion of dermal melanocytes. By convention, two well defined histologic variants, designated as "common" and "cellular", have been recognized. These lesions have attracted much attention due to its confusion with malignant melanoma. We present a case of a giant congenital cellular blue nevus of neck clinically presenting as malignant melanoma and infiltrating vessels and underlying muscles resulting in incomplete removal. It is important to differentiate this lesion from malignant blue nevus and malignant melanoma on the basis of presence or absence of severe nuclear pleomorphism, nucleoli, mitotic activity and necrosis. However, malignant transformation is known to occur in these lesions and the importance of careful follow up is mandatory. This case highlights the difficulty in diagnosing this lesion and emphasizes the need for long term follow up in view of its uncertain malignant potential. Introduction Blue nevi are common lesions which represent arrested melanocytic migration. Histologically, there is presence of pigmented spindle and dendritic melanocytes in a focal area of reticular dermis. Cellular blue nevus is a distinctive variant of blue nevus suspected of being malignant because of its large size and intense pigmentation. These lesions tend to be 1-3 cm in diameter, usually solitary and present as elevated smooth-surfaced gray-blue papules or plaques. They are most commonly seen on buttocks, sacral region, occasionally on dorsal aspect of hands and feet and rarely on head and neck. Blue nevi can develop at any age but are usually noticed in second decade of life or later and are twice as common in women as in men. Although rare, malignant degeneration of cellular blue nevi can occur. Case Report We report a case of an unusually large pigmented tumor present in the neck of a 20yr old man extending from behind the left ear to the left angle of mandible and infiltrating left sternocledomastoid muscle (SCM). The tumor began as a small nodule behind the ear, a few weeks after birth, and gradually increased in size over the years. Patient was otherwise asymptomatic. A diagnosis of fibromatosis was made on the basis of FNAC report from an outside center and surgical removal was planned for cosmetic reasons. Intraoperatively, the tumor and surrounding vessels, muscles and facial nerve were all seen to be pigmented and tumor was seen infiltrating deep into SCM. Complete surgical resection was not possible because of infiltration and encasement of vital structures like facial nerve and carotid artery. A small skin flap was excised along with the tumor and the defect repaired. Postoperative period was uneventful.Histopathological FeaturesMacroscopic examination of specimen submitted for histopathological examination showed a black tumor mass measuring 15x10x5 cm with a small skin flap (Fig 1).