A melanocytoma is a rare pigmented tumor that has been described as a variant of the melanocytic nevus[1] and is a derivative of the neural crest.[2] The term "melanocytoma" was introduced by Limas and Tio in 1972.[3][4]
Histologically, the tumor is described by large, uniformly shaped polyhedral nevus cells that are pigmented and closely packed.[5] Typically, it lacks signs of malignancy such as high mitotic rate, necroses or infiltrative growth.[6] Like the malignant melanoma, it shows an immunohistological profile with S-100 protein-, vimentin- and HMB-45-positive tumor cells.[6]
Further information: Optic nerve tumor |
Most commonly the melanocytoma is found on or adjacent to the optic nerve[7] as the optical melanocytoma. The lesion can be found at any age. Location and size could lead to clinical symptoms. While the melanocytoma is generally considered to be a benign tumor,[7] it has a potential for growth, recurrence, and transformation to a malignant melanoma.[5] Because malignant transformation is rare, optical melanocytomas can usually be observed.[1] Thus, in asymptomatic patients, regular observation by fundoscopy is indicated, perhaps supported by ocular ultrasonography.[8][9][10]
The meningeal melanocytoma is found on the leptomeninges of the brain,[6][7] typically in the area of the base of the brain and brain stem,[2] or the spine.[4][11] Symptoms may be absent or related to growth and location. Like with the optic version, growth, recurrence, and malignant transformation are the main problems. Meningeal melanocytomas represent 0.06-0.1% of brain tumors.[12] In a 2003 review of 95 cases by Rahimi-Movaghar et al, 45 were intracranial (mostly supratentorial) and 50 spinal or along spinal roots.[13] The authors noted that the median age was 40 years for patients with intracranial and 49 for those with spinal tumors. Lesions were more common in women (57.9%). The review showed a recurrence rate of 26.3% and a death rate of 10.5% over 46 months.[13] A 2001 review by Rades et al concluded that complete resection is the best treatment.[14] If resection is incomplete, postoperative radiotherapy should be applied.[citation needed]
Pigmented tumors raise the possibility of a malignant melanoma, a condition that may present diagnostic and therapeutic dilemmas.[9] In the differential diagnosis, schwannoma and meningioma with pigmentation are to be considered as well.[11]
Melanocytomas have been described in animals, for instance, dogs and cats.[15][16]