Melanocytoma - A Rare Pigmented Tumor

What Is Melanocytoma?

Melanocytome, or magnocellular nevus, is a benign pigmented tumor that develops anywhere uveal melanocytes are present. The most frequently formed site is adjacent to or on the optic nerve head. Melanocytoma is a rare and pigmented tumor known to be a variant of melanocytic nevus. Melanocytic nevus refers to a non-cancerous disease of melanocytes (pigment-producing cells).

What Are the Different Forms of Melanocytoma?

Melanocytoma can occur in the eyes adjacent to the optic nerve or the brain of the meninges.

Optic Melanocytoma:

Optical or optic melanocytoma is a more common form. Here, the melanocytoma is seen adjacent to the second cranial nerve, called the optic nerve. There is no age or gender predilection for optic melanocytoma. The clinical symptoms occur according to the site and the size of the lesion. This condition is generally a benign tumor but can grow, progress, recur, and evolve into a malignant melanocytoma. However, malignant transformation occurs in rare instances.

Meningeal Melanocytoma:

This firm is typically found in the meninges (the membrane enveloping the brain and spinal cord) of the brain. Melanocytoma can generally form at the base of the brain, spine, or brain stem. Most cases of meningeal melanocytoma are asymptomatic. However, there can be symptoms associated with the site and growth. Meningeal melanocytoma accounts for about 0.06 to 0.1 percent of total brain tumors. The melanocytoma in the meninges can progress, recur, and evolve into a malignant transformation. The clinical reports say that complete resection of the lesion can be an effective treatment. Postoperative radiotherapy should be considered if the resection is incomplete.

What Are the Symptoms Associated With Optic Melanocytoma?

Optic nerve or optic melanocytoma generally does not present any symptoms or growth. But, if the lesion gradually proliferates, people with optic melanocytoma can experience the following problems. Visual field problems and acuity loss are possible as the tumor adjacent to the optic nerve could compress the nerve.

Acuity Loss: Optic melanocytoma generally does not cause significant visual acuity loss. However, about 25 percent of people could experience mild vision loss in their affected eyes. The predominant cause of vision loss in melanocytoma is retinal exudation with the involvement of the macula. Retinal exudation refers to fluid accumulation in the subretinal area or space (the space between the retinal pigmented epithelium and the sensory part of the retina). The risk factors for melanocytoma-associated vision loss include subretinal fluid (SRF) and the extension of melanocytoma lesions over the retina.

People with optic melanocytoma can only have mild vision impairment or loss. Severe vision loss is rare, but it can result in certain cases as secondary changes to central retinal vein occlusion (partial or complete obstruction of the central retinal vein), malignant transformation, and spontaneous necrosis of the lesion.

Visual Field Problems: Most people with optic melanocytoma experience visual field defects. About 90 percent of the cases would involve marked differences in perimetry (systemic measurement of the function of the visual field). However, the visual defects are symptomatic only in rare instances. The manifestations of visual field defects in optic melanocytoma include the following.:

• Enlarged blind spot as a result of the extension of the tumor lesion beyond the optic disc (optic nerve head) margin.

• Nerve fiber bundle defects are due to the compression of lesions at the optic disc.

What Are the Diagnostic Tests Used For Optic Melanocytoma?

• Ultrasound: This approach uses high-frequency ultrasound waves to determine and present detailed images of the eye and orbit.

• Optical Coherence Tomography (OCT): OCT is a non-invasive diagnosis that provides both inner and cross-sectional views of the retina. Such pictures help healthcare providers take direct photographs of developed eye images.

• Visual Field Testing: Visual field testing, also known as perimetry exam, predicts changes or defects in peripheral vision.

• Fluorescein Angiography: Fluorescein angiography is a diagnostic technique used to examine the optic nerve and retinal circulation. This technique involves a specialized camera and fluorescent dye for eye imaging.

• Optomap: This approach is the most common diagnostic method for assessing eye-related tumor lesions like melanoma and melanocytoma. This approach takes an image of the lesion with two distinct lasers (green and red). Optomap signifies whether the lesion is benign or malignant.

How Is Optic Melanocytoma Treated?

Optic melanocytoma does not need any type of intervention. However, diagnostic (imaging) and clinical follow-up should be done periodically. Following the appropriate diagnosis, repetition of visual field testing should be considered if there is a tumor suspicion. OCT can be used to diagnose and document the extent and progression of the lesion. Malignant transformation and its associated diagnosis should be considered if there is any vision loss.

If there is severe vision loss, suspicion of malignancy should increase. The healthcare providers consider the enucleation of the lesion.

What Are the Complications Associated With Melanocytoma?

The malignant transformation of melanocytoma is a profound complication associated with optic melanocytoma. In addition, this condition can sequentially enlarge, resulting in vitreous seeding (a condition characterized by vitreous cavities accumulated with floating tumor cells) and neovascularization (abnormal growth of new blood vessels) in very few cases.

What Are the Differential Diagnoses of Melanocytoma?

There is a condition that leads to dilemmas in diagnosing and treating melanocytoma. The pigmented tumor melanocytoma in the eye increases the probability of finding malignant melanoma. Malignant melanoma is a tumor that develops from melanocytes (pigment-producing cells).

The other differential diagnosis includes the pigmentation features of the following conditions.

• Meningioma: The meningioma, or meningeal tumor, is a slow-progressing tumor that develops from the meninges.

• Schwannoma: It is a benign nerve sheath cancer made up of Schwann cells. Schwann cells are chiefly utilized for insulating and providing nutrients to the nerve fibers.

Conclusion

Optic melanocytoma is a benign tumor that rarely presents a malignant transformation. However, it can exhibit clinical symptoms, growth, and certain complications. The clinical findings say that about ten to fifteen percent of the cases present subtle lesion progression over the years. Pigmented lesions of the optic disc can be the cause of such concern. The treatment of melanocytoma chiefly involves observation, diagnosis, management, and follow-up.