Malignant melanoma is a potentially fatal tumor that arises from melanocytes, most often in the sun exposed skin (1). Less commonly, melanoma originates from other tissues and mucous membranes such as conjunctiva. Conjunctival melanoma represents only 1.6% of all non-cutaneous melanoma, being the most infrequent of the ocular melanomas (8). It is proposed to originate from preexisting conjunctival nevus (as Ota's nevus) or primary acquired melanosis (PAM) or melanoma de novo (10). On the other hand, ooccupational skin cancers resemble skin tumors found in non-occupational subjects (including melanoma) and have particularly been due to industrial exposure of human beings to chemical carcinogens such as arsenic, ionizing radiation such as X-rays and polycyclic hydrocarbons (e.g. from coal tar products). Besides, an uncommon but well-recognized cause of occupational skin cancer is that which results from scar formation following an industrial burn(5). Some of that mechanism might have promoted the appearance of the initial conjunctival lesion in our case. The most important factors that affect patient outcome include greater tumor thickness and base, epithelioid cell type, and, if PAM is present along with the melanoma, then the following factors are significantly related to patient death: the presence of atypical melanocytes, pagetoid invasion, in situ growth pattern, caruncular and palpebral involvement, rarity of small polyhedral cell, lack of inflammation and high mitotic activity (4,9). Recurrence has been related to tumors not touching the limbus (extralimbal) (7,10), extension to the margins on histopathology (10) development of metastasis and treatment modality of the primary tumour (7). Therefore, proper surgical planning with wide tumor free margins is important (7,10). Usually, conjunctival melanomas, like those of the skin, first metastasize to draining regional lymph nodes, being the preauricular chain the most commonly involved (3), although distant metastasis in lung, liver, digestive tract, brain, bones, glands and skin have been reported (3,7,10). Development of metastasis has been related to tumors not touching the limbus (extralimbal) (10), extension to the margins on histopathology (10), tumour thickness over 2mm (7) and multilocular tumors (7). Isolated distant metastases (without evidence of prior or concurrent regional lymph node involvement) have been reported, especially in patients with history of local recurrence. The presence of more aggressive histological features in recurrent melanoma could enable tumor cells to skip the lymph nodes. On the other hand, hematogenous spreading to distant organs may occur following multiple surgical interventions for recurrence (2,3). Based on it, our patient did not show perioperative evidences to become a candidate for isolated distant metastases. The diagnosis of metastatic conjunctival melanoma requires close ophthalmological and systemic follow up at regular interval. High index of suspicion along with typical MRI findings help to confirm the diagnosis. Melanin produces stable free radicals, causing paramagnetic effect that shortens T1 and T2 relaxion values on MRI. This results in hyperintensity of the lesion on T1 and T2-weighted images (6).
Contributed by by Julio César Gutiérrez Morales, MD, PhD, Sandra Eugenia Gutiérrez Morales and Aurora Astudillo González, MD, PhD