Neurocutaneous melanoma in association with giant congenital melanocytic nevi in a child (Touraine syndrome) – A dermatoradiological correlation

INTRODUCTION

Touraine syndrome or neurocutaneous melanosis/melanoma (NCM) is a rare, non-familial, condition described by Rokitansky in 1861.^[1-3] The diagnostic criteria include multiple (three or more) or large congenital nevi (measuring 9 cm or more on the scalp or 6 cm or more on the body) with melanin-containing cells in the leptomeninges (melanosis or melanoma). Giant congenital melanocytic nevi (GCMN) occur in approximately 1/20,000 of live births.^[1] The prognosis is bad when neurological manifestations appear. Central nervous system (CNS) involvement is established by MRI.

CASE REPORT

A 12-year-old boy presented with focal seizures lasting for a few seconds of 2 months duration. He had a large pigmented nevus around the lower trunk since birth. He did not have any neurological deficits. Dermatological examination revealed a giant melanocytic nevus around the lower trunk (size 52 × 30 cm). There were multiple similar smaller circumscribed nevi of size varying from a few millimeters to several centimeters on the right scapular region, anterior chest wall, the right side of the forehead, [Figure 1a-c] left mastoid region, and right leg. MRI brain revealed a curvilinear T1 and T2 hyperintense 20 × 2 mm lesion which was not suppressed in T1-weighted fat-suppressed sequence in the amygdala of the right temporal lobe consistent with brain melanoma [Figure 2a-c].

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Figure 1:

(a) Giant melanocytic nevus reaching up to scapulae on the back. Another circumscribed lesion on the (r) scapular region. (b) Melanocytic nevus extending to the lower abdomen and a few small nevi on the anterior chest. (c) A circumscribed melanocytic nevus in the right temporal region.

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Figure 2:

(a) Axial T1 W MRI brain showing a curvilinear hyperintense lesion in the right amygdala. (b) Axial T2 W MRI brain showing a curvilinear hyperintense lesion in the right amygdala. (c) Axial T1 fat-suppressed MRI brain showing a curvilinear hyperintense lesion in the right amygdala consistent with cerebral melanoma.

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DISCUSSION

Neurocutaneous melanosis is characterized by congenital cutaneous nevi (one large nevus or multiple nevi) associated with benign or malignant CNS proliferation of melanocytes.^[1-4]

The diagnostic criteria, which were first described by Fox and later revised by Kadonaga and Frieden in 1991, include the combination of the following: A single giant congenital nevus (measuring at its greatest diameter ≥20 cm in adults or ≥9 cm on the head or ≥6 cm on the trunk in neonates and infants) or multiple (three or more) congenital nevi, accompanied by meningeal melanosis or CNS melanoma.^[1] CNS involvement includes parenchymal or leptomeningeal lesions such as melanosis (aggregation of benign melanocytic cells) or melanomas.^[5] Patients with large cutaneous lesions, particularly over the back, neck, or scalp and multiple (more than three) nevi, have a greater risk for neural involvement.^[6]

MR imaging findings of NCM show hyperintense T1 signal within the brain parenchyma and leptomeninges due to the paramagnetic effects of stable free radicals within melanin.^[7] The parenchymal foci are most commonly found in the anterior temporal lobes, specifically the amygdala, but may also be seen in the cerebellar hemispheres, dentate nuclei, basal ganglia, thalami, and pons.^[8-10]

CONCLUSION

Patients with GCMN are at risk for NCM and those with GCMN on the posterior axis or in conjunction with many satellite melanocytic nevi have the greatest risk. The presence of large numbers of satellite nevi is the most important risk factor for NCM in patients with LCMN.