What is the expected finding on brain MRI in a 2-year-old female patient with seizures, hyperpigmented plaques, and hypertrichosis (excessive hair growth) on the face, upper and lower limbs?

Leptomeningeal Melanosis is the Expected MRI Finding in This Patient

The expected finding on brain MRI in this 2-year-old female patient with seizures, hyperpigmented plaques with hypertrichosis on the face and extremities would be leptomeningeal melanosis (option D). 1

Clinical Presentation Analysis

The patient presents with a classic triad of:

1. Seizures
2. Hyperpigmented plaques on face, upper and lower limbs
3. Hypertrichosis (excessive hair growth) in the same areas

This constellation of findings strongly suggests neurocutaneous melanosis (NCM), a rare congenital syndrome characterized by:

• Large or multiple congenital melanocytic nevi (CMN)
• Abnormal melanocytic deposits in the leptomeninges (leptomeningeal melanosis)
• Neurological manifestations, particularly seizures

Neuroimaging Findings in This Condition

MRI is the preferred screening modality for patients with suspected neurocutaneous melanosis 1. The American College of Radiology recommends MRI as the most appropriate imaging modality to characterize intracranial abnormalities in children with seizures 1.

In this patient, we would expect to see:

• Leptomeningeal melanosis: Abnormal melanin deposits in the leptomeninges appearing as T1 hyperintense and T2 hypointense areas
• These deposits typically involve the base of the brain, cerebellum, and ventral surface of the medulla
• The melanin deposits may be diffuse or focal

Differential Diagnosis of the Neuroimaging Options

Let's analyze each option:

1. Lissencephaly: A malformation of cortical development with smooth brain surface. Not typically associated with cutaneous findings of hyperpigmentation and hypertrichosis.

2. Leptomeningeal enhancement: While enhancement can occur in various inflammatory or infectious conditions, it's not the characteristic finding in neurocutaneous melanosis.

3. Leptomeningeal angioma: This is the characteristic finding in Sturge-Weber syndrome, which typically presents with port-wine stain (not hyperpigmented plaques with hypertrichosis) 2.

4. Leptomeningeal melanosis: This is the characteristic finding in neurocutaneous melanosis, which matches the patient's presentation of hyperpigmented plaques with hypertrichosis and seizures 1.

Risk Factors and Clinical Correlations

The risk of neurocutaneous melanosis and leptomeningeal melanosis is higher in patients with:

• Multiple congenital melanocytic nevi
• Large or giant congenital melanocytic nevi (>40 cm projected adult size)
• Trunk location of the largest nevus
• More than 20 satellite nevi 1

Patients with neural melanosis may present with:

• Seizures (as in this case)
• Headaches
• Hydrocephalus
• Developmental delays 1

Management Implications

Identification of leptomeningeal melanosis has important management implications:

• Referral to pediatric neurology
• Ongoing neurological monitoring
• Anti-seizure medication management
• Monitoring for potential malignant transformation (melanoma can develop in 8% of patients with multiple CMN) 1

The presence of hypertrichosis with hyperpigmented plaques should raise suspicion for neurocutaneous melanosis, and leptomeningeal melanosis would be the expected finding on brain MRI in this 2-year-old patient with seizures.