hallmark of neurocutaneous melanosis in the neonatal period is the presence
of a large bilateral hairy dark nevus with satellite nevi over the trunk
and neck (Figure 303.1). The diagnosis should be considered in neonates
with large pigmented nevi and in those with more than three hairy dark
nevi regardless of their size. Neonates with neurocutaneous melanosis
are at risk of developing neurological problems. The neurological complications
of neurocutaneous melanosis are hydrocephalus, seizures, cranial
nerve dysfunction, and signs of spinal cord and root involvement.
Hydrocephalus may have different
causes. The most frequent cause of hydrocephalus is obstruction of the
cerebrospinal fluid flow at the base of the skull due to thickening of
the meninges (communicating hydrocephalus). This phenomenon occurs in
neonates with a pigmented nevus in the distribution of the neck. Thickening
of the meninges results from melanocytic infiltration of the arachnoid.
Noncommunicating hydrocephalus due to aqueductal stenosis may also occur.
resonance imaging of the area underlying the nevus or guided by the neurological
findings is the study of choice in neonates with neurocutaneous melanosis.
The most frequent MRI finding is the presence
of areas of increased signal on T1. These areas of increased signal represent
accumulation of melanocytic cells (Figure 303.1 B). The most frequent
areas of melanocytic cell infiltration are the anterior temporal region,
close to the amygdala, and the cerebellum. Malignant transformation of
these areas is suggested by the presence of necrosis, hemorrhages, edema,
growth, or contrast enhancement by CT.
The cerebrospinal fluid of
neonates with neurocutaneous melanosis may reveal increased protein, decreased
sugar, and a normal cell count. Melanin-filled cells are sometimes found
in the cerebrospinal fluid. Neurocutaneous melanosis is a sporadic condition.
Figure 303.1.— Neurocutaneous
melanosis. [A] Hyperpigmented nevus; [B] MRI findings showing bilateral
increased signal from deep brain regions and the left mesial temporal
MRI of the spine may demostrate the presence of an arachnoid cyst (Figure
Figure 303.2.— Neurocutaneous
melanosis. [A and B] Large dorsal arachnoid cyst with mass effect.