CMN can be associated with neurological (brain) complications in a small percentage of people.  These neurological problems are very variable, and therefore lots of different types of complications have been described in different people.

Melanosis (a bit like moles) is the most common finding in the substance of the brain.  This is usually found on MRI scan, and only around 50% have any symptoms of this. When the melanosis does give symptoms directly, this is usually identified by fits which are usually in the temporal lobe (temporal lobe epilepsy).  However, the other symptom that is associated with seeing melanosis on the scan but does not seem to be directly caused by the melanosis, is developmental delay.  In other words, the melanosis we can see on a scan seems to be a marker for abnormal brain development, rather than being the actual cause.  This is currently being investigated in more detail.

All other complications are much rarer, and when these complications are present, they are usually identified from birth or soon afterwards. Therefore, if children have not been scanned by the age of 2 years old, and are entirely well, it is very unlikely they would have any of the following rare complications:

Brain tumours (not melanoma), usually benign, but usually need to be removed.

Hydrocephalus (too much fluid in the brain), this is caused by melanosis in the coverings of the brain and spine, which is not always visible on scan. Hydrocephalus always needs treatment with a special operation to shunt the fluid out of the brain and into the abdomen.

Malformations of the brain.

Melanoma can occur in the brain. This is rare but can occur at any age.

Mosaic Disorder – As CMN is a Mosaic Disorder, caused by a genetic mutation, an MRI scan is recommended for all children born with CMN to determine the presence of any pigment in the brain or nervous system using a spinal contrast. MRI results can be used as a framework for the child’s development and expression of CMN, as it will determine whether the CMN is internal. An earlier MRI allows for a clearer scan.

Support available

If you or your child has been diagnosed with any of the above, there is dedicated support available. Please contact the charity’s support helpline 0300 373 3422 or email