Diagnosis and Risk Stratification: Understanding the Criteria

When a child is born with a large birthmark, or if an older patient is newly evaluated, doctors use specific frameworks to understand the chance that melanocytes (pigment-producing cells) might also be present in the nervous system. This process is called risk stratification, and it helps your care team decide if and when additional tests, like an MRI, are necessary.

How Doctors Classify Birthmarks: The PAS System

Because a baby’s skin grows as they do, doctors don’t just look at the size of the birthmark today. Instead, they use a formula to calculate the Projected Adult Size (PAS) ^[1]. This estimates how large the mole will be once the individual is fully grown. For adult patients, the actual size is used.

The 2013 Kinsler consensus is the international standard for these categories ^[1]:

• Large CMN: A projected adult size between 20 cm and 40 cm (roughly 8 to 16 inches) ^[2].
• Giant CMN: A projected adult size greater than 40 cm (over 16 inches) ^[3].

The larger the PAS, the higher the statistical risk for Neurocutaneous Melanocytosis (NCM) ^[4][5].

The Three Main Risk Factors

Size is important, but it isn’t the only factor. Your doctor will evaluate three specific “red flags” that increase the likelihood of NCM:

1. Giant PAS: A birthmark projected to be larger than 40 cm ^[3].
2. Satellite Count: The presence of multiple satellite nevi (smaller moles appearing away from the main one). While having 2 or more satellites is a starting point for monitoring, the risk increases significantly with more than 20 satellites at birth ^[3][6].
3. Location: Birthmarks located on the head, neck, or posterior midline (the area directly over the spine) are considered higher risk because of their proximity to the central nervous system ^[7][8].

The Kadonaga and Frieden Diagnostic Criteria

To make a formal diagnosis of NCM, many specialists use a set of rules called the Kadonaga and Frieden criteria ^[9]. For a diagnosis to be made, a patient typically must meet the following:

1. Cutaneous (Skin) Findings: The presence of a “large” or “giant” nevus (as defined by PAS) or the presence of three or more smaller congenital nevi ^[10]. Note: While the criteria allow for a diagnosis with three or more smaller nevi, NCM is statistically much rarer in the absence of a large or giant primary nevus.
2. Neurological Findings: Evidence of melanosis (benign pigment deposits) or melanoma (cancerous pigment cells) within the brain or spinal cord, usually identified via MRI ^[11].
3. Exclusion of Other Causes: There must be no evidence of a primary melanoma in the skin that has spread to the brain ^[9].

Diagnosis is a tool for preparation; knowing the risk level allows you to build the right team of specialists early on ^[4].