How the Condition Forms and Is Classified

To understand why every child’s experience with lipomyelomeningocele (LMMC) is different, it helps to look at how the condition begins and how doctors categorize it. For an overview of the diagnosis, see Understanding Your Child’s Lipomyelomeningocele Diagnosis.

The “Premature Disjunction” Theory

LMMC occurs very early in pregnancy, usually within the first month. During a process called primary neurulation, the flat layer of cells that will become the brain and spinal cord (the neuroectoderm) rolls up into a tube and separates from the layer that will become the skin (the cutaneous ectoderm) ^[1][2].

In children with LMMC, researchers believe this separation happens too early, a theory called premature disjunction ^[1]. Because the tube isn’t fully closed when it separates from the skin, nearby cells that are destined to become fat and muscle (the mesoderm) “slip” inside ^[1][2]. These cells then grow into a fatty mass—a lipoma—that is physically fused to the spinal cord ^[2].

How Doctors Classify the Lipoma

Not all spinal lipomas are the same. Surgeons use classification systems to “map” the relationship between the fat and the spinal nerves. This map tells them how difficult a surgery might be and what symptoms to watch for.

The Chapman Classification

Historically, doctors have used the Chapman system, which looks at where the fat enters the spinal cord:

• Dorsal: The fat attaches only to the back (top) of the spinal cord. This is often the most straightforward type for surgeons to address ^[3][4].
• Caudal: The fat is located at the very tip (tail) of the spinal cord ^[3].
• Transitional: The fat attaches to the back of the cord but also extends down to the very tip. It is more complex than the dorsal or caudal types ^[3][5].

The New Classification (Morota/NCSL)

In recent years, a newer system called the New Classification of Spinal Lipomas (NCSL), or the Morota classification, has become popular because it better predicts surgical outcomes ^[6][7]. It focuses on the placode-lipoma interface—the exact “seam” where the fat meets the nerve tissue ^[8][7].

Why the Subtype Matters

Knowing your child’s specific subtype is crucial because some types carry higher risks for the nerves that control the legs and bladder.

The Chaotic type (often part of the newer NCSL system) is especially complex because the fat is deeply interwoven with the nerves, making it very difficult to remove completely without risking nerve damage ^[8][9]. However, specialized neurosurgeons use advanced monitoring tools during surgery to safely navigate this complexity and protect function. Children with transitional or chaotic types are more likely to experience retethering—where the spinal cord gets stuck again after surgery—and may need more frequent monitoring of their bladder function ^[5][8]. Areas of “residual fat” left behind after surgery are more common in these complex types ^[8].