Pathology of Spinal Lipoma in Children

Pathophysiology

Spinal lipomas can be categorized according to their surgical anatomy, as described by Chapman in 1982 and modified by Pang in 2012 (1,2).

• Dorsal lipoma: The interface between the lipoma and the spinal cord is exclusively on the cord’s dorsal aspect. The conus remains unaffected, and the lipoma does not encompass nerve roots.

Dorsal lipoma: (Left) Illustration of a dorsal lipoma. (Right) MRI sagittal T1 slice of a patient with a dorsal lipoma.  (Saenz, Amparo. Dorsal lipoma. September 2023, Private collection, London.)

• Transitional lipoma: The lipoma is transitional between dorsal and terminal types. The conus is invariably involved and may be discernible as the conus or obliterated by the lipoma. The placode is commonly rotated and, while nerve roots may be shortened, the lipoma attachment does not extend beyond the DREZ (22).

Transitional lipoma: (Left) Illustration of a transitional lipoma. (Right) MRI sagittal T2 slice of a patient with a transitional lipoma. (Saenz, Amparo. Transitional lipoma. September 2023, Private collection, London.)

• Terminal/Caudal lipoma: In terminal lipomas, the lipoma is attached to the caudal section of the conus, while leaving the sacral roots unaffected. The conus appears normal or blunted and can be low-lying, but the dural sac and dorsal myofascial layers typically remain intact.

Terminal lipoma: (Left) Illustration of a terminal lipoma. (Right) MRI sagittal T2 slice of a patient with a terminal lipoma. (Saenz, Amparo. Terminal lipoma. September 2023, Private collection, London.)

• Chaotic lipoma: This is a variant of transitional lipoma and may only be recognized at the time of surgery. The characteristic feature of chaotic lipoma is the extension of the lipoma beyond the DREZ, thus precluding safe resection.

Chaotic lipoma: (Left) Illustration of a chaotic lipoma. (Right) MRI sagittal T1 slice of a patient with a chaotic lipoma. (Saenz, Amparo. Chaotic lipoma. September 2023, Private collection, London.)

• Lipoma with extraspinal extension (lipomyelomeningocele): In this case, the terminal spinal cord herniates outside the confines of the spinal canal, with a small CSF sac extending subcutaneously (41, 42).

Lipoma with extraspinal extension, or Lipomyelomeningocele: (Left) Illustration of a lipoma with an extraspinal extension. (Right) MRI sagittal T2 slice of a patient with a lipoma with an extraspinal extension. (Saenz, Amparo. Lipoma with extraspinal extension. September 2023, Private collection, London.)

Molecular/Genetic Pathology

• Underlying causes unclear: Despite over 200 small animal models and more than 100 candidate genes, understanding of the genetic causes underlying occult spinal dysraphism, including spinal lipomas, remains limited. Remarkably, less than 20% of these candidate genes have demonstrated minor effects on risk association (23).
• Emerging strategies hold promise: Nonetheless, emerging strategies, such as genome-wide association studies and whole genome sequencing, hold potential in identifying genes that contribute to the risk of human neural tube defects, including spinal lipomas. Such genetic and molecular investigations could significantly enhance diagnostic accuracy and treatment stratification for spinal lipomas.

Histopathology

• Predominantly mature adipose tissue: Spinal lipomas primarily consist of mature adipose tissue. Typically, these adipocytes are encased within a slender fibrous capsule. When viewed microscopically, spinal lipomas manifest as groupings of adipocytes characterized by clear cell boundaries and a large lipid droplet dominating most of the cell’s interior.
• Contain tissue from all germ cell layers: Importantly, histological analysis of surgical specimens demonstrates a range of tissues derived from all germ cell layers (24). This suggests a more complex, hamartoma-like malformation.