Pseudo-Onion Bulbs

Circumferential Schwann cell processes often surrounding Axons or Axon sprouts

• Axon Regeneration
  • Pseudo-Onion Bulb Structure
    • Central: Axon(s)
      • Regenerated axons & Axon Sprouts: Individual or Clusters, or
      • Larger myelinated axon
    • Peripheral region of Pseudo-Onion Bulbs
      • Layers of Schwann cell processes
      • Small, Unmyelinated axons: May be surrounded by Schwann cell processes
  • Other features
    • Axon Loss in nerve: Often moderate to severe
    • No demyelination
• Chronic Demyelination without Remyelination
  • Central: Demyelinated axon
  • Peripheral: Multiple concentric Schwann cell processes

• Perineurioma
  
• Thinly myelinated axons surrounded by regions of collagen granules: No other associated cells or structures
  
• Onion bulbs
  
• Basal lamina onion bulbs (BLOBs): Very chronic demyelination (Demyelinating CMT)
  
• Büngner bands: Clustered Schwann cells, & their interdigitated processes, with no axons
  

H&E stain

VvG stain

Beaded axon sprouts extend circumferentially around central large axon Neurofilament stain

Toluidine blue stain

Toluidine blue stain

Toluidine blue stain

Toluidine blue stain

Toluidine blue stain

Pseudo-Onion bulbs: Ultrastructure

From: Chunyu Cai

From: Sara Stone

From: Sara Stone

From: Sara Stone

From: Sara Stone

From: Sara Stone