Pseudo-Onion Bulbs

Circumferential Schwann cell processes often surrounding Axons or Axon sprouts

    Surrounded by: Layers of Schwann cell processes
    Loss: Often severe
    Regeneration & Sprouts: May be formed with regenerating axon clusters
  No demyelination

H&E stain
Whorled structures: Contain nuclei & connective tissue; Myelinated axon may be in center

VvG stain

Beaded axon sprouts extend circumferentially around central large axon

Neurofilament stain

Toluidine blue stain
Whorled structures: Central myelinated axon is present within some pseudo-onion bulbs

Toluidine blue stain

Toluidine blue stain

Pseudo-Onion Bulbs
  Around regenerated axons with thin myelin sheaths
  Also present in regions with no axons

Toluidine blue stain

Pseudo-Onion Bulbs
  Around regenerating axon clusters

Toluidine blue stain

Pseudo-Onion bulbs: Ultrastructure

Interdigitated Schwann cell processes
Schwann cell processes may surround central axon or collagen

From: Chunyu Cai
Pseudo-Onion bulbs
Multiple Schwann cell processes surround regenerated, thinly myelinated, axons

Return to: Onion bulbs