Onion bulb formation

Onion bulb formation is a histopathologic finding in hypertrophic neuropathies such as Charcot-Marie-Tooth type 1A (CMT1A) and chronic inflammatory demyelinating polyneuropathy (CIDP).


Onion bulb formations are concentric layers of Schwann cell processes and collagen surrounding axons 1,3. They are the result of repeated cycles of demyelination and remyelination 3. These formations in microscopic cross-section resemble the bulb of an onion.

Radiographic features


Onion bulb formation in the hypertrophic neuropathies correlates with the imaging findings of nerve hypertrophy (bulbous thickening) with the following signal characteristics 2,4:

  • T1 C+ (Gd): usually demonstrate enhancement
  • T2: usually hyperintense

Article information

rID: 26751
Section: Signs
Tag: cases, cases, ref
Synonyms or Alternate Spellings:
  • Onion bulb sign
  • Onion bulb nerves
  • Onion bulb formation in hypertrophic neuropathies

ADVERTISEMENT: Supporters see fewers/no ads

Updating… Please wait.

 Unable to process the form. Check for errors and try again.

 Thank you for updating your details.