Onion bulb formation

A.Prof Frank Gaillard et al.

Onion bulb formation is seen in hypertrophic neuropathies such as Charcot-Marie-Tooth type 1A (CMT1A) and chronic inflammatory demyelinating polyneuropathy (CIDP). It is the result of proliferation of Schwann cells and deposition of collagen 1

Radiographic features


The nerve roots appear bulbous tapering as they extend along the nerve, with the following signal characteristics 2:

  • T2: hyperintense in most cases
  • T1 C+ (Gd): usually demonstrate enhancement
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Article information

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

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