Placode

Placode (or neural placode) refers in terms of radiology to a segment of non-neurulated neural tissue, which has had development frozen in the neural plate stage. A placode can be found in all open spinal dysraphisms and in some closed spinal dysraphisms. In the former, the placode is exposed to air.

It should be noted that when embryologists also refer to placodes they are referring to thickenings of ectoderm destined to become certain parts of the neurological system present as a part of normal development.

Classification

The placodes can be classified according to its location (terminal or segmental)  and extension (apical, parietal).

Location

• terminal: caudal end of the spinal cord (commoner)
• segmental: located in another segment than the spinal cord caudal end 

Extension

• apical: involvement of the apex proper
• parietal: involvement of a longer segment of the cord