It is a well known fact that laboratory animals not injected with adrenal cortical extracts may survive the removal of both adrenal glands because of accessory adrenal cortical tissue which is usually located in close approximation to the kidneys.
Gilmore, James W.
"Accessory Adrenal Cortical Bodies in the Pig,"
Iowa State University Veterinarian: Vol. 2
, Article 15.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol2/iss2/15