Adrenal gland: 15 week fetus
At this stage of development, the adrenal gland consists mostly of fetal cortex. There is a thin rim of definitive (adult) cortex at the periphery (here in the upper margin). The groups of dark cells within the fetal cortex are migrating neuroblasts which will form the adrenal medulla centrally. Sometimes these do not complete their migration and form neuroblastoma-in-situ. These lesions are thought to usually resolve spontaneously.
Adrenal gland: 23 week fetus
Throughout fetal life the fetal cortex occupies most of the gland. Here, at 23 weeks, one sees a rim of definitive adult cortex surrounding the fetal cortex. The migrating neuroblasts have arrived at or almost reached their final position in the medulla.
At higher magnification the capsule, definitive adult cortex, and the fetal cortex can be seen from left to right in this photo. In the fetal adrenal, the 3 layers of the adult cortex are not yet apparent microscopically.
Adrenal gland: Normal child
The adrenal gland of this 2 year old child consists of the centrally placed adrenal medulla and the surrounding adrenal cortices with their 3 layers. The fetal cortex disappeared during the first few months of life.
From upper to lower one sees the 3 layers of the cortex and the medulla. The outer layer, the zona glomerulosa, is easily distinguished from the underlying zona fasciculata (ZF). The boundary between the ZF and the underlying zona reticularis is less distinct.