A neonate born at term to a 19-year-old woman is noted not to be gaining weight as expected. At a one month checkup, the nurse practitioner palpates fullness to the baby's abdomen. An abdominal CT scan shows a left retroperitoneal mass that is 6 cm is size and solid. The mass displaces the left kidney downward.
What is the mass?
This is a neuroblastoma of the adrenal gland. It is composed of small blue cells with a primitive appearance resembling early embryologic tissues. The suffix -blastoma applied to a neoplasm implies that the neoplasm resembles primitive embryologic tissue.
What is the origin of the cells that gave rise to the mass?
When the embryo is 8 mm, coelomic epithelial cells proliferate in response to induction by the ureteric bud (a wolffian duct structure) giving rise to the adrenal cortical primordium. These mesodermal cells arise from a wide plate of coelomic epithelium in the most internal region of the mesonephric blastema between the mesenteric root and the gonadal primordium. The cells penetrate the underlying mesenchyme forming the primitive adrenal cortex, also known as the fetal adrenal cortex, which later becomes the zona reticularis in the adult adrenal. The developing fetal adrenal cortex is then invaded by sympathogonia of neural crest origin that will form the adrenal medulla. At the end of the first trimester, another proliferation of coelomic epithelium occurs, penetrating the mesenchyme and surrounding the fetal cortex to eventually become the adult adrenal cortical glomerulosa and fasciculata layers.
How does this mass occur?
As cells proliferate, mutations can arise. A mutation in the n-myc oncogine, which participates in control of cell growth, can lead to uncontrolled growth - a neoplasm. This particular mutation arising in the neuroblasts gives rise to a neuroblastoma. Neoplasms in the fetus and infant are quite rare. Such neoplasms tend to resemble the primitive fetal cells giving rise to various organs. Thus, many of these tumors are -blastomas.
Name some other examples of congenital or early childhood masses.