How do phocomelia and hemimelia differ as limb malformations?

Phocomelia and hemimelia are both forms of peromelia, which refers to the congenital absence or malformation of extremities. While both conditions involve limb development issues, they differ in the specific segments of the limb that are affected:

• Phocomelia: Often described as "seal extremity," this condition occurs when the upper portion of a limb is missing or severely underdeveloped. As a result, the lower part of the limb is attached directly to the trunk, giving it an appearance similar to a seal's flipper.12
• Hemimelia: In this condition, the upper part of the limb is well-formed, but the lower part is either rudimentary or entirely absent.12

Both malformations typically result from errors occurring during the development of the limb bud between the fourth and eighth weeks of intrauterine life.1