Extramedullary hematopoiesis refers to hematopoiesis occurring outside of the medulla of the bone.

In some cases, it may be physiologic. For example, during fetal development, hematopoiesis occurs at many different locations, such as the liver

Liver

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

 and spleen.

However, it is more frequently associated with pathologic processes. For example, it can be caused by myelofibrosis

Myelofibrosis

Myelofibrosis, also known as myeloid metaplasia, chronic idiopathic myelofibrosis, osteomyelofibrosis and primary myelofibrosis is a disorder of the bone marrow...

.

It can sometimes be identified via computed tomography

Computed tomography

X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...

.