“Onion skin,” which doctors call lamellated periosteal reaction, occurs when multiple layers of bone form in a concentric circle around the outer surface of the bone. It can occur with Ewing sarcoma.

Ewing sarcoma is a type of cancer. If a person has the condition, a doctor may detect the onion-like appearance of lamellated periosteal reaction on imaging tests.

This article reviews what onion skin periosteal reaction is, how it relates to Ewing sarcoma, and more.

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Onion skin periosteal reaction occurs when multiple layers of bone form in a concentric circle around the outside of the bone. The nature of the growth resembles the layers of an onion. The condition is also known as laminated periosteal reaction or lamellated periosteal reaction.

There are several potential causes of onion skin periosteal reaction. At first, experts believed that the condition occurred due to cycles of rapid and slow injury to the bone.

More recently, health experts have shown that it may be due to changes in connective tissue, which doctors call fibroblasts, in the adjacent soft tissue. This may cause osteoblasts to form sheets of new bone. Osteoblasts are the cells on the surface of the bones that form new bone cells.

Another suggestion is that a new layer of bone lifts off the surface of the bone. The lifting creates a space that may stimulate the formation of new bone tissue.

Ewing sarcoma is a potential cause of periosteal reaction. The tumor may cause onion skin or hair-on-end subtypes of periosteal reaction. The hair-on-end subtype suggests the presence of Ewing sarcoma.

Ewing sarcoma is a cancerous tumor that typically appears in children and young adults, often first showing up during the teenage years. It also often starts in long bones of the body, such as the thigh bone, shin, or upper arm.

It is a rare form of cancer that can spread to other areas of the body. However, experts do not know the exact type of cell where the cancer begins.

Learn more about Ewing sarcoma.

If a person seeks medical attention for pain or swelling around a bone, a doctor will likely order imaging tests. These may include:

These tests can help determine the underlying cause of the swelling or pain. Onion skin periosteal reaction will look like multiple layers of bone.

Onion skin periosteal reaction could indicate the presence of a condition such as Ewing sarcoma. It may also be the result of a benign tumor.

Imaging tests alone will not allow a doctor to determine the severity of the condition. Instead, some experts suggest one way to determine severity is to examine how fast the growth is growing. They can then categorize them into slow growth and fast growth.

A doctor will be able to advise on the seriousness of a person’s diagnosis and answer any questions they may have.

Examples of other signs and symptoms of Ewing sarcoma include:

  • swelling
  • pain at the site of the tumor
  • noticeable mass near the bone

A person may first notice a mass form near their bone. This may last several months and precede pain or swelling.

Other possible causes of onion skin periosteal reaction include:

Chondroblastomas are benign, rare tumors that often develop in the long bones of the body near the joints. Although benign, the tumor can continue to grow and may destroy healthy bone cells, leading to breaks and other symptoms. A person may require surgical removal of the mass.

Osteomyelitis is an infection of the bone. Early, aggressive treatment of the infection can generally lead to favorable outcomes for people with this condition.

Learn more about osteomyelitis.

Onion skin periosteal reaction occurs when a growth develops in a concentric pattern around the outside of the bone. The growth appears like the layers of an onion.

Ewing sarcoma is one possible cause of onion skin periosteal reaction. Symptoms of Ewing sarcoma may include a noticeable mass, swelling, and tenderness or pain at the site. A doctor can see the growth on an imaging test and then provide treatment as necessary.