Periosteal Reactions in Bone Lesions
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Direct answer
A periosteal reaction is new bone laid down by the periosteum in response to injury, infection or tumour, and its pattern helps judge how aggressive a lesion is. The classic patterns are solid, lamellated, sunburst and Codman, with sunburst and Codman favouring aggressive lesions such as osteosarcoma. Lodwick grading of lytic lesions complements these patterns by describing how fast the lesion margin is advancing.
What you must remember
- Solid reaction: a uniform, smooth layer of new bone that suggests slow or long-standing growth.
- Lamellated (onion-skin): several concentric layers of periosteal new bone, seen in Ewing sarcoma and in repeated periosteal irritation.
- Sunburst: spicules of new bone radiating outward from the cortex, classically seen in osteosarcoma.
- Codman triangle: a triangular shadow where an aggressive lesion lifts the periosteum off the cortex at its edge.
- Hair-on-end: spicules perpendicular to the cortex, seen with marrow expansion such as thalassaemia and in Ewing sarcoma.
- Lodwick grading: grade 1 is geographic and well defined, grade 2 is moth-eaten and grade 3 is permeative, so grade rises with aggressiveness.
- Interpretation: the periosteal pattern is always read together with the cortex, the margin and the surrounding soft tissue.
Reading the pattern by its aggressiveness
A periosteal reaction is the periosteum's response to a lesion, and the pattern reflects the speed at which the lesion is growing. The table lists the patterns most often asked in examinations and what each one implies. Examiners test the pattern mainly as a clue to aggressiveness, not as a diagnosis.
| Pattern | Appearance | Usual association |
|---|---|---|
| Solid | Uniform, smooth layer of new bone laid along the cortex | Slow or long-standing growth, often benign |
| Lamellated | Multiple concentric onion-skin layers of new bone | Ewing sarcoma, repeated periosteal irritation |
| Sunburst | Fine spicules radiating outward from the cortex | Osteosarcoma, an aggressive lesion |
| Codman triangle | Triangular lifted periosteum at the edge of the lesion | Rapidly growing aggressive lesion, often osteosarcoma |
| Hair-on-end | Spicules running perpendicular to the cortex | Marrow expansion such as thalassaemia, and Ewing sarcoma |
Sunburst and Codman patterns signal an aggressive process that needs urgent staging and biopsy. Solid patterns usually point to a benign or slow process, and the final grade depends on the cortex and margin as well as the periosteum. A pattern alone rarely settles a diagnosis, so age, site and the Lodwick grade are weighed together.
Where the exam tries to catch you
Most errors come from reading a periosteal pattern on its own, without the rest of the image.
- Trap: reading a sunburst pattern as a benign healing reaction Correct: sunburst spicules signal aggressive growth, classically osteosarcoma, and they need urgent staging.
- Trap: calling a solid periosteal reaction malignant by default Correct: a solid, uniform reaction suggests slow or long-standing growth, so the cortex and margin decide the grade.
- Trap: treating Codman triangle as a specific sign of osteosarcoma Correct: Codman triangle indicates an aggressive lesion but is not specific, so it must be read with the rest of the image.
Frequently asked questions
What is a Codman triangle in bone imaging?
A Codman triangle is a triangular shadow formed where an aggressive lesion lifts the periosteum off the cortex at its edge. It is a sign of rapid growth rather than a specific diagnosis. Codman triangle is seen in osteosarcoma and in other aggressive bone lesions.
What does a lamellated periosteal reaction indicate?
A lamellated periosteal reaction shows several concentric layers of new bone, giving an onion-skin appearance. It suggests repeated periosteal irritation, and it is classic for Ewing sarcoma. Each layer reflects an episode of periosteal lifting over time.
How does Lodwick grading help assess lytic bone lesions?
Lodwick grading classifies lytic bone lesions by how well their margins are defined, with grade 1 geographic and well defined, grade 2 moth-eaten and grade 3 permeative and aggressive. The grade helps predict growth rate and biological behaviour. It is used alongside the periosteal reaction, not in isolation.
Why is the sunburst periosteal reaction important in examinations?
The sunburst periosteal reaction is important because it signals an aggressive lesion, classically osteosarcoma, and prompts staging and biopsy. In examinations it is commonly paired with a metaphyseal lesion in a young patient. It should not be read as a simple fracture callus.
What causes a hair-on-end periosteal pattern?
A hair-on-end pattern is caused by rapid marrow expansion that pushes the cortex outward and produces perpendicular spicules of periosteal bone. It is seen in thalassaemia and in Ewing sarcoma, particularly in the skull. Recognising the pattern prompts a search for the underlying marrow disorder.