4. Aggressive Lesions Flashcards
There are tons of primary osseous malignancies, the most common are
myeloma/plasmacytoma (27%)
Osteosarcoma (20%)
Chondrosarcoma (20%).
FIrst mental calculus in multiple choice questions
Aggressive vs Not aggressive
What makes a lesion “aggressive ” ?
wide zone of transition is the best sign that a lesion is aggressive
Ask yourself if you can trace the edges of the lesion with a pencil. If you can the lesion is probably benign
If the edges are blurry or there is a gradient to the edge - this is a more likely an aggressive lesions.
The margins are the reflection of bone formation.
If the margins are not distinct =
Wide zone of transition = FASTer growing lesions = malignancy/infection
Codman triangle
If the tumor grows rapidly enough it can break through the cortex and destroy the newly formed bone capsule / lamellated bone. When this happens you end up with a triangular structure
Codman triangle
Bone destruction =
occurs from complex methods best understood as either:
Direct obliteration via the tumor
or
Pissed off osteoclasts enraged by the uninvited tumor / hyperemia.
Bone destruction that occurs in a uniform geographic pattern (especially with a sharp well defined border) =
Suggestive of slow growinglesion
OSTEOSARCOMA (OS)
There are a bunch of subtypes, but for the purpose of this discussion there are 4:
Intramedullary (85%)
Parosteal (4%)
Periosteal (1%)
Telangiectatic (rare).
All the subtypes produce bone or osteoid from neoplastic cells
Conventional Intramedullary Osteosarcoma
More common, and higher grade than the surface subtypes (periosteal, and parosteal)
Primary subtypes = young patients (10-20)
Most common location = Femur (40%), Proximal Tibia (15%)
Conventional Intramedullary Osteosarcoma features:
include various types of aggressive periosteal reactions:
“Codman Triangle” in OS
periosteum does not have time to ossify completely with new bone (e.g. as seen in single layer and multi-layered periosteal reaction), so only the edge of the raised periosteum will ossify - creating the appearance o f a triangle.
True classic cause of occult pneumothorax
OS mets to the lung
Skip Lesions/Mets in Osteosarcoma
Synchronous tumor in the same bone or the immediate opposing side of a joint - separated by normal marrow.
They are usually proximal to the main tumor and occur
around 5% of the time in OS. This is the reason you image the ENTIRE bone during staging.
Classic Osteosarcoma Pathway
Parosteal Osteosarcoma
Low Grade BULKY parosteal bone formation
think BIG! Just Say BIG!
Common location: Distal femue (because ofthis location it can mimic a cortical desmoid “tug lesion ” early on)
Metaphyseal 90% of the time
Parosteal Osteosarcoma
“string sign”
which refers to a radiolucent line separating the bulky tumor from the cortex.
Periosteal Osteosarcoma
Worse prognosis than parosteal but better than conventional osteosarcoma.
DIAPHYSEAL
Parosteal vs Periosteal Osteosarcoma
Telangiectatic Osteosarcoma
About 15% have a narrow zone of transition.
Fluid-Fluid levels on MRl is classic.
They are High on T1 (from methemoglobin).
Can be differentiated from ABC or GCT (maybe) by tumor nodularity and enhancement.
FLUID-FLUID LEVELS DDx
Telangiectatic Osteosarcoma
Aneurysmal Bone Cyst
Giant Cell Tumor
Osteosarcoma Spectrum
Ewings Sarcoma
Permeative lesion in the diaphysis of a child = Ewings (same look could also be infection, or EG).
Ewings
Permeative / Moth-Eaten is classic
Lamellated / Onion Skin Periosteal Reaction
Chondrosarcomna
“Chondroid matrix” - “arcs and rinsk”
Enchondroma vs Low Grade Chondrosarcoma
Chordoma
most common sacrum, second most common clivus, third most common vertebral body), and the fact that they are very T2 bright.
