OSTEOCHONDROMA Figure 6-7 OSTEOCHONDROMA Above: Axial CT image of pedunculated osteochondroma shows continuity between the cortices and medullary cavity of the osteochondroma and underlying bone. Right: Frontal radiograph of sessile osteochondroma of the proximal tibia shows a broad-based osseou... More about this image found in OSTEOCHONDROMA Above: Axial CT image of pedunculated osteochondroma shows ...

OSTEOCHONDROMA Figure 6-14 OSTEOCHONDROMA Left: A resected osteochondroma from a young (skeletally immature) patient demonstrates a thick and cellular cartilaginous cap undergoing endochondral ossification at the base. The surface of the cartilaginous cap is covered by a thin pink layer of perich... More about this image found in OSTEOCHONDROMA Left: A resected osteochondroma from a young (skeletally im...

OSTEOCHONDROMA Figure 6-15 OSTEOCHONDROMA A resected osteochondroma from an older (skeletally mature) individual shows a thin and hypocellular cartilaginous cap, covered by a thin layer of perichondrium, and a base that has been formed by horizontally oriented (lamellar) bone. More about this image found in OSTEOCHONDROMA A resected osteochondroma from an older (skeletally mature)...

MULTIPLE OSTEOCHONDROMAS Figure 6-21 MULTIPLE OSTEOCHONDROMAS Coronal reformatted CT image of the pelvis in a patient with hereditary multiple osteochondromas shows a dominant pedunculated osteochondroma arising from the left iliac bone with a calcified cartilage cap. A smaller osteochondroma ari... More about this image found in MULTIPLE OSTEOCHONDROMAS Coronal reformatted CT image of the pelvis in a p...

OSTEOCHONDROMA GENESIS Figure 6-18 OSTEOCHONDROMA GENESIS Biallelic inactivation of the EXT1 or EXT2 gene in a cartilaginous cell of the growth plate or perichondrium is required for osteochondroma formation. In patients with solitary osteochondroma, two somatic hits are found, which usually contain larger deletions of the EXT gene regions. Patients with multiple osteochondromas have an inactivating mutation of either EXT1 or EXT2 in their germline. The complete inactivation of EXT (indicated in blue) disturbs the diffusion of hedgehog, hampering the formation of the bony collar, enabling EXT mutant cells to grow out of the bone. In collaboration with EXT wildtype or heterozygous cells (indicated in yellow), they will form an osteochondroma. Thus, the cartilage cap of osteochondroma is composed of a mixture of normal and mutated cells. (Modified from fig. 1 in Bovée JVMG. EXTra hit for mouse osteochondroma. Proc Natl Acad Sci U S A 2010;107:1813-4.) More about this image found in OSTEOCHONDROMA GENESIS Biallelic inactivation of the EXT1...

PEDUNCULATED OSTEOCHONDROMA OF THE DISTAL FEMUR Figure 6-6 PEDUNCULATED OSTEOCHONDROMA OF THE DISTAL FEMUR Left: Frontal radiograph shows a pedunculated osteochondroma arising from the distal femoral metaphysis and growing away from the joint. Cartilage cap with rings and arc calcification is pre... More about this image found in PEDUNCULATED OSTEOCHONDROMA OF THE DISTAL FEMUR Left: Frontal radiograph s...

MULTIPLE OSTEOCHONDROMAS Figure 6-20 MULTIPLE OSTEOCHONDROMAS Top: Frontal radiograph of both knees demonstrates multiple osteochondromas arising on the distal femoral condyles and the proximal tibias. The distal femoral shafts are widened. Bottom: Reconstructed 3D CT image shows continuity of t... More about this image found in MULTIPLE OSTEOCHONDROMAS Top: Frontal radiograph of both knees demonstrate...

OSTEOCHONDROMA Figure 6-9 OSTEOCHONDROMA Above: Coronal fat-suppressed T2-weighted MRI of the distal femur demonstrates bursa formation on the surface of an osteochondroma (arrow). Right: Sagittal fat-suppressed T2-weighted MRI of the distal femur in a different patient demonstrates osteochondro... More about this image found in OSTEOCHONDROMA Above: Coronal fat-suppressed T2-weighted MRI of the distal...

OSTEOCHONDROMA Figure 6-12 OSTEOCHONDROMA A: Cross-section shows a cartilaginous cap with irregular endochondral ossification, resulting in areas of calcification, and a long stalk (bottom of image). B: A cross-section of a resected osteochondroma shows a cartilaginous cap and underlying cancell... More about this image found in OSTEOCHONDROMA A: Cross-section shows a cartilaginous cap with irregular e...

PEDUNCULATED OSTEOCHONDROMA Figure 6-10 PEDUNCULATED OSTEOCHONDROMA Frontal radiograph shows a fracture through the stalk of a pedunculated osteochondroma (black arrow). A non-ossifying fibroma is incidentally noted (white arrow). More about this image found in PEDUNCULATED OSTEOCHONDROMA Frontal radiograph shows a fracture through th...

OSTEOCHONDROMA Figure 6-13 OSTEOCHONDROMA Low-power view shows three histologic layers: the surface of the osteochondroma is covered by pink perichondrium; underneath the perichondrium is a cartilaginous cap that under goes endochondral ossification. More about this image found in OSTEOCHONDROMA Low-power view shows three histologic layers: the surface o...

SECONDARY CHONDROSARCOMA ARISING IN THE CARTILAGINOUS CAP OF AN OSTEOCHONDROMA Figure 7-28 SECONDARY CHONDROSARCOMA ARISING IN THE CARTILAGINOUS CAP OF AN OSTEOCHONDROMA A,B: Frontal radio graph (A) and axial CT (B) show the abundant popcorn-like calcifications associated with osteochondroma. Lyt... More about this image found in SECONDARY CHONDROSARCOMA ARISING IN THE CARTILAGINOUS CAP OF AN OSTEOCHONDR...

SECONDARY PERIPHERAL ACT/CS1 ARISING IN OSTEOCHONDROMA Figure 7-30 SECONDARY PERIPHERAL ACT/CS1 ARISING IN OSTEOCHONDROMA The thickness of the cartilaginous cap should be adequately documented, as it helps identify malignant progression from an osteochondroma. It should be measured perpendicular ... More about this image found in SECONDARY PERIPHERAL ACT/CS1 ARISING IN OSTEOCHONDROMA The thickness of th...

SECONDARY CHONDROSARCOMA IN A PATIENT WITH MULTIPLE OSTEOCHONDROMAS SYNDROME Figure 7-29 SECONDARY CHONDROSARCOMA IN A PATIENT WITH MULTIPLE OSTEOCHONDROMAS SYNDROME A: Frontal radiograph of the pelvis demonstrates multiple osteochondromas (black arrows), with a lytic destructive lesion of the le... More about this image found in SECONDARY CHONDROSARCOMA IN A PATIENT WITH MULTIPLE OSTEOCHONDROMAS SYNDROM...

PEDUNCULATED OSTEOCHONDROMA OF THE PROXIMAL TIBIA Figure 6-8 PEDUNCULATED OSTEOCHONDROMA OF THE PROXIMAL TIBIA A: Lateral radiograph demonstrates pedunculated osteochondroma arising from the posterior tibia with typical matrix mineralization. B: Sagittal fat-suppressed T2-weighted MRI demonstrat... More about this image found in PEDUNCULATED OSTEOCHONDROMA OF THE PROXIMAL TIBIA A: Lateral radiograph de...

RESECTED PEDUNCULATED OSTEOCHONDROMA Figure 6-11 RESECTED PEDUNCULATED OSTEOCHONDROMA The tumor has a long narrow stalk and a nodular cartilaginous cap. More about this image found in RESECTED PEDUNCULATED OSTEOCHONDROMA The tumor has a long narrow stalk and...

OSTEOCHONDROMA Figure 6-16 OSTEOCHONDROMA Cellularity can be high, especially in younger patients, and degenerative cystic/mucoid changes can be seen. This is not a sign of malignancy. More about this image found in OSTEOCHONDROMA Cellularity can be high, especially in younger patients, an...

OSTEOCHONDROMA WITH AN OVERLYING BURSA Figure 6-17 OSTEOCHONDROMA WITH AN OVERLYING BURSA The cartilaginous cap has partly undergone endochondral ossification. The bursa is lined by synovium and is filled with synovial fluid. More about this image found in OSTEOCHONDROMA WITH AN OVERLYING BURSA The cartilaginous cap has partly un...

MULTISTEP PROGRESSION MODEL FOR SECONDARY PERIPHERAL CHONDROSARCOMA Figure 7-34 MULTISTEP PROGRESSION MODEL FOR SECONDARY PERIPHERAL CHONDROSARCOMA Osteochondromas are caused by biallelic inactivation of the exostosin genes EXT1 or -2. In osteochondroma and secondary peripheral ACT/CS1, both EXT mutant cells and EXT wild-type cells are found within the cartilaginous cap. However, upon progression to high-grade secondary peripheral chondrosarcoma, which is probably caused by alterations in the pRB or TP53 pathway, the EXT wild-type cells predominate, indicating that the EXT wild-type cells in osteochondroma are most likely to obtain additional alterations and to progress to full blown malignancy. These chondrosarcomas display chromosomal instability and a complex karyotype. (Based on fig. 5 from reference 54.) More about this image found in MULTISTEP PROGRESSION MODEL FOR SECONDARY PERIPHERAL CHONDROSARCOMA Osteoc...