Name: 骨軟骨腫 (Osteochondroma)
Uploaded: 2021-01-14T07:28:25.000Z
Duration: 10 min 36 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

Osteochondromas or osteocartilaginous exostoses are the most common benign

tumors of the bones. The tumors take the form of cartilage-capped bony

projections or outgrowth on the surface of bones. It is characterized as a type

of overgrowth that can occur in any bone where cartilage forms bone. Tumors most

commonly affect long bones in the leg, pelvis, or scapula. Development of

osteochondromas take place during skeletal growth between the ages of 13

and 15 and ceases when the growth plate fuses at puberty. They arise within the

first three decades of life affecting children and adolescents.

Osteochondromas occur in 3% of the general population and represent 35% of

all benign tumors and 8% of all bone tumors. Majority of these tumors are

solitary non-hereditary lesions and approximately 15% of osteochondromas

occur as hereditary multiple osteochondromas. They can occur as a

solitary lesion or multiple lesions within the context of the same bone.

Osteochondromas do not result from injury and the exact cause remains

unknown. Recent research has indicated that multiple osteochondromas is an

autosomal dominant inherited disease. Germ line Mutations in EXT1 and EXT2

genes located on chromosomes 8 and 11 have been associated with the cause of

the disease. The treatment choice for osteochondroma is surgical removal of

solitary lesion or partial excision of the outgrowth, when symptoms cause

motion limitations or nerve and blood vessel impingements.

Mechanism  Osteochondromas are long and slender,

pedunculated on a stalk often taking the shape of a cauliflower. The cartilage

cap is covered by fibrous perichondrium and continues with the periosteum of the

underlying bone. The cartilage cap is less than 2 cm thick and the thickness

decreases with age. A cap more than 2 cm thick, indicates malignant

transformation of a tumor. The cartilage cap merges with the epiphyseal area of

the long bones called spongiosa. In the spongiosa, the chondrocytes are arranged

in accordance with the epiphyseal growth plate. The spongiosa of the stalk

continues with the underlying cancellous bone. Fractures within the stalk causes

fibroblastic proliferation and formation of a new bone. Development of bursa

takes place over the osteochondroma, which is attached to the perichondrium

of the cap. Inflammation of the bone is indicated by the bursal wall lined by

the synovium. As a result, patients may have swelling for years related to the

location and site of the lesion indicative of mechanical obstruction,

nerve impingement, pseudoaneurysm of the overlying vessel, fracture at the stalk

of the lesion, or formation of bursa over the osteochondroma. Heparan

sulphate are glycosaminoglycans which are involved in the formation of

proteoglycans. The biosynthesis of HS takes place in the Golgi apparatus and

Endoplasmic Reticulum, where glycosaminoglycans chains are maintained

by type II glycosyltransferases encoded by EXOSTOSIN genes EXT1 and EXT2.

Decreased levels of HS leads to mutations in EXT1 or EXT2 causing

skeletal abnormality. The underlying mechanism for solitary and multiple

osteochondromas have been associated with genetic alterations in EXT1 or EXT2

genes located on chromosomes 8 and 11. Approximately 65% of osteochondromas

arise in the EXT1 gene loci on chromosome 8 and 35% arise in EXT2 gene

loci on chromosome 11. About 70–75% of multiple osteochondromas are caused by

point mutations, often involving deletion of single or multiple axons as

found in 10% of all hereditary cases. In about 10–15% of all cases no genomic

alterations are detected. The mechanism behind the formation of multiple

osteochondroma is large genomic deletions of EXT1 and EXT2 genes. The

identified mechanism behind solitary osteochondromas is the homozygous

deletions of the EXT1 gene. However, the exact cause of osteochondroma is

unknown. Additionally, the molecular basis of genetics and clinical

variability of multiple osteochondroma as well as the underlying causes for the

malignant transformation and the onset of osteochondroma in EXT negative

patients is also currently unknown. Symptoms

Limited normal functions and movements are caused by osteochondromas growing

slowly and inwardly. The majority of osteochondromas are symptomless and are

found incidentally. Each individual with osteochondroma may experience symptoms

differently and most of the time individuals will experience no symptoms

at all. Some of the most common symptoms are a hard immobile painless palpable

mass, adjacent muscle soreness, and pressure or irritation with heavy

exercising. Major symptoms arise when complications such as fractures, bone

deformity or mechanical joint problems occur. If the occurrence of an

osteochondroma is near a nerve or a blood vessel, the affected limb can

experience numbness, weakness, loss of pulse or color change. Periodic changes

in the blood flow can also take place. Approximately 20% of patients

experiencing nerve compression commonly acknowledge vascular compression,

arterial thrombosis, aneurysm, and pseudoaneurysm. Formation of

pseudoaneurysm and venous thrombosis lead to claudication, pain, acute

ischemia, and symptoms of phlebitis. If the tumor is found under a tendon, it

can cause pain during movement causing restriction of joint motion. Pain can

also occur due to bursal inflammation, swelling or fracture at the base of the

tumor stalk. Some of the clinical signs and symptoms of malignant osteochondroma

are pain, swelling, and mass enlargement.

Diagnosis  Osteochondromas are often asymptomatic

and may not cause any kind of discomfort. They are often found

accidentally when an X-ray is done for an unrelated reason.

X-rays are the first tests performed that characterize a lesion. They show a

clear picture of dense structures of bones, and will also indicate bone

growth pertaining to osteochondroma. Computed Tomography scan can identify

the bony lesion in great details and show the presence of calcification.

These tests also provide great details, especially in soft tissues with the aide

of cross-sectional images. Magnetic Resonance Imaging is the most

accurate method for detecting bone masses in symptomatic cases to depict

precise morphology of a tumor. It is used to verify if the palpable mass is

continuous with the cortex of the affected bone and to differentiate an

osteochondroma from other lesions on the surface of the bone. MRI can also be

used to look for cartilage on the surface of tumor and can depict any

vascular complications caused by the tumor. An MRI can identify tumors of the

spinal column and is often used to diagnose low grade osteosarcoma.

Ultrasound is done if aneurysms or pseudoaneurysms and venous or arterial

thrombosis is suspected. Ultrasound is an accurate method for examining the

cartilaginous cap of the osteochondroma. It is also a way of pinpointing

bursitis. However, it cannot be used to predict if the growth of tumor is inward

in regards to the cap. Angiography is used to detect vascular

lesions caused by osteochondroma due to ossified cartilaginous cap. It is also

used to characterize malignant transformation lesions through

neovascularity. Clinical testing such as sequence

analysis can be done of the entire coding regions of both EXT1 and EXT2 to