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
detect mutations. A biopsy of the tissue sample of the
tumor can also be taken to check for cancer.
Tests for osteochondroma can also identify diseases such as secondary
peripheral chondrosarcoma and Multiple osteochondromatosis. In large, secondary
chondrosarcoma arises at the site of osteochondroma due to increased
thickness of the cartilage cap indicating potential malignant
transformation. The symptoms of multiple osteochondromatosis are similar to
solitary osteochondroma, but they are often more severe. Painless bumps can
arise at the site of tumor and pain and other discomforts can also take place if
pressure is put on the soft tissues, nerves, or blood vessels. Dysplasia
Epiphysealis Hemimelica or Trevor's disease and metachondromatosis are
considered differential diagnosis of both solitary and hereditary
osteochondromas. DEH is described as a type of over growth at one or more
epiphyses. Similar to osteochondroma, DEH is diagnosed prior to 15 years of
age and the growth of lesions end at puberty, when the growth plates close.
Metachondromatosis is a rare disorder that exhibit symptoms of both multiple
osteochondromas and enchondromas in children and is also inherited in
autosomal dominant mode. Treatment and prognosis
Osteochondromas are benign lesions and do not affect life expectancy. Complete
excision of osteochondroma is curative and the reoccurrences take place when
the removal of tumor is incomplete. Multiple reoccurrences in a well-excised
lesion indicate that it may be malignant. The risk of malignant
transformation takes place in 1–5% of individuals. If any symptoms of
cancerous tumor takes place, then the patient should be evaluated by a bone
specialist. No treatment is necessary for Solitary osteochondromas that are
asymptomatic. Treatments for solitary osteochondroma are careful observation
over time and taking regular x-rays to monitor any changes in the tumor. If the
lesion is causing pain with activity, nerve or vessel impingement, or if the
bone growth has fully matured and the presence of a large cartilage cap is
prominent, then it is advised that the tumor be surgically removed.
Osteochondromas have a low rate of malignancy (