50% of cases involve the femur or tibia, where they commonly arise in the cortex.
Osteoid osteomas are painful lesions.
The pain is caused by excess prostaglandin E 2 which is produced by the proliferating osteoblasts.
It characteristically occurs at night and is dramatically relieved by aspirin.
Failure to increase in size with time
Replacement by scar tissue
These features are unlike those
of other benign tumors
suggesting that the etiology
still remains an enigma.
10-11% of all benign bone tumors
2.5%-5% of all bone tumors
First three decades of life
Most common-second decade
Most common-in men (2:1)
Diaphysis of femur and tibia
Medial side of neck of femur
Posterior elements of spine
Phalanges of hand
Pain which has characteristic pattern described variously as sharp,dull,boring deep,or intense often worst at night and very frequently relieved by salicylates*(aspirin)
Muscular atrophy due to disuse
Swelling and warmth if it is superficial
Adjacent joint stiffness
In children overgrowth and angular deformities
Nerve root compression or cord compression
Point tenderness over the lesion
Cherry red to gray red tissue
Overlying cortex distorted
Reactive periosteal new bone formation
Nidus may vary
from few mm to
1.5 cm in diameter.
Surrounding reactive bone
usually thick hard and
Numerous osteoblasts forming highly irregular trabeculae of osteoid and woven bone
Woven bone trabeculae variably mineralized
Calcification more near centre of lesion.
At times no calcification of nidus
Surrounding bone shows reactive bone formation which is lamellar bone in contrast to woven bone of nidus
Thin zone of fibrovascular tissue between nidus and reactive bone .
Small to round to oval focus of decreased density called nidus .sometimes nidus also sclerotic.
Surrounding area of sclerosis which is normal reactive bone .
Lesions usually in diaphysis
Mostly cortical sometimes inside medullary canal or subperiosteally
Periosteal reaction when occurs is large but smooth in contrast to “codman triangle ” of malignant lesions
Useful in detecting small lesions
“ Double density sign” which is a focal area of increased activity with a second smaller area of increased uptake superimposed on it is said to be diagnostic.
Sometimes required to localise the lesion accurately.
Osteoid osteoma. A lateral view (A) of the proximal tibia shows a very dense lesion in the posterior cortex. A darker central area contains a white nidus. This lesion in a 20-year-old man caused pain in this area, relieved by aspirin. B, A nuclear medicine bone scan in a different patient with an osteoid osteoma in the left lower tibia shows increased activity (arrows) at the site of the lesion.
Osteoid osteomas, especially those that arise beneath the periosteum, usually elicit a tremendous amount of reactive bone formation that encircles the lesion. The actual tumor, known as the nidus, manifests radiographically as a small round lucency that is variably mineralized
Specimen radiograph of intracortical osteoid osteoma. The round radiolucency with central mineralization represents the lesion and is surrounded by abundant reactive bone that has massively thickened the cortex.
High levels of prostaglandins present in osteoid osteoma which mediate pain receptor pathway
Aspirin (salicylates) act as prostaglandin synthetase inhibitors
Surgical removal of lesion
To relieve pain.secondary manifestations like synovitis ,scoliosis, nerve root compression
Necessary to remove the “NIDAL” tissue
Block resection of the nidus
Increases risk of subsequent # if lesion is in cortical bone
Alternative method is to shave the reactive bone with sharp osteotome until the nidus is exposed ,then curette the exposed nidus
Intraoperative localization of nidus possible with pre operatively injected technetium labelled methylene diphosphonate and sterile wrapped geigercounter.
Intraoperative xrays of excised specimen to document complete removal of nidus
K-wire inserted into the nidus
Biopsy punch inserted over k-wire
Percutaneous CT guided resection using a trephine 2mm larger then the lesion to ensure complete removal.
Initial core needle biopsy after which radiofrequency electrode is inserted through cannula of biopsy needle
Temperature at the tip raised to 90 degrees centigrade for 6 minutes
Results:claim to be equivalent to surgical excision
Used only in extraspinal lesions that are away from neurovascular structures
Osteoid osteomas’ are considered benign and are normally treated by conservative surgery. However there is a possibility of malignant transformation. This is rare except when treated with radiation, which promotes this complication.