Bone Tumors
Osteoid Osteoma
James C. Wittig, MD
Orthopedic Oncologist
Sarcoma Surgeon
GENERAL INFORMATION
Osteoid Osteoma is a benign osteoblastic (bone forming) tumor that is usually less than 2cm in size. It consists of a central vascularized nidus that represents the neoplastic tissue. The nidus is surrounded by normal reactive bone. It is usually a single lesion that is very painful. The nidus microscopically resembles the same type of tissue as an osteoblastoma.
CLINICAL PRESENTATION
Signs/Symptoms:
Progressive pain that is significantly relieved by aspirin or an NSAID (very rarely, less than 1%, may be painless)
The pain is often the worst an night
Unmyelinated nerve fibers have been demonstrated in osteoid osteomas
Osteoid Osteomas produce high levels of PGE2 (this may be the reason why aspirin works at relieving pain, by inhibiting PGE2 production)
Tumors next to growth plates may increase growth and cause skeletal asymmetry
Epiphyseal lesions may cause a joint effusion and clinical picture similar to rheumatoid arthritis
Vertebral lesions may cause a scoliosis due to muscle spasm
Prevalence: Males more commonly affected than females ~ 3:1
Age:
Osteoid Osteoma is most common in second decade of life
75%-80% of patients < 25 years
Rarely over 30 years
Sites:
Femoral neck most common but can occur in any bone and any site within a bone (metaphyseal, diaphyseal, epiphyseal; cortical, medullary and periosteal)
50% occur in long bones of lower extremities
Most osteoid osteomas are intracortical in origin but can also occur in the medullary canal or subperiosteal
RADIOGRAPHIC PRESENTATION
Plain X-Rays:
Lucent nidus surrounded by a zone of marked sclerosis
The nidus may demonstrate mineralization/ossification usually from the center outward that appears as a central zone of density within the nidus
A nidus that is heavily ossified may blend in with the surrounding sclerosis and be difficult to detect on a plain x-ray.
Periosteal bone is solid, rarely lamellated
Cortical and subperiosteal osteoid osteomas are usually associated with much more reactive sclerosis than medullary tumors
The periosteal reaction is continuous and often appears as cortical thickening (benign appearing reaction)
Intracapsular osteoid osteomas are difficult to identify because there is no periosteum in the intracapsular region and hence a periosteal reaction does not occur.
CT Scan:
Well defined nidus with a smooth peripheral margin; +/- mineralization (CT more sensitive than XR and MRI for detecting mineralization); CT is better for detecting nidus in presence of exuberant sclerosis
Radiographic Presentation
Bone Scan:
Double Density Sign: Hot within the nidus and less intense accumulation peripherally within the sclerotic bone
MRI:
MRI should be performed with gadolinium if possible. The nidus should enhance with gadolinium
An osteoid osteoma on MRI may mimic findings of a malignant tumor such as Ewing’s sarcoma or osteomyelitis because of the presence of marrow and soft tissue edema that can be extensive and make it difficult to discern a nidus.
CT is more useful for detecting the nidus if there is extensive edema
Osteoid Osteomas are Intermediate intensity on T1
High intensity on T2 in areas of nidus and surrounding edema
Reactive marrow edema may obscure the lesion on T2
MRI is good for detecting synovitis and joint effusion with intraarticular osteoid osteomas
Plain X-ray: Osteoid Osteoma
Plain X-Ray: Osteoid Osteoma
Radiolucent Nidus (arrow)
Surrounding Sclerosis
Benign Periosteal Reaction causing Cortical Thickening
CT Scan: Osteoid Osteoma
CT Reformatted Image: Osteoid Osteoma
MRI: Osteoid Osteoma
MRI: Osteoid Osteoma
Plain X-ray: Osteoid Osteoma of Femur
CT Scan: Osteoid Osteoma of Femur
Xray: Intramedullary Osteoid Osteoma of Proximal Femur
Radiolucent nidus
Mild reactive sclerosis around lesion
Intramedullary lesions are associated with less reactive bone than intracortical lesions that usually demonstrate intense reactive sclerosis
X-ray: Osteoid Osteoma of Distal Humerus Olecranon Fossa
Osteoid Osteoma of Distal Humerus:
CT Shows Nidus with Extensive Mineralization
X-Ray: Osteoid Osteoma of Tibia
X-Ray: Osteoid Osteoma of Tibia
Bone Scan: Osteoid Osteoma of Tibia
Bone Scan: Osteoid Osteoma of Tibia
CT Scan: Osteoid Osteoma of Tibia
CT Scan: Osteoid Osteoma of Tibia
Extensive Sclerosis Obliterated the Canal of the Right Tibia
X-ray: Osteoid Osteoma of Left Acetabulum
(Not Detectable on Plain X-ray)
Bone Scan: Osteoid Osteoma of Left Acetabulum
CT Scan: Osteoid Osteoma of Left Acetabulum (The nidus is a few millimeters)
MRI of Osteoid Osteoma of Acetabulum
(Nidus not Clearly Visualized)
There is Extensive Surrounding Edema
GROSS PATHOLOGY
The nidus is distinct oval/round and reddish from vascularity;
It is well circumscribed and easily separated from surrounding bone;
The nidus is usually less than 1 cm but may be up to 2 cm;
The nidus may have a variable consistency depending on the extent of mineralization
Friable, soft and granular to densely sclerotic
Gross Pathology: Osteoid Osteoma
Gross Pathology: Osteoid Osteoma Nidus
The nidus is reddish due to its vascularity
It may be friable, granular and gritty
Gross Pathology: Osteoid Osteoma
MICROSCOPIC PATHOLOGY
The nidus of an osteoid osteoma consists of vascularized fibrovascular stroma and trabeculae of immature woven bone
Nidus is sharply demarcated from surrounding reactive bone and there is an abrupt zone of transition between normal bone and the osteoid osteoma. There is no permeation of the lesion through the surrounding reactive trabeculae of bone,
The trabeculae are uniformly lined by plump, uniform, active osteoblasts (“Osteoblastic Rimming)
Osteoclasts may be prominent
Mature nidus consists of more heavily calcified trabeculae of woven bone and osteoid
No abnormal mitoses
Microscopic Pathology: Osteoid Osteoma
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Interlacing trabeculae of woven (immature) bone and osteoid (Arrows)
Bone is lined by plump, uniform, regularly arranged osteoblasts (Osteoblastic Rimming)
No mitotic figures
No pleomorphism
The intervening stroma is very well vascularized |
Microscopic Pathology: Osteoid Osteoma Nidus
Low Power View
Osteoid Osteoma
Intermediate Power
Osteoid Osteoma High Power
This is a high power view
Notice the plump, regularly arranged osteoblasts that surround and line the woven bone trabeculae. This is referred to as “Osteoblastic Rimming”
There are no mitoses and minimal pleomorphism
Microscopic Pathology: Osteoid Osteoma
Microscopic Pathology: Osteoid Osteoma
DIFFERENTIAL DIAGNOSIS
Differential DX of Cortical Osteoid Osteoma
Brodie Abscess
Stress Fracture
Eosinophilic Granuloma
Intracortical Hemangioma
Bone Island
Intracortical Osteosarcoma
Ewing’s Sarcoma
BIOLOGICAL BEHAVIOR
Osteoid osteomas exhibit limited growth potential and grow to a certain size and then stop growing;
Some tumors may spontaneously regress;
Osteoid osteomas that occur next to joints or intra-articularly may cause the adjacent synovium to become thickened -
There may be chronic inflammatory cell infiltrates with lymphofollicular features in the
synovium that can be mistaken for rheumatoid arthritis
TREATMENT
Today, most osteoid osteomas are amenable to CT guided percutaneous radiofrequency ablation (RF Ablation). This is a minimally invasive technique in which the patient is put under general anesthesia and the nidus is localized under a CT scan. A needle is placed in the nidus and then the nidus is burned by means of radiofrequency waves. It is over 90% successful and there are minimal risks. Most patients notice that the pain is gone the very next day. There is little down time and most patients return to normal activities within a day or two.
Some patients may require open surgical excision or "Burr Down Resection" of the osteoid osteoma.
PROGNOSIS
This is a benign tumor and there is no risk of metastasis;
RF Ablation is effective over 90% of the time;
Results of RF ablation are better than those reported with surgical excision and there is far less morbidity and potential complications.
OTHER IMPORTANT INFORMATION
May be difficult to identify nidus grossly - especially in sclerotic intracortical regions
Tetracycline labeling is of great assistance in locating nidus
Osteoid osteoma of the extremities may cause atrophy of nearby muscles
If nidus is radiographically undetectable, patient may be mistakenly treated for arthritis
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