Thursday 8 December 2005
Digital cases - Digital slides
Definition: Osteoid osteoma is a benign bone-forming tumour with limited growth potential, inducing disproportionate pain.
Osteoid osteomas are usually smaller than 1.5-2 cm and characterized by an osteoid-rich nidus in a highly loose, vascular connective tissue.
The nidus is well-demarcated and may contain a variable amount of calcification. Surrounding the nidus is a zone of sclerotic but otherwise normal bone.
Osteoid osteomas are painful lesions of bone that are relatively common, small (less than 1 cm in diameter), solitary, and benign.
Characteristically seen in children and adolescents, with boys affected more than twice as frequently as girls, about half the cases present in the lower extremity.
The etiology of this bizarre self-limiting condition remains obscure.
The characteristic clinical presentation is nocturnal pain, which is usually relieved by aspirin.
On physical examination, local swelling may be apparent and the lesion may be exquisitely tender; mild leukocytosis may be present.
- pain with nocturnal exacerbation, relieved by salicylates and NSAID
- exquisite, localized tenderness
The typical lesion is located within the cortex of a long bone, and exhibits on imaging studies a central lucent zone (or nidus) with increased sclerosis of the surrounding bone, which may also show marked periosteal new bone formation.
Osteoid osteomas located subperiosteally or in the cancellous portion of the bone may have much less surrounding sclerosis.
On bone scans, the lesions show increased uptake of radioactive isotope.
The radiologic differential diagnosis includes a small focus of osteomyelitis or a stress fracture.
When the lesion is close to or within a joint (often the hip), the patient may present with an effusion and symptoms of synovitis.
Indeed in such a case, synovial biopsy often reveals a marked lymphoproliferative synovitis.
This type of clinical presentation, which is not likely to be immediately diagnosed as osteoid osteoma, is seen in approximately 20% of the cases that are juxta-articular.
Osteoid osteomas that are close to the epiphysis may occasionally result in growth disturbance and deformity.
Another group of patients in which the diagnosis may be delayed are individuals with lesions in the vertebral column, who might present with scoliosis.
At surgery, the lesion is often difficult to find, although there may be a mild pinkish cast to the overlying cortical bone due to the periosteal reaction and increased vascularity.
Preoperative technetium [99Tc] isotope injection has been used for intraoperative localization of the lesion.
The lesion itself may appear as a well-demarcated nodule, often cherry red, but occasionally very dense and white.
Magnetic resonance imaging scan (MRI) shows increased blood flow or edema both of the bone and surrounding tissues.
Osteoid osteoma is a relatively common bone tumor, accounting for approximately one eighth to one tenth of all symptomatic benign bone tumors and 5% of all primary bone tumors.
Osteoid osteoma is generally a condition of the young, but it can affect a wide range of individuals aged 8 months to 70 years.
The literature reports that people aged 10-30 years are most susceptible.
About 90% of cases occur in patients younger than 25 years.
The tumor is less common in patients older than 30 years, accounting for 13% of cases. About 3% of cases occur in children younger than 5 years
Men are affected more frequently than women. The male-to-female ratio is 2-3:1.
No racial or ethnic predilection is noted for osteoid osteoma.
The lesions tend to occur near the end of the diaphysis, but almost any bone may be involved and in any location.
Osteoid osteoma can occur anywhere and can involve a single bone or several bones. Osteoid osteoma is reported to occur in the cortex of the shafts of long bones in 80-90% of cases.
Osteoid osteoma is also reported in the epiphyseal and metaphyseal regions of both small and large bones of the axial and appendicular skeletons, especially the femur, tibia, and humerus.
A fine grain radio graph may be helpful in determining the location of the nidus of an osteoid osteoma in the curetted tissue submitted at the time of operation for microscopic examination.
most common in long bones (femur)
virtually every bone (except sternum)
dense cortical sclerosis around a radiolucent nidus
- rarely : target-like lesion (if central sclerosis)
area of cortical thickening, in the center of which is a lucent defect
important amount of reactive bone tissue
Osteoid osteoma typically consists of a discrete central nidus usually < 1 cm with diffuse peripheral sclerosis.
The nidus is usually a distinct, well-circumscribed cavity, surrounded by dense reactive bone of varying thickness.
The nidus is typically cherry red in color and can be shelled out of the surrounding reactive bone.
The nidus varies in consistency from vascular, soft, friable, gritty, and granular to densely sclerotic.
During surgery, an increased number of fine, punctuate vessels and adherent periosteum overlying the lesion may be observed.
Osteoid osteoma is usually cortical and may extend into the periosteal or endosteal surface of the bone. It is rare in the spongiosa.
- central nidus
- connective tissue
- differentiating osteoblasts producing osteoid and sometimes bone
- with or without osteoclasts
- woven immature bone with prominent osteoblasts and osteoclasts
- surrounding sclerotic bone
Osteoid osteomas are characterized microscopically by a maze of small spicules of immature bone, most often lined with prominent osteoblasts and increased numbers of osteoclasts.
In more mature lesions, the intervening stroma is sparsely cellular, with readily apparent vascular spaces.
Cartilage matrix formation does not occur. Very rare cases have been observed in which multiple nidi were present.
The nidus is typically composed of a mass of irregular osteoid tissues that lie in a highly vascular stroma of connective tissue containing osteoblastic cells.
The nidus consists of irregular lace-like osteoid and calcified matrix lined by plump osteoblasts and osteoclasts with a well-vascularized but bland stroma.
The microscopic appearance of osteoid osteoma may vary with the degree of lesional maturity:
During the initial stage of the disease, proliferation occurs in osteoblasts and vascularized spindle cell stroma with minimal new bone formation.
In the intermediate stage, patches of calcified osteoid between the neoplastic stromal cells appear.
The mature stage manifests with densely packed atypical bony trabeculae with decreased vascularity and stroma.
The histologic stage is not correlated with the patient’s clinical picture.
The pathophysiology of osteoid osteoma has been controversial as to whether it is neoplastic or inflammatory.
However, its relatively small size, self-limited nature, and intracellular viral particles (as observed on electron microscopy) may suggest an inflammatory process.
Pain in osteoid osteoma has been typically attributed to the nidus, with its associated hyperostosis and neural elements in the reactive fibrous tissue.
Golding described radially oriented trabeculae of surrounding reactive bone, which implied an increased pressure in the vascular nidus.
This arrangement of the bony trabeculae was attributed to the stresses placed on them.
This increased pressure due to vasodilatation and edema is thought to directly stimulate intraosseous nerve endings, generating pain. Schulman et al supported this observation, finding increased amounts of unmyelinated nerve fibers, with greatest abundance next to arterioles. These fibers were believed to be sensitive to changes in vascular pressure.
Prostaglandins have been implicated and linked to osteoid osteoma.
Several authors have even suggested that they may have a fundamental role in the development of osteoid osteoma.
Support is derived from reports of a 100- to 1000-fold increase in levels of prostaglandins, particularly prostaglandins E2 and I2 (prostacyclin), in the nidus that was reversible on extirpation of the tumor.
Furthermore, the dramatic response to salicylates or nonsteroidal anti-inflammatory drugs (NSAIDs), which affect prostaglandin synthesis, supports the suggested role of prostaglandins in the pathophysiology of pain.
Healey and Ghelman described 2 pathways of pain generation due to prostaglandins. The first involves permeability and vasodilatory effects, which increase the size and flow of vessels in the bony lesion, increasing pressure and pain. The second involves its effect in the bradykinin system, which potentiates pain akin to injured soft tissues.