OSTEIOD OSTEOMA

A commonly occurring benign bone forming tumour can occur in any age group with increased male preponderance. It was first described in 1930 and later identified as a separate disease in mid of 1930s. osteoid osteoma can involve any bone but is more commonly found in long bones and that too in tibia, femur and humurus. Involvement of spine, hand and feet is also documented.

Almost two third of all cases of osteoid osteoma occur in the long bones involving shaft, epiphyses of diaphysial region. When spine is the site, involvement is mor.e commonly seen in posterior components like spinous processes, lamina or pedicles. Facet joint involvement can also occur.

Patient presents with onset of pain in the region of affected bone. Pain is sharp and agonizing and starts more often at night. It is relieved by taking medications like disprin. Pain usually does not occur in the morning of day time. Sometimes patient may present with swelling at the site of lesion.

On examination, there may be element of tenderness at the site of tumor. There may be obvious swelling. Sometimes, although not common, there may be warmth and redness suggesting inflammatory process.

Laboratory findings are usually normal and the diagnosis is often delayed for quite some time. There have been evidences that a 3 year delay was documented from the onset of symptoms. This delay is contributed by many factors including equivocal imaging findings, complete pain relief by salicylates and sometimes complete resolution with time.

DIAGNOSING OSTEOID OSTEOMA:

X-RAY:

Imaging has evolved greatly and routine use of radiography is still considered to the first modality of choice in the diagnosis of osteoid osteoma. On x-ray, there is a lucent line in the region of tumor with surrounding rim of increased bone density or sclerosis. There is thickening of cortex. The central lucent area is called nidus and consists of highly vascular soft tissue component of the tumor. Sometimes the lesion is in the subperiosteal region and lucent line may not be appreciated. It is quite possible that only sclerotic rim is visible and no lucent nidus appreciated. If the lesion is intra-articular, then it may be possible to only appreciate minimal sclerosis around the central lucency.

Tumor usually does not extend beyond 2 cm size. If spine is involved, there are much more chances of scoliosis with concave side towards the tumor. Any young who complains of neck or back pain should be suspected of having this tumor and be investigated accordingly. Most common age of this tumor is about twenty five years.

CT SCAN IN THE DIAGNOSIS OF OSTEOID OSTEOMA:

Computational tomography is now considered best modality of choice for those lesions which are not picked on routine x-ray examination. CT helps to better localize and define the lesion. A nidus can be found easily in this modality. It also confirms the presence of surrounding sclerosis and thickening of cortex. This modality is considered best for detecting intra-articular lesions specially hip joints. With the advent of multiplaner reconstruction, it is easier to localize the tumor.

BONE SCANNING IN THE DIAGNOSIS OF OSTEOID OSTEOMA:

This modality has a hundred percent sensitivity in the diagnosis of osteoid osteoma. It can detect lesions which were missed on x-ray. It can also differentiate it from other lesions like spondylolysis by performing immediate and delayed scanning. In case of osteoma, there is tracer uptake immediately after injection, a feature which is not seen in case of spondylolysis.

MAGNETIC RESONANCE IMAGING IN THE DIAGNOSIS OF OSTEOID OSTEOMA:

MRI is not considered better option because it can miss the lesion and also there is sometimes confusion in interpretation of lesion. Features may suggest malignancy when it is not there. Nevertheless, MRI will show hypointense signals in the lesion on T1W imaging with post-contrast enhancement which may be uniform of ring like.

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