Background
Osteoid osteoma is a benign bone tumor and constitutes 11% of all benign bone tumors and 5% of all primary bone tumors [1]. It usually affects the young man, in second or third decade of life. However it can affect a wide range of individuals aged 8 months to 70 years. The male to female ratio is 3:1 [2] . Osteoid osteoma can occur in any bone. It predominantly involves the cortex of shaft of long bones of lower limbs (90%) [3]. It rarely affects the scapula and only few cases have been reported in literature. Mosheiff et al, reviewed the literature of 1236 cases of osteoid osteoma and reported the involvement of 12 scapula [4].
Case description
A 46 years old male, presented with pain in left shoulder for 1 month. The pain increased at night, worsened with physical activities and improved with rest and analgesics. He had no history of significant trauma or previous joint disease.
On physical examination, his shoulder had no swelling and deformity, however there was mild limitation in the movement of affected joint.
Plain radiograph showed an ambiguous oval shaped lytic lesion with ill-defined margins and no periosteal reaction or marginal sclerosis. Differential diagnosis include, primary bony tumor, osteoid osteoma, osteoblastoma, Brodie’s abscess and geode. Bone scan done with Tc99m MDP showed osteoblastic response in the lesion seen on X-ray. Correlative SPECT – CT images showed a lesion in acromion with central lucent nidus measuring 13.5 × 7.6 mm, favoring the diagnosis of osteoid osteoma.
Discussion
Osteoid osteoma is a benign tumor which can occur anywhere in the skeleton. However the acromion of scapula is a rare site of osteoid osteoma location and therefore often is neglected, when listing differential diagnosis of shoulder pain. Degreef et al. first in 2005 described the occurrence of an osteoid osteoma in the acromion in a female patient aged 56 years [5].
A characteristic history of night pain relieved by aspirin is seen in many patients with osteoid osteoma, however it can attribute to rotator cuff pathology in case of shoulder pain [6]. An atypical history and lesions in unusual locations can confuse the diagnosis with inflammatory arthritis, osteomyelitis, especially Brodie abscess, eosinophilic granulomas and other benign cysts. In the present case, patient’s history is typical for osteoid osteoma, however the site is unusual for osteoid osteoma.
Plain X-rays are not usually sufficient for diagnosis. Tc99m MDP bone scan is quite sensitive tool for localization of any osteoblastic lesion. The sensitivity of bone scan for detection of osteoid osteoma is virtually 100% [7]. However the detection is often difficult with planner images and correlative SPECT – CT imaging may play an important role in the diagnosis, especially in unusual locations.
Treatment depends upon the symptoms of the patient. If the patient’s symptoms are adequately controlled, anti-inflammatory medications can be used as a final treatment, which may lead to final healing (autolysis) of the lesion in three to five years [8]. Other treatment options involve percutaneous ablation by radiofrequency and surgical procedures involving complete removal of the nidus by curettage, en bloc resection or by arthroscopic route [9].
In osteoid osteoma pain aggravates at night, the reason is still unknown. Spontaneous regression has been reported in some cases of osteoid osteoma. However; the reason why there is spontaneous regression is so far unclear. Further research is required to completely understand the pathophysiology of such lesions.