Osteoid osteoma (OO) is a solitary benign bone-forming tumor, which accounts for approximately 10% of all benign bone tumors. 8 Although most publications attribute the first report to Jaffe in 1935, 3,13 Bergstrand was probably the first to describe two cases, in 1930. 16,25,29 OO appears most commonly between the second and third decades of life, usually in men. 16,23,25 The most frequent location is in the cortical region of the diaphysis of long bones (especially the femur, tibia, and humerus), mainly in the lower limbs. The foot is only rarely involved. 27 In a review of a series of 860 cases of OO, Jackson found an incidence of less than 4% in the foot and of 1.7% in the metatarsals. 12 The typical clinical presentation is severe pain, in spite of the small size of the tumor. This pain is predominantly nocturnal and typically remits with anti-inflammatory drugs; 16 there is usually an increase in local temperature. 14 If the lesion is superficial there may also be slight local swelling, which may raise the suspicion of an infection. 9,24 The typical radiographic image when the tumor affects the cortical region shows a hypodense hypervascular focal area, or nidus, usually less than 1 cm in diameter, surrounded by a thickening of the cortical region of the reactive bone.Atypical location and clinical symptoms may hinder diagnosis. Shereff et al reported that this tumor is often located in the cancellous bone, or in the subperiosteal region in the small bones of the foot. 23 In these cases x-ray will not produce the standard image; in many cases the cortical reinforcement limiting the nidus is missing. 24,26 Moreover, when the OO is intra-articular, the symptoms may include arthritis as the tumor may cause inflammation of the synovium, thus adding the range of inflammatory joint diseases to the differential diagnosis and complicating clinical diagnosis even further. 7,24,25,27,29 Case Report A 26-year-old woman consulted for pain in the first metatarsophalangeal joint of the right foot over 7 months, with no previous history of trauma. The patient presented with swelling and slightly increased local temperature and painful limitation of joint mobility. The pain was worse at night, but remitted partially with oral anti-inflammatory drugs. Local palpation exacerbated the pain. There were no neurovascular disorders in the limb, and laboratory parameters were within normal limits. Plain x-ray ( Figure 1) showed a lytic lesion of about 4 mm in diameter on the dorsal side of the first metatarsal head. Bone scintigraphy with technetium-99 ( Figure 2) revealed a nonspecific focal increase in isotope uptake, located in the dorsal area of the first metatarsal head, which may have corresponded to an arthropathic process or even to a stress fracture. This picture was confirmed on CT (Figure 3), which detected an osteolytic lesion less than 1 cm in the first metatarsal head, with a sclerotic central area surrounded by a faint sclerotic rim, suggesting an osteoid osteoma. The lesion extended to the articular cartilage at th...
