Presentation
Football player presented with a six-month history of posterior thigh pain. While he related the onset of pain to playing football, he did not give a clear history of trauma. The pain reliably woke him from sleep (at about 4am) each night and was almost completely eliminated when he took oral ibuprofen before bed.
Patient Data
Radiograph shows fusiform cortical thickening of the anterolateral cortex of the proximal femur.
There is a small intracortical osteolytic lesion without central calcification, surrounded by a prominent zone of reactive sclerosis due to periosteal and endosteal reaction.
MR T1 coronal image demonstrates the wide cortical thickening. T1-weighted images show the low-signal-intensity nidus, which has strong enhancement. STIR images shows a intracortical osteoid osteoma of the right proximal femur, with inflammatory reaction in the adjacent cancellous bone and in the soft tissues.
Histological report
Translation from Italian to English: nidus to be formed by osteoid tissue and newly formed bone trabeculae, immersed in a fibrous tissue, rich in vessels. The perifocal reaction zone is characterized by thickening and sclerosis phenomena with thickened bone trabeculae associated with edema of the loose connective tissue. Proceeding to the examination of the furthest layers of the cancellous bone it is observed that the trabeculae have normal dimensions and disposition, but the medulla is fibroadipose, with notes of edema and does not show any trace of hematopoietic tissue. Histological diagnosis: Osteoid osteoma.
Case Discussion
Osteoid osteoma is a benign osteoblastic tumor that is usually less than 2 cm in size. It consists of a central vascularized nidus that represents the neoplastic tissue. The nidus is surrounded by normal reactive bone. It is most frequently found in long bones, such as the femur and tibia, but can occur at any site. Cortical thickening surrounding a small central core of lower density, the nidus, are the classical radiological finding.
X-rays may be normal; however, the cortical thickening is generally well visualized with this imaging modality. The central “nidus” is sometimes visible on x-rays as a well-circumscribed lucent region, occasionally with a central sclerotic dot. CT imaging considered to be the imaging modality of choice. On this imaging modality appearing as a focally lucent area within surrounding sclerotic reactive bone. In juxta-articular localization, the reactive sclerosis may be absent.
Kayser et al. have classified osteoid osteoma into four categories according to the relation of the lesion with the bone cortex: subperiosteal (located on the external aspect of the cortex, surrounded by periosteal reaction), intracortical (located within the cortex), endosteal (on the internal of the cortex) and medullary (located within the medullary bone).