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In this report, we discuss a case of a 30-month-old male presenting with a painful limp. Plain radiographic studies gave a preliminary diagnosis of a Brodie abscess. Further studies, including magnetic resonance imaging (MRI), were more consistent with that of an osteoid osteoma located within the tibial medullary canal, which is a rare location. The patient had an excisional biopsy. The final pathologic diagnosis confirmed intramedullary osteoid osteoma.
The cause of limp in a child may be a result of trauma, infection or neoplasm. If findings on plain radiographs are consistent with infection or neoplasm, further non-invasive studies may be warranted prior to any surgical intervention. Potential diagnoses include osteoblastoma, osteomyelitis, eosinophilic granuloma, osteogenic sarcoma, Ewing sarcoma or healing fracture. While studies such as computerized tomography (CT) scans, MRI, or bone scan may help delineate these lesions, a final diagnosis frequently requires a pathologic specimen.
A 30-month-old male patient presented to our pediatric orthopedic clinic with a two-to-three-month history of right leg pain. The mother reported mild relief of pain with acetaminophen during the day and ibuprofen at night. She denied any recent trauma. The patient's medical history was significant for craniofacial reconstruction for craniosynostosis at the age of nine months, and slightly delayed motor development. Physical exam showed symmetric non-tender lower extremities with normal strength and sensation. No leg-length discrepancy was noted. The patient was ambulatory with an antalgic gait. He localized the pain to the distal aspect of his right lower extremity. Initial plain radiographs of the right lower extremity were normal. The patient was given a fracture boot for comfort.
At his one-month follow up appointment, the patient had increasing pain. His mother reported frequent falls and stated that he often held his ankle complaining of pain. His limp had progressed with a diminished stance phase on the right limb. Repeat radiographs revealed a lesion of localized sclerosis with central lucency within the distal tibial diaphysis (Figures 1A and 1B). This was consistent with a Brodie abscess, a region of chronic localized osteomyelitis. An MRI with intravenous contrast was performed to further delineate this lesion. On T1- and T2-weighted images of the distal tibial diaphysis, a centrally placed 5mm x 4mm x 16mm area of decreased signal intensity was identified (Figures 2 and and3).3). This lesion was associated with bone marrow edema and peripheral enhancement; however, there was no fluid collection or soft tissue mass present. While this lesion was in an unusual location, it was more consistent with osteoid osteoma. The patient underwent an open excisional biopsy of the lesion. The nidus, with surrounding sclerotic bone, was excised. The cavity was then filled with demineralized bone matrix. Final pathologic specimen analysis confirmed the diagnosis of osteoid osteoma. Post-operatively the patient was placed into a short-leg cast and allowed to bear weight as tolerated. At his one-month follow-up, the patient had no pain or recurrence of his symptoms.
Osteoid osteoma is a common benign bone lesion in the pediatric and young adult populations. Typical age of patients ranges from five to 40 years old, with reports of patients from nine months to 77 years of age reported in the literature.6 Males are more commonly affected at a 1.6–4 ratio.3 Long bones are the most common location for these lesions with the majority occurring in the lower extremity.7 Presenting symptoms in children are often pain, which is worse at night and relieved with salicylates,3 and a noticeable limp.6
The location of these lesions within the bone may vary. The classic and most common location is within the cortex.7,8 These lesions have also been found in the periosteal region of long bones.7 Children can have lesions involving the epiphyses of long bones. In all patients, the intramedullary location within bone is relatively infrequent, 2/38 in one study and 6/67 in another.7,8 In our review of the literature, only one report of two intramedullary osteoid osteomas in young pediatric patients was described, in the French literature.5 Similar to our patient, both of these patients in the literature were under 3 years of age, and the lesions were in the distal tibia. However, unlike our patient, the two in the literature had reactive bone formation more characteristic of cortical lesions.
The differential diagnosis of an osteoid osteoma includes osteoblastoma, osteomyelitis, eosinophilic granuloma, osteogenic sarcoma, Ewing sarcoma or healing fracture. Typical radiographic findings are of a dense ivory-like sclerotic mass attached to the bone with sharply demarcated borders.4 When localized in the cortex, these lesions often evoke a reactive sclerosis; however, intramedullary lesions often fail to elicit such a response.8 Further delineation can be obtained using computerized tomography (CT) scan or MRI. CT scans generally show a small lucent nidus surrounded by reactive sclerosing bone, sometimes seen on plain films.2 Visualizing the nidus by MRI can be difficult, and intramedullary soft tissue changes may produce a misleading aggressive appearance.1 Typically, an intermediate signal is seen on T1 and a high-intensity signal on T2-weighted images. Low-intensity signal within the nidus on T2 images suggests calcification.2
Treatment options for an osteoid osteoma include prolonged non-steroidal anti-inflammatory drug (NSAID) use, CT-guided ablation and surgical excision.3 In this case, we chose surgical excision. While prolonged NSAID use has been shown to be effective, we were uncomfortable placing a two-year-old on long-term non-steroidal medication due to skeletal and renal complications. Likewise, CT-guided ablation could have been performed and this is done regularly at our institution. However, performing this on a two-year-old would have required anesthesia during the procedure. Therefore, we proceeded with an open excisional biopsy performed under the controlled environment of the operating room. This allowed for an adequate tissue sample to be sent for pathology and direct visualization of the nidus, helping to ensure complete excision.
In this case, we present a rather common pathologic lesion, osteoid osteoma, found at an atypical age, 30 months, in an uncommon location, within the medullary canal of the distal tibia. Because this lesion did not have the common reactive sclerosis often seen in cortical osteoid osteomas, diagnosis is more difficult.
The cause of pain in a limping child can often be difficult to discern. Osteoid osteoma should be kept in mind as a source of pain in the pediatric age group, with or without "classic" radiographic features.