Limping In A 12-Year-Old Boy

A 12-year-old boy reported a gradual onset of left thigh and knee pain and limping for 18 months before presenting to the authors’ institution. Plain radiographs taken 12 months before presentation revealed a lesion in his left femur. He had been admitted to another institution for evaluation, where magnetic resonance imaging (MRI) and computed tomography (CT) scanning were done. An incisional biopsy was done at the outside institution and revealed reactive bone. After the biopsy specimen was obtained, the extremity was placed in a long leg cast, and the patient used a wheelchair for 1 month. After cast removal, the patient received outpatient rehabilitation for 2 months. A slight clinical improvement was reported during this period, but pain and limping soon returned. The patient otherwise was healthy with only one previous surgery of bilateral myringotomies at age 3. His mother’s pregnancy, and the developmental, and family histories were normal. On presentation to the authors’ institution, the patient described some discomfort in the distal part of his left thigh. There was no swelling, erythema, or tenderness over the area of the well-healed incision from the previous biopsy. There was mild atrophy of his left thigh musculature, but the patient had full active range of motion (ROM) in the left knee. The neurovascular examination was normal. His gait was abnormal with a mild antalgic limp on the left lower extremity. Plain radiographs, MRI scans, and CT scans of the patient’s extremity obtained before the first incisional biopsy are shown in Figures 1 through 6.Fig 1 A–B.: Plain (A) anteroposterior and (B) lateral radiographs of the left distal femur.Fig 2.: Axial CT scan of the left distal femur.Fig 3.: Coronal T1-weighted MRI scan of the left distal femur.Fig 4.: Coronal STIR image of the left distal femur.Fig 5.: Axial T1-weighted image of the left distal femur.Fig 6.: T1-weighted image of the left distal femur taken after gadolinium enhancement.Based on the history, physical findings, and imaging studies, what is the differential diagnosis? RADIOGRAPHIC INTERPRETATION The anteroposterior (AP) and lateral plain radiographs (Fig 1) of the distal femur showed irregularly thickened and lamellated periosteal reaction and cortical thickening along the anteromedial aspect of the distal femoral diametaphysis. There was increased radiodensity of the adjacent medullary cavity and peripheral disruption of the periosteal reaction. The axial CT scan (Fig 2) showed the irregular periosteal reaction and cortical thickening and a small, cortically-based lucent lesion with a central calcified nidus. The coronal T1-weighted image (Fig 3) showed mixed low and intermediate signal intensity involving the distal femur. An anterior coronal short tau inversion recovery (STIR) image (Fig 4) revealed a central focus of heterogeneous, but predominantly high signal with surrounding mixed intermediate and low signal. Also observed was the thickened, high signal intensity periosteum. The axial T1-weighted image (Fig 5) showed the intermediate signal intensity nidus surrounded by cortical thickening of low signal intensity and periosteal reaction of intermediate signal. The T1-weighted, fat saturated image (Fig 6) taken after gadolinium enhancement showed dense enhancement of the lesion and the periosteal reaction. DIFFERENTIAL DIAGNOSIS Based on plain radiographs: Osteosarcoma Langerhans cell histiocytosis Chronic osteomyelitis Osteoid osteoma Osteoblastoma Based on plain radiographs, CT scans, and MRI scans: Osteoid osteoma Chronic osteomyelitis After presentation to the authors’ institution, the patient had CT scanning, which revealed the same findings as CT scanning taken before the first biopsy. An excisional biopsy with a frozen section then was done (Fig 7).Fig 7 A–B.: Photomicrographs of the lesion (Stain, hematoxylin and eosin; magnification (A) ×20 and (B) ×40).Based on the history, physical findings, radiographic studies, and the histologic picture, what is the diagnosis and how should this lesion be treated? HISTOLOGIC EVALUATION Grossly, the specimen consisted of oval, tank-pink to dark pink-red bony tissue measuring 1.5 × 1.0 × 0.7 cm in aggregation. The hematoxylin and eosin stained sections (Fig 7) revealed a nidus showing a vascularized stroma with numerous dilated capillaries, and irregular trabeculae of bone associated with osteoblasts and osteoclasts. This area easily was demarcated from the reactive surrounding bone. DIAGNOSIS Osteoid osteoma TREATMENT AND DISCUSSION Based on the history, physical examination, imaging studies, and histologic appearance, the diagnosis of osteoid osteoma was confirmed. Complete excision of the nidus was done using a high-speed surgical burr. Precise preoperative anatomic localization of the lesion was aided by preoperative imaging studies (in particular, thin-section CT scanning) and direct visualization of the lesion intraoperatively by fluoroscopy. By successive passes with a high-speed burr through the dense, sclerotic cortical bone, the softer, red nidus was encountered easily. The nidus was removed with a curette and sent for histologic analysis; the bed was extended 5 to 6 mm with the high-speed burr. The bone defect then was grafted with allograft cancellous cubes. A unilateral hip spica cast allowing free ankle motion was applied (walking spica cast), and the patient ambulated with toe touch weightbearing and crutches. The cast was removed at 4 weeks and physical therapy was started. At 10 months followup, the patient was symptom-free with functional ROM and has returned to normal activities. Osteoid osteoma first was recognized as a separate entity by Jaffe in 1935, in a report of 5 cases. 15 It is a relatively common entity; it accounts for approximately 11% of benign bone tumors and 2% to 3% of all primary bone neoplasms. 20 Osteoid osteoma mainly affects adolescents and young adults. Approximately 70% of patients are younger than 20 years. 16,20 The male to female ratio has been reported as approximately 2:1. 6,25 Most patients who have osteoid osteoma have a history of extremity pain, often insidious in onset, that is characteristically worse at night and is relieved significantly by salicylates. 4,10 The duration of pain before the patient seeks medical care may vary from weeks to several years. The second most frequent presenting symptom is limping, which may be present in children who deny having symptomatic pain. 16 Between 70% and 80% of osteoid osteomas are located in long bones, most frequently in the femur, tibia, and humerus. 13,20 The lesion may occur in the metaphysis or diaphysis. 13 Other locations most commonly described for osteoid osteoma are the spine and the bones of the foot and hand. 2 On conventional radiography, the nidus of osteoid osteoma is round or ovoid in shape, usually less than 1 cm in diameter, variable in density, and has a thin, 1 to 2 mm peripheral radiolucent zone. The nidus often is not seen, especially if there is reactive bone, as seen initially in the current case. Thick, smooth, convex, and homogeneous periosteal reaction usually overlies the nidus. The radiographic appearance varies with the location of the lesion. When the nidus arises in cancellous rather than cortical bone, the periosteal reaction may be less intense or there only may be osteoporosis. 20 Intraarticular lesions very rarely provoke reactive bone formation but instead cause pain, effusion, and ultimately degenerative change. 17 The appearance of an osteoid osteoma on CT scans and conventional radiographs is similar. On CT scans, the nidus usually appears as a well-defined area of low attenuation, which is surrounded by a variably sized region of high attenuation reactive sclerosis. Computed tomography scanning can accurately determine the extent of the lesion, thereby enabling exact measurement of the size and location of the nidus. 5,7,11 To delineate the lesion, thin (preferably 1–1.5 mm) contiguous sections are most appropriate. Also, CT scanning can be particularly helpful for detection of radiographically subtle lesions or when there is dense periosteal reaction obscuring visualization of the nidus, as in the current patient. On MRI scans, the nidus of an osteoid osteoma usually is low or intermediate signal on T1-weighted images and low, intermediate or high signal on T2-weighted images. When present, associated cortical new bone is low signal intensity on all imaging sequences. The nidus enhances variably after intravenous gadolinium administration. The nidus, however, is not always well seen and MRI scans often show signal abnormalities in the medullary bone and soft tissues that overestimate the extent of disease. For these reasons, CT scanning is preferred when there is a strong clinical suspicion for osteoid osteoma. 18 Grossly, osteoid osteoma is a small, round or oval, reddish-brown tumor with a diameter of 1 cm or less. Histologic examination reveals a distinct demarcation between the nidus and the surrounding reactive bone. The nidus consists of an interlacing network of osteoid and bony trabeculae having a variable amount of mineralization. 24 Focal areas of osteoblastic rimming and osteoclast activity frequently are present. A fibrovascular stroma with numerous dilated capillaries is responsible for the vascularity of the tumor. 2 In the differential diagnosis, differentiating osteoid osteoma from osteoblastoma can be difficult. Clinical manifestations and size of the lesion usually are helpful. In the current case, the nidus of the lesion (seen on thin section CT scanning) was relatively small and discrete, which is typical of osteoid osteoma. However, the patient did not have the characteristic pattern of pain that is associated with osteoid osteoma. Osteoid osteoma and osteoblastoma also are similar histologically, but a marked perilesional sclerosis, a feature only occasionally encountered in osteoblastoma, usually is present in osteoid osteoma, as in the current case. Radiologically, the presence of intense reactive bone formation around the lesion also favors the diagnosis of osteoid osteoma. 8 On radiography, intracortical osteosarcoma appears as a radiolucent focus within the cortex surrounded by a zone of sclerosis. 19 However, intracortical osteosarcoma is rich in osteoid and woven bone with anaplasia, which were not the histologic features of the current case. In the long bones, Langerhans cell histiocytosis presents as a destructive lesion, and the condition is characterized by the presence of Langerhans cells and eosinophils morphologically. 9 On radiographs, chronic osteomyelitis appears as a thickened, dense area of bone caused by the long-term depositions of reactive medullary and periosteal new bone. On CT scans, abscesses may be visible as focal lucent areas, but they usually are associated with sequestered fragments of dead bone and sinus tracks. 12 The standard treatment for patients with osteoid osteoma is complete removal of the nidus. 2,24 Surgery usually is effective, providing immediate and complete relief of symptoms. Symptoms often persist or recur if any part of the nidus remains postoperatively. 14,21 The nidus may be removed through several surgical techniques. Some authors recommend en bloc excision of the nidus because of the risk of local recurrence after inadequate resection. 5,6,14 However, en bloc excision often creates unnecessary resection of reactive bone, which may weaken the bone and predispose it to fracture. If bone elements that are critical for stability are removed, bone grafting, cast immobilization, protective weightbearing, and occasionally, internal fixation may be necessary. 26 Also, with en bloc excision, it is difficult to identify the nidus intraoperatively. 26 The surgeon usually can localize the lesion precisely by comparing preoperative imaging, using thin section (1–1.5 mm) CT scans, and direct intraoperative findings, allowing for biopsy and intralesional excision with curettage and high-speed burr. 2 Successive thin layers of bone can be removed with a high-speed burr until the nidus is visualized. The nidus then is removed with a curette, after which its bed is extended 2 to 5 mm using a high-speed burr. 2 Ward et al 26 compared this burr-down technique with a wide resection technique, and with both techniques, there were no local recurrences and both techniques relieved the patients’ complaints. The patients who had burr-down, however, had less morbidity with less postoperative immobilization, a shorter duration of protected weightbearing, and earlier return to activity. They also reported that the burr-down technique provided good intraoperative nidus identification in most cases. Intraoperative localization of the nidus may be a problem in the treatment of some patients with osteoid osteoma. To address this problem, intraoperative conventional radiography, bone scintigraphy, CT-guidance, and tetracycline labeling have been used. 1,3,27 However, all of these methods have some disadvantages. 2 A newer technique for the treatment of osteoid osteoma is percutaneous core removal or thermal ablation of the lesion under CT guidance. 22,23 Rosenthal et al 22 advocate the thermal ablation technique for the treatment of patients with extraspinal lesions because it is minimally invasive, generally does not necessitate hospitalization, has not been associated with a high rate of complications, and it is associated with a rapid convalescence. Currently, the standard therapeutic approach for osteoid osteoma involves preoperative imaging (CT scan with fine cuts being the most helpful advanced imaging technique) and operative planning with complete removal of the nidus either with a burr-down technique or percutaneous CT-guided technique. Intralesional excision with use of a high-speed burr is as effective as wide resection when locally controlling the lesion and has less morbidity. This technique also provides good intraoperative nidus identification. The initial results of the percutaneous CT-guided techniques are very promising, but long-term followup is necessary. Percutaneous CT-guided removal has become the preferred technique at the author’s institution for the past 2 years.