Osteoid osteoma is a benign osteogenic tumor with a small nest surrounded by many mature reactive bones. The age of prevalence is 8 to 18 years. The most common sites are the lesser trochanter of the femur, the medial cortex of the proximal humerus, the distal 1/3 of the tibia, and also the spinal appendages. It is rarely seen in flat bones, intramedullary and cancellous bones.
Etiology and pathology
The cause is unknown. Some scholars previously thought that it was an infection, and some thought that it was a residual of congenital placental tissue. Since it can cause typical pain, it was presumed to be a repair phase of bone hemangioblastoma, and now it is recognized as a benign tumor.
Clinical manifestations]
The lesion is characterized by very limited pain, mostly occurring at night or at rest. The intensity of the pain varies, initially it is limited intermittent pain, which is relieved after rest. Salicylates can relieve the pain, and alcohol consumption can aggravate the pain is the characteristic of this disease. The painful scoliosis may occur in those located in the spinal appendages.
Auxiliary examination
1, X-ray manifestation of the lesion “nest” is round or oval, the maximum diameter of the transmission shadow does not exceed 2cm, the transmission of the central dot-like density increase shadow, there is often reactive bone hyperplasia around the transmission area. In the long bones it can be divided into the following 3 types.
(1) Osteocortical type: It shows small round or ovoid hypodense shadows located in the cortex, and sometimes high-density punctate calcified areas are seen in the nest of the tumor. There are dense reactive bones around the periphery, and the reaction area is usually shuttle-shaped, but it can also be asymmetrical, and in severe cases, the nest can be concealed and not shown.
(2) Osteochondral type: The nests are occasionally located in cancellous bone, with only mild to moderate sclerotic margins around the nests, and calcification may appear in the center of the nests, which may also have periosteal reaction.
(3) Subperiosteal type: Rarely, there is mild sclerosis around the nest, and the central nest may cause the bone cortex to show mild indentation.
2.Radionuclide scan: In the active stage, it shows extensive radionuclide concentration. Since both the tumor nest and the reaction area take radionuclide, the range of radionuclide concentration greatly exceeds the range of the tumor nest shown on the X-ray.
3.CT examination: CT examination can show the size, location and central calcification of tumor nest, and the center of tumor nest is rich in blood flow and has obvious enhancement after enhancement.
4.MRI examination: The tumor nests show low to medium signal on T1-weighted image, and low, medium or high signal on T2-weighted image, and most of them are low signal if the internal calcification or ossification is obvious (Figure 1-2-4). After enhancement, most of the tumor nests strengthen significantly, and a few of them may show ring-like strengthening.
5.Pathological examination
Intraoperatively, the bone surrounding the nest was white hard cortical bone, covered with normal periosteum, which could be easily peeled off. The nest is a round or oval cherry-red sphere, and sometimes a white ossification point of 1 to 2 mm in its center can be seen. Sometimes the nests are long or dumbbell shaped.
Microscopically: low magnification: the central part of the intact nest is composed of bone-like tissue, with osteoblasts surrounding bone-like tissue trabeculae and hyperplastic fibrovascular tissue at the edge of the nest. High magnification: The nest is composed of richly vascularized osteogenic connective tissue, which forms a large amount of bone-like tissue. The nests were surrounded by sclerotic bone.
Diagnostic points
1. The clinical manifestation is limited pain, which can be relieved by salicylate, and can be aggravated by alcohol consumption.
2.X-ray shows small round or ovoid low-density shadow located in the cortex, with dense reactive bone at the periphery, and the reactive bone thickens the cortex up to several centimeters from the nest.
3.Microscopic examination shows indeterminate, disorganized bone-like tissue in the center of the nest, with a large number of deeply stained osteoblasts caught in between. The edge of the nest was proliferated fibrovascular tissue.
Differential diagnosis
1. Brodie’s abscess Both show nests of low density, but Brodie’s abscess is located in the medullary cavity or cancellous bone, while osteoid osteoma is mostly located in the cortex. The former has a history of infection, with local inflammatory manifestations such as redness, swelling, heat and pain, and often recurrent. Because osteoid osteoma is rich in blood flow, it strengthens significantly after contrast injection, while Brodie’s abscess is a pus cavity without blood flow and does not strengthen after contrast injection.
2, osteoblastoma Histologically, the cell characteristics of osteoid osteoma and osteoblastoma are almost the same, except that osteoblastoma has more abundant osteoblasts and more neovascularization, and it is difficult to distinguish between the two, which is mainly through clinical and imaging. In contrast, osteoblastoma has large foci, is located in cancellous bone, and has a thinner shell of reactive bone.
【Treatment and rehabilitation
1.Non-surgical treatment
For patients with mild symptoms, especially for those who are more difficult to operate or will have serious complications after surgery, conservative treatment is feasible, i.e. oral salicylate symptomatic treatment.
2.Surgical treatment
(1)Osteotomy for nest scraping and inactivation: For active stage 2 osteoid osteoma, when the location of the nest is clear, scraping is performed. The cyst wall can be inactivated with carbolic acid, 95% alcohol or freezing, etc. Generally, autologous bone, artificial bone or allogeneic bone graft is performed after local scraping, and bone cement can also be applied to fill the cavity to reduce the recurrence rate.
(2) Marginal mass excision: When the location of the nest is not clear, a marginal mass excision is performed to remove the nest and the reactive bone (Figure 1-2-5).
(3) Percutaneous nest removal: When the location of the nest is clear, a hollow drill can be used to drill into the lesion and remove the lesion under CT guidance (Figure 1-2-6), or the grinding head of a variable-speed grinding drill can be introduced into the nest to destroy the nest and the surrounding reactive bone. Another method is microwave therapy, in which a probe is inserted under CT guidance and the high-frequency “microwave” generated by it is used to destroy the nest.
Review]
According to WHO statistics, osteoid osteoma accounts for 5.10% of primary bone tumors and 11.23% of benign bone tumors. In adolescents, it is an active symptomatic stage 2 lesion, which rarely grows, and the nest is usually less than 1 cm. The usual duration of symptoms is 3 years, and during the course of self-healing, the lesion gradually transforms from an active stage 2 to a quiescent stage 1. As the nest ossifies, the translucent zone between the nest and the responding bone gradually disappears, but these dense shadows will persist for many years.
Osteoid osteoma can become asymptomatic and self-resolving. After 3 to 5 years of active stage lesions, symptoms gradually disappear as the nests ossify. However, the reactive bone surrounding the lesion will persist for decades.
Osteoid osteoma is not malignant. Therefore, for those with mild symptoms, conservative treatment is feasible. For active stage 2 osteoid osteoma, large resection of the margins to remove the nest and reactive bone is feasible, and the recurrence rate is high after scraping out the nest alone. Surgical treatment of osteoid osteoma is very effective and can be satisfactory to both physician and patient. The surgery can completely and thoroughly relieve the pain, and individual surgical resection incomplete can recur.
Difficulties and countermeasures
How to reach and clearly show the nodule during surgery and remove it completely, while removing as little bone tissue around it as possible so as not to weaken its strength. Preoperative localization of the nodule to guide the surgery is crucial. Before isotope scanning, serial tomographic radiographs are the most effective means of localization, but there is a greater risk of localization errors; isotope scanning has improved localization accuracy, and now thin-layer CT images can provide more precise localization, which can reduce the defect caused by resection. CT-assisted planning of the procedure is required first. In femoral neck osteoid osteomas are generally superficial, often close to the anterior bone cortex rarely near the posterior, and often within the joint; obviously, based on two different sites, surgical access and arthrocentesis can only be chosen between anterior or posterior.
When the site of the lesion can be clearly visualized by imaging, if it is confined to the surface of the bone, it can be seen immediately during surgery; if, as in many cases, it is located within the bone, it is best to open the bone window until it is seen. At this point, wide, marginal or intra-focal resection of the entire tumor will be easily performed, as well as incisional biopsy. If this method is used, postoperative immobilization is not required and recovery can be rapid and safe.