Benign Bone Tumors and Pseudotumoral Bone Lesions

Osteoid osteoma is one of the most common benign bone tumors in children and young adults. It typically occurs between the ages of 5 and 30 and tends to affect the central portion of long bones, known as the diaphysis, or the structures of the spine. The most frequently involved sites are the femur, tibia, and humerus, although it can develop in any bone of the skeleton.



Osteoid osteoma typically presents early with well-localized bone pain that arises without any history of trauma and can be quite intense. The pain is characteristically worse at night and usually responds well to anti-inflammatory medications, particularly aspirin and ibuprofen. In some cases, the nocturnal pain is so severe that it disrupts the patient’s sleep every night. Other symptoms such as swelling, redness, or fever are generally absent. The pain tends to persist over time, even with the use of analgesics and rest.

When clinical suspicion points to an osteoid osteoma, the first imaging test usually performed is a standard X-ray of the affected bone. The radiograph may reveal a small, darker area known as a nidus, typically surrounded by a denser, sclerotic zone—an indication of the bone’s reactive response. To confirm the diagnosis, a targeted CT scan is typically performed. This exam is often sufficient to provide a clear diagnosis, without the immediate need for a biopsy. In some cases, an MRI may also be used, especially to evaluate the involvement of adjacent soft tissues. Bone scintigraphy can serve as an additional diagnostic tool, as the osteoid osteoma typically appears as a focal area of increased tracer uptake due to its rich vascular supply. In selected cases, a percutaneous needle biopsy may be performed to obtain a small tissue sample for microscopic analysis, particularly when the diagnosis remains uncertain after imaging.

The first-line treatment for osteoid osteoma is radiofrequency ablation, a minimally invasive procedure performed under CT guidance. During the procedure, a special needle is precisely inserted into the lesion (nidus), and high-intensity heat is generated using a radiofrequency device to destroy the tumor tissue. This technique does not require visible incisions and typically involves only a one- or two-day hospital stay. Pain relief is usually rapid: in most cases, symptoms significantly improve or resolve within the first few days, allowing a gradual return to normal daily activities. In the past, treatment consisted of a more invasive surgical procedure to remove the entire affected area. Today, surgery is reserved for selected cases.  After ablation, regular clinical and radiological follow-up is recommended to confirm complete resolution. Although the procedure is effective in the vast majority of cases, recurrences may occasionally occur. In such cases, a second ablation or, if needed, surgical intervention can be considered.

A unicameral bone cyst is a bone lesion that resembles a tumor in appearance (pseudotumoral), and it typically develops during childhood or adolescence, more commonly in males. On X-ray, it appears as a single, well-defined cavity, often centrally located just below the growth plate (the area of the bone responsible for skeletal elongation). The most frequent sites are the proximal humerus and femur, although any bone can be affected. In the early stages, the cyst is usually filled with blood, but over time its content may become serous. In some cases, it may even appear completely empty.

A unicameral bone cyst may be completely asymptomatic, especially when small, and can sometimes be diagnosed in adulthood during imaging performed for unrelated reasons. The most common symptom associated with unicameral bone cysts is localized pain, often caused by microfractures within the cyst. A full fracture of the affected bone segment (pathological fracture) may occur, frequently triggered by minor trauma. This happens because the cyst causes thinning of the bone’s outer wall (the cortical bone). Unicameral bone cysts are classified as active or inactive. Active cysts are located adjacent to the growth plate, while inactive cysts are separated from it by a layer of normal bone. Active cysts may interfere with bone development, potentially leading to growth disturbances or axial deformities, meaning that the limb may grow in an abnormal direction.



Taking the patient’s medical history and performing a physical examination can raise the clinical suspicion of a unicameral bone cyst.

X-ray imaging is typically sufficient to support the diagnosis and may be complemented by MRI, which allows better visualization of the cyst’s fluid content, if present. To confirm the diagnosis, a biopsy of the cyst is required, followed by microscopic examination of the tissue samples.

Treatment of a unicameral bone cyst can be either surgical or conservative, depending on the size of the lesion. One option is image-guided injection of slow-absorbing corticosteroids, using fluoroscopy or CT guidance. Alternatively, the cyst can be surgically emptied and the cavity filled with either autologous bone grafts (typically harvested from the patient’s pelvis) or synthetic bone substitutes. In cases of large cysts or those located in weight-bearing bones (such as the lower limbs), stabilization of the affected bone may be necessary. This is commonly achieved by inserting flexible titanium nails inside the bone to prevent fracture. The same approach is used when treating a pathological fracture caused by the cyst. In fact, the fracture and subsequent internal fixation often stimulate healing, promoting gradual bone regeneration within the cavity. Once healing is complete, the titanium nails can be removed. However, all these treatments carry a risk of recurrence, particularly in newly formed unicameral bone cysts.

An aneurysmal bone cyst is a benign, non-neoplastic lesion (classified as a pseudotumoral condition) that can appear at any age, but most commonly occurs between 10 and 20 years of age. It may sometimes be associated with other bone tumors, such as giant cell tumor or osteoblastoma. The cyst is filled with blood, and its exact cause remains unknown—it is considered a reactive lesion triggered by an unidentified stimulus. It typically develops in the metaphysis—the region of long bones between the growth plate (epiphysis) and the shaft (diaphysis). However, it can also occur in the pelvis and frequently in the vertebrae. In long bones, the lesion tends to form near the outer edge of the bone, causing an outward bulge that often helps differentiate it from a unicameral bone cyst, which rarely causes bone expansion. The internal structure of an aneurysmal bone cyst is characteristically "honeycombed," made up of multiple interconnected chambers. It can become quite large, especially when located in the pelvis or spine. The term pseudotumoral refers to skeletal conditions that mimic bone tumors on clinical and radiological examination—such as X-rays—but differ significantly in their microscopic appearance, clinical course, and prognosis.

An aneurysmal bone cyst typically presents with localized pain and swelling in the affected area. In some cases, it may lead to a bone fracture.

Sometimes, an aneurysmal bone cyst is discovered incidentally during an X-ray performed for another reason. In other cases, the patient's clinical history and physical examination may raise diagnostic suspicion. The first imaging study used to confirm this suspicion is typically an X-ray of the symptomatic area. On radiographs, an aneurysmal bone cyst appears as a honeycomb-like area of bone demineralization, often with cortical bone destruction or surrounded by a thin shell of remaining bone. Once identified on X-ray, further evaluation with additional imaging—such as bone scintigraphy, magnetic resonance imaging (MRI), and computed tomography (CT)—is recommended. To confirm the diagnosis, a bone biopsy is required, involving the removal of a small tissue sample for microscopic examination. No cases of malignant transformation of an aneurysmal bone cyst have ever been reported.



Treatment of an aneurysmal bone cyst varies and can be either surgical or injection-based. Surgical treatment involves curettage of the cavity followed by filling with bone grafts—either autologous (taken from the patient, typically from the pelvis) or heterologous (using synthetic bone substitutes). The second therapeutic option, which is increasingly used, is scleroembolization. This minimally invasive technique involves injecting chemical agents into the cyst to dry it out, leading to its collapse and closure. For lesions located in the spine or pelvis, embolization of the feeding artery (nutrient artery) may be appropriate. Arterial scleroembolization is especially useful for sites that are difficult to access surgically, such as the vertebrae, sacrum, and pelvis. Recurrence occurs in approximately 10% of cases.

Non-ossifying fibroma is the most common benign bone lesion in children and adolescents. It is also known by other names such as fibrous cortical defect or metaphyseal fibrous defect. It typically appears between the ages of 2 and 18 and is found in about one-third of individuals under the age of 20, often without causing any symptoms. It occurs more frequently in males and is usually located in the metaphyseal regions of the femur and tibia—areas near the growth plates between the shaft and ends of long bones. In rare cases, it may appear in multiple sites at the same time.

In the vast majority of cases, non-ossifying fibroma causes no symptoms and is discovered incidentally during X-rays performed for other reasons. Only rarely, when the lesion is particularly large, may localized pain occur. The pain is usually caused by small bone fractures that can happen if the lesion weakens the bone structure. It is important to emphasize that this is a completely benign condition, and progression to more aggressive forms is extremely rare—virtually nonexistent.



Non-ossifying fibroma is almost always diagnosed incidentally during an X-ray performed for unrelated reasons, such as trauma. In most cases, a standard radiograph is sufficient to identify the lesion. On X-ray, it appears as a well-defined, radiolucent (clear) area in the bone, usually small in size (less than 6 cm), with a multiloculated appearance and a location near the outer edge of the bone. A thin, sclerotic rim is often visible around the lesion. In radiology reports, it may also be referred to as a fibrous defect or non-osteogenic fibroma. If the lesion shows atypical features, further imaging—such as CT, MRI, or bone scintigraphy—may be performed to rule out other conditions. Biopsy is rarely necessary and is reserved for cases in which the diagnosis remains uncertain after comprehensive imaging.

In most cases, non-ossifying fibroma does not require any treatment. Periodic follow-up is usually sufficient to monitor its progression. As the child grows, the lesion tends to regress spontaneously and, in nearly all patients, it completely disappears by the age of 30. Only in rare cases—if the fibroma increases in size or significantly weakens the bone—a specific treatment may be considered.

Chondromyxoid fibroma (CMF) is an extremely rare benign bone tumor, accounting for about 1% of all bone tumors. It originates from cartilage tissue within the bone. The typical location for chondromyxoid fibroma is the metaphysis of long bones (in about 60% of cases), which is the region that connects the ends of the bone (epiphysis) to the shaft (diaphysis). The most common sites include the proximal tibia near the knee (25% of cases), the small bones of the foot, the femur, and the pelvis. In rare cases, the skull may be involved. Chondromyxoid fibroma usually appears during the second or third decade of life, with approximately 75% of cases occurring before the age of 30, although cases in older individuals have also been reported. It is slightly more common in males than in females. Chondromyxoid fibroma is a benign tumor. It is not cancerous, and its cells do not metastasize to other parts of the body. However, it can locally invade surrounding tissues, potentially causing pain and other symptoms.

Symptoms are usually mild and appear late in the course of the disease. Joint involvement is rare. Patients typically experience progressive pain, which is often persistent, and in some cases, swelling and reduced mobility in the affected area—especially when small bones of the hands or feet are involved. Fractures may occur, as the tumor can erode the cortical bone, weakening its structure.



Diagnosis of chondromyxoid fibroma is relatively straightforward when the lesion affects long bones. On standard X-rays, it typically appears as a round or oval area of complete bone destruction, usually located near the outer edge of the bone and bordered by a sclerotic rim. Within the lesion, one may observe thin bony septa (trabeculae) and small areas of calcification. Additional imaging studies—such as MRI, CT scan, and bone scintigraphy—help further characterize the lesion, but they are not definitive for diagnosis. In other locations, a bone biopsy is essential for diagnosis. This involves extracting a small sample of bone tissue for microscopic (histological) examination. Under the microscope, the tumor shows a variable combination of cartilaginous cells, myxoid changes in connective tissue (giving it a gelatinous appearance), and fibrous areas. These are benign lesions, and malignant transformation is exceedingly rare. However, due to the symptoms they can cause and their radiological resemblance to more aggressive tumors like chondrosarcoma, a biopsy is required to reach a definitive diagnosis, which must be based on histological evaluation.



Treatment is generally surgical. It consists of thorough curettage of the tumor tissue from the bone. Unfortunately, this procedure carries a relatively high recurrence rate—about 25% of cases. In the event of recurrence, it may be necessary to perform a wide surgical excision, removing the affected portion of bone in its entirety.