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Osteoid osteoma constitutes 10-12% of all benign neoplasms of the bone. The tumor more frequently involves the male sex (male to female ratio 2.1:1) and it may be observed in all age groups, with evident predilection for the second decade of life. All of the skeletal segments may be affected, but the most frequent site is the long bones, in the diaphyseal, metaphyseal and more rarely epiphyseal regions. The lesion is characterized by an osteolytic area, the nidus, which is at times partially calcified, surrounded by an osteosclerotic zone that is more or less accentuated. Clinical suspicion and traditional radiography are essential in diagnostic orientation; usually, further imaging methods are also recommended, such as bone scan with Tc99, CT scan and MRI. This last method allows for easy localization of the lesion, although with a sensitivity that is less than that of the CT scan. Nonetheless, the finding, if not supported by clinical suspicion, may be dangerously deviating and it may orient diagnosis towards a more aggressive disease.

Purpose: To report our experience pertaining to three cases of intra-articular osteoid osteoma assessed by means of integrated imaging and review of literature., Materials and Methods: Medical records, radiologic and nuclear medicine findings pertaining to three cases of intra-articular osteoid osteoma were retrospectively evaluated and compared with those of surgery. All the patients (2 males, one female; age range 8-38 ys) affected by intra-articular osteoid osteoma respectively of the elbow, tibio-talar joint and hip were evaluated by means of radiographic examination and Magnetic Resonance Imaging (MRI). SE T1-w and T2-w, GRE T2*-w, GRE 3D T1-w and STIR pulse sequences were used and axial, coronal and sagittal images were acquired. Two patients underwent CT scan. One patient underwent skeletal scintigraphy. All the patients underwent surgery., Results: In 2 out of 3 cases plain radiography allowed the radiologist to suspect the presence of the lesion. In the remaining one, plain radiography failed to detect both the nidus and the perilesional osteosclerosis; nevertheless, a small osteochondral erosion of the humeral condyle suggested the presence of joint inflammation, thus leading to further investigation. CT scan well depicted the presence of the nidus and, in one case, the presence of joint effusion. MRI was always able to detect the nidus, which presented as lesion of low to intermediate signal in T1-w images, low signal in the T2-w images in one patient and high signal in the remaining two; in these latter STIR images showed high intensity nidus and edema of neighbouring cancellous bone. Furthermore, in all patients MRI clearly depicted joint effusion. Skeletal scintigraphy demonstrated both the lesion and the inflammatory involvement of neighbouring soft tissue. In all patients histologic specimen confirmed the diagnosis of osteoid osteoma with joint inflammation and synovitis., Conclusions: According to our results and literature data the pre-surgical diagnosis of osteoid osteoma is very difficult to achieve. Indeed, only the combination of clinical information and radiologic and nuclear medicine findings enables the radiologist to make the right diagnosis.

The authors report the case of a patient aged 10 years with late diagnosis of osteoid osteoma localized in the right pedicle of L1 due to a paucisymptomatic and aspecific clinical onset, characterized only by the occurrence of left-convex wide-range scoliosis that was completely solved after surgical excision of the neoformation.

A group of 50 pediatric patients affected with tumors or pseudotumors of the spine were studied with the purpose of determining the interval between the onset of symptoms and definitive diagnosis, the incidence of various symptoms, the statistical frequency based on age, sex, histologic type, localization, site. Also studied were diagnostic procedures adopted, therapy, recurrence, complications. The child affected with benign tumor pathology of the spine is rarely submitted early to appropriate diagnostic testing. Tumors are more frequently localized in the lumbar and thoracic spine and there is predilection for the vertebral arch. The most frequent histologic types are in decreasing order: histiocytosis X, osteoid osteoma, and aneurysmal cyst. Treatment is constituted by simple curettage in histiocytosis X, complete resection of the neoplasm in osteoid osteoma and osteoblastoma, partial resection associated with radiotherapy or selective embolization in aneurysmal bone cyst.

The authors describe a case of osteoid osteoma in a child and another of eosinophilic granuloma in an adult, localized in a lumbar vertebral body. A study by CT scan images, which is rather typical in the case of osteoid osteoma, could led to chronic osteitis or even to atypical osteoid osteoma in the case of eosinophilic granuloma. Histological examination defined diagnosis, and the two cases healed after surgical excision by anterior approach.

When combining clinical examination, laboratory information and noninvasive imaging studies the differential diagnosis of bone lesions is narrowed. For those who are not experts in the field the major purpose of the IOC is to insure that adequate tissue has been obtained and to triage the tissue in the process preparing imprints, whenever possible; fixing some tissue for possible electron microscopic review; placing some tissue in B5 fixative for better cytologic detail; and to save some undecalcified tumor tissue in formalin in case immunostaining procedures are required. Most community pathologists should not be attempt to make an absolute diagnosis at the time of IOC, in many cases. The surgeon should always be warned that despite seeming benignancy 50% of primary bone tumors are malignant, that benign lesions can prove to be low grade sarcomas after full review, and vice versa that occasional cellular, "pleomorphic" lesions can be benign (aneurysmal bone cyst, early reparative and pseudosarcomatous lesions). Following review of the permanent sections, and other appropriate procedures an accurate diagnose is possible in the majority of cases. If the diagnosis is particularly difficult or questionable the above materials can be sent to a bone tumor specialist.

Conventional radiography, bone scintigraphy and Computed Tomography (CT) are the most useful tools to identify osteoid osteomas. We examined 26 patients (14 men and 12 women) with osteoid osteoma in different skeletal sites (13 femora, 3 tibiae, 3 hands, 2 peroneal bones, 2 humera, 2 spines and 1 talus) and compared the diagnostic yield of the above techniques. The fundamental radiographic findings in this benign bone lesion are the presence of a "nidus", with or without calcifications, perilesional sclerosis and periosteal new bone formation. Four patients in our series had soft tissue edema. In the majority of cases, conventional radiography is the imaging method of choice, because it is easily available and its diagnostic yield is adequate (17 patients in our series), especially if combined with bone scintigraphy-whose high diagnostic sensitivity was proved in all of our patients. CT is recommended for its better spatial resolution, in view of surgery, especially when soft tissues are involved. MRI is a highly valuable tool in bone tumor staging because it demonstrates cortical involvement and intramedullary and soft tissue spread. However, MR findings might be misinterpreted as indicating a more aggressive pathologic process.

The authors present one case of osteoid osteoma of the carpal scaphoid, emphasizing the clinical rareness of the disease. Methods of diagnosis used and surgical treatment performed are described.

The authors report their experience in the treatment of "osteoid osteoma", drawing attention to the great clinical polymorphism of this affection. They also demonstrate the reliability of a preliminary systematic study with bone scan and CT, which are indispensable to early diagnosis and correct surgical procedure.

We relate about our direct clinical experience on 8 cases of osteoid osteoma localized in the bones of the foot. Some atypical appearances, clinical and roentgenographic, of the osteoid osteoma in this bony district may sometimes cause problems in diagnosis and localization, which are exposed and discussed in this paper. Particularly, we underline the importance of bone scan in the detection of the lesion.

We report one case of osteoid osteoma of olecranon fossa in a female with pain and functional limitation of the elbow. The articular variety of osteoid osteoma is relatively uncommon and its diagnosis is very difficult. Conventional radiology, tomography and scintigraphy are employed for diagnosis, however computed axial tomography is particularly useful for diagnosis and correct treatment of osteoid osteoma of olecranon fossa.