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Background: Much discussion about benign notochordal cell tissue in vertebrae has centered on the nature of its relationship, if any, to chordoma. Often referred to as benign notochordal cell tumors (BNCTs), these lesions have unique morphological features, however, differentiating between notochordal cells in discs, BNCT, and chordoma can be difficult. They are described as radiologically distinct from chordoma, with lysis, contrast enhancement, and a soft tissue mass indicating chordoma., Methods: All chordomas diagnosed at our institution, the Istituto Ortopedico Rizzoli (Bologna, Italy), prior to 2008 were reviewed, yielding 174 cases. Five were limited to bone; one was a recurrent chordoma without original data available. The remaining four were re-evaluated in detail., Results: There were three women and one man, aged 33-57 years (mean, 48 years). Two were BNCTs and two were mixed lesions containing BNCT and chordoma. On computed tomography, all were radiopaque with areas of lysis. One BNCT was heterogeneous on magnetic resonance imaging, enhancing after contrast. Microscopically, one BNCT had a well-defined cystic area with a sclerotic border. The other had a minute atypical area; it recurred as chordoma. The mixed lesions had areas of definitive BNCT, definitive chordoma, and atypical areas that did not meet the criteria for either. The atypical areas in all three cases 'blended' with areas of chordoma or BNCT., Conclusion: These cases illustrate the ongoing challenges in differentiating between BNCT and chordoma. All had unique imaging features; three had atypical microscopic areas blending with BNCT or chordoma, strengthening the argument for a relationship between the two entities and supporting the idea that some BNCTs may progress to chordoma. Our study dispels the notion that any single radiologic criterion used to distinguish between chordoma and BNCT is reliable, opening the discussion as to whether or how to monitor BNCTs.

Introduction: There is no clear radiologic or pathologic agreement on the differences between enchondroma and conventional chondrosarcoma, which has huge therapeutic consequences. Microscopically, an enchondroma is composed of "islands of intramedullary hyaline cartilage surrounded by marrow fat", and a chondrosarcoma a "diffuse cartilaginous replacement (invasion) of the marrow which leads to complete 'trapping' of host lamellar bone trabeculae." The marrow around islands of cartilage should be detectable on magnetic resonance imaging (MR). Enchondroma may be the precursor of chondrosarcoma; benign cartilaginous islands are often seen microscopically at the periphery of chondrosarcoma. We attempted to detect these islands at the periphery of chondrosarcomas on MR and correlate them microscopically., Materials and Methods: We examined our database for all patients with a chondrosarcoma of the long and flat bones between 1990 and 2007. Only those with a preoperative MR who underwent an en bloc resection were included, yielding 32 patients. We looked for low-signal islands surrounded by high (fat) signal on T1-weighted images, and high-signal islands surrounded by low signal on T2-weighted fat saturated images at the periphery of the main tumour mass. Microscopic correlation was performed in all cases., Results: On microscopy, there were 23 conventional chondrosarcomas, nine dedifferentiated. Peripheral islands surrounded by fat were detected on MR in 19 cases, corresponding to benign cartilage in 18 cases and to the benign scar of a needle biopsy tract in one. There were no peripheral islands detected radiographically or microscopically in 13 cases., Conclusion: Cartilaginous islands microscopically detected at the periphery of some chondrosarcomas are easily and reliably diagnosed on MR., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Two patients were evaluated for the possibility of hypersensitivity to a Metasul articulation (Centerpulse, Austin, Tex) coupled with total hip arthroplasty. Serum was tested with a lymphocyte proliferation assay, and the capsular tissues from the hip were examined for perivascular lymphocytes. The diagnosis of hypersensitivity to Metasul could not be confirmed in these patients, and ultimately, the painful hip arthroplasties were felt to be caused by a combination of musculoskeletal problems.

Two cases are reported of a newly described intraosseous entity of vertebral bodies deemed "giant notochordal hamartoma of intraosseous origin". This entity is commonly mistaken for chordoma and must be distinguished from it as the consequences of misinterpretation may be serious. The clinical, radiological and histologic criteria that can be used to distinguish these two entities are emphasized. Included is a proposed pathogenesis for this lesion, its probable notochordal origin, and a review of other probable cases.

A 65-year-old man with osteoarthritis of the hip underwent a cementless total hip replacement with a modern generation, metal-on-metal bearing. Two years later the patient presented with localized osteolysis at the tip of the femoral stem. At the time of revision, the stem was found to be well-fixed. Extensive analyses of the bearing surfaces and periprosthetic tissues were done. There was minimal bearing surface wear and only small numbers of inflammatory cells, such as macrophages, in the tissues, and it was concluded that this was not a typical case of particle-induced osteolysis. All cultures and laboratory studies were negative for infection. This case report supports the multifactorial nature of osteolysis, which includes the osteolytic potential of joint fluid access to and fluid pressures within, the effective joint space.

Glomus tumor is a rare, benign vascular tumor and intraosseous glomus tumor, which arises primarily within bone, is even rarer. Fewer than 20 cases have been reported in the literature. We present the case of a 34-year-old woman with glomus tumor primarily in the midshaft of the fibula that radiologically mimicked chondromyxoid fibroma, aneurysmal bone cyst or adamantinoma, together with a review of other reported cases.

There is a general conception that resurfacing arthroplasty causes femoral head osteonecrosis and subsequent failure of the implant. This study histologically analyzed 25 resurfaced femoral heads up to 12 years postoperatively and found that osteonecrosis was not induced by the procedure.

Tau proteins are microtubule-associated proteins required for the polymerization of tubulin. The abnormal accumulation of tau proteins in neurofibrillary tangles is a well-known phenomenon and has been studied extensively. However, the role of tau protein in chondroid tissue and its neoplasia is unknown. In the present study, 2 extraskeletal myxoid chondrosarcomas (EMCs), 6 chordomas, 6 chondrosarcomas, 3 myxoid chondrosarcomas of bone, 2 osteochondromas, 6 chondroblastomas, and 2 nonneoplastic adult articular cartilages were immunostained with monoclonal antibodies against tau proteins and tubulin. The results showed that the coexpression of tau proteins and tubulin was present only in EMCs (2/2) and chordomas (4/6). Although tubulin was detected in chondroblastomas (5/6), osteochondromas (2/2), chondrosarcomas (5/6), and myxoid-chondrosarcomas of bone (3/3), tau expression was absent in these tumors. The perichondrial chondroblasts but not chondrocytes from nonneoplastic articular cartilage also localize tau and tubulin with a much weaker staining intensity. The results mainly demonstrate that there is frequent expression of tau proteins in some microtubule-rich neoplasms, such as EMC and chordoma. The different immunostaining pattern of tau proteins between chordoma and myxoid chondrosarcoma of bone may be useful in the differential diagnosis, especially when both neoplasms occur in the base of skull.

Marked nuclear atypia can be found in a variety of benign mesenchymal tumors, including ancient schwannomas, symplastic leiomyomas, osteoblastomas, and chondromyxoid fibromas. Such nuclear atypia is believed to represent a degenerative phenomenon and does not indicate aggressive behavior. Separation of these pleomorphic but benign lesions from true sarcomas may be difficult. We are aware of only one prior description of such degenerative atypia in benign giant cell tumor of bone. We report a benign giant cell tumor of bone arising in the sacrum of a 21-year-old white female. Preoperative embolization of this lesion had been performed, and subsequent curetting revealed marked atypia suggestive of an anaplastic malignancy. However, only very rare mitotic figures were present, and the radiographs were consistent with a benign giant cell tumor. A diagnosis of benign giant cell tumor was made, and no recurrence or metastases have been observed during the 4-year postoperative period.

In part I, we reviewed the varied clinical presentations, pathogenesis, histologic findings, radiologic findings, and treatment of intramedullary cartilaginous lesions of bone. In this section, we will evaluate our cases and consultations of juxtacortical cartilaginous tumors. Radiographic differential diagnosis includes the numerous juxtacortical lesions particularly osteochondroma, parosteal chondroma, Trevor's disease, trauma (fracture and periostitis ossificans), and the low- and high-grade surface osteosarcomas. By emphasizing pathogenesis in conjunction with radiographic and histologic findings, pitfalls in diagnosis and subsequent treatment can be avoided in such cases.

A 19-year-old man presented with a chondromyxoid fibroma of the distal phalanx of the great toe that was originally diagnosed as osteosarcoma rather than "dedifferentiated" chondrosarcoma. Radiographs showed a large, expansive, and calcified tumor of the distal phalanx. Although the tumor had the architectural and matrix patterns of a chondromyxoid fibroma, high-power examination demonstrated that the lesion had such severe nuclear pleomorphism that it was mistaken for high-grade sarcoma. The purpose of this report is to present the criteria used to differentiate a benign pseudoanaplastic chondromyxoid fibroma from chondrogenic high-grade sarcomas.

Objective: Our purpose was to describe a rare juxtacortical bone sarcoma with deceptively benign, osteochondromalike histologic characteristics. We present criteria by which this low-grade malignant neoplasm can be distinguished from other benign and malignant surface lesions of bone with particular emphasis on the imaging features., Materials and Methods: Six cases of a low-grade, chondroossifying parosteal sarcoma of bone were reviewed. Patients included four males and two females 11 months to 66 years old. Histologic findings from initial tumors and from recurrent tumors were reviewed. Two musculoskeletal radiologists analyzed the imaging studies, which included plain films, CT scans, MR images, and a bone scan., Results: Histologically, the lesions were characterized by a thin layer of proliferating, periosteally derived spindle cells overlying a thin, low-grade malignant cartilage cap that underwent calcification, neovascularization, and conversion into benign bone and marrow fat. These lesions were unique in that the malignant elements were only at their periphery. All six cases were initially misdiagnosed as benign lesions on pathologic evaluation. In each patient, imaging revealed a "pasted-on" ossified surface lesion with an intact underlying cortex and no medullary involvement. In three cases, recurrent tumors had histologic appearances consistent with conventional parosteal osteosarcoma. Dedifferentiation, metastases, and death occurred in one of these three cases., Conclusion: To our knowledge, this surface lesion of bone has not been specifically described. Whether this tumor constitutes a distinct entity or is a specialized variant of parosteal osteosarcoma is unclear. Precise radiologic-pathologic correlation is essential for appropriate diagnosis and management.

We report the case of a patient with a rare miliary variant of osteosarcoma associated with symptomatic hypocalcemia and review the literature regarding the pathogenesis of multifocal osteosarcoma, treatment options, and the associated hypocalcemia.

A femoral neck fibrous cortical defect with typical radiographic features had bizarre nuclear features on histological examination. Recognition of the benign radiographic appearance, similar bizarre features of accompanying macrophages, and paucity of mitoses led us to consider this a pseudoanaplastic ischemic or degenerative change in an old fibrous cortical defect. Because the biological behavior was not known with certainty, we closely followed this case. After 25 months, there has been no recurrence or regrowth. The close cooperation between the pathologist and other disciplines facilitates recognition of these pseudoanaplastic lesions and development of treatment strategies for lesions of unknown or uncertain biological behavior.

We reviewed 845 cases of benign and 356 cases of malignant cartilaginous tumors from a total of 3067 primary bone tumors in our database. Benign cartilaginous lesions are unique because the epiphyseal plate has been implicated in the etiology of osteochondroma, enchondroma (single or multiple), periosteal chondromas and chondroblastoma. In the first part of this paper, we will review important clinical, radiologic and histologic features of intramedullary cartilaginous lesions in an attempt to support theories related to anatomic considerations and pathogenesis.

It is not uncommon for sarcomatous transformation of giant cell tumor (GCT) of bone to occur after radiation, but rarely does malignant transformation occur spontaneously, with less than 15 cases reported up to 1995. Only four of these cases have been documented in detail. We report two additional cases of GCT of bone spontaneously transforming or "dedifferentiating" into osteosarcoma without radiation therapy. The first case is absolutely unique and most interesting in that the dedifferentiation process occurred in one of multiple GCT lung metastases 6 years after successful eradication of a primary tibial tumor. The right lung was resected due to development of a large tumor, and at pathologic examination, demonstrated several small nodules of conventional GCT and a much larger, 14-cm mass composed of a mixture of GCT and high-grade osteosarcoma. The second case involved a physician, who had a large tumor in the sacrum with vague symptoms for 8 years. Open biopsy revealed conventional, benign GCT of bone with a secondary aneurysmal bone cyst. Complete curettage 2 weeks later revealed, in addition to areas of conventional, benign GCT a second component of very high grade osteosarcoma. Both patients died less than 1.5 years from diagnosis. This report of osteosarcomatous transformation of a conventional GCT of bone strengthens the theory that there is a mesenchymal cell line in GCT that may spontaneously transform to sarcoma.

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.

This paper report a case of a pelvic clear-cell chondrosarcoma that was initially diagnosed as clear-cell osteosarcoma after needle biopsy. Preoperatively, laboratory studies revealed an elevated alkaline phosphatase and needle biopsy showed clear cells producing osteoid. Internal hemipelvectomy was performed and final pathology was most consistent with clear-cell chondrosarcoma, despite a negative S-100 immunohistochemical stain. Distinguishing between these two entities is clinically important because treatment differs. In this case, the patient did not receive pre-or postoperative chemotherapy and is disease free more than 2 years later.

Objective: This study describes the clinical presentation and the course of Ribbing disease in six patients and illustrates imaging features on plain radiography, conventional and computed tomography, and 99mTc-methylene diphosphonate bone scans., Materials and Methods: Between 1982 and 1990, six female patients presented with painful bony lesions that were believed to be Ribbing disease. Ten bones were affected: both tibiae in three patients, a unilateral tibia in one, both femora in one, and a unilateral femur in one. Plain radiographs and either conventional or computed tomography were available for all patients and 99mTc-methylene diphosphonate bone scans, for five patients. All patients underwent open biopsy and/or surgical decompression., Results: The diagnosis was reached in all patients through a combination of clinical findings (lack of systemic signs of infection or laboratory values suggesting metabolic bone disease), imaging, histologic evaluation, and specimen cultures. Radiographs and tomographic studies showed benign-appearing endosteal and periosteal cortical thickening. Intense uptake of radionuclide tracer was confined to the shaft of all involved bones. All pathologic specimens revealed nonspecific changes that included a slow increase in the mass of cortical and endosteal bone. These specimens also assisted in excluding neoplastic or infectious causes for the new bone formation., Conclusion: Ribbing disease is a rare disorder that, on imaging studies, may simulate stress fracture, chronic infection, bone-forming neoplasia, or a systemic metabolic or endocrine disorder. Clinical and imaging features may suggest the correct diagnosis.

The periprosthetic tissue reaction to polyethylene wear debris in metal on polyethylene total hip replacements is strongly implicated as the cause of osteolysis. This has led to a renewed interest in metal on metal total hip replacements. However, little is known about the role of wear debris in failures of these prostheses. Capsular and interface tissues from 9 long and short term metal on metal total hip replacement retrievals were studied to assess the tissue reaction around these prostheses. As compared with metal on polyethylene cases, the extent of the granulomatous inflammatory reaction and the presence of foreign body type giant cells was much less intense in metal on metal cases, likely because of the lower numbers and overall smaller size of metal wear debris particles. This may lead to a better transport of the particles from the joint tissues and a lower incidence of periprosthetic osteolysis around metal on metal hip replacement.

Retinoblastoma, though uncommon, frequently is associated with other second malignant neoplasms, especially bone sarcomas. These second neoplasms can occur in sporadic cases of retinoblastoma, though they more commonly are associated with genetic forms of the disease. This is the first known report of 2 histologically distinct bone sarcomas in a patient with retinoblastoma.

Pigmented villonodular synovitis is a well-described disease that almost universally involves a single site. This is a report of an unusual case of multiple site involvement of pigmented villonodular synovitis in a child. In addition to multiple site involvement, the case is unusual for several reasons: asymmetric involvement, involvement of both upper and lower extremities, involvement of the pes anserine tendons, and the patient is an otherwise healthy child.

A 42-year old male with the largest reported giant bone island (10.5 cm in length) is presented. Due to its ominous size, association with some degree of pain and increased uptake on radionuclide bone scan, a biopsy was considered necessary definitively to rule out a slow-growing osteosarcoma or blastic metastasis. Documentation of growth in adult patients of conventional and giant bone islands, coupled with evidence of increased radionuclide uptake, makes the clinicoradiological distinction between bone islands and blastic malignancies difficult. Guidelines for biopsy versus serial radiographic follow-up of such lesions are addressed.

The seventh case of primary malignant mesenchymoma of bone is reported. It is compared to the other six cases in the literature and clinicopathologic pattern of this entity is developed. Primary malignant mesenchymoma of bone is compared to mesenchymal chondrosarcoma and dedifferentiated chondrosarcoma. Differences as well as similarities are discussed and a more current classification scheme for malignant mesenchymoma of bone is proposed.

Chondroblastoma is a rare, benign primary bone tumor usually involving secondary centers of enchondral ossification. The consistent epiphyseal location in the great majority of chondroblastomas signifies that the tumor may arise from an aberrant germ cell of the physeal plate. This case report describes a chondroblastoma located in a atypical nonphyseal location, namely in the right fourth metatarsal base. Cases such as these imply that the cell of origin may not exclusively be derived form the physeal plate. The clinical-radiographic significance is that historically chondroblastoma is considered an epiphyseal lesion, but rare cases such as the one reported here and those of the skull demonstrate that this is not always a characteristic of these tumors. The implication from a histogenetic standpoint is that chondroblastoma may, on rare occasions, occur in an area of an enchondrally formed bone other than adjacent to the physeal plate. We are presently investigating the histogenetic relationship of the chondroblastoma (CB) of bone to CB of soft tissue, giant-cell tumor of tendon sheath (GCT-TS), pigmented villonodular synovitis (PVNS) and chondroma of tendon sheath (chondroma of soft parts). We now have collected about 15 cases of GCT-TS and PVNS with extensive areas of chondroid and/or cartilage differentiation that cannot be distinguished from CB of bone by histologic or electron microscopic features alone. From these interesting observations we are developing the histogenetic concept that all of these lesions are interrelated to multipotential mesenchymal and/or synovial cells of the tendon sheath.(ABSTRACT TRUNCATED AT 250 WORDS)

Part I discusses the correlation between the clinical, radiology and histologic features with the three phases (incipient, mid- and late phase) of Paget's disease. In this section, we will discuss in detail the radiologic features by location as well as aberrant radiographic presentations in addition to secondary tumors such as post radiation sarcomas and giant cells tumors which occur in Paget bone. Because Paget's disease generally affects people in their middle and late ages, the differential diagnosis often includes metastatic disease and the differentiation can often be quite challenging. Moreover, metastatic disease to bones afflicted with Paget's disease can further add diagnostic confusion. These critical aspects will be discussed in this section of Paget's disease of bone.

Distinctive clinical, radiologic and pathologic features are seen in Paget's disease of bone. These distinct features can be divided into three phases; initial phase, midphase, and late phase. The clinical features may vary from patients being asymptomatic (involving a single bone) to patients having severe, multiple bone involvement with systemic disease. Radiologically, there are unique features which can differentiate Paget's disease from other bone diseases. The radiologic features follows the histologic findings on light microscopy. The correlation of the different phases with the clinical, radiologic and pathologic features of Paget's disease allows for early accurate diagnosis and treatment.

A case has been presented of a 14-year-old male patient who developed a fusiform mass on the volar aspect of his left forearm following two fractures. Microscopic features and plain radiography, CT, and MRI appearance of juxtacortical aggressive fibromatosis are discussed.

Purpose: This study investigated prognostic factors in nonmetastatic high-grade extremity osteosarcoma and the prognosis following resection of subsequent pulmonary metastases, with emphasis on the effect of chemotherapy-induced tumor necrosis., Patients and Methods: We reviewed 111 consecutive patients with high-grade nonmetastatic extremity osteosarcoma treated with preoperative chemotherapy and surgical resection, with additional review of 36 patients who had subsequent pulmonary metastases resected., Results: The overall 5-year survival rate was 53%. In resected primary tumors, tumor-free resection margin (P < .001) and increasing chemotherapy-induced tumor necrosis (> 90% threshold, P < .003) correlated with increased metastasis-free survival. Relative risk factors for metastases were as follows: tumor-containing resection margin (most likely to metastasize); poor response to preoperative chemotherapy and/or lack of postoperative chemotherapy (next worse prognosis); and excellent response to preoperative chemotherapy (> or = 90% necrosis) combined with postoperative chemotherapy (best prognosis). The 5-year survival rate following pulmonary metastasis resection was 23%, whereas a 0% 4-year survival rate followed development of bony metastases (P < .001). The extent of tumor necrosis in resected pulmonary metastases did not affect prognosis. Survival was best in patients with three or fewer pulmonary nodules (P < .048), four or fewer recurrent pulmonary nodules (P < .047), unilateral pulmonary metastases (P < .037), or longer intervals between primary tumor resection and metastases (P < .082)., Conclusion: Intensive preoperative and postoperative chemotherapy combined with complete resection of both primary and metastatic pulmonary osteosarcomas is justified, with a goal of 100% tumor necrosis and excision. Although current treatment regimens allow effective salvage therapy for a few patients with pulmonary metastases, more effective systemic treatment is needed.

Benign giant cell tumor of bone, despite being classified as benign, has the unusual ability to metastasize. Metastasis of such a tumor has been thought to be rare, with only approximately 50 such cases having been reported. However, as awareness of the metastatic potential of these tumors has increased, and methods of detection have improved, metastasis of benign giant cell tumor has been increasingly recognized. Six patients with pulmonary metastasis of giant cell tumor have been treated at a Los Angeles hospital since 1980. This represents 9.1% of all patients treated for benign giant cell tumor of bone over the same period at this institution, a higher rate than that encountered in previously published series. The early detection and treatment of this tumor is important, because those with complete resection of tumor have the best prognosis. The nature of these pulmonary metastases remains unpredictable, however, as evidenced by two of the cases in this series: one of spontaneous regression, and another of death caused by pulmonary failure.

We presented the case of a 26-year-old woman with a blastic, miliary form of osteosarcomatosis involving the axial skeleton, skull, and long bones to the elbow and knee joint regions who subsequently developed hypocalcemic tetany. Radiologically the lesions mimicked the spread of breast carcinoma, and because of the distribution of the lesions we surmised that the spread was by means of Batson's vertebral plexus of veins. The literature on multiple osteosarcomas was reviewed and an updated clinical subclassification of patients with multiple skeletal osteosarcomas presented.

A unique lesion discovered in the scapula of a 36-year-old woman is presented. The lesion has microscopic features resembling those of fibrous dysplasia and osteoid osteoma which we believe is identical to an entity previously only documented in the rib (fibro-osseous lesion of rib). We are of the opinion that the lesion probably represents a reactive response to trauma rather than a neoplasm and suggest the name of "fibro-osseous reparative pseudotumor" for this entity.

We have presented the first case of a lipoma-like liposarcoma of the soft tissues with high-grade malignant transformation to a high-grade osteosarcoma, the latter component of which responded well to systemic chemotherapy. With 4 months of follow-up the patient is without evidence of disseminated disease. The various types of liposarcoma are listed and several described in some detail. Of particular importance is the potential for development of a highly malignant sarcoma from a relatively indolent low-grade liposarcoma, with even osteosarcoma developing.

In 27 patients with extremity lesions (24 osteosarcoma, three malignant fibrous histiocytoma), a notable decrease in thallium-201 uptake was correlated with a good response to preoperative chemotherapy of the primary tumor. A good response is indicated by a greater than 95% tumor necrosis. Serial quantitative thallium-201 uptake of malignant bone tumors in patients receiving preoperative chemotherapy therefore can accurately predict a good histologic response and prognosis. Serial thallium scintigraphy can furthermore identify poor responses within two weeks after the initiation of treatment, or can prompt an early change in preoperative chemotherapy and facilitate limb salvage surgery.

Wide excision, a recommended treatment for osteoid osteoma, creates needless resection of surrounding bone and causes difficult intraoperative nidus identification. Less bone resection is required by successively burring through the reactive bone to identify the nidus, which is then removed with curettes and burrs. This burr-down technique requires precise preoperative anatomic localization by thin section (1-1.5 mm) computed tomography (CT) scans. In a consecutive series of 19 osteoid osteomas, 18 were accurately diagnosed before operation, using a combination of clinical findings, plain roentgenograms, and CT scans. The burr-down technique was successfully used in 15 cases, and four were treated with wide excision. There have been no local recurrences. The follow-up period for all 19 patients was at least six months. No bone grafts were required in the burr-down group in nonspinal locations; there have been no fractures despite early return to unrestricted activity. The burr-down technique was associated with less postoperative immobilization, a shorter duration of protected weight bearing, and an earlier return to activity. The burr-down technique is recommended for accessible osteoid osteoma lesions.

The first three well-documented cases of pure, extraskeletal telangiectatic osteosarcoma of the soft tissues are presented in this article. The distinctive gross features were a predominance of large, blood-filled spaces, which, on histologic examination, were large blood-filled cavities in association with cyst-like walls containing anaplastic spindle cells and definite osteoid production in two of three cases. One of the cases is of additional clinical interest because the teen-aged daughter of the woman patient had died 1 year previously of a high-grade intramedullary osteosarcoma of bone.

We evaluated sequential thallium scans, made before and after a period of preoperative chemotherapy, for sixteen patients who had a high-grade sarcoma of bone or soft tissue. The purpose was to determine whether this technique could be used to ascertain accurately the amount of viable tumor as well as to predict the response to chemotherapy. Nine of the ten patients who had a reduced thallium uptake after chemotherapy also had a marked histological response, with necrosis of the tumor of at least 95 per cent. Six patients were seen to have no improvement on the thallium scans, and this finding correlated with necrosis of the tumor of less than 95 per cent. Thallium chloride has been shown to have an affinity for a variety of osteosarcomas and soft-tissue sarcomas. The mechanism of intracellular uptake is one of active transport, which makes thallium chloride a more accurate barometer of the viability of the tumor cells and of metabolic activity than scanning agents that are flow-dependent. We believe that sequential thallium scintigraphy should be used in conjunction with other imaging modalities in the diagnosis, planning of treatment, and follow-up evaluation of patients who have a sarcoma of bone or soft tissue. This technique appears to be useful in the prediction of the histological response of high-grade osteosarcomas and soft-tissue sarcomas to preoperative chemotherapy.

Melorheostosis is a rare congenital disease, some 300 cases have been reported in the literature. The main purpose of this case report is twofold: (1) to present an unusual case of melorheostosis of the right hand, beginning in infancy, with serial radiographic studies to show the gradual progression of the disease; and (2) to present the first case with the development of "aggressive" fibromatosis (desmoid tumor) of the adjacent soft tissues, associated with melorheostosis.

Five cases of a previously undescribed variant of epithelioid sarcoma are presented. This variant differs from the usual lesion in its absence of the typical necrobiotic nodular epithelioid pattern. It is instead composed of deceptively bland fibrohistiocytic and myoid cells arranged in a fibroma-like or dermatofibroma-like pattern with an affinity for osseous involvement. The clinical presentation, ultrastructural features, and presence of vimentin and low molecular weight keratin within the tumor cells justifies their designation as an epithelioid sarcoma variant.

A case of chondroblastoma associated with an aneurysmal bone cyst has been described. The radiographic appearance of the lesion understandably reflects the combined features of both tumors. Up to one-half of all cases of aneurysmal bone cysts are found in association with other tumors, benign or malignant, and up to 15% of chondroblastomas are combined with an aneurysmal bone cyst (4).

We present a giant cell tumor of the distal end of the femur that exhibited unusual diaphyseal extension and atypical MRI features. MRI demonstrated differing zonal signal characteristics in the distal metaphyseal/epiphyseal versus the diaphyseal components of the tumor. It also depicted an irregular, proximal tumor margin with an unusual, enhancing, peripheral zone. The atypical MRI features may be related to the unusual finding at pathological examination of an almost entirely necrotic giant cell tumor. This massive necrosis may illustrate a stage in the evolution of some giant cell tumors to fibrous histiocytoma-like variants of giant cell tumor or to conventional, benign fibrous histiocytoma of bone.