Richard A. McLeod

Aneurysmal bone cyst : a clinicopathologic study of 238 cases

Aneurysmal bone cyst (ABC) is a nonneoplastic expansile bone lesion that mainly affects children and young adults. Primary ABC is relatively rare, with an incidence one half that of giant cell tumor of bone. In 238 patients with ABC studied in the Mayo Clinic files, more than 80% of the lesions were in long bones, flat bones, or the spinal column. Of the lesions initially treated at the Mayo Clinic, 95% were typical ABC; the rest were „solid”︁ variants. Except for the absence of obvious cavernous channels and spaces, there was no significant histologic difference between solid variant and typical ABC. Radio‐graphically, ABC is an eccentric expansile lesion commonly located at the metaphysis of long bones. Computed tomography and magnetic resonance imaging may show multiple internal septations or fluid levels. In the 153 patients treated, 19% had recurrence after curettage (intralesional excision). Recurrence was most common during the first 2 postoperative years.

Osteoblastoma: Clinicopathologic study of 306 cases

The clinical, radiologic, and pathologic features of 306 osteoblastomas were analyzed. Seventy-five were Mayo Clinic cases and 231 were from consultation files. Males outnumbered females two to one. The age range was 6 months to 75 years (mean age, 20.4 years). The vertebral column including the sacrum was the most frequent site (32%). Pain was the usual complaint and neurologic findings were associated with vertebral tumors. Although most tumors were well circumscribed, cortical expansion and destruction were common radiographic findings (39%), and 12% had features suggestive of malignancy. Large, epithelioid osteoblasts were seen in 24% and were the predominant cellular element in 10%. A distinctive epithelioid multifocal pattern was recognized. Recurrence rates were 16% (Mayo Clinic cases) and 21% (consultation cases). Tumors involving the central neuraxis were associated with greater morbidity and mortality. Aggressive behavior is within the biologic spectrum of osteoblastomas, and histopathology alone does not appear to be a reliable predictor of aggressiveness. The most important differential diagnosis is osteosarcoma.

Chondrosarcoma arising in osteochondroma

Secondary chondrosarcomas are rare. An analysis of 75 cases of chondrosarcomas secondary to osteochondroma (42 lesions were from the Mayo Clinic files and 33 were from consultation files) revealed that 40 of the patients had single exostosis and 35 had multiple lesions. More males than females were affected, and most of the patients were age 20 to 40 years. The tumors involved various bones. Malignant change was manifested radiologically by fuzzy margins of the cartilage cap and by the presence of lucent zones within the lesion. Grossly, the surface of the thickened cartilage cap was irregular. Microscopically, most of the tumors were well‐differentiated (Grade 1). Treatment was surgical. Simple excision of the tumor resulted in a large recurrence rate. Resection and amputation were generally curative. Only 12 of the patients have died of their tumor. Most patients died of local recurrence. Only two of the 75 patients had definite evidence of metastatic disease.

Primary chondrosarcoma of long bones and limb girdles

Chondrosarcomas are common solid malignant tumors of bone, second in incidence only to osteosarcomas. The biologic evolution of chondrosarcomas is slow, requiring long follow‐up intervals for meaningful survival analysis.

Epithelioid hemangioendothelioma of bone

Epithelioid hemangioendothelioma of bone is a rare tumor of vascular origin. A series of 40 cases from the Mayo Clinic files was studied to define the pathologic features of this disease and to evaluate any histologic or clinical factor influencing outcome. More than 50% of the tumors were multicentric, with a predilection for bones of a particular anatomical area. In this series, patients with multifocal tumors did not have a better prognosis than those with unicentric disease. We could not predict the outcome of cases on the basis of the histologic features. Visceral involvement was the most important criterion in predicting prognosis. Resection is still the primary treatment for these tumors. Radiotherapy may be useful for surgically inaccessible tumors. Too few patients have received adjuvant chemotherapy to evaluate its usefulness in this setting.

Low-grade intraosseous osteosarcoma.

A study of 80 well‐differentiated osteosarcomas, 16 from the Mayo Clinic files and 64 from our consultation files, revealed that males and females were about equally affected, most of the patients were young adults, and skeletal distribution was similar to the distribution seen in conventional osteosarcoma. Radiographs generally showed poor margination, suggestive of malignancy. Histologically, the tumors were composed of spindle cells with only minimal atypia. Some tumors had bone spicules similar to those seen in fibrous dysplasia. An invasive growth pattern was the most helpful feature in differentiating low‐grade osteosarcoma from fibrous dysplasia. Initial treatment was highly variable. Local excision was almost always associated with recurrence. Wide excision was almost never followed by recurrence. The recurrent tumor was a high‐grade, conventional osteosarcoma in 15% of the patients, and this was associated with a poor prognosis. Wide excision seems to be the treatment of choice for this very rare variant of osteosarcoma.

Intraosseous well-differentiated osteosarcoma.

A series of 27 patients with intramedullary osteogenic sarcomas that were so well‐differentiated histologically as to be confused with benign lesions was studied. Of the 27 patients, 14 were females and 13 were males, and most were adults. The tibia and femur were involved commonly. Roentgenographically, the tumors showed a mixture of sclerosis and lysis with poor margination. However, they lacked the highly destructive appearance of high‐grade osteosarcomas. Histologically, spindle cells with minimal cytologic atypia were arranged in interlacing bundles. Mitotic figures were scarce. The amount of osteoid was variable, commonly being abundant. With recurrence, three tumors became highly anaplastic. Excision of tumor almost invariably led to recurrences. Resection or amputation has led to good results in seven patients. Only three of the 27 patients died with metastatic tumor; one patient is alive with metastasis. Central low‐grade osteosarcomas have been misdiagnosed frequently and hence treated inadequately. Careful roentgenographic and histo‐logic correlation is required to make the diagnosis.

Chondroblastoma of bone.

Chondroblastomas are unusual benign lesions of bone. They classically occur at the ends of long bones in young persons. The roentgenographic and histologic features are typical. We had an opportunity to study a large number of chondroblastomas. Most of the cases came from the consultation file started by Dr D. C. Dahlin at the Mayo Clinic. This method of ascertainment may tend to load our series with unusual and atypical examples. We found some unusual locations, such as the skull and facial bones and the small tubular bones of the hands and feet. We also found some unusual histologic features, such as mitotic activity, necrosis, and cellular atypia. However, despite the unusual features, the biological behavior of these tumors was that of a benign process with only limited local aggressiveness.

Telangiectatic osteogenic sarcoma

Of approximately 1,000 cases of osteogenic sarcomas at the Mayo Clinic, 25 were diagnosed as telangiectatic osteogenic sarcomas. Of the 25 patients involved, 16 were males and 9 were females, and their ages ranged from 6 to 49 years. Six patients had had pathologic fracture. The lesions were typically located centrally and usually in the distal femur or proximal humerus and roentgenographically were large and purely lytic with destruction of cortex. Grossly, the lesions were cystic and contained clotted blood. Histologically, cystic spaces that contained blood were lined with anaplastic spindle cells and benign giant cells; sometimes, there were so few malignant cells that diagnosis was difficult. Usually, fine, lacelike osteoid was present. Of the 25 patients, 23 have died of metastatic disease, and another has developed pulmonary metastasis 11 months after amputation. Only one patient has survived for more than five years; however, he has developed pneumothorax. Data from this series suggest that the outlook in telangiectatic osteogenic sarcoma is more bleak than in conventional osteosarcoma.

Osteoid osteoma. Detection, diagnosis, and localization

One hundred surgically proved cases of osteoid osteoma were reviewed, with emphasis on the modalities used in the detection, diagnosis, and localization of this benign tumor. These included plain radiography, tomography, radionuclide imaging, and angiography. Diagnosis may require all of these techniques. Radionuclide imaging is valuable when no abnormalities are visible on the plain radiographs.