Body Computed Tomography
Computed Tomography of Long-Bone Osteosarcoma 1 Judy M. Destouet, M.D., Louis A. Gilula, M.D., and WIlliam A. Murphy, M.D.
Six cases of osteosarcoma, including medullary, parosteal, periosteal, and intracortical types, were studied by computed tomography (CT).ln selected cases, CT provided additional preoperative information as to osseous size and soft-tissue extent. CT helped determine intramedullary involvement and specific sites of cortical destruction and thereby helped to plan the surgical approach to biopsy and the definitive excision. INDEX TERMS: Bone neoplasms, diagnosis. Computed tomography, bones, 4(0}.1211 • (Skeletal system, osteosarcoma, 4[0].3221)
Radiology 131:439-445, May 1979
HE ROLE of routine radiography in the detection and diagnosis of osteosarcoma is well recognized. Computed tomography (CT) may help to evaluate these tumors by more clearly demonstrating aspects of the extent and character of bone and soft-tissue involvement (1-7). This report illustrates the roles CT may play in the preoperative assessment of medullary, parosteal, periosteal, and intracortical osteosarcoma in long bones.
T
METHODS AND RESULTS Between December 1976 and March 1978,6 cases of osteosarcoma were studied utilizing EMI 5000 and 5005 CT units. Pre-CT evaluation included conventional radiography of the involved bone. Assessment for potential metastatic disease which included a bone scan, full-chest tomography, and a liver-spleen scan was negative in all patients. The bone scans all showed increased uptake that correlated precisely with the area of radiographically demonstrated bone involvement. Clinical information, pathologic correlation, and short-term follow-up were available in all cases. Because of the need to assess symmetry when determining tumor extent, both extremities were placed in the CT scanner in as identical a position as possible. The site of interest was localized either by palpation or by a preliminary radiograph with overlying lead markers. Scans were obtained at 1-2-cm intervals from above the tumor site until tumor was no longer found, and the surrounding tissues were symmetric. Contrast agents were not used. Specimen radiographs in each case were compared with the CT sections; however, correlations were not as exact as desired because the specimens were sectioned in coronal or sagittal rather than transverse planes. As the ability to reconstruct images in both coronal and sagittal planes is developed, more exact pathologic correlation will be possible.
CASE REPORTS CASE I: A 12-year-old boy presented after six months of progressive pain in the right knee. He had a distal thigh mass which had slowly enlarged for two months. Routine radiographs (Fig. 1, a and b) demonstrated an osteoblastic lesion with permeation of the medullary cavity and destruction of the medial femoral cortex. Tumor bone partially enveloped the femoral shaft. On CT, the soft tissues were displaced around the lesion as compared to the opposite thigh (Fig. te), Extensive tumor within the medullary cavity (Fig. 1d) extended through an area of cortex and partially surrounded the femoral shaft, leaving a cleavage plane between the remaining cortex and the tumor bone. Histopathology of a biopsy specimen showed an osteoblastic osteosarcoma, and an above-the-knee amputation was performed. Adjuvant chemotherapy was initiated.
COMMENT: Osteosarcoma was preoperatively diagnosed on plain radiographs. The main value of CT was to more clearly identify the proximal limit of disease and to thereby help plan the level of amputation. Of additional interest was the tumor encasement of the femoral shaft. Although the overall increased circumference of the thigh could be detected clinically, the CT preoperatively showed that it was due to large tumor volume with no gross softtissue infiltration. Additional CT sections showed the proximal extent of disease more clearly than did routine radiographs. CASE II: A 16-year-old girl presented with a history of pain in the right knee for three years following minor trauma. Radiographic examination (Fig. 2a) showed an ill-defined mixed sclerotic and destructive process in the distal right femur. A small amount of periosteal new bone extended medially along the femoral shaft. On CT, when compared with the normal side, the adductor muscle group next to the tumor was slightly enlarged (Fig. 2b). The adjacent medullary activity was sclerotic and the medial cortex thickened. No cortical break was seen. Histopathologic examination of a biopsy specimen showed osteosarcoma and, after correlation with the extent of disease as shown by CT, a high thigh amputation was performed and adjuvant chemotherapy instituted.
1 From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, St.Louis, Mo. Received Aug. 30, 1978; accepted and revision requested Nov. 21; revision received Jan. 5, 1979. jr
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Fig. 1. CASE I. Medullary osteosarcoma. 8 and b. Radiographs show a mixed lytic and blastic lesion of the distal rightfemoral diaphysis. c. Although the muscles and soft tissues are not increased in volume, CT shows that they are displaced about the anteromedial and anterolateral aspects of the right femur by tumor bone. Dense tumor (t) obliterates the medullary cavity and encompasses the right femoral shaft. d. With window settings optimized for bone, the medial site of cortical break in the right femur is displayed (arrow). Extensive tumor bone surrounds two-thirds of the femur, leaving a cleavage plane (arrowheads), and fills much of the medullary cavity (t).
COMMENT: The diagnosis of osteosarcoma was made preoperatively by routine radiographs. CT displayed softtissue involvement not detected on the radiographs and thereby enabled more accurate preoperative determination of disease extent.
tumor bone production. In this case, CT showed that extensive soft-tissue invasion was the reason for increased leg circumference, as opposed to CASES I and IV where increased circumference was due to tumor bone displacing rather than invading the tissues.
CASE III: A 16-year-old boy had pain and swelling over his proximal left tibia for six months after sustaining minor trauma. Radiographs demonstrated a mixed lytic and sclerotic lesion of the proximal tibia with lamellated periosteal bone formation along its posterior and lateral borders (Fig. 3, 8 and b). CT showed soft-tissue thickening circumferentially about the tibia (Fig. 3c). Tumor extended beyond the tibia with soft-tissue deformity extending to the fibular shaft. Osteosarcoma was found on histopathologic examination of a biopsy specimen, and an above-the-knee amputation followed, complemented by adjuvant chemotherapy.
CASE IV: A 21-year-old woman had decreased motion of the right knee for six months and local pain for three weeks. Radiographs demonstrated an expanded distal femoral shaft with a very dense lesion along its posterior aspect (Fig. 4, 8 and b). The tumor margins blended into normal bone. Involvement of the medullary cavity, although suspected, could not be confidently shown. CT demonstrated displacement of the surrounding soft tissues due to the size of the bony mass, but no invasion of soft-tissue planes (Fig. 4c). The irregular, sclerotic tumor expanded the posterior distal femur and both thickened the cortex and invaded the medullary cavity (Fig. 4d). An en-bloc excision of the tumor was performed, and histopathology verified a parosteal osteosarcoma.
COMMENT: The diagnosis made on routine radiographs was osteosarcoma. CT more precisely localized the cortical destruction and tumor bone formation and helped the surgeon plan to biopsy the exact area of destruction and
COMMENT: The major diagnosis considered, based on plain radiographs, was parosteal osteosarcoma. CT clearly
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Fig. 3. CASE III. Medullary osteosarcoma. a and b. A mixed lytic and blastic lesion involves the metadiaphyseal portion of the proximal tibia, with associated lamellated periosteal bone formation (arrowheads). c. CT localizes cortical destruction to the posterolateral sideof the tibia (arrowhead) and shows diffuse soft-tissue thickening (t). Fig. 2. CASE II. Medullary osteosarcoma. a. A sclerotic, lytic process involvesthe distalfemoralmetadiaphysis. Minimal tumorbone extends along the medial cortex (arrowheads). b. CT showsan enlarged soft-tissue andmusclemass (m) adjacent to the sclerotic tumor (t) whichpartially obliterates the medial medullary cavity. Tumor bone and periosteal reaction are prominent along the medial cortex (arrowhead).
demonstrated medullary involvement as well as confirmed lobulated parosteal proliferation. These findings were diagnostic of a malignant lesion. CASE V: A 14-year-old boy presented one monthafter detectinga small painful massovertheanterior aspectof hisdistalleft tibia.Routine radiographs demonstrated a localized soft-tissue massalong theanterior distal tibia, with underlying bony changes (Fig. 5a). CTshoweda softtissue mass along the anteromedial and anterolateral aspects of the tibia (Fig. 5b). Sclerotictumorbonewas limited to the periosteal surface of the tibia, while the endosteal surface and medullary cavity were normal (Fig. 5c). Periosteal osteosarcomawas diagnosed on biopsy, and a below-the-knee amputation was performed subsequently (Fig. 5d). Adjuvant chemotherapy was instituted. COMMENT:
As in the previous cases, routine radio-
graphs provided the main features to make the most likely preoperative diagnosis. CT showed the nature of the endosteal surface and provided more information about the soft-tissue component. However, due to the lack of fat between leg muscles, CT failed to demonstrate the exact posterior extent of the abnormal soft tissues. As an adequate local resection of a periosteal osteosarcoma may be curative (8), a local resection could have been strongly considered on the basis of the radiographic appearance alone. The CT demonstration of the abnormal anterior two-thirds of the tibial cortex and the inexact posterior extent of soft tissues showed that obtaining an adequate surgical margin around the lesion would be extremely difficult, if not impossible. CT swayed surgical planning toward amputation. Subsequent examination of the amputated specimen showed that the tumor involved the anterior and lateral tibial surfaces and bowed the anterior tibial artery and nerve. Thus an adequate surgical margin could not have been obtained without resecting most of
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4b
Fig. 4. CASE IV. Parostealosteosarcoma. 8 and b. A lobulated sclerotic lesion involves the posterolateral aspect of the distal right femur. The outer edge of the lesion is well defined, but its inner surface is poorly delineated. c. CT shows involvement of the medullary cavity. The soft tissues are relatively symmetric, allowing for expansion of the femoral shaft. d. An enlarged view of the distal right femur with CT windows optimized for bone shows extensive tumor (t) involvement of the medullary cavity to better advantage.
the tibia and sacrificing the artery and nerve. On pathologic examination, the soft tissues posteromedial to the tibia were normal, and we have no explanation for the slight asymmetry of these tissues (Fig. 5b). CASE VI: A 24-year-old man presented with a two-month history of a slightly tender lump involving the anterior aspect of his left midtibia. Routine radiographs demonstrated a fairly well defined lytic lesion of the medial midtibal cortex (Fig. 6, 8 and b). A tangential view showed a slight cortical permeation and a periosteal reaction (Fig. 6c). On CT, a lytic lesion was located completely within the anteromedial tibial cortex (Fig. 6d) without evident medullary extension. Soft-tissue swelling anterior to the tumor was very limited and indicated excisional biopsy. After biopsy, histopathology revealed intracortical osteosarcoma arising from and limited to the tibial cortex (Fig. 6e). An above-the-knee amputation followed ten days later with no evidence of remaining tumor in the amputated specimen. Chemotherapy was instituted.
COMMENT: The preoperative diagnosis with the help of both standard radiographs and CT was still difficult. Major considerations included adamantinoma or a slowgrowing tumor, such as an unusual fibro-osseous lesion. Correlation between the radiographs and CT encouraged the surgeon to perform an excisional rather than an incisional biopsy. The entire lesion was removed, and intracortical osteosarcoma diagnosed. We could find only 2 previously reported cases of intracortical osteosarcoma (9); those involved the distal
femur and the midtibia and were similar in appearance. Histopathologically, intracortical osteosarcoma is indistinguishable from medullary osteosarcoma but is confined to the cortex where it presumably originated. On gross pathology, its periosteum can be stripped from the underlying tumor, whereas the periosteum in a periosteal osteosarcoma is intimately involved with the tumor. Radiographically, intracortical osteosarcoma presents as a slow-growing lesion and may have areas of surrounding sclerosis. Close radiographic and pathologic correlation is necessary to make the diagnosis. DISCUSSION
Medullary, parosteal, and periosteal forms of osteosarcoma have been well described in the literature (8, 10-18). Intracortical osteosarcoma (9) is not widely recognized as another form of osteosarcoma; however, increased awareness of it will undoubtedly lead to identification of more cases. Because of cross-sectional display, CT offers a unique image of osteosarcoma and other bone tumors. The location of bone involvement, whether cortical, medullary, or both, can be readily discerned. Due to superimposition of the diameter of bone from cortex to cortex, routine radiography does not always allow differentiation of cortical and medullary involvement. CT shows the exact site and
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Fig. 5. CASE V. Periosteal osteosarcoma. a. A localized, soft-tissue mass (arrows) lies along the anterior distal left tibia with a concave defect of the adjacent cortex. Spiculated tumor bone is oriented perpendicular to the tibial shaft (arrowhead). b. CT demonstrates a soft-tissue mass along the anteromedial and anterolateral aspects of the left tibia (arrows). A questionable cleavage plane between the tumor and normal soft tissues can be discerned (arrowheads). The soft tissues posteromedial to the tibia are slightly fuller than the normal side (see CASE V COMMENT). c. With window settings optimized for bone, CT shows that the endosteal surface and medullary cavity are normal. Periosteal bone lies on the anterolateral tibial surface (arrowheads). d. A specimen radiograph of a coronal section shows a well defined soft-tissue mass encompassing the tibia. Adherent periosteum forms the outer margin of this mass (arrows).
extent of macroscopic bone destruction. Recognition of involvement of the medullary-cavity obviously helps to identify a medullary (central) osteosarcoma, but may also indicate whether or not the other three types of osteosarcoma have advanced to involve the cancellous bone. This was particularly evident in CASE IV, where CT demonstrated an abnormal medullary cavity as well as focal cortical thickening. Due to its improved display of soft tissue, CT can more accurately determine the type and extent of soft-tissue involvement than can other radiographic modalities. Such evaluation is aided by distinct fat planes and by comparison with the opposite extremity. When fat cannot be seen between muscles, soft-tissue extent may not be easily assessed. Soft tissues may be distorted by pushing from an underlying bone mass, tumor invasion, or infiltration from hemorrhage or edema. In our experience, CT has not yet been able to differentiate tumor infiltration from edema or hematoma and should therefore be performed before
a biopsy, as the postoperative hematoma or swelling may significantly interfere with evaluation of the true preoperative soft-tissue involvement. CT cross-sectional display and its improved soft-tissue imaging have provided useful information in surgical planning among these osteosarcomas. In some cases, the choice of biopsy site was influenced by the location of tumor bulk and focal cortical destruction shown by CT. Knowledge of tumor extent is important to determine resectability in periosteal and parosteal osteosarcomas and the level of amputation in central osteosarcoma. In CASE IV, CT showed that excision would have to include a large portion of the metaphyseal cancellous bone. In CASE V, it showed that excisional biopsy probably could not be performed without amputation; subsequent specimen radiography was confirmatory. In CASE VI, CT clearly indicated that definitive excision could be accomplished. Detection of skip metastases proximal to the lesion in
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Fig. 6. CASE VI. Intracorticalosteosarcoma. a. A slightly expansile lytic defect involves the medial cortex of the midtibia. b. On a lateral radiograph, the midtibial lesion has well defined borders. c. A tangential view of the lesion with magnification technique demonstrates irregular bone formation along the periosteal margin (arrows). d. CT through the lesion confirms intracortical location (arrowheads). (m = medullary portion of tibia) e. After excisional biopsy, a longitudinal section through the irregular marginated lytic lesion shows that its periosteum is thickened (arrows) and endosteum (arrowheads) is attenuated.
long bones or in adjacent soft tissues is possible with CT (3, 19). Radionuclide bone scanning may eventually prove to be a more sensitive detector for small osseous metastases some distance from the primary lesion. No skip metastases were present in our cases. We believe CT is complementary to conventional radiography and to pathological examination (CASE VI). CT may also gradually prove to provide prognostic information. For example, the demonstration of medullary involvement in parosteal osteosarcoma would indicate an advanced stage of that tumor. Similarly, invasion of soft tissue by
central osteosarcoma is a later stage of that neoplasm. When studied in a prospective fashion and related to therapeutic decisions, CT may help show the way to improve therapeutic choices. CT also had shortcomings in evaluation of these tumors. Soft-tissue tumor margins are difficult to determine, as in CASE V, when there is not sufficient fat between muscles and along fascial planes, and when tumor tissue has the same density as normal tissue. de Santos et et. (3) point out that most of their tumors increased in density only minimally after contrast enhancement. We did not use
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contrast; however, using contrast to identify major vessels next to the tumor may routinely be of more value when planning surgery than using it only to show tumor enhancement. The averaging of 13 mm for each CT section creates an artificial display which is usually representative of what is present, but at times may be inaccurate at the level of interest. A curved surface may be displayed as an unsharp edge as a result of averaging, and unless such a surface is placed at right angles to the scanning gantry, subtle cortical reactions may not be shown. Scanners which will display information over narrower sections, such as 2 mm, may largely eliminate this inaccuracy. CT may shorten the work-up of osteosarcomas as well as other bone tumors by eliminating additional nonstandard radiographs or laminographs. We did not use laminography in our study because we found that it does not offer the necessary detail for determining medullary involvement; it also fails to provide information concerning the adjacent soft tissues. Furthermore, we have not routinely used arteriography to outline the soft-tissue limits of tumors. The combination of standard radiographs and CT: (a) takes less time; (b) is performed at similar or less cost than a battery of additional radiographs, laminograms, and arteriograms; and (c) exposes the patient to less radiation than that comb ination.
Louis A. Gilula, M.D. Mallinckrodt Institute of Radiology 510 South Kingshighway Boulevard St. Louis, Mo. 63110
REFERENCES 1.
Weinberger G, Levinsohn EM: Computed tomography in the
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evaluation of sarcomatous tumors of the thigh. Am J Roentgenol 130:115-118, Jan 1978 2. Weis L, Heelan RT, Watson RC: Computed tomography of orthopedic tumors of the pelvis and lower extremities. Clin Orthop 130:254-259, Jan-Feb 1978 3. deSantos LA, Goldstein HM, Murray JA, et al: Computed tomography in the evaluation of musculoskeletal neoplasms. Radiology 128:89-94, Jul 1978 4. Wilson JS, Korobkin M, Genant HK, et al: Computed tomography of musculoskeletal disorders. Am J RoentgenoI131:55-61, Jul 1978 5. McLeod RA, Stephens DH, Beabout JW, et al: Computed tomography of the skeletal system. Semin RoentgenoI13:235-247, Jul 1978 6. Schumacher TM, Genant HK, Korobkin M, et al: Computed tomography. Its use in space-occupying lesions of the musculoskeletal system. J Bone Joint Surg 60:600-607, Jul 1978 7. de Santos LA, Murray JA: Evaluation of giant cell tumor by computerized tomography. Skeletal RadioI2:205-212, 1978 8. Unni KK, Dahlin CD, Beabout JW, et al: Periosteal osteogenic sarcoma. Cancer 37:2476-2485, May 1976 9. Jaffe HL: Intracortical osteogenic sarcoma. Bull Hosp Joint Dis 21:189-197, Oct 1960 10. Dahlin DC, Coventry MB: Osteogenic sarcoma. J Bone Joint Surg 49:101-110, Jan 1967 11. Dahlin DC, Unni KK: Osteosarcoma of bone and its important recognizable varieties. Am J Surg PathoI1:61-72, Mar 1977 12. deSantos LA, Murray JA, Finklestein JB, et al: The radiographic spectrum of periosteal osteosarcoma. Radiology 127:123-129, Apr 1978 13. Edeiken J, Farrell C, Ackerman LV, et al: Parosteal sarcoma. Am J RoentgenoI111:579-583, Mar 1971 14. EdeikenJ, HodesPJ: Roentgen Diagnosisof Diseases of Bone. Baltimore, Williams & Wilkins, 1976, Vol. 2, pp 939-977 15. Spjut HJ, Dorfman HD, Fechner RE, et al: Tumors of bone and cartilage. Atlas of Tumor Pathology, 2nd Ser., Fasc. 5., Washington, D.C., AFIP, 1971, pp 141-174. 16. Unni KK, Dahlin DC, Beabout JW, et al: Parostealosteogenic sarcoma. Cancer 37:2467-2475, May 1976 17. Van der Heul R, Von Ronnen A: Juxtacorticalosteosarcoma. J Bone Joint Surg 49:415-439, Apr 1967 18. Wolfel DA, Carter PR: Parosteal osteosarcoma. Am J RoentgenoI105:142-146, Jan 1969 19. Kumar AP, Wrenn EL Jr, Fleming ID, et al: Transmedullary amputation and resection of metastases in combined therapy of osteosarcoma. J Pediatr Surg 12:427-435, Jun 1977
Computed Tomography of Long-Bone Osteosarcoma 1 Judy M. Destouet, M.D., Louis A. Gilula, M.D., and WIlliam A. Murphy, M.D.
Six cases of osteosarcoma, including medullary, parosteal, periosteal, and intracortical types, were studied by computed tomography (CT).ln selected cases, CT provided additional preoperative information as to osseous size and soft-tissue extent. CT helped determine intramedullary involvement and specific sites of cortical destruction and thereby helped to plan the surgical approach to biopsy and the definitive excision. INDEX TERMS: Bone neoplasms, diagnosis. Computed tomography, bones, 4(0}.1211 • (Skeletal system, osteosarcoma, 4[0].3221)
Radiology 131:439-445, May 1979
HE ROLE of routine radiography in the detection and diagnosis of osteosarcoma is well recognized. Computed tomography (CT) may help to evaluate these tumors by more clearly demonstrating aspects of the extent and character of bone and soft-tissue involvement (1-7). This report illustrates the roles CT may play in the preoperative assessment of medullary, parosteal, periosteal, and intracortical osteosarcoma in long bones.
T
METHODS AND RESULTS Between December 1976 and March 1978,6 cases of osteosarcoma were studied utilizing EMI 5000 and 5005 CT units. Pre-CT evaluation included conventional radiography of the involved bone. Assessment for potential metastatic disease which included a bone scan, full-chest tomography, and a liver-spleen scan was negative in all patients. The bone scans all showed increased uptake that correlated precisely with the area of radiographically demonstrated bone involvement. Clinical information, pathologic correlation, and short-term follow-up were available in all cases. Because of the need to assess symmetry when determining tumor extent, both extremities were placed in the CT scanner in as identical a position as possible. The site of interest was localized either by palpation or by a preliminary radiograph with overlying lead markers. Scans were obtained at 1-2-cm intervals from above the tumor site until tumor was no longer found, and the surrounding tissues were symmetric. Contrast agents were not used. Specimen radiographs in each case were compared with the CT sections; however, correlations were not as exact as desired because the specimens were sectioned in coronal or sagittal rather than transverse planes. As the ability to reconstruct images in both coronal and sagittal planes is developed, more exact pathologic correlation will be possible.
CASE REPORTS CASE I: A 12-year-old boy presented after six months of progressive pain in the right knee. He had a distal thigh mass which had slowly enlarged for two months. Routine radiographs (Fig. 1, a and b) demonstrated an osteoblastic lesion with permeation of the medullary cavity and destruction of the medial femoral cortex. Tumor bone partially enveloped the femoral shaft. On CT, the soft tissues were displaced around the lesion as compared to the opposite thigh (Fig. te), Extensive tumor within the medullary cavity (Fig. 1d) extended through an area of cortex and partially surrounded the femoral shaft, leaving a cleavage plane between the remaining cortex and the tumor bone. Histopathology of a biopsy specimen showed an osteoblastic osteosarcoma, and an above-the-knee amputation was performed. Adjuvant chemotherapy was initiated.
COMMENT: Osteosarcoma was preoperatively diagnosed on plain radiographs. The main value of CT was to more clearly identify the proximal limit of disease and to thereby help plan the level of amputation. Of additional interest was the tumor encasement of the femoral shaft. Although the overall increased circumference of the thigh could be detected clinically, the CT preoperatively showed that it was due to large tumor volume with no gross softtissue infiltration. Additional CT sections showed the proximal extent of disease more clearly than did routine radiographs. CASE II: A 16-year-old girl presented with a history of pain in the right knee for three years following minor trauma. Radiographic examination (Fig. 2a) showed an ill-defined mixed sclerotic and destructive process in the distal right femur. A small amount of periosteal new bone extended medially along the femoral shaft. On CT, when compared with the normal side, the adductor muscle group next to the tumor was slightly enlarged (Fig. 2b). The adjacent medullary activity was sclerotic and the medial cortex thickened. No cortical break was seen. Histopathologic examination of a biopsy specimen showed osteosarcoma and, after correlation with the extent of disease as shown by CT, a high thigh amputation was performed and adjuvant chemotherapy instituted.
1 From the Mallinckrodt Institute of Radiology, Washington University School of Medicine, St.Louis, Mo. Received Aug. 30, 1978; accepted and revision requested Nov. 21; revision received Jan. 5, 1979. jr
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Fig. 1. CASE I. Medullary osteosarcoma. 8 and b. Radiographs show a mixed lytic and blastic lesion of the distal rightfemoral diaphysis. c. Although the muscles and soft tissues are not increased in volume, CT shows that they are displaced about the anteromedial and anterolateral aspects of the right femur by tumor bone. Dense tumor (t) obliterates the medullary cavity and encompasses the right femoral shaft. d. With window settings optimized for bone, the medial site of cortical break in the right femur is displayed (arrow). Extensive tumor bone surrounds two-thirds of the femur, leaving a cleavage plane (arrowheads), and fills much of the medullary cavity (t).
COMMENT: The diagnosis of osteosarcoma was made preoperatively by routine radiographs. CT displayed softtissue involvement not detected on the radiographs and thereby enabled more accurate preoperative determination of disease extent.
tumor bone production. In this case, CT showed that extensive soft-tissue invasion was the reason for increased leg circumference, as opposed to CASES I and IV where increased circumference was due to tumor bone displacing rather than invading the tissues.
CASE III: A 16-year-old boy had pain and swelling over his proximal left tibia for six months after sustaining minor trauma. Radiographs demonstrated a mixed lytic and sclerotic lesion of the proximal tibia with lamellated periosteal bone formation along its posterior and lateral borders (Fig. 3, 8 and b). CT showed soft-tissue thickening circumferentially about the tibia (Fig. 3c). Tumor extended beyond the tibia with soft-tissue deformity extending to the fibular shaft. Osteosarcoma was found on histopathologic examination of a biopsy specimen, and an above-the-knee amputation followed, complemented by adjuvant chemotherapy.
CASE IV: A 21-year-old woman had decreased motion of the right knee for six months and local pain for three weeks. Radiographs demonstrated an expanded distal femoral shaft with a very dense lesion along its posterior aspect (Fig. 4, 8 and b). The tumor margins blended into normal bone. Involvement of the medullary cavity, although suspected, could not be confidently shown. CT demonstrated displacement of the surrounding soft tissues due to the size of the bony mass, but no invasion of soft-tissue planes (Fig. 4c). The irregular, sclerotic tumor expanded the posterior distal femur and both thickened the cortex and invaded the medullary cavity (Fig. 4d). An en-bloc excision of the tumor was performed, and histopathology verified a parosteal osteosarcoma.
COMMENT: The diagnosis made on routine radiographs was osteosarcoma. CT more precisely localized the cortical destruction and tumor bone formation and helped the surgeon plan to biopsy the exact area of destruction and
COMMENT: The major diagnosis considered, based on plain radiographs, was parosteal osteosarcoma. CT clearly
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Fig. 3. CASE III. Medullary osteosarcoma. a and b. A mixed lytic and blastic lesion involves the metadiaphyseal portion of the proximal tibia, with associated lamellated periosteal bone formation (arrowheads). c. CT localizes cortical destruction to the posterolateral sideof the tibia (arrowhead) and shows diffuse soft-tissue thickening (t). Fig. 2. CASE II. Medullary osteosarcoma. a. A sclerotic, lytic process involvesthe distalfemoralmetadiaphysis. Minimal tumorbone extends along the medial cortex (arrowheads). b. CT showsan enlarged soft-tissue andmusclemass (m) adjacent to the sclerotic tumor (t) whichpartially obliterates the medial medullary cavity. Tumor bone and periosteal reaction are prominent along the medial cortex (arrowhead).
demonstrated medullary involvement as well as confirmed lobulated parosteal proliferation. These findings were diagnostic of a malignant lesion. CASE V: A 14-year-old boy presented one monthafter detectinga small painful massovertheanterior aspectof hisdistalleft tibia.Routine radiographs demonstrated a localized soft-tissue massalong theanterior distal tibia, with underlying bony changes (Fig. 5a). CTshoweda softtissue mass along the anteromedial and anterolateral aspects of the tibia (Fig. 5b). Sclerotictumorbonewas limited to the periosteal surface of the tibia, while the endosteal surface and medullary cavity were normal (Fig. 5c). Periosteal osteosarcomawas diagnosed on biopsy, and a below-the-knee amputation was performed subsequently (Fig. 5d). Adjuvant chemotherapy was instituted. COMMENT:
As in the previous cases, routine radio-
graphs provided the main features to make the most likely preoperative diagnosis. CT showed the nature of the endosteal surface and provided more information about the soft-tissue component. However, due to the lack of fat between leg muscles, CT failed to demonstrate the exact posterior extent of the abnormal soft tissues. As an adequate local resection of a periosteal osteosarcoma may be curative (8), a local resection could have been strongly considered on the basis of the radiographic appearance alone. The CT demonstration of the abnormal anterior two-thirds of the tibial cortex and the inexact posterior extent of soft tissues showed that obtaining an adequate surgical margin around the lesion would be extremely difficult, if not impossible. CT swayed surgical planning toward amputation. Subsequent examination of the amputated specimen showed that the tumor involved the anterior and lateral tibial surfaces and bowed the anterior tibial artery and nerve. Thus an adequate surgical margin could not have been obtained without resecting most of
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4b
Fig. 4. CASE IV. Parostealosteosarcoma. 8 and b. A lobulated sclerotic lesion involves the posterolateral aspect of the distal right femur. The outer edge of the lesion is well defined, but its inner surface is poorly delineated. c. CT shows involvement of the medullary cavity. The soft tissues are relatively symmetric, allowing for expansion of the femoral shaft. d. An enlarged view of the distal right femur with CT windows optimized for bone shows extensive tumor (t) involvement of the medullary cavity to better advantage.
the tibia and sacrificing the artery and nerve. On pathologic examination, the soft tissues posteromedial to the tibia were normal, and we have no explanation for the slight asymmetry of these tissues (Fig. 5b). CASE VI: A 24-year-old man presented with a two-month history of a slightly tender lump involving the anterior aspect of his left midtibia. Routine radiographs demonstrated a fairly well defined lytic lesion of the medial midtibal cortex (Fig. 6, 8 and b). A tangential view showed a slight cortical permeation and a periosteal reaction (Fig. 6c). On CT, a lytic lesion was located completely within the anteromedial tibial cortex (Fig. 6d) without evident medullary extension. Soft-tissue swelling anterior to the tumor was very limited and indicated excisional biopsy. After biopsy, histopathology revealed intracortical osteosarcoma arising from and limited to the tibial cortex (Fig. 6e). An above-the-knee amputation followed ten days later with no evidence of remaining tumor in the amputated specimen. Chemotherapy was instituted.
COMMENT: The preoperative diagnosis with the help of both standard radiographs and CT was still difficult. Major considerations included adamantinoma or a slowgrowing tumor, such as an unusual fibro-osseous lesion. Correlation between the radiographs and CT encouraged the surgeon to perform an excisional rather than an incisional biopsy. The entire lesion was removed, and intracortical osteosarcoma diagnosed. We could find only 2 previously reported cases of intracortical osteosarcoma (9); those involved the distal
femur and the midtibia and were similar in appearance. Histopathologically, intracortical osteosarcoma is indistinguishable from medullary osteosarcoma but is confined to the cortex where it presumably originated. On gross pathology, its periosteum can be stripped from the underlying tumor, whereas the periosteum in a periosteal osteosarcoma is intimately involved with the tumor. Radiographically, intracortical osteosarcoma presents as a slow-growing lesion and may have areas of surrounding sclerosis. Close radiographic and pathologic correlation is necessary to make the diagnosis. DISCUSSION
Medullary, parosteal, and periosteal forms of osteosarcoma have been well described in the literature (8, 10-18). Intracortical osteosarcoma (9) is not widely recognized as another form of osteosarcoma; however, increased awareness of it will undoubtedly lead to identification of more cases. Because of cross-sectional display, CT offers a unique image of osteosarcoma and other bone tumors. The location of bone involvement, whether cortical, medullary, or both, can be readily discerned. Due to superimposition of the diameter of bone from cortex to cortex, routine radiography does not always allow differentiation of cortical and medullary involvement. CT shows the exact site and
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Fig. 5. CASE V. Periosteal osteosarcoma. a. A localized, soft-tissue mass (arrows) lies along the anterior distal left tibia with a concave defect of the adjacent cortex. Spiculated tumor bone is oriented perpendicular to the tibial shaft (arrowhead). b. CT demonstrates a soft-tissue mass along the anteromedial and anterolateral aspects of the left tibia (arrows). A questionable cleavage plane between the tumor and normal soft tissues can be discerned (arrowheads). The soft tissues posteromedial to the tibia are slightly fuller than the normal side (see CASE V COMMENT). c. With window settings optimized for bone, CT shows that the endosteal surface and medullary cavity are normal. Periosteal bone lies on the anterolateral tibial surface (arrowheads). d. A specimen radiograph of a coronal section shows a well defined soft-tissue mass encompassing the tibia. Adherent periosteum forms the outer margin of this mass (arrows).
extent of macroscopic bone destruction. Recognition of involvement of the medullary-cavity obviously helps to identify a medullary (central) osteosarcoma, but may also indicate whether or not the other three types of osteosarcoma have advanced to involve the cancellous bone. This was particularly evident in CASE IV, where CT demonstrated an abnormal medullary cavity as well as focal cortical thickening. Due to its improved display of soft tissue, CT can more accurately determine the type and extent of soft-tissue involvement than can other radiographic modalities. Such evaluation is aided by distinct fat planes and by comparison with the opposite extremity. When fat cannot be seen between muscles, soft-tissue extent may not be easily assessed. Soft tissues may be distorted by pushing from an underlying bone mass, tumor invasion, or infiltration from hemorrhage or edema. In our experience, CT has not yet been able to differentiate tumor infiltration from edema or hematoma and should therefore be performed before
a biopsy, as the postoperative hematoma or swelling may significantly interfere with evaluation of the true preoperative soft-tissue involvement. CT cross-sectional display and its improved soft-tissue imaging have provided useful information in surgical planning among these osteosarcomas. In some cases, the choice of biopsy site was influenced by the location of tumor bulk and focal cortical destruction shown by CT. Knowledge of tumor extent is important to determine resectability in periosteal and parosteal osteosarcomas and the level of amputation in central osteosarcoma. In CASE IV, CT showed that excision would have to include a large portion of the metaphyseal cancellous bone. In CASE V, it showed that excisional biopsy probably could not be performed without amputation; subsequent specimen radiography was confirmatory. In CASE VI, CT clearly indicated that definitive excision could be accomplished. Detection of skip metastases proximal to the lesion in
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Fig. 6. CASE VI. Intracorticalosteosarcoma. a. A slightly expansile lytic defect involves the medial cortex of the midtibia. b. On a lateral radiograph, the midtibial lesion has well defined borders. c. A tangential view of the lesion with magnification technique demonstrates irregular bone formation along the periosteal margin (arrows). d. CT through the lesion confirms intracortical location (arrowheads). (m = medullary portion of tibia) e. After excisional biopsy, a longitudinal section through the irregular marginated lytic lesion shows that its periosteum is thickened (arrows) and endosteum (arrowheads) is attenuated.
long bones or in adjacent soft tissues is possible with CT (3, 19). Radionuclide bone scanning may eventually prove to be a more sensitive detector for small osseous metastases some distance from the primary lesion. No skip metastases were present in our cases. We believe CT is complementary to conventional radiography and to pathological examination (CASE VI). CT may also gradually prove to provide prognostic information. For example, the demonstration of medullary involvement in parosteal osteosarcoma would indicate an advanced stage of that tumor. Similarly, invasion of soft tissue by
central osteosarcoma is a later stage of that neoplasm. When studied in a prospective fashion and related to therapeutic decisions, CT may help show the way to improve therapeutic choices. CT also had shortcomings in evaluation of these tumors. Soft-tissue tumor margins are difficult to determine, as in CASE V, when there is not sufficient fat between muscles and along fascial planes, and when tumor tissue has the same density as normal tissue. de Santos et et. (3) point out that most of their tumors increased in density only minimally after contrast enhancement. We did not use
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contrast; however, using contrast to identify major vessels next to the tumor may routinely be of more value when planning surgery than using it only to show tumor enhancement. The averaging of 13 mm for each CT section creates an artificial display which is usually representative of what is present, but at times may be inaccurate at the level of interest. A curved surface may be displayed as an unsharp edge as a result of averaging, and unless such a surface is placed at right angles to the scanning gantry, subtle cortical reactions may not be shown. Scanners which will display information over narrower sections, such as 2 mm, may largely eliminate this inaccuracy. CT may shorten the work-up of osteosarcomas as well as other bone tumors by eliminating additional nonstandard radiographs or laminographs. We did not use laminography in our study because we found that it does not offer the necessary detail for determining medullary involvement; it also fails to provide information concerning the adjacent soft tissues. Furthermore, we have not routinely used arteriography to outline the soft-tissue limits of tumors. The combination of standard radiographs and CT: (a) takes less time; (b) is performed at similar or less cost than a battery of additional radiographs, laminograms, and arteriograms; and (c) exposes the patient to less radiation than that comb ination.
Louis A. Gilula, M.D. Mallinckrodt Institute of Radiology 510 South Kingshighway Boulevard St. Louis, Mo. 63110
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Weinberger G, Levinsohn EM: Computed tomography in the
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evaluation of sarcomatous tumors of the thigh. Am J Roentgenol 130:115-118, Jan 1978 2. Weis L, Heelan RT, Watson RC: Computed tomography of orthopedic tumors of the pelvis and lower extremities. Clin Orthop 130:254-259, Jan-Feb 1978 3. deSantos LA, Goldstein HM, Murray JA, et al: Computed tomography in the evaluation of musculoskeletal neoplasms. Radiology 128:89-94, Jul 1978 4. Wilson JS, Korobkin M, Genant HK, et al: Computed tomography of musculoskeletal disorders. Am J RoentgenoI131:55-61, Jul 1978 5. McLeod RA, Stephens DH, Beabout JW, et al: Computed tomography of the skeletal system. Semin RoentgenoI13:235-247, Jul 1978 6. Schumacher TM, Genant HK, Korobkin M, et al: Computed tomography. Its use in space-occupying lesions of the musculoskeletal system. J Bone Joint Surg 60:600-607, Jul 1978 7. de Santos LA, Murray JA: Evaluation of giant cell tumor by computerized tomography. Skeletal RadioI2:205-212, 1978 8. Unni KK, Dahlin CD, Beabout JW, et al: Periosteal osteogenic sarcoma. Cancer 37:2476-2485, May 1976 9. Jaffe HL: Intracortical osteogenic sarcoma. Bull Hosp Joint Dis 21:189-197, Oct 1960 10. Dahlin DC, Coventry MB: Osteogenic sarcoma. J Bone Joint Surg 49:101-110, Jan 1967 11. Dahlin DC, Unni KK: Osteosarcoma of bone and its important recognizable varieties. Am J Surg PathoI1:61-72, Mar 1977 12. deSantos LA, Murray JA, Finklestein JB, et al: The radiographic spectrum of periosteal osteosarcoma. Radiology 127:123-129, Apr 1978 13. Edeiken J, Farrell C, Ackerman LV, et al: Parosteal sarcoma. Am J RoentgenoI111:579-583, Mar 1971 14. EdeikenJ, HodesPJ: Roentgen Diagnosisof Diseases of Bone. Baltimore, Williams & Wilkins, 1976, Vol. 2, pp 939-977 15. Spjut HJ, Dorfman HD, Fechner RE, et al: Tumors of bone and cartilage. Atlas of Tumor Pathology, 2nd Ser., Fasc. 5., Washington, D.C., AFIP, 1971, pp 141-174. 16. Unni KK, Dahlin DC, Beabout JW, et al: Parostealosteogenic sarcoma. Cancer 37:2467-2475, May 1976 17. Van der Heul R, Von Ronnen A: Juxtacorticalosteosarcoma. J Bone Joint Surg 49:415-439, Apr 1967 18. Wolfel DA, Carter PR: Parosteal osteosarcoma. Am J RoentgenoI105:142-146, Jan 1969 19. Kumar AP, Wrenn EL Jr, Fleming ID, et al: Transmedullary amputation and resection of metastases in combined therapy of osteosarcoma. J Pediatr Surg 12:427-435, Jun 1977
