Inr. J. Radrorion Oncology Bid. Phw.. Vol. Pnnted in the U.S.A. All rights reserved.
21.
pp.1643-1651 Copyright
0360.3016191 $3.00 + .C0 6 1991 Per@non Press plc
??Technical Innovations and Notes
MUSCULOSKELETAL ONCOLOGIC IMAGING B. J. MANASTER, Department
of Radiology,
University
M.D.,
PH.D.
of Utah, Medical Center, Salt Lake City, UT 84132
A cost efficient algorithm is presented for workup of musculoskeletal tumors. This is given within the framework of requirements for surgical staging. Considerations regarding both percutaneous and open biopsy are outlined. The advantages as well as limitations of MR imaging are stressed. Musculoskeletal tumors, Tumor staging, Biopsy, MRI. certain diagnosis which may be followed clinically, (3) benign symptomatic lesion with highly probably diagnosis that may be treated without further work-up, (4) a radiographically confusing lesion that cannot clearly be categorized as benign or malignant, and (5) an obviously malignant lesion. Lesions falling into categories 4 and 5 need further work-up for staging, according to Fig. 1. The staging system most widely used for osseous lesions was developed by the Musculoskeletal Tumor Society (4) and is notable for being practical both for prognostic and therapeutic applications. Staging is based on the surgical grade (histology) of the lesion, on its anatomic confines (“site,” with a determination of whether the lesion is encapsulated, intracompartmental, or extracompartmental), and on the presence of metastatic disease. Radiographic imaging procedures address the latter two concerns. The algorithm directs that once it is determined that an osseous lesion is aggressive, the next imaging procedure be a bone (99mTcMDP) scan. This examination is not used to evaluate the extent or character of the lesion, but simply to determine if the lesion is monostotic. Early identification of an aggressive lesion as polyostotic limits the differential diagnosis (including metastatic disease, multiple myeloma, primary bone sarcoma with osseous metastases, histiocytosis, and Paget’s disease); in such cases the remaining work-up would be modified, often eliminating CT, MRI and biopsy. Following bone scan determination that the aggressive osseous lesion is monostotic, chest films and CT should be obtained since the lung is the primary site of metastatic dissemination of primary bone sarcomas. If these show metastatic deposits, the work-up may be modified and therapy directed toward palliation rather than cure, again often eliminating the need for CT or MRI. In some cases (particularly osteosarcoma), a limited number of lung nodules may be resected in a curative attempt, and complete staging of the primary lesion will still be required.
Accurate imaging of musculoskeletal tumors has assumed an even greater importance in recent years since the advent of improved survival rates in patients treated with combinations of limb-sparing surgery, pre- and postoperative chemotherapy, and radiation therapy. An impressive array of imaging modalities is available, including plain radiographs, conventional tomography, radionuclide imaging, computed tomography (CT), ultrasound (US), angiography, and magnetic resonance imaging (MRI). Only a limited number of these examinations is required to obtain all the necessary information in each case. It is important to maximize information while minimizing the number of imaging procedures in a responsible fashion in order to help contain health care costs. The work-up should be tailored to each individual patient case, designed to answer specific questions. The goals in each case should be similar: (a) the arrival at a reasonable differential diagnosis or at least categorization of the lesion as to its degree of aggressiveness, (b) guidance of lesion staging, biopsy, and resection, and (c) knowledgeable post-treatment follow-up. This paper is designed to outline these concerns in greater detail and offer an algorithmic approach that optimizes the choice and order of procedures. This approach should avoid overly extensive staging, avoid overly aggressive surgery on lowgrade lesions, and, most importantly, avoid irreversible under-treatment of aggressive lesions. Intraosseous lesions must first be evaluated by plain film, since their superb resolution allows the best assessment of biologic activity and probable histologic diagnosis. While establishing a short differential diagnosis of such a lesion is helpful, an accurate assessment of degree of agressiveness is imperative for responsible guidance of an osseous tumor work-up. Proper evaluation of the plain roentgenogram should allow one to categorize an osseous lesion as (1) benign with certain diagnosis and no further work-up necessary, (2) benign asymptomatic lesion of unReprint requests to: B.J. Manaster,
M.D.,
Ph.D.
Accepted for publication 1643
30 May 1991.
1644
I.J. Radiation Oncology 0 Biology0 Physics
November 1991,Volume 21, Number 6
Aggressive osseous lesion (categories 4 and 5 above) by plain film
I, Bone
Monostotic
scan
Polyostotic
les .on
lesion
I Plain film of other sites of abnormality for diagnosis
Chest plain film and CT
metastases
metastases
MR (or rarely CT, but not both) for staging, planning of biopsy, and therapeutic planning
needed
for
I Biopsy
Fig. 1. Algorithm for work-up of aggressive osseous lesions.
The “site” component of the staging process is best evaluated by CT or MRI. Osseous and soft tissue extent must be evaluated, as well as involvement of adjacent joints or neurovascular structures. The latter parameters will determine feasibility of limb salvage surgical attempts. Note that the determination of “site” comes relatively late in the algorithm for work-up of an aggressive osseous lesion, after it has been determined to be malignant but not metastatic. MRI examination of a soft tissue lesion is recommended much earlier in the algorithm (Fig. 2). Plain
films and radionuclide imaging are rarely helpful in these lesions. Soft tissue lesions are often benign, despite appearing aggressive on MRI; we therefore are not as accurate in predicting malignancy in soft tissue lesions than osseous lesions. It is cost-efficient and logical to perform the chest CT to search for metastatic disease only after biopsy confirms malignancy in a soft tissue lesion. Studies to date agree that MRI is equal or superior to CT in evaluation of local intraosseous extent, local soft tissue extent, involvement of neurovascular bundles, in-
L3 stop
MR for staging, planning of biopsy, and therapeutic planning
I
7
Biopsy
if malignant,
chest
CT
Fig. 2. Algorithm for work-up of a soft tissue lesion.
Musculoskeletal oncologic imaging ??B. J. MANASTER
1645
(4 Fig. 3. ABOVE AND FOLLOWING PAGE Illustration of the use of CT and MR in the work-up of an osseous lesion. (a) demonstrates a cortically or periosteally based lesion located in the tibia1 diaphysis of a 14-year-old male (arrow). The lesion appears aggressive, with spiculated periosteal reaction and both cortical scalloping and thickening. No definite intramedullary involvement and thickening is seen. The differential diagnosis includes juxtacortical chondroma, periosteal osteosarcoma, and infection. Bone scan demonstrated that the lesion was monostotic, and CT showed no evidence of metastatic disease. Since differentiating the spiculated periosteal reaction from tumor matrix is crucial to the diagnosis and this finding is best demonstrated by CT, a CT was performed. The bone algorithm of the CT (b) shows that all the osseous change appears to be reactive, rather than representing a matrix and suggests that the epicenter of the lesion may actually be soft tissue rather than osseous. The soft tissue CT windows (c) show only an abnormal fullness in the deep posterior compartment (arrows) and does nothing further to define the soft tissue mass. Thus, MR is required (d). Note that the patient is in a prone position in this exam. This T2 weighted axial image defines the mass as arising in the flexor digitorum muscle with infiltrative characteristics. The bone is involved only in a reactive pattern, and the lesion abuts but does not encase the neurovascular bundle. Less clearly defined high signal intensity is seen in the soleus muscle; at least some of this represents reactive edema, but the exact extent of tumor versus edema cannot be defined. At this point, diagnosis is felt to be either infection or a malignant soft tissue tumor eliciting significant reaction in both soft tissue and bone. In either event, biopsy and therapy can be adequately planned (with the use of the remaining MR images to fully define extent of lesion). At biopsy, the lesion proved to be a very rare soft tissue Ewing’s sarcoma.
volvement of cortical bone, and involvement of adjacent joints (l-3, 10, 11, 15). CT is clearly superior only in evaluation of matrix calcification or of a thin cortical rim. It should only rarely be the case that both CT and MRI are required (and use of both usually represents significant over-imaging). It is the consensus that MRI is the staging modality of choice, and that CT should be reserved to answer specific questions regarding matrix or rim calcification (Fig. 3). The preference for MRI over CT is reinforced
by the capability for multiplanar imaging, as well as the superb soft tissue contrast produced by MRI, which allows staging with greater confidence. Although MRI generally is extremely accurate in evaluating extraosseous extent of a lesion, two conditions may lead to an overestimation of soft-tissue tumor extent. Hematoma, often arising from biopsy of a lesion, may at some phase of its evolution be isointense to tumor and therefore indistinguishable. Similarly, reactive edema, which sur-
646
I. J. Radiation Oncology
0 Biology 0 Physics
November
1991, Volume 21, Number 6
Musculoskeletal
oncologic
imaging 0 B. J. MANASTER
1647
Fig. 4. This T2 weighted MR of a malignant sarcoma demonstrates the difficulty of differentiating tumors from edema. The patient is lying prone, and the high signal intensity tumor is in the deep posterior compartment adjacent to the interosseous membrane. The tumor is surrounded by intermediate signal edema in all compartments. Tumor surrounds the neurovascular structures. The exact demarcation between the tumor and edema is not clear. Wide resection would require a cuff of normal tissue surrounding the reactive tissue; in this case, amputation would be required to achieve wide resection. A riskier marginal resection (presuming all edema and no nests of tumor cells in the anterior compartment) could allow salvage of the limb.
rounds some tumors, may demonstrate high signal intensity equal to that of tumor. This may occur in up to 50% of malignant tumors and a smaller percent of benign lesions; in the case of malignant tumors, this area of “edema” occasionally contains small nests of tumor cells. The difficulty of distinguishing edema from tumor is frustrating, but in most cases is a moot point since the recommended wide tumor resection requires resection of tumor, reactive tissue, and a cuff of normal tissue. Clearly, however, there are cases in which a very wide margin of reactive tissue (several centimeters) can exist which may convert a limb salvage procedure to an amputation if the “wide resection margin” is observed; in such a case, differentiation of tumor from edema might be required for informed patient consent and surgical planning (Fig. 4). In most cases, MRI does not aid in the histological diagnosis of a musculoskeletal lesion since the signal intensity characteristics of most lesions show significant overlap (8. 9). Furthermore, signal intensity alone is insufficient even to distinguish most malignant from benign lesions. Morphologic characteristics are more useful. Generally, malignant soft tissue lesions are large, inhomogeneous (especially well seen on T2 weighted sequences), and may appear infiltrative (Fig. 4). However, many benign soft tissue lesions (especially infection and hematoma) are inho-
mogeneous as well (Fig. 5), while a few malignant lesions (especially synovial cell sarcoma) may be homogeneous (1, 15). Furthermore, some benign lesions (especially desmoids) are locally aggressive and infiltrative (Fig. 6), while many malignant lesions acquire a pseudocapsule of reactive tissue which gives the false appearance both on MRI and at surgery of containing the tumor. Thus far, neither the use of gadolinium, MRI spectroscopy, nor dynamic MR scanning shows significant promise of improving histologic diagnostic capabilities or of distinguishing malignant from benign tumors with an acceptably high degree of accuracy. In cases that are difficult to evaluate, clinical information may be the most important determinant; time spent questioning the patient can be extremely rewarding. MRI of lesions is thus more useful in determining site and extent of involvement than diagnosis; diagnosis based on MRI is often correct, but virtually always requires biopsy for confirmation. MRI aids in planning the biopsy, when tissue must be obtained which represents the most active part of the tumor. The planned biopsy site must not compromise plans for limb-sparing definitive surgery (which requires excision of the biopsy track, so only a single compartment should be crossed, without violation of the neurovascular bundle or joint and without crossing skin or muscle which will be required for reconstruction). In
I. J. Radiation Oncology 0 Biology 0 Physics
November
199 1, Volume 2 1, Number 6
(a)
(b)
Fig. 5. The non-specificity of the MR appearance of soft tissue masses is illustrated by these cases. In each, a high signal intensity lesion is seen which is infiltrative, crosses compartmental boundaries, and is both large and inhomogeneous. These characteristics are usually descriptive of malignant tumors. However, in these cases the diagnoses were (a) hematoma from a partial thigh muscle rupture (seen on a gadolinium-enhanced Tl weighted axial cut), and (b) staphylococcus infection (T2 weighted axial cut).
many cases, percutaneous needle biopsy, often performed under ultrasound guidance, is a cost-effective alternative to open biopsy. The crucial nature of biopsy accuracy and choice of biopsy site was highlighted by a multi-institutional study which demonstrated that 18% of tumor cases had major errors in diagnosis and 18% of patients required alteration of the optimum therapy plan because of the
choice
of biopsy
complications occurred 3 to 5 when the biopsies were performed at rather than at a major tumor treatled to a recommendation that biopsy the treating institution, and planned the surgeon offering the definitive
site. These
times more frequently a referring institution ment center (7). This only be performed in in conjunction with treatment.
Musculoskeletal oncologic imaging 0 B. J. MANASTER
(b) Fig. 6. ABOVE AND FOLLOWING PAGE While the MR appearance of most benign soft tissue tumors is of a homogeneous encapsulated mass, benign desmoid tumors are a notable exception. The T2 weighted images of this desmoid tumor demonstrate it to be a very large mass arising in the adductor muscle (arrow), but crossing compartments to also involve the obturator muscles (a). This mass extends through the obturator foramen to surround the ischial tuberosity (arrow) both anteriorly and posteriorly (b). It pushes the neurovascular bundle anteriorly but does not surround it. It is of high signal intensity and inhomogeneous, and therefore indistinguishable from a malignant lesion. It was treated with surgery and radiation. Follow-up examination two years later demonstrates persistent high signal intensity in the tumor bed (arrow) but no mass (c); this is felt to represent granulation and radiation necrosis, as it showed no interval change over several follow-up MR exams. Interestingly, at the two year exam a higher section (d) shows high signal in the iliacus muscle (arrow), a region previously demonstrated to be normal. This is a recurrent tumor, and represents a common feature of the benign but locally aggressive lesion.
1650
1. J. Radiation
Oncology
0 Biology 0 Physics
November
1991. Volume 21, Number 6
Cd)
If a patient is given preoperative therapy, a repeat MR is obtained prior of therapy may be judged by the MRI is not yet a reliable method of tumor necrosis, which is a major
chemo- or radiation to surgery. Efficacy tumor volume, but assessing percent of factor in prognosis
(9, 12). Post-therapeutic imaging protocols should be designed for early detection of recurrent and metastatic disease. Pro-
tocols for type, frequency, and duration of follow-up should be based on patterns of tumor spread and time course of recurrence or metastases. Unfortunately, such “hazard” rates and patterns have not been established for many lesions. Generally, a patient with a malignant lesion should be followed by chest films and CT for pulmonary metastases. Intraosseous lesions are followed by a combination of plain film and MRI (depending on amount of
Musculoskeletal oncologic imaging 0 B. J.
hardware present, which can cause significant artifact on MRI), while soft tissue tumors are best followed by MRI. Post-surgical (or post-therapy) scanning is recommended at about 3 months to establish a baseline appearance. A favorable response to any therapeutic modality should result in reduction in the size of the soft tissue component and decrease in the signal intensity on MR T2 weighting. However, such high signal intensity may persist after therapy (Fig. 6); there may be an overlap in the signal intensities of recurrent tumor and benign post-therapeutic change (edema, granulation, necrosis, postoperative or radiation fibrosis) (5, 13). Dynamic MRI with contrast or MR spec-
MANASTER
1651
troscopy may be helpful with this differentiation in the future, but is not reliable at this point. Furthermore, the intraosseous component appears to respond differently from the soft tissue component, with reduction in size and signal intensity of lesions not occurring despite histologic response (6). Consequently, MRI criteria for post-therapeutic evaluation of intraosseous and extraosseous lesions are different and not altogether reliable. Biopsy or close follow-up (to watch morphologic characteristics rather than signal intensity) may be recommended frequently until further criteria or imaging methodologies for tumor recurrence are developed.
REFERENCES 1. Aisen, A. M.; Mattel, W.; Braunstein, E. M.; McMillin, K.; Phillips, W.; Kling, T. MRI and CT evaluation of primary bone and soft-tissue tumors. AJR 146:749-756; 1986. 2. Bloem, J. L.; Taminiau, A. H. M.; Eulderink, F.; Hermans, J.; Pauwels, E. K. J. Radiologic staging of primary bone sarcoma: MR imaging, scintigraphy, angiography, and CT correlated with pathologic examination. Radiology 169:805810; 1988. 3. Boyko, 0. B.; Gory, D. A.; Cohen, M. D.; Provisor, A.; Mirkin, D.; DeRosa, G. MR imaging of osteogenic and Ewing’s sarcoma. A. J. R. 148:317-322; 1987. 4. Enneking, W. F. (Project Chairman). Staging of musculoskeletal neoplasms. Skeletal Radiology 13: 183-194; 1985. 5. Golden, P.; Raymond, A. K.; Carrasco, C. H.; Wallace, S.; Kim, E. E.; Shirkhoda, A.; Jaffe, N.; Murray, J. A.; Benjamin, R. S. Osteosarcoma: MR imaging after preoperative chemotherapy. Radiology 174517-526; 1990. 6. Holscher, H. C.; Bloem, J. L.; Nooy, M. A.; Taminiau, A.; Eulderink, F.; Hermans, J. The value of MR imaging in monitoring the effect of chemotherapy on bone sarcomas. A. J. R. 154:763-769; 1990. 7. Mankin, H. J.; Lange, T. A.; Spanier, S. S. The hazards of biopsy in patients with malignant primary bone and soft-tissue tumors. J. Bone Joint Surg. 64-A(8):1121-1127; 1982. 8. Nurenberg, P.; Harms, S. E. Magnetic resonance imaging of musculoskeletal tumors. Critical Reviews in Diagnostic Imaging 28(4):331-366; 1988.
9. Pan, G.; Raymond, A.; Carrasco, C.; Wallace, S.; Kim, E.; Shirkhoda, A.; Jaffe, N.; Murray, J.; Benjamin, R. ,Osteosarcoma: MR imaging after preoperative chemotherapy. Radiology 174:517-526; 1990. 10. Pettersson, H.; Gillespy, T.; Hamlin, D. J.; Enneking, W.; Springfield, D.; Andrew, E.; Spanrer, S.; Slone, R. Primary musculoskeletal tumors: examination with MR imaging compared with conventional modalities. Radiology 164:237-241; 1987. 11. Pettersson, H.; Hamlin, D. J.; Scott, K. N. Magnetic resonance imaging of musculoskeletal tumors. CRC Critical Reviews in Diagnostic Imaging 26(3):241-263; 1986. 12. Sanchez, R.; Quinn, S.; Walling, A.; Estrada, J.; Greenberg, H. Musculoskeletal neoplasm after intraarterial chemotherapy: correlation of MR images with pathologic specimens. Radiology 174:237-240; 1990. 13. Sanchez, R. B.; Quinn, S. F.; Walling, A.; Estrada, J.; Greenberg, H. Musculoskeletal neoplasms after intraarterial chemotherapy: Correlation of MR images with pathologic specimens. Radiology 174:237-240; 1990. 14. Sumdaram, M.; McGuire, M. H.; Schajowicz, F. Soft-tissue masses: histologic basis for decreased signal (short T2) on T2-weighted MR images. A. J. R. 146:1247-1250; 1987. 15. Zimmer, W. D.; Berquist, T. H.; McLeod, R. A.; Sim, F. H.; Pritchard, D. J.; Shives, T. C.. Weld, L. E., May, G. R. Bone tumors: magnetic resonance imaging versus computed tomography. Radiology 155:709-718; 1985.
21.
pp.1643-1651 Copyright
0360.3016191 $3.00 + .C0 6 1991 Per@non Press plc
??Technical Innovations and Notes
MUSCULOSKELETAL ONCOLOGIC IMAGING B. J. MANASTER, Department
of Radiology,
University
M.D.,
PH.D.
of Utah, Medical Center, Salt Lake City, UT 84132
A cost efficient algorithm is presented for workup of musculoskeletal tumors. This is given within the framework of requirements for surgical staging. Considerations regarding both percutaneous and open biopsy are outlined. The advantages as well as limitations of MR imaging are stressed. Musculoskeletal tumors, Tumor staging, Biopsy, MRI. certain diagnosis which may be followed clinically, (3) benign symptomatic lesion with highly probably diagnosis that may be treated without further work-up, (4) a radiographically confusing lesion that cannot clearly be categorized as benign or malignant, and (5) an obviously malignant lesion. Lesions falling into categories 4 and 5 need further work-up for staging, according to Fig. 1. The staging system most widely used for osseous lesions was developed by the Musculoskeletal Tumor Society (4) and is notable for being practical both for prognostic and therapeutic applications. Staging is based on the surgical grade (histology) of the lesion, on its anatomic confines (“site,” with a determination of whether the lesion is encapsulated, intracompartmental, or extracompartmental), and on the presence of metastatic disease. Radiographic imaging procedures address the latter two concerns. The algorithm directs that once it is determined that an osseous lesion is aggressive, the next imaging procedure be a bone (99mTcMDP) scan. This examination is not used to evaluate the extent or character of the lesion, but simply to determine if the lesion is monostotic. Early identification of an aggressive lesion as polyostotic limits the differential diagnosis (including metastatic disease, multiple myeloma, primary bone sarcoma with osseous metastases, histiocytosis, and Paget’s disease); in such cases the remaining work-up would be modified, often eliminating CT, MRI and biopsy. Following bone scan determination that the aggressive osseous lesion is monostotic, chest films and CT should be obtained since the lung is the primary site of metastatic dissemination of primary bone sarcomas. If these show metastatic deposits, the work-up may be modified and therapy directed toward palliation rather than cure, again often eliminating the need for CT or MRI. In some cases (particularly osteosarcoma), a limited number of lung nodules may be resected in a curative attempt, and complete staging of the primary lesion will still be required.
Accurate imaging of musculoskeletal tumors has assumed an even greater importance in recent years since the advent of improved survival rates in patients treated with combinations of limb-sparing surgery, pre- and postoperative chemotherapy, and radiation therapy. An impressive array of imaging modalities is available, including plain radiographs, conventional tomography, radionuclide imaging, computed tomography (CT), ultrasound (US), angiography, and magnetic resonance imaging (MRI). Only a limited number of these examinations is required to obtain all the necessary information in each case. It is important to maximize information while minimizing the number of imaging procedures in a responsible fashion in order to help contain health care costs. The work-up should be tailored to each individual patient case, designed to answer specific questions. The goals in each case should be similar: (a) the arrival at a reasonable differential diagnosis or at least categorization of the lesion as to its degree of aggressiveness, (b) guidance of lesion staging, biopsy, and resection, and (c) knowledgeable post-treatment follow-up. This paper is designed to outline these concerns in greater detail and offer an algorithmic approach that optimizes the choice and order of procedures. This approach should avoid overly extensive staging, avoid overly aggressive surgery on lowgrade lesions, and, most importantly, avoid irreversible under-treatment of aggressive lesions. Intraosseous lesions must first be evaluated by plain film, since their superb resolution allows the best assessment of biologic activity and probable histologic diagnosis. While establishing a short differential diagnosis of such a lesion is helpful, an accurate assessment of degree of agressiveness is imperative for responsible guidance of an osseous tumor work-up. Proper evaluation of the plain roentgenogram should allow one to categorize an osseous lesion as (1) benign with certain diagnosis and no further work-up necessary, (2) benign asymptomatic lesion of unReprint requests to: B.J. Manaster,
M.D.,
Ph.D.
Accepted for publication 1643
30 May 1991.
1644
I.J. Radiation Oncology 0 Biology0 Physics
November 1991,Volume 21, Number 6
Aggressive osseous lesion (categories 4 and 5 above) by plain film
I, Bone
Monostotic
scan
Polyostotic
les .on
lesion
I Plain film of other sites of abnormality for diagnosis
Chest plain film and CT
metastases
metastases
MR (or rarely CT, but not both) for staging, planning of biopsy, and therapeutic planning
needed
for
I Biopsy
Fig. 1. Algorithm for work-up of aggressive osseous lesions.
The “site” component of the staging process is best evaluated by CT or MRI. Osseous and soft tissue extent must be evaluated, as well as involvement of adjacent joints or neurovascular structures. The latter parameters will determine feasibility of limb salvage surgical attempts. Note that the determination of “site” comes relatively late in the algorithm for work-up of an aggressive osseous lesion, after it has been determined to be malignant but not metastatic. MRI examination of a soft tissue lesion is recommended much earlier in the algorithm (Fig. 2). Plain
films and radionuclide imaging are rarely helpful in these lesions. Soft tissue lesions are often benign, despite appearing aggressive on MRI; we therefore are not as accurate in predicting malignancy in soft tissue lesions than osseous lesions. It is cost-efficient and logical to perform the chest CT to search for metastatic disease only after biopsy confirms malignancy in a soft tissue lesion. Studies to date agree that MRI is equal or superior to CT in evaluation of local intraosseous extent, local soft tissue extent, involvement of neurovascular bundles, in-
L3 stop
MR for staging, planning of biopsy, and therapeutic planning
I
7
Biopsy
if malignant,
chest
CT
Fig. 2. Algorithm for work-up of a soft tissue lesion.
Musculoskeletal oncologic imaging ??B. J. MANASTER
1645
(4 Fig. 3. ABOVE AND FOLLOWING PAGE Illustration of the use of CT and MR in the work-up of an osseous lesion. (a) demonstrates a cortically or periosteally based lesion located in the tibia1 diaphysis of a 14-year-old male (arrow). The lesion appears aggressive, with spiculated periosteal reaction and both cortical scalloping and thickening. No definite intramedullary involvement and thickening is seen. The differential diagnosis includes juxtacortical chondroma, periosteal osteosarcoma, and infection. Bone scan demonstrated that the lesion was monostotic, and CT showed no evidence of metastatic disease. Since differentiating the spiculated periosteal reaction from tumor matrix is crucial to the diagnosis and this finding is best demonstrated by CT, a CT was performed. The bone algorithm of the CT (b) shows that all the osseous change appears to be reactive, rather than representing a matrix and suggests that the epicenter of the lesion may actually be soft tissue rather than osseous. The soft tissue CT windows (c) show only an abnormal fullness in the deep posterior compartment (arrows) and does nothing further to define the soft tissue mass. Thus, MR is required (d). Note that the patient is in a prone position in this exam. This T2 weighted axial image defines the mass as arising in the flexor digitorum muscle with infiltrative characteristics. The bone is involved only in a reactive pattern, and the lesion abuts but does not encase the neurovascular bundle. Less clearly defined high signal intensity is seen in the soleus muscle; at least some of this represents reactive edema, but the exact extent of tumor versus edema cannot be defined. At this point, diagnosis is felt to be either infection or a malignant soft tissue tumor eliciting significant reaction in both soft tissue and bone. In either event, biopsy and therapy can be adequately planned (with the use of the remaining MR images to fully define extent of lesion). At biopsy, the lesion proved to be a very rare soft tissue Ewing’s sarcoma.
volvement of cortical bone, and involvement of adjacent joints (l-3, 10, 11, 15). CT is clearly superior only in evaluation of matrix calcification or of a thin cortical rim. It should only rarely be the case that both CT and MRI are required (and use of both usually represents significant over-imaging). It is the consensus that MRI is the staging modality of choice, and that CT should be reserved to answer specific questions regarding matrix or rim calcification (Fig. 3). The preference for MRI over CT is reinforced
by the capability for multiplanar imaging, as well as the superb soft tissue contrast produced by MRI, which allows staging with greater confidence. Although MRI generally is extremely accurate in evaluating extraosseous extent of a lesion, two conditions may lead to an overestimation of soft-tissue tumor extent. Hematoma, often arising from biopsy of a lesion, may at some phase of its evolution be isointense to tumor and therefore indistinguishable. Similarly, reactive edema, which sur-
646
I. J. Radiation Oncology
0 Biology 0 Physics
November
1991, Volume 21, Number 6
Musculoskeletal
oncologic
imaging 0 B. J. MANASTER
1647
Fig. 4. This T2 weighted MR of a malignant sarcoma demonstrates the difficulty of differentiating tumors from edema. The patient is lying prone, and the high signal intensity tumor is in the deep posterior compartment adjacent to the interosseous membrane. The tumor is surrounded by intermediate signal edema in all compartments. Tumor surrounds the neurovascular structures. The exact demarcation between the tumor and edema is not clear. Wide resection would require a cuff of normal tissue surrounding the reactive tissue; in this case, amputation would be required to achieve wide resection. A riskier marginal resection (presuming all edema and no nests of tumor cells in the anterior compartment) could allow salvage of the limb.
rounds some tumors, may demonstrate high signal intensity equal to that of tumor. This may occur in up to 50% of malignant tumors and a smaller percent of benign lesions; in the case of malignant tumors, this area of “edema” occasionally contains small nests of tumor cells. The difficulty of distinguishing edema from tumor is frustrating, but in most cases is a moot point since the recommended wide tumor resection requires resection of tumor, reactive tissue, and a cuff of normal tissue. Clearly, however, there are cases in which a very wide margin of reactive tissue (several centimeters) can exist which may convert a limb salvage procedure to an amputation if the “wide resection margin” is observed; in such a case, differentiation of tumor from edema might be required for informed patient consent and surgical planning (Fig. 4). In most cases, MRI does not aid in the histological diagnosis of a musculoskeletal lesion since the signal intensity characteristics of most lesions show significant overlap (8. 9). Furthermore, signal intensity alone is insufficient even to distinguish most malignant from benign lesions. Morphologic characteristics are more useful. Generally, malignant soft tissue lesions are large, inhomogeneous (especially well seen on T2 weighted sequences), and may appear infiltrative (Fig. 4). However, many benign soft tissue lesions (especially infection and hematoma) are inho-
mogeneous as well (Fig. 5), while a few malignant lesions (especially synovial cell sarcoma) may be homogeneous (1, 15). Furthermore, some benign lesions (especially desmoids) are locally aggressive and infiltrative (Fig. 6), while many malignant lesions acquire a pseudocapsule of reactive tissue which gives the false appearance both on MRI and at surgery of containing the tumor. Thus far, neither the use of gadolinium, MRI spectroscopy, nor dynamic MR scanning shows significant promise of improving histologic diagnostic capabilities or of distinguishing malignant from benign tumors with an acceptably high degree of accuracy. In cases that are difficult to evaluate, clinical information may be the most important determinant; time spent questioning the patient can be extremely rewarding. MRI of lesions is thus more useful in determining site and extent of involvement than diagnosis; diagnosis based on MRI is often correct, but virtually always requires biopsy for confirmation. MRI aids in planning the biopsy, when tissue must be obtained which represents the most active part of the tumor. The planned biopsy site must not compromise plans for limb-sparing definitive surgery (which requires excision of the biopsy track, so only a single compartment should be crossed, without violation of the neurovascular bundle or joint and without crossing skin or muscle which will be required for reconstruction). In
I. J. Radiation Oncology 0 Biology 0 Physics
November
199 1, Volume 2 1, Number 6
(a)
(b)
Fig. 5. The non-specificity of the MR appearance of soft tissue masses is illustrated by these cases. In each, a high signal intensity lesion is seen which is infiltrative, crosses compartmental boundaries, and is both large and inhomogeneous. These characteristics are usually descriptive of malignant tumors. However, in these cases the diagnoses were (a) hematoma from a partial thigh muscle rupture (seen on a gadolinium-enhanced Tl weighted axial cut), and (b) staphylococcus infection (T2 weighted axial cut).
many cases, percutaneous needle biopsy, often performed under ultrasound guidance, is a cost-effective alternative to open biopsy. The crucial nature of biopsy accuracy and choice of biopsy site was highlighted by a multi-institutional study which demonstrated that 18% of tumor cases had major errors in diagnosis and 18% of patients required alteration of the optimum therapy plan because of the
choice
of biopsy
complications occurred 3 to 5 when the biopsies were performed at rather than at a major tumor treatled to a recommendation that biopsy the treating institution, and planned the surgeon offering the definitive
site. These
times more frequently a referring institution ment center (7). This only be performed in in conjunction with treatment.
Musculoskeletal oncologic imaging 0 B. J. MANASTER
(b) Fig. 6. ABOVE AND FOLLOWING PAGE While the MR appearance of most benign soft tissue tumors is of a homogeneous encapsulated mass, benign desmoid tumors are a notable exception. The T2 weighted images of this desmoid tumor demonstrate it to be a very large mass arising in the adductor muscle (arrow), but crossing compartments to also involve the obturator muscles (a). This mass extends through the obturator foramen to surround the ischial tuberosity (arrow) both anteriorly and posteriorly (b). It pushes the neurovascular bundle anteriorly but does not surround it. It is of high signal intensity and inhomogeneous, and therefore indistinguishable from a malignant lesion. It was treated with surgery and radiation. Follow-up examination two years later demonstrates persistent high signal intensity in the tumor bed (arrow) but no mass (c); this is felt to represent granulation and radiation necrosis, as it showed no interval change over several follow-up MR exams. Interestingly, at the two year exam a higher section (d) shows high signal in the iliacus muscle (arrow), a region previously demonstrated to be normal. This is a recurrent tumor, and represents a common feature of the benign but locally aggressive lesion.
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1991. Volume 21, Number 6
Cd)
If a patient is given preoperative therapy, a repeat MR is obtained prior of therapy may be judged by the MRI is not yet a reliable method of tumor necrosis, which is a major
chemo- or radiation to surgery. Efficacy tumor volume, but assessing percent of factor in prognosis
(9, 12). Post-therapeutic imaging protocols should be designed for early detection of recurrent and metastatic disease. Pro-
tocols for type, frequency, and duration of follow-up should be based on patterns of tumor spread and time course of recurrence or metastases. Unfortunately, such “hazard” rates and patterns have not been established for many lesions. Generally, a patient with a malignant lesion should be followed by chest films and CT for pulmonary metastases. Intraosseous lesions are followed by a combination of plain film and MRI (depending on amount of
Musculoskeletal oncologic imaging 0 B. J.
hardware present, which can cause significant artifact on MRI), while soft tissue tumors are best followed by MRI. Post-surgical (or post-therapy) scanning is recommended at about 3 months to establish a baseline appearance. A favorable response to any therapeutic modality should result in reduction in the size of the soft tissue component and decrease in the signal intensity on MR T2 weighting. However, such high signal intensity may persist after therapy (Fig. 6); there may be an overlap in the signal intensities of recurrent tumor and benign post-therapeutic change (edema, granulation, necrosis, postoperative or radiation fibrosis) (5, 13). Dynamic MRI with contrast or MR spec-
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troscopy may be helpful with this differentiation in the future, but is not reliable at this point. Furthermore, the intraosseous component appears to respond differently from the soft tissue component, with reduction in size and signal intensity of lesions not occurring despite histologic response (6). Consequently, MRI criteria for post-therapeutic evaluation of intraosseous and extraosseous lesions are different and not altogether reliable. Biopsy or close follow-up (to watch morphologic characteristics rather than signal intensity) may be recommended frequently until further criteria or imaging methodologies for tumor recurrence are developed.
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9. Pan, G.; Raymond, A.; Carrasco, C.; Wallace, S.; Kim, E.; Shirkhoda, A.; Jaffe, N.; Murray, J.; Benjamin, R. ,Osteosarcoma: MR imaging after preoperative chemotherapy. Radiology 174:517-526; 1990. 10. Pettersson, H.; Gillespy, T.; Hamlin, D. J.; Enneking, W.; Springfield, D.; Andrew, E.; Spanrer, S.; Slone, R. Primary musculoskeletal tumors: examination with MR imaging compared with conventional modalities. Radiology 164:237-241; 1987. 11. Pettersson, H.; Hamlin, D. J.; Scott, K. N. Magnetic resonance imaging of musculoskeletal tumors. CRC Critical Reviews in Diagnostic Imaging 26(3):241-263; 1986. 12. Sanchez, R.; Quinn, S.; Walling, A.; Estrada, J.; Greenberg, H. Musculoskeletal neoplasm after intraarterial chemotherapy: correlation of MR images with pathologic specimens. Radiology 174:237-240; 1990. 13. Sanchez, R. B.; Quinn, S. F.; Walling, A.; Estrada, J.; Greenberg, H. Musculoskeletal neoplasms after intraarterial chemotherapy: Correlation of MR images with pathologic specimens. Radiology 174:237-240; 1990. 14. Sumdaram, M.; McGuire, M. H.; Schajowicz, F. Soft-tissue masses: histologic basis for decreased signal (short T2) on T2-weighted MR images. A. J. R. 146:1247-1250; 1987. 15. Zimmer, W. D.; Berquist, T. H.; McLeod, R. A.; Sim, F. H.; Pritchard, D. J.; Shives, T. C.. Weld, L. E., May, G. R. Bone tumors: magnetic resonance imaging versus computed tomography. Radiology 155:709-718; 1985.
