AJR 2000; 175:575-587
© American Roentgen Ray Society
Radiologic Evaluation of Soft-Tissue Masses
A Current Perspective
Mark J. Kransdorf1,2 and
Mark D. Murphey2,3,4
1
Department of Radiology, Mayo Clinic, 4500 San Pablo Rd., Jacksonville, FL
32224-3899.
2
Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Walter Reed Army Medical Center, Bldg. 54, Alaska and Georgia Aves.,
Washington, DC 20306-6000.
3
Department of Radiology and Nuclear Medicine, Uniformed Services University of
the Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799.
4
Department of Radiology, University of Maryland School of Medicine, 22 South
Greene St., Baltimore, MD 21201-1595.
Received March 7, 2000;
accepted after revision April 12, 2000.
Honoring Lewis G. Cole, MD and Willis F. Manges, MD
This is the ninth in a series of Centennial Dissertations that the
AJR is publishing this year in honor of the former presidents of the
American Roentgen Ray Society, two of whom are pictured above.
The opinions or assertions contained herein are the private views of the
authors and are not to be construed as official or as reflecting the views of
the Department of the Army or the Department of Defense.
Address correspondence to M. J. Kransdorf.
Introduction
The radiologic evaluation of soft-tissue masses has changed dramatically
within the last two decades. Before the advent of computer-assisted imaging,
assessment of clinically suspicious soft-tissue masses was usually limited to
radiographs. Although radiographs were sensitive to the identification of
adipose tissue and soft-tissue mineralization, they provided little other
diagnostic information. When lesions were small, radiologists of those dark
days were happy just to confirm the presence of a mass, much less give a
confident diagnosis. The emergence of CT improved this situation dramatically.
Masses could be not only delineated with great confidence but well staged with
excellent depiction of anatomic detail. However, diagnosis remained
problematic, with images sufficiently characteristic to suggest the correct
histology in only a minority of cases: typically, lipomas and hemangiomas
[1]. The introduction of MR
imaging was met with great enthusiasm because of the markedly improved
soft-tissue contrast and multiplanar image acquisition capabilities. The
imaging of soft-tissue masses was now on a par with that of other
imaging-intense radiologic subspecialties, with exquisite depiction of
anatomic detail. This ability to accurately anatomically characterize masses
spurred new interest in the evaluation of soft-tissue tumors. Attempts were
made to develop rules analogous to those for bone tumors for differentiating
benign and malignant processes on the basis of lesion morphology and signal
intensity; however, with few exceptions, these rules proved unreliable
[2,3,4,5,6,7].
What has emerged is an approach to evaluation that is a combination of
science and gestalt: a few well-tested general principles as well as a number
of lesions with a characteristic imaging appearance. Despite our initial
fervor for the superiority of MR imaging in assessing soft-tissue tumors, MR
imaging remains relatively limited in its ability to precisely characterize
these tumors, with a correct histologic diagnosis reached on the basis of
imaging studies in only approximately one quarter to one third of cases
[5,6,7].
More recently, the superiority of MR imaging in the staging of musculoskeletal
tumors has also come into question. In a multiinstitutional study of 133
patients with primary soft-tissue malignancies, the Radiology Diagnostic
Oncology Group found no statistically significant difference between CT and MR
imaging in determining tumor involvement of muscle, bone, joint, or
neurovascular structures
[8].
Despite these limitations, most radiologists are comfortable with the use
of MR imaging in the evaluation of soft-tissue lesions. We strongly believe it
is the modality of choice and also think that, when it is used in conjunction
with a systematic approach, one can correctly diagnose most masses.
Accordingly, this review will present a systematic approach to the evaluation
of soft-tissue tumors, highlighting MR imaging in diagnosis and in
differentiating benign from malignant soft-tissue lesions. In addition, an
approach is provided for establishing a differential diagnosis for those
lesions with a nonspecific imaging appearance, as well as indications for
contrast-enhanced imaging.
General Concepts
Soft tissue is derived primarily from mesenchyme and, by convention,
consists of skeletal muscle, fat, fibrous tissue, and the serving vascular
structures as well as the associated peripheral nervous system
[9]. Soft-tissue tumors are
classified histologically on the basis of the adult tissue they resemble
[9,
10]. The designation of
liposarcoma, for example, does not indicate a lesion arose from fat, but
rather that it is a malignant mesenchymal tumor that has differentiated into
tissue that microscopically resembles normal adult fat
[9]. Many sarcomas are poorly
differentiated and, consequently, lack the microscopic features required to
make a specific diagnosis. In such cases, immuno-histochemical stains have
aided pathologists in identifying their pattern of differentiation, allowing
accurate classification. Despite the pathologist's best efforts, however,
approximately 5-15% of soft-tissue sarcomas cannot be further classified
[11,12,13,14].
Soft-tissue sarcomas, unlike benign soft-tissue lesions, are relatively
uncommon and are estimated to represent about 1% of all malignant tumors
[15,
16]. Hajdu
[15] noted that the incidence
in the United States is about the same as that of multiple myeloma or
carcinoma of the thyroid. Soft-tissue sarcomas are two to three times as
common as primary malignant bone tumors
[9,
16]. Benign soft-tissue tumors
are more common, although it is difficult to estimate the annual incidence
because many lipomas, hemangiomas, and other benign lesions are not biopsied.
The annual clinical incidence of benign soft-tissue tumors is estimated at 300
per 100,000, and these tumors are about 100 times more common than malignant
soft-tissue tumors [9,
12].
Preliminary Evaluation
The initial evaluation of a patient with a soft-tissue mass begins with a
thorough clinical history and radiologic evaluation.
Clinical History
As radiologists, we are trained to evaluate cases as unknowns. As we
complete our training, we are cautioned that Board examiners will require an
explanation if additional information is sought. In daily practice, histories
are often scant, with little substantive data. The concept that we should take
a clinical history requires a significant change in paradigm. The clinical
history is an important factor in establishing an accurate diagnosis. In many
circumstances it may provide key information that will allow a specific
diagnosis when imaging is nonspecific. Is there a history of a previous lesion
or underlying malignancy? Has there been previous surgery or radiation? It is
essential to know how the patient presented: Is the lesion painful or did the
patient note a painless mass? A painful mass always requires that an
inflammatory process be included in the differential diagnosis. Is there a
history of notable trauma or use of anticoagulants? Has the lesion remained
stable over a long period of time or varied in size, or is it growing? A
history of continued growth is always suggestive of malignancy. Unlike bone
tumors, however, a slowly growing soft-tissue mass is not invariably
indicative of a benign process. Variation in lesion size with time or activity
would be exceedingly unusual for a malignancy and suggests a process such as a
ganglion or hemangioma.
Is there more than one lesion? Soft-tissue tumors are typically solitary,
and the identification of multiple lesions markedly limits the differential
diagnosis. Multiple lipomas are seen in 5-15% of patients presenting with a
soft-tissue mass
[17,18,19].
The diagnosis in these cases can be made confidently on the basis of signal
intensity on MR imaging. Aggressive fibromatosis is multifocal in 10-15% of
patients [20,
21]. A second soft-tissue mass
in a patient with a previously confirmed desmoid tumor should be regarded as a
second desmoid tumor until proven otherwise
[22]. Patients with
neurofibromatosis have multiple lesions, and although the diagnosis is often
known or suspected, such is not always the case
(Fig. 1). The diagnosis may be
suggested on the basis of imaging findings by the identification of multiple
lesions in a major nerve distribution.
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Fig. 1. —36-year-old woman with neurofibromatosis and multiple neurofibromas.
Coronal contrast-enhanced T1-weighted spin-echo MR image (500/15, TR/TE) shows
multiple left paraspinal masses with cystic change.
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Angiomatous lesions are quite common and are multiple in as many as 20% of
patients [9]. In such cases,
superficial and deep lesions may coexist. Multiple lesions may also be seen
with metastatic disease. Soft tissue is relatively resistant to metastasis,
and although soft tissue comprises about 40% of total body weight, soft-tissue
metastases are quite rare. The skin and subcutaneous tissue is also a frequent
site of extraosseous involvement in patients with multiple myeloma, with
involvement typically in the form of multiple subcutaneous nodules
[23]. Extraosseous
manifestations are found in less than 5% of patients with multiple myeloma and
are associated with a more aggresive clinical course
[23]. Metastatic melanoma may
display a similar pattern of multiple nodular subcutaneous metastases
[24] (Fig.
2A,2B).
These metastases are seen in more than 30% of patients with melanoma
metastatic disease, usually in patients with Clark level IV or V disease
(depth of tumor invasion into the deep dermis or through the dermis into the
subcutaneous fat) and may be the only radiologic manifestation of metastases
[24]. Finally, multiple
myxomas may be seen in association with fibrous dysplasia of bone (Mazabraud
syndrome) [25]. The myxomas
are usually intramuscular and the association is most typically with
polyostotic disease [25,
26].
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Fig. 2A. —35-year-old woman with metastatic melanoma and multiple metastases.
Coronal T1-weighted spin-echo MR image (600/20, TR/TE) shows lobulated nodule
(asterisk) in subcutaneous adipose tissue of buttocks. Note subtle
intraosseous metastasis (arrow) in ischium.
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Fig. 2B. —35-year-old woman with metastatic melanoma and multiple metastases.
Axial conventional T2-weighted MR image (2500/80) shows fluid-fluid level
(arrow) indicative of previous hemorrhage.
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Radiography
Despite dramatic technologic advances in our ability to image soft-tissue
tumors, the radiologic evaluation of a suspected soft-tissue mass must begin
with the radiograph. Although frequently unrewarding, it is impossible to
predetermine those cases in which radiographs will be critical for diagnosis.
Radiographs may be diagnostic of a palpable lesion caused by an underlying
skeletal deformity (such as exuberant callus related to prior trauma) or
exostosis, which may masquerade as a soft-tissue mass. Radiographs may also
reveal soft-tissue calcifications, which can be suggestive and, at times, very
characteristic of a specific diagnosis. For example, they may reveal
phleboliths within a hemangioma (Fig.
3A,3B),
juxtaarticular osteocartilaginous masses of synovial chondromatosis,
peripherally more mature ossification of myositis ossificans, or
characteristic bone changes of other processes with associated soft-tissue
involvement. When not characteristic of a specific process, soft-tissue
calcification can suggest certain diagnoses. For example, nonspecific
dystrophic calcifications in a slowly growing lower extremity mass in a young
adult should suggest a synovial sarcoma as the diagnosis of exclusion (Fig.
4A,4B).
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Fig. 3A. —52-year-old man with hemangioma of hypothenar eminence of hand.
Radiograph shows multiple small, smooth, rounded calcifications (solid
arrow), more opaque peripherally, characteristic of phleboliths. Note
small nonspecific calcifications (open arrow).
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Fig. 4A. —17-year-old girl with synovial sarcoma of foot who presented with
slowly growing painless mass. Axial conventional T2-weighted spin-echo MR
image (1800/80, TR/TE) shows well-defined nonspecific soft-tissue mass
(asterisk).
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Fig. 4B. —17-year-old girl with synovial sarcoma of foot who presented with
slowly growing painless mass. Corresponding radiograph shows peripheral and
central clacification. This radiographic appearance (calcified soft-tissue
mass) in context of slowly growing juxtaarticular mass in young adult strongly
suggests appropriate diagnosis of synovial sarcoma.
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In addition, radiographs are the best initial method of assessing
coexistent osseous involvement, such as remodeling, periosteal reaction, or
overt osseous invasion and destruction
[27]. However, unlike bone
tumors, the biologic activity of a soft-tissue mass cannot be reliably
assessed by its growth rate. A slowly growing soft-tissue mass that may
remodel adjacent bone (causing a scalloped area with well-defined sclerotic
margins) may still be highly malignant on histologic examination
[9].
A soft-tissue mass may also be the initial presentation of a primary bone
tumor or inflammatory process. In such cases, the radiograph may be useful in
identifying the osseous origin of the lesion. The diagnosis of a malignant
bone tumor such as Ewing's sarcoma or primary lymphoma of the bone should be
considered when there is a large circumferential soft-tissue mass in
association with an underlying destructive permeative bone lesion. A subtle
radiologic feature, which may help to separate inflammatory and neoplastic
processes, is that an inflammatory process typically obliterates fascial
planes rather than displaces them. CT may be a useful adjunct in specific
circumstances. We generally reserve CT for patients in whom radiographs do not
adequately depict the lesion, its pattern of mineralization, or its
relationship to the host. This inadequacy typically occurs in areas in which
the osseous anatomy is complex, such as the pelvis, shoulder, and paraspinal
regions.
MR Imaging
MR imaging has emerged as the preferred modality for evaluating soft-tissue
lesions
[2,3,4,
28,29,30,31,32,33,34,35].
It provides superior soft-tissue contrast, allows multiplanar image
acquisition, obviates iodinated contrast agents and ionizing radiation, and is
devoid of streak artifacts commonly encountered with CT
[2,
28,29,30].
Although initial investigations maintained that CT was superior to MR imaging
in detecting destruction of cortical bone
[29,
30,
35], later studies suggest
that these two modalities are comparable in this regard
[28,
36].
Technique
Lesions should be imaged in at least two orthogonal planes, using
conventional T1-weighted and T2-weighted spin-echo MR pulse sequences in at
least one of these planes. Standard spin-echo MR images are most useful in
establishing a specific diagnosis, when possible, and this technique is both
the most reproducible technique and the one most often referenced in the tumor
imaging literature. It is the imaging technique with which we are most
familiar for tumor evaluation, and it has been established as the standard by
which other imaging techniques must be judged
[37]. The main disadvantage of
spin-echo MR imaging remains the relatively long acquisition times, especially
for double-echo T2-weighted MR imaging sequences
[37]. Radiologists are most
familiar with conventional axial anatomy, and axial T1- and T2-weighted
spin-echo MR images should be obtained in almost all cases. The choice of an
additional imaging plane or planes varies with the involved body part, the
lesion location, and the lesion's relationship to crucial structures. In
general, the additional plane is sagittal with anterior or posterior masses
and coronal with medial or lateral lesions. Oblique planes may also be a
useful adjunct. In these additional planes, it is useful to use a combination
of conventional T1- and T2-weighted spin-echo MR images, turbo (fast)
spin-echo MR images, gradient MR images, and short tau inversion recovery
(STIR) images, as the case requires.
Fast scanning techniques may be useful in the evaluation of soft-tissue
masses. They allow shorter imaging times, decreased motion artifacts, and
increased patient tolerance, as well as patient throughput
[37,
38]. They may add additional
information and be helpful in specific instances, although fast scanning
techniques have not replaced standard spin-echo imaging. Gradient-echo imaging
may be a useful supplement in revealing hemosiderin because of the greater
magnetic susceptibility of hemosiderin. In general, susceptibility artifacts
related to metallic material, hemorrhage, and air are accentuated on
gradient-echo MR images [38]
(Fig.
5A,5B,5C,5D).
Gradient-echo MR images may also be better, in some instances, for showing the
lesion—fat interfaces and depicting small surrounding vessels
[39].
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Fig. 5B. —27-year-old woman with foreign body and associated abscess. Coronal
T1-weighted spin-echo MR image (600/15, TR/TE) shows prominent signal void
(asterisk), with "parenthetic" artifact, compatible with
foreign body.
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Fig. 5C. —27-year-old woman with foreign body and associated abscess.
Corresponding conventional T2-weighted spin-echo MR image (2500/80) shows
foreign body (asterisk) with associated inflammatory change.
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STIR imaging can be an adjunct in selective cases. STIR imaging produces
fat suppression and enhances the identification of abnormal tissue with
increased water content and, as a result, is useful to confirm subtle areas of
soft-tissue abnormality [40].
This technique increases lesion conspicuity
[40,
41], but it typically has a
lower signal-to-noise ratio than does spin-echo imaging and is also more
susceptible to degradation by motion
[37,
40]. Lesions are generally
well seen on standard imaging, and, in our opinion, STIR imaging tends to
reduce the variations in signal intensities identified on conventional
spin-echo MR imaging that are most helpful in tissue characterization.
Fat suppression on T2-weighted MR images is useful to increase
lesion-to-background signal intensity differences for high-signal-intensity
lesions within the marrow or fatty soft tissue
[37]. Fat-suppression imaging
is also useful in decreasing or eliminating the MR signal from fat, allowing
increased conspicuity of lesions containing paramagnetic substances (such as
methemoglobin) on T1-weighted MR images, and revealing contrast enhancement.
As with STIR techniques, fat-suppressed T2-weighted MR imaging decreases
variations in tumor signal intensities, and we do not use this technique in
place of conventional T2-weighted MR imaging.
Field of view is dictated by the size and location of the lesion. In
general, a small field of view is preferred; however, the field of view must
be large enough to allow evaluation of the lesion and appropriate staging.
When an extremity is being evaluated, it is not usually necessary to examine
the contralateral extremity for comparison, unless no lesion is detected on
initial sequences. It is useful to place a marker over the area of clinical
concern to ensure it is appropriately imaged. This becomes important in
evaluation of a lesion such as a subcutaneous lipoma or lipomatosis in which
the lesion may not be appreciated as distinct from the adjacent adipose tissue
(Fig. 6). When small
superficial lesions are being evaluated, care should be taken to ensure the
marker or patient position does not compress the mass.
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Fig. 6. —54-year-old woman with mild lipomatosis of right lower extremity,
who presented with "fullness" around knee. Axial T1-weighted
spin-echo MR image (700/16, TR/TE) of both distal thighs shows increased
adipose tissue on right as compared with contralateral side. Images of both
distal thighs were obtained after no cause for clinical findings was found on
axial images of right knee.
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MR Imaging Contrast Enhancement
Although there is general agreement on the value of MR imaging in the
detection, diagnosis, and staging of soft-tissue tumors and tumorlike lesions,
the use of IV contrast material in their evaluation remains controversial. In
general, MR imaging contrast agents enhance the signal intensity of many
tumors on T1-weighted spin-echo MR images, in some cases enhancing the
demarcation between tumor and muscle and tumor and edema as well as providing
information on tumor vascularity
[42,
43]. In actuality,
differentiation between tumor and muscle is usually quite well delineated
without contrast-enhanced imaging on T2-weighted MR images, and the accurate
distinction between tumor and edema is probably of little practical value.
Edema, which is infrequent without superimposed trauma or hemorrhage, is
considered to be part of the reactive zone around the neoplasm and, as a
result, is removed en bloc with the tumor
[44].
Information on tumor enhancement is not without a price. The use of IV
contrast material substantially increases the length and cost of the
examination. Although contrast-enhanced MR imaging may provide some additional
information, it has not been shown to increase lesion conspicuity or to
replace conventional T2-weighted MR imaging
[45]. Moreover, although the
incidence of untoward reaction as a result of contrast material administration
is small, it is present. Severe reactions have been reported with both
gadopentetate dimeglumine (Magnevist; Berlex Laboratories, Wayne, NJ) and
gadoteridol (ProHance; Squibb Diagnostics, Princeton, NJ), including
hypotension, laryngospasm, bronchospasm, anaphylactoid reaction, and
anaphylactic shock
[46,47,48,49,50],
as well as a full spectrum of less serious reactions. Jordan and Mintz
[51] described a fatal
reaction to gadopentetate dimeglumine that was presumed to be caused by
anaphylactic reaction with associated bronchospasm. Consequently,
gadolinium-enhanced imaging should be reserved for cases in which the results
would influence patient care.
One specific circumstance in which gadolinium-enhanced imaging is useful is
in the evaluation of hematomas. In the case of hematoma, contrast-enhanced
imaging may reveal a small tumor nodule that may have been inapparent within
the hemorrhage on conventional MR imaging
[52,
53]. Caution is required,
however, because the fibrovascular tissue in organizing hematomas may show
enhancement [54].
Gadolinium-enhanced imaging has also been used to differentiate solid from
cystic (or necrotic) lesions or to identify cystic or necrotic areas within
solid tumors, with these necrotic or cystic areas showing no enhancement
[42]. This distinction is
especially important to guide biopsy and may be difficult or impossible to
make on conventional T2-weighted MR images when both tumor and fluid show high
signal intensity, well-defined margins, and homogeneous signal intensity.
Note, however, that myxoid lesions such as intramuscular myxoma or myxoid
liposarcoma, and hyaline cartilage lesions such as synovial chondromatosis may
show little or mild enhancement and may mimic cysts or lesions with cystic
components (Fig.
7A,7B,7C,7D).
In general, sonography is fast and inexpensive and is an ideal method for
differentiating solid and cystic lesions when the lesion is in an anatomic
location accessible to sonographic evaluation.
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Fig. 7A. —35-year-old man with extra articular synovial chondromatosis,
mimicking loculated fluid. Axial T1-weighted spin-echo MR image (763/18,
TR/TE) shows large lobulated mass, with signal intensity similar to that of
skeletal muscle, in adductor compartment (asterisk).
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Fig. 7B. —35-year-old man with extra articular synovial chondromatosis,
mimicking loculated fluid. Corresponding conventional T2-weighted spin-echo MR
image (2912/80) shows lesion to have signal intensity greater than that of
fat.
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Fig. 7C. —35-year-old man with extra articular synovial chondromatosis,
mimicking loculated fluid. Fat-suppressed axial T1-weighted spin-echo MR image
(475/18) after contrast material administration shows peripheral and septal
enhancement, suggesting loculated fluid.
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MR Imaging Diagnosis
Despite the superiority of MR imaging in delineating soft-tissue tumors, it
remains limited in its ability to precisely characterize them, with most
lesions showing a nonspecific appearance with prolonged T1 and T2 relaxation
times. Consequently, a correct histologic diagnosis is reached solely on the
basis of MR imaging studies in only 25-35% of cases
[5,6,7].
There are instances, however, in which a specific diagnosis may be made or
strongly suspected on the basis of MR imaging features. This diagnosis is
usually made on a basis of lesion signal intensity, pattern of growth,
location, and associated signs and findings (Figs.
8,9A,9B,10A,10B).
The MR imaging appearances of these lesions have been well reported and is not
reviewed here. They are listed in Appendix 1.
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Fig. 8. —36-year-old woman with intramuscular lipoma. Coronal T1-weighted
spin-echo MR image (600/14, TR/TE) shows mass in right neck, with signal
intensity identical to that of fat on all pulse sequences. Diagnosis can be
made with confidence on basis of signal intensity.
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Fig. 9A. —41-year-old woman with hemangioma of foot. Axial T1-weighted
spin-echo MR image (600/15, TR/TE) shows large lobulated mass with signal
intensity similar to that of skeletal muscle infiltrating soft tissue of first
interspace and fat (arrow) within interstices of lesion.
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Fig. 9B. —41-year-old woman with hemangioma of foot. Corresponding
conventional T2-weighted spin-echo MR image (2500/80) shows lesion to have
signal intensity greater than that of fat. Infiltrating pattern of growth,
interspersed adipose tissue, and signal intensity are highly characteristic of
diagnosis.
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Fig. 10A. —22-year-old man with schwannoma in upper arm. Axial T2-weighted
spin-echo MR image (2000/80, TR/TE) shows large mass associated with
neurovascular bundle with target sign, characteristic of peripheral nerve
sheath tumor.
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Fig. 10B. —22-year-old man with schwannoma in upper arm. Corresponding coronal
T1-weighted spin-echo MR image (650/20) shows lesion is contiguous with median
nerve (arrow). Signal intensity of lesion, target sign, and location
allow diagnosis of peripheral nerve sheath tumor to be made with
confidence.
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More commonly, MR imaging may reveal a nonspecific appearance. In such
cases, it is often not possible to establish a meaningful differential
diagnosis or reliably determine if a lesion is benign or malignant. In such
situations, it is useful to formulate a suitably ordered differential
diagnosis on the basis of a knowledge of tumor prevalence, patient age, and
lesion anatomic location. This diagnosis can be further refined by considering
clinical history and radiologic features, such as pattern of growth, signal
intensity, and localization (subcutaneous, intramuscular, or intermuscular).
The most common malignant and benign lesions, by tumor location and patient
age, have been previously published
[13,
14]. Appendix 2 includes the
localization of common lesions (Fig.
11A,11B,11C).
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Fig. 11A. —34-year-old man with malignant fibrous histiocytoma of thigh, who
presented with slowly growing painless mass. Axial conventional T2-weighted
spin-echo MR image (1800/80, TR/TE) shows relatively well-defined mass in
anterior compartment of thigh with nonspecific high signal intensity.
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Fig. 11B. —34-year-old man with malignant fibrous histiocytoma of thigh, who
presented with slowly growing painless mass. Corresponding unenhanced
(B) and contrast-enhanced (C) axial T1-weighted spin-echo MR
images (400/20) show uniform enhancement. Although appearance of lesion is
nonspecific, malignant fibrous histiocytoma is statistically most likely
diagnosis based on patient age and lesion location.
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Fig. 11C. —34-year-old man with malignant fibrous histiocytoma of thigh, who
presented with slowly growing painless mass. Corresponding unenhanced
(B) and contrast-enhanced (C) axial T1-weighted spin-echo MR
images (400/20) show uniform enhancement. Although appearance of lesion is
nonspecific, malignant fibrous histiocytoma is statistically most likely
diagnosis based on patient age and lesion location.
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Benign Versus Malignant
There is general agreement on the diagnostic value of MR imaging in many
cases, but the issue of whether MR imaging can reliably distinguish benign
from malignant is much less clear. One study has suggested that MR imaging can
differentiate benign from malignant masses in more than 90% of cases on the
basis of the morphology of the lesion
[6]. Criteria used for benign
lesions included smooth well-defined margins, small size, and homogenous
signal intensity, especially on T2-weighted MR images. Other studies, however,
note that malignant lesions may appear as smoothly marginated homogeneous
masses and MR imaging cannot reliably distinguish benign from malignant
processes
[2,3,4,5,
7,
42]. This discrepancy likely
reflects differences in the studied populations.
When the MR images of a lesion are not sufficiently characteristic to
suggest a specific diagnosis, a conservative approach is warranted.
Malignancies, by virtue of their very nature and potential for autonomous
growth, are generally larger and more likely to outgrow their vascular supply
with subsequent infarction, necrosis, and heterogeneous signal intensity on
T2-weighted spin-echo MR imaging. Consequently, the larger a mass is, the
greater its heterogeneity, the greater is the concern for malignancy. Only 5%
of benign soft-tissue tumors exceed 5 cm in diameter
[55,
56]. In addition, most
malignant tumors are deep, whereas only about 1% of all benign soft-tissue
tumors are deep [55,
56]. Although these figures
are based on surgical series, these trends are likely still valid for
radiologists.
When sarcomas are superficial, they generally have a less aggressive
biologic behavior than do deep lesions
[57]. As a rule, most
malignancies grow as deep space-occupying lesions, enlarging in a centripetal
fashion [57], pushing rather
than infiltrating adjacent structures (although clearly there are exceptions
to this general rule). As sarcomas enlarge, a pseudocapsule of fibrous
connective tissue is formed around them by compression and layering of normal
tissue, associated inflammatory reaction, and vascularization
[57]. Generally, they respect
fascial borders and remain within anatomic compartments until late in their
course [57]. It is this
pattern of growth that gives most sarcomas relatively well-defined margins, in
distinction to the general concepts of margins used in the evaluation of
osseous tumors.
Although our experience with metastatic carcinoma to soft tissue is
limited, we have generally found these lesions appear more infiltrative with
ill-defined margins and often violating fascial planes and anatomic
compartments. This pattern of growth is quite different from that seen in most
primary soft-tissue tumors.
Increased signal intensity in the skeletal muscle surrounding a
musculoskeletal mass on T2-weighted spin-echo MR images or other
fluid-sensitive sequences (i.e., STIR) has also been suggested as a reliable
indicator of malignancy [58,
59]. These results are based
on studies in which both bone and soft-tissue lesions were evaluated. Although
this increased signal intensity may be seen with malignancy, in our
experience, this finding is quite nonspecific. In fact, prominent high signal
intensity surrounding a soft-tissue mass more commonly suggests an
inflammatory process, abscess, myositis ossificans, local trauma, hemorrhage,
biopsy, or the effect of radiation therapy rather than a primary soft-tissue
neoplasm (Fig.
12A,12B).
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Fig. 12A. —14-year-old boy with myositis ossificans in forearm. Axial fast
spin-echo T2-weighted spin-echo MR image (2600/80, TR/TE) shows poorly defined
mass in extensor compartment of forearm and adjacent to ulna. Lesion
predominantly involves extensor carpi ulnaris, although there is abnormal
signal in and between adjacent muscles.
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Fig. 12B. —14-year-old boy with myositis ossificans in forearm. Corresponding
axial T1-weighted spin-echo MR image (650/20) shows only minimal signal
alteration with effacement of subcutaneous adipose tissue
(arrow).
|
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Gadolinium-enhanced imaging has also been proposed as useful in
differentiating benign and malignant soft-tissue lesions, with malignant
lesions showing a greater enhancement as well as a greater rate of enhancement
[43,
45,
47,
60]. Enhancement reflects
tissue vascularity and tissue perfusion, and, in general, the rate of
enhancement in malignant lesions is greater than that seen in benign lesions.
However, the overlap between benign and malignant is so great that, in our
opinion, this finding is of little practical value in any specific case
[60]. When a lesion has a
nonspecific MR imaging appearance, one is ill-advised to suggest a lesion is
benign or malignant solely on the basis of its MR imaging characteristics and
rate or degree of enhancement.
DeSchepper et al. [61]
performed a multivariate statistical analysis of 10 imaging parameters,
individually and in combination. These researchers found that malignancy was
predicted with the highest sensitivity when a lesion had a high signal
intensity on T2-weighted MR images, was larger than 33 mm in diameter, and had
a heterogeneous signal intensity on T1-weighted MR images. Signs that had the
greatest specificity for malignancy included tumor necrosis, bone or
neurovascular involvement, and mean diameter of more than 66 mm (Figs.
13A,13B
and
14A,14B,14C).
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Fig. 13B. —15-year-old girl with rhabdomyosarcoma of leg. Corresponding
contrast-enhanced MR image (641/16) shows nonenhancing area compatible with
necrosis. Bone invasion and necrosis are both specific for malignancy. Note
nodal involvement (arrows).
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Fig. 14B. —57-year-old woman with liposarcoma of thigh. Corresponding coronal
unenhanced (B) and contrast-enhanced (C) T1-weighted spin-echo
MR images (600/16) show adipose tissue within lesion, compatible with fat
differentiation. Enhancement in portions of tumor is extensive. Large size and
deep location with adipose differentiation suggest diagnosis of
liposarcoma.
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Fig. 14C. —57-year-old woman with liposarcoma of thigh. Corresponding coronal
unenhanced (B) and contrast-enhanced (C) T1-weighted spin-echo
MR images (600/16) show adipose tissue within lesion, compatible with fat
differentiation. Enhancement in portions of tumor is extensive. Large size and
deep location with adipose differentiation suggest diagnosis of
liposarcoma.
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Staging
Simply stated, the purpose of a staging system is to provide a standard
manner in which to readily communicate the state of a malignancy, defining the
extent of the local and distant tumor. Local staging is best accomplished
using MR imaging, which can accurately depict the anatomic spaces
(compartments) involved by the tumor
[62]. A review of compartment
anatomy is beyond the scope of this article, but accurate staging is critical
for optimum patient care and planning of percutaneous biopsy. It must be
emphasized that coordination with the orthopedic surgeon who will perform the
definitive surgery is essential before biopsy.
Summary
MR imaging is the preferred modality for the evaluation of a soft-tissue
mass after radiography. The radiologic appearance of certain soft-tissue
tumors or tumorlike processes, such as myositis ossificans, fatty tumors,
hemangiomas, peripheral nerve sheath tumors, pigmented villonodular synovitis,
and certain hematomas may be sufficiently unique to allow a strong presumptive
radiologic diagnosis. It must be emphasized that MR imaging cannot reliably
distinguish between benign and malignant lesions and when radiologic
evaluation is nonspecific, one is ill-advised to suggest that a lesion is
benign or malignant solely on its MR imaging appearance. When a specific
diagnosis is not possible, knowledge of tumor prevalence by location and age,
with appropriate clinical history and radiologic features, can be used to
establish a suitably ordered differential diagnosis.
References
-
Weekes RG, McLeod RA, Reiman HM, Pritchard DJ. CT of soft-tissue
neoplasms. AJR 1985;144
: 35-360
-
Sundaram M, McGuire MH, Herbold DR. Magnetic resonance imaging of
soft tissue masses: an evaluation of fifty-three histologically proven tumors.
Magn Reson Imaging
1988;6:237
-248[Medline]
-
Petasnick JP, Turner DA, Charters JR, Gitelis S, Zacharias CE.
Soft-tissue masses of the locomotor system: comparison of MR imaging with CT.
Radiology
1986;160:125
-133[Abstract/Free Full Text]
-
Totty WG, Murphy WA, Lee JKT. Soft-tissue tumors: MR imaging.
Radiology
1986;160:135
-141[Abstract/Free Full Text]
-
Kransdorf MJ, Jelinek JS, Moser RP, et al. Soft-tissue masses:
diagnosis using MR imaging. AJR
1989;153:541
-547[Abstract/Free Full Text]
-
Berquist TH, Ehman RL, King BF, Hodgman CG, Ilstrup DM. Value of MR
imaging in differentiating benign from malignant soft-tissue masses: study of
95 lesions. AJR
1990;155:1251
-1255[Abstract/Free Full Text]
-
Crim JR, Seeger LL, Yao L, Chandnani V, Eckardt JJ. Diagnosis of
soft-tissue masses with MR imaging: can benign masses be differentiated from
malignant ones? Radiology
1992;185:581
-586[Abstract/Free Full Text]
-
Panicek DM, Gatsonis C, Rosenthal DI, et al. CT and MR imaging in
the local staging of primary malignant musculoskeletal neoplasms: report of
the Radiology Diagnostic Oncology Group. Radiology
1997;202:237
-246[Abstract/Free Full Text]
-
Enzinger FM, Weiss SW. General considerations. In: Enzinger FM,
Weiss SW, eds. Soft tissue tumors, 3rd ed. St. Louis:
Mosby—Year Book, 1995:1
-16
-
Angervall L, Kindblom LG. Principles for pathologic—anatomic
diagnosis and classification of soft-tissue sarcomas. Clin
Orthop 1993;289:9
-18
-
Baldursson G, Agnarsson BA, Benediktsdottir KR, Hrafnkelsson J.
Soft tissue sarcomas in Iceland 1955-1988. Acta Oncol
1991;30:563
-568[Medline]
-
Mettlin C, Priore R, Rao U, Gamble D, Lane W, Murphy GP. Results of
the national soft-tissue sarcoma registry: analysis of survival and prognostic
factors. J Surg Oncol
1982;19:224
-227[Medline]
-
Kransdorf MJ. Malignant soft-tissue tumors in a large referral
population: distribution of diagnoses by age, sex, and location.
AJR
1995;164:129
-134[Abstract/Free Full Text]
-
Kransdorf MJ. Benign soft-tissue tumors in a large referral
population: distribution of diagnoses by age, sex, and location.
AJR
1995;164:395
-402[Abstract/Free Full Text]
-
Hajdu SI. Soft tissue sarcomas: classification and natural history.
CA Cancer J Clin
1981;31:271
-280[Free Full Text]
-
du Boulay CEH. Immunohistochemistry of soft tissue tumors: a
review. J Pathol
1985;146:77
-94[Medline]
-
Osment LS. Cutaneous lipomas and lipomatosis. Surg
Gynecol Obstet
1968;127:129
-132[Medline]
-
Leffert RD. Lipomas of the upper extremity. J Bone Joint
Surg Am 1972;54-A:1262
-1266[Abstract/Free Full Text]
-
Rydholm A, Berg NO. Size, site and clinical incidence of lipoma:
factors in the differential diagnosis of lipoma and sarcoma. Acta
Orthop Scand 1983;54:929
-934[Medline]
-
Disler DG, Alexander AA, Mankin HJ, O'Connell JX, Rosenberg AE,
Rosenthal DI. Multicentric fibromatosis with metaphyseal dysplasia.
Radiology
1993;187:489
-492[Abstract/Free Full Text]
-
Rock MG, Pritchard DJ, Reiman HM, Soule EH, Brewster RC.
Extraabdominal desmoid tumors. J Bone Joint Surg Am
1984;66-A:1369
-1374[Abstract/Free Full Text]
-
Sundaram M, Duffrin H, McGuire MH, Vas W. Synchronous multicentric
desmoid tumors (aggressive fibromatosis) of the extremities.
Skeletal Radiol
1988;17:16
-19[Medline]
-
Moulopoulos LA, Granfield CAJ, Dimopoulos MA, Kim EE, Alexanian R,
Libshitz HI. Extraosseous multiple myeloma: imaging features.
AJR
1993;161:1083
-1087[Abstract/Free Full Text]
-
Patten RM, Shuman WP, Teefey S. Subcutaneous metastases from
malignant melanoma: prevalence and findings on CT. AJR
1989;152:1009
-1012[Abstract/Free Full Text]
-
Sundaram M, McDonald DJ, Merenda G. Intramuscular myxoma: a rare
but important association with fibrous dysplasia of bone.
AJR
1989;153:107
-108[Free Full Text]
-
Wirth WA, Leavitt D, Enzinger FM. Multiple intramuscular myxomas:
another extraskeletal manifestation of fibrous dysplasia.
Cancer
1971;27:321
-340
-
Madewell JE, Moser RP. Radiologic evaluation of soft tissue tumors.
In: Enzinger FM, Weiss SW, eds. Soft tissue tumors,
3rd ed. St. Louis: Mosby—Year Book, 1995:39
-88
-
Dalinka MK, Zlatkin MD, Chao P, Kricum ME, Kressel HY. The use of
magnetic resonance imaging in the evaluation of bone and soft tissue tumors.
Radiol Clin North Am
1990;28:461
-470[Medline]
-
Pettersson H, Gillespy T, Hamlin DJ, et al. Primary musculoskeletal
tumors: examination with MR imaging compared with conventional modalities.
Radiology
1987;164:237
-241[Abstract/Free Full Text]
-
Tehranzadeh J, Mnaymneh W, Ghavam C, Morillo G, Murphy BJ.
Comparison of CT and MR imaging in musculoskeletal neoplasms. J
Comput Assist Tomogr
1989;13:466
-472[Medline]
-
Aisen AM, Martel W, Braunstein EM, McMillin KI, Phillips WA, Kling
TF. MRI and CT evaluation of primary bone and soft-tissue tumors.
AJR
1986;146:749
-756[Abstract/Free Full Text]
-
Chang AE, Matory YL, Dwyer AJ, et al. Magnetic resonance imaging
versus computed tomography in the evaluation of soft tissue tumors of the
extremities. Ann Surg
1987;205:340
-348[Medline]
-
Demas BE, Heelan RT, Lane J, Marcove R, Hajdu S, Brennan MF.
Soft-tissue sarcomas of the extremities: comparison of MR and CT in
determining the extent of disease. AJR
1988;150:615
-620[Abstract/Free Full Text]
-
Hudson TM, Hamlin DJ, Enneking MD, Pettersson H. Magnetic resonance
imaging of bone and soft-tissue tumors: early experience in 31 patients
compared with computed tomography. Skeletal Radiol
1985;13:134
-146[Medline]
-
Weekes RG, Berquist TH, McLeod RA, Zimmer WD. Magnetic resonance
imaging of soft-tissue tumors: comparison with computed tomography.
Magn Reson Imaging
1985;3:345
-352[Medline]
-
Bloem JL, Taminiau AHM, Eulderink F, Hermans J, Pauwels EK.
Radiologic staging of primary bone sarcoma: MR imaging, scintigraphy,
angiography, and CT correlated with pathologic examination.
Radiology
1988;169:805
-810[Abstract/Free Full Text]
-
Rubin DA, Kneeland JB. MR imaging of the musculoskeletal system:
technical considerations for enhancing image quality and diagnostic yield.
AJR
1994;163:1155
-1163[Abstract/Free Full Text]
-
Mirowitz SA. Fast scanning and fat-supression MR imaging of
musculoskeletal disorders. AJR
1993;161:1147
-1157[Abstract/Free Full Text]
-
Fujimoto H, Murakami K, Ichikawa T, et al. MRI of soft-tissue
lesions: opposed-phase T2*-weighted gradient-echo images.
J Comput Assist Tomogr
1993;17:418
-424[Medline]
-
Shuman WP, Baron RL, Peters MJ, Tazioli PK. Comparison of STIR and
spin-echo MR imaging at 1.5 T in 90 lesions of the chest, liver, and pelvis.
AJR
1989;152:853
-859[Abstract/Free Full Text]
-
Dwyer AJ, Frank JA, Sank VJ, Reinig JW, Hickey AM, Doppman JL.
Short-Ti inversion-recovery pulse sequence: analysis and initial experience in
cancer imaging. Radiology
1988;168:827
-836[Abstract/Free Full Text]
-
Beltran J, Chandnani V, McGhee RA, Kursungoglu-Brahme S.
Gadopentetate dimeglumine—enhanced MR imaging of the musculoskeletal
system. AJR
1991;156:457
-466[Abstract/Free Full Text]
-
Verstraete KL, De Deene Y, Roels H, Dierick A, Uyttendaele D,
Kunnen M. Benign and malignant musculoskeletal lesions: dynamic
contrast-enhanced MR imaging-parametric "first pass" images depict
tissue vascularization and perfusion. Radiology
1994;192:835
-843[Abstract/Free Full Text]
-
McDonald DJ. Limb-salvage surgery for treatment of sarcomas of the
extremities. AJR
1994;163:509
-513[Abstract/Free Full Text]
-
Benedikt RA, Jelinek JS, Kransdorf MJ, Moser RP, Berrey BH. MR
imaging of soft-tissue masses: role of gadopentetate dimeglumine. J
Magn Reson Imaging
1994;4:485
-490[Medline]
-
Takebayashi S, Sugiyama M, Nagase M, Matsubara S. Severe adverse
reaction to IV gadopentetate dimeglumine. AJR
1993;160:659[Medline]
-
Tardy B, Guy C, Barral G, Page Y, Ollagnier M, Bertrand C.
Anaphylactic shock induced by intravenous gadopentetate dimeglumine.
Lancet
1992;339:494[Medline]
-
Tisher S, Hoffman JC. Anaphylactoid reaction to IV gadopentetate
dimeglumine. AJNR
1990;174:17
-23
-
Omohundro JE, Elderbrook MK, Ringer TV. Laryngospasm after
administration of gadopentetate dimeglumine. J Magn Reson
Imaging 1992;2:729
-730[Medline]
-
Shellock FG, Hahn HP, Mink JH, Itskovich E. Adverse reaction to
intravenous gadoteridol. Radiology
1993;189:151
-152[Abstract/Free Full Text]
-
Jordan RM, Mintz RD. Fatal reaction to gadopentetate dimeglumine.
AJR
1995;164:743
-744[Free Full Text]
-
Harkens KL, Moore TE, Yuh WTC, et al. Gadolinium-enhanced MRI of
soft-tissue masses. Australas Radiol
1993;37:30
-34[Medline]
-
Seeger LL, Widoff BE, Bassett LW, Rosen G, Eckardt JJ. Preoperative
evaluation of osteosarcoma: value of gadopentetate dimeglumine—enhanced
MR imaging. AJR
1991;157:347
-351[Abstract/Free Full Text]
-
Kransdorf MJ, Murphey MD. The use of gadolinium in the MR
evaluation of soft tissue tumors. Semin Ultrasound CT
MR 1997;18:251
-268[Medline]
-
Myhre-Jensen O. A consecutive 7-year series of 1331 benign
Top
Introduction
General Concepts
