Download Magnetic Resonance Imaging of Soft

Magnetic Resonance Imaging of Soft-Tissue Masses
Eric A. Walker, MD,*,† Albert J. Song, MD,‡ and Mark D. Murphey, MD*,‡
B
enign soft-tissue lesions outnumber their malignant
counterparts by a factor of 100:1,1 but many are small
and superficial and do not lead to imaging or biopsy. Softtissue sarcomas are estimated to represent 1% of malignant
tumors.2,3 The incidence of soft-tissue sarcoma revealed a
rate of 2.7 per 100,000.4 The incidence of soft-tissue sarcoma
increases significantly with age, and in patients 80 and older
is 8 per 100,000.5 Magnetic resonance (MR) imaging (MRI) is
the favored modality for evaluation of soft-tissue tumors and
tumor-like conditions. It is valuable for lesion detection, diagnosis, and staging. Although advances in thin-section computed tomography (CT) have recently allowed detailed multiplanar reconstructions, MRI allows superior soft-tissue
contrast without radiation exposure.
When planning an MRI study for evaluation of a soft-tissue
lesion at least 2 orthogonal planes should be obtained. In our
experience lesions are typically best evaluated in the axial
plane and this is usually the most familiar to radiologists. The
secondary plane of imaging for an anterior or posterior lesion
is typically the sagittal plane. Coronal sequences are optimal
for evaluation of medial or lateral masses.
T1-weighted (T1W) and T2-weighted (T2W) sequences
should be obtain as most soft-tissue lesions have been described with their spin-echo (SE) T1W and T2W signal characteristics. Fast SE sequences in place of SE sequences can
reduce scanning time and patient motion artifacts. Gradientecho sequences can be useful in demonstrating hemosiderin
with “blooming,” but also is subject to artifact caused by
metal, hemorrhage, and air. Short tau inversion recovery and
T2 fat saturation images increase sensitivity to abnormal tissue containing increased water content. However, these techniques also reduce information concerning various tissue
consistencies and should be used in the secondary, not the
*Departments of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD.
†Department of Radiology, Milton S. Hershey Medical Center, Hershey, PA.
‡Department of Radiologic Pathology, Armed Forces Institute of Pathology,
Washington, DC.
The opinions or assertions contained herein are the private views of the
authors and are not to be construed as official nor as reflecting the views
of the Departments of the Army, Navy, or Defense.
Address reprint requests to Eric A. Walker, MD, Department of Radiology,
Milton S. Hershey Medical Center, 266 Townhouse, Hershey, PA 17033.
E-mail: [email protected]
0037-198X/10/$-see front matter © 2010 Elsevier Inc. All rights reserved.
doi:10.1053/j.ro.2009.12.004
primary plane of imaging. The smallest diagnostic field of
view is preferable when evaluating these lesions.
The use of intravenous contrast in lesion evaluation is controversial, but can be useful. Gadolinium contrast agents increase the T1W signal intensity of many soft-tissue tumors,
allowing distinction between tumor and muscle or tumor
and edema, but the surrounding area of edema may enhance
as well. Information about tumor vascularity is also obtained.6,7 Contrast may allow distinction of small tumor nodules in a predominantly cystic lesion or a “spontaneous
hematoma.” Malignant lesions may show increased neovascularity at their periphery and high interstitial pressure at
their center leading to a high rim-to-center differential enhancement ratio.8 The use of intravenous contrast also increases the cost and length of time of the examination. Severe
reactions to gadolinium and nephrogenic systemic fibrosis
are rare, but they do occur.
Many investigators have evaluated if dynamic enhancement with gadolinium can help differentiate benign from
malignant soft-tissue lesions.6,9,10 High soft-tissue vascularity
and perfusion demonstrates an increased rate of enhancement. Malignant lesions usually reveal greater enhancement
and an increased rate of enhancement.11 One difficulty with
dynamic contrast-enhanced imaging is a significant overlap
between the rate of enhancement of benign and malignant
lesions.12 We do not routinely perform dynamic enhancement sequences, at our institutions.
Although MR imaging is excellent at delineating soft-tissue
lesions, a correct histologic diagnosis based on imaging studies alone is seen in only 25%-30% of cases.13-15 However, we
believe that this percentage continues to increase and ultimately will approach the 75%-90% range.16 Most cases are
nonspecific with intermediate T1 and intermediate to high
T2 signal. A specific diagnosis should be obtained by using a
combination of lesion signal intensity, location, growth pattern, and other unique characteristics of the lesion. Unless a
specific diagnosis can be determined, the lesion should be
considered indeterminate and an appropriate biopsy path
should be discussed with the orthopedic oncologist or treating surgeon. A poorly selected biopsy path may violate compartments needed for reconstruction and an amputation may
result.
Some authors have proposed that criteria such as tumor
margins, homogenous vs. heterogeneous signal intensity,
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and lesion size can distinguish a benign from malignant lesion in greater than 90% of cases.13 Other reports note malignant lesions can appear smoothly marginated and homogenous and MR appearance cannot accurately separate benign
and malignant processes.6,14,15,17-19 Malignancies tend to
grow pushing against adjacent structures and form a pseudocapsule as they enlarge. The pseudocapsule consists of compressed fibrous connective tissue, normal tissue, vascularization, and inflammatory reaction. Malignant lesions tend to
respect anatomic compartments and fascial borders until late
in their course.20 Heterogeneous signal may represent mixed
tissue types, necrosis, or hemorrhage within the lesion. Only
a minority (5%) of benign soft-tissue tumors are greater than
5 cm in diameter and about 1% of benign lesions are deep.5,21
In general, well-defined, smooth margins, homogenous signal intensity, and small size are seen with benign lesions and
irregular margins, heterogeneous signal and large size are
indications of malignant lesions. Unless a specific diagnosis
can be determined, a lesion should be considered indeterminate and an appropriate biopsy path should be discussed
with the orthopedic oncologist or treating surgeon.
An intracompartmental lesion is one which has not
crossed any natural anatomic boundaries, such as cortical
bone, articular cartilage, joint capsule, fascial septa, tendon
or ligament. Identification of invasion of other compartments
is important for tumor staging and is often apparent on MR.
More aggressive lesions more readily invade surrounding tissues and cross anatomic boundaries. Vascular channels and
poorly planned biopsy paths may assist in invasion of adjacent compartments.
Lesion location is important for restricting the differential
diagnosis. MRI with its excellent soft-tissue contrast is the
most valuable modality for determining location. Lesion location includes intramuscular, intermuscular, subcutaneous,
and intra-articular/periarticular. Multifocal or an extensive
lesion also limits diagnostic considerations to include angiomatous lesions, neurofibromatosis, fibromatosis, lipomatosis, myxoma (Mazabraud syndrome), metastases, or lymphoma. The anatomic location may also aid in diagnosis,
such as elastofibroma occurring deep to the scapular tip.
Lesions discussed in the following paragraphs are included
for their frequency, specific location, or unique imaging characteristics allowing a specific diagnosis or a limited differential diagnosis. For the common but nonspecific lesions, a
reasonable differential diagnosis requires knowledge of lesion prevalence, anatomic distribution, and age range. Lesions that predominantly affect pediatric patients are not discussed in this article.
Fibromatoses
Fibromatosis refers to a family of benign fibrous proliferations. The soft-tissue fibromatoses may be divided into superficial (fascial) and deep (musculoaponeurotic) lesions.
These are benign lesions, but deep-seated lesions can display
aggressive local biological behavior with rapid growth and
frequent recurrence (19%-77% in the first 2 years), but no
E.A. Walker, A.J. Song, and M.D. Murphey
metastases.22 In some cases, amputation may be necessary or
patient demise may result from involvement of crucial structures.
Superficial Fibromatosis—
Palmar and Plantar Fibroma
Palmar fibromatosis (Dupuytren disease) is the most common of the superficial fibromatoses, affecting 1%-2% of the
population.23,24 These lesions occur 3-4 times more commonly in men and most frequently in patients aged more
than 65 years (up to 20%). Bilateral lesions are present in up
to 50% of cases. The lesions are painless, slow-growing palmar nodules, which may cause a flexion contracture, affecting the flexor tendons of the fourth and fifth fingers.25 MR
typically shows multiple nodular or cordlike superficial softtissue masses, which involve the aponeurosis of the volar
aspect of the hand, extending superficially in parallel to the
flexor tendons. Lesion signal intensity on T1W and T2W
images is low (similar to tendon) reflecting hypocellularity
and dense collagen. MR can be helpful for surgical planning
as more immature lesions demonstrate intermediate to
higher signal on T1W and T2W images, reflecting the high
cellularity, and have a higher local recurrence rate after local
resection. Mature lesions with low T1W and T2W signal
intensity are less likely to locally recur.26-28 Lesions show
diffuse enhancement, which is more prominent in lesions
with higher cellularity.
Plantar fibromatosis (Ledderhose disease) occurs less frequently than the palmar lesion, with an incidence of 0.23%.29
In our experience, Ledderhose disease is more frequently
imaged in our institutions than Dupuytren disease. It presents most frequently in patients aged 30-50 years. Men are
affected twice as often as females, and lesions are bilateral in
20%-50% of cases. Associated palmar fibromatosis may be
present in 10%-65% of cases.30 Patients present with one or
more subcutaneous nodules, which most frequently (78%)
are found in the medial aspect of the plantar arch and can
extend to the skin or deep structures of the foot. The lesions
are typically painless, but may have pain with prolonged
standing or walking. With MR imaging, superficial lesions
along the deep plantar aponeurosis typically blend with the
adjacent plantar musculature. Lesions typically show heterogeneous signal (92%), which is isointense to hypointense to
skeletal muscle on T1W and T2W sequences (Fig. 1). The
degree of enhancement has been reported as marked in approximately 67% and mild in 33% of cases.31 Linear tails of
extension (“fascial tail sign”) along the aponeurosis are frequent and best seen following contrast.23,26
Deep Fibromatosis
The World Heath Organization in April 2002 designated the
term desmoid-type fibromatosis for all deep fibromatoses.
Desmoid tumor is a descriptive term from the Greek word
desmos meaning “band” or “tendon.”23 Deep, or musculoaponeurotic, fibromatoses include extra-abdominal fibromatosis or aggressive fibromatosis (49%), abdominal fibromatosis (43%), and intra-abdominal fibromatosis (8%).
MRI of soft-tissue masses
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Figure 1 Plantar Fibromatosis. A 26-year-old woman presenting with a bilateral “lump” on the bottom of both feet with
increasing size and irritation while walking since 1 year. MR images demonstrate a well-defined mass (arrows) in the
medial aspect of the plantar aponeurosis. (A) Sagittal T1-weighted (TR/TE; 500/18) sequence with lesion signal
intensity similar to skeletal muscle, mild heterogeneity, and linear extension along the aponeurosis. This mass is
hyperintense and heterogeneous on (B) short-axis STIR (TR/TE; 1500/12) and (C) short-axis fat-suppressed T1weighted post-contrast (TR/TE; 500/17) images.
Intra-abdominal fibromatosis is the type most commonly associated with Gardner syndrome.32,33 Abdominal fibromatosis tends to occur in women during or immediately after
pregnancy or with oral contraceptive use. Estrogen appears
to be a stimulatory growth factor.34 The most common locations of extra-abdominal fibromatosis in a large series by the
AFIP are the shoulder/upper arm (28%), chest wall/paraspinal (17%), and thigh (12%). Desmoid-type fibromatosis is
most common in the second and third decades with a peak
incidence between the ages 25 and 35.23,35 Two to 4 people
per million are affected with this lesion and less than 5% are
seen in the pediatric age group.24 There is a female predilection in younger patients, which equalizes in older patients.
Desmoid type fibromatosis presents as a deep, firm, and
poorly circumscribed soft-tissue mass, which is usually slow
growing and painless. Lesions may be multicentric in 10%15% of cases and may insinuate about vital neurovascular
structures.23 A skeletal dysplasia has been reported in 19% of
patients with multicentric desmoid-type fibromatosis. MR is
the optimal modality for evaluation of deep fibromatosis, due
to its superior soft-tissue contrast. Lesions are usually centered intermuscularly with a rim of fat (split fat sign). Invasion of the surrounding muscle is frequent. The lesions are
equally likely to be well defined or have irregular infiltrative
margins.36,37 Linear extension along fascial planes (fascial tail
sign) is a common manifestation (80% of cases).37 The signal
intensity of desmoid-type fibromatosis is quite variable reflecting the amount of collagen and degree of cellularity of the
lesion. Immature lesions with marked cellularity reveal
higher signal intensity on long repetition time (TR) images. In
our experience, these lesions are also associated with a higher
local recurrence rate after resection. More mature hypocellular lesions with abundant collagen reveal lower signal intensity on T1W and T2W sequences.37,38 Large studies of
patients have shown the most common appearance of desmoid-type fibromatosis on MR is intermediate signal intensity on both T1W (similar to muscle) (83%-95% of cases) and
T2W images (lower than fat but higher than muscle on images without fat suppression) (46%-77% of cases).36,37,39-41
T1W and T2W sequences commonly show significant heterogeneity (Fig. 2). Postcontrast images reveal moderate to
marked heterogeneous enhancement with less than 10% of
lesions lacking significant enhancement.42 Although low-signal T2W areas are not specific for desmoid-type fibromatosis
(See suggested differential later in the text) the bandlike morphology (low-signal bands are seen in 62%-91% of cases) of
low signal intensity suggests the diagnosis. These low-signal
bands are best observed on T2W or T1W fat-saturated images post contrast (the hypocellular collagenized bands do
not enhance).
Differential diagnosis for soft-tissue lesions with areas of
low signal intensity on T1W and T2W sequences includes
E.A. Walker, A.J. Song, and M.D. Murphey
280
Figure 2 Deep Fibromatosis. Deep fibromatosis in a 35-year-old woman with a slowly enlarging shoulder mass for 10
months. (A) Axial T1-weighted (TR/TE; 516.664/14), (B) STIR (TR/TE; 4950/19.872), and (C) T1 postcontrast,
fat-suppressed (TR/TE; 11.92/766.664) MR images demonstrate a heterogeneous mass lying deep to the latissimus
dorsi muscle with intermediate T1 and high T2 signal, with diffuse enhancement. Fascial linear extension (white arrow)
can be seen medially. Areas of bandlike nonenhancing low T1 and T2 signal (white arrowheads) correspond with
hypocellular areas of collagen. The bandlike morphology (open arrow) are better depicted on the (D) sagittal T1weighted postcontrast fat-suppressed (TR/TE; 12.936/566.664) MR image.
desmoid-type fibromatosis, densely calcified masses, pigmented villonodular synovitis/giant cell tumor of tendon
sheath (GCTTS), granular cell tumor, and malignant fibrous
histiocytoma (MFH)/fibrosarcoma.
Elastofibroma
Elastofibroma dorsi is a slow-growing myofibroblastic
pseudotumor and likely represents a reactive rather than
neoplastic process.23,43 It is found between the inferior scapula tip and the chest wall in 95%-99% of cases.44 The etiology
is thought to be repetitive mechanical friction between the
chest wall and scapular tip. These lesions were found in 24%
of women and 11% of men in an autopsy series of patients
greater than 55 years of age.45 Most patients are older adults
with peak incidence in the sixth and seventh decades. Lesions may be bilateral in 10%-66% of cases.23 Most patients
are asymptomatic. The most common symptom is stiffness,
present in 25% of cases. There is a 2:1 female predominance.44 A key imaging feature is entrapped fat within the
lesion, which is well seen with CT or MR. T1W images show
a crescentic, heterogeneous lesion with signal similar to adjacent skeletal muscle and streaks of high signal representing
trapped fat (Fig. 3). Intermediate and heterogeneous signal is
also present on T2W sequences and heterogeneous enhancement is common. Characteristic location with demonstration
of entrapped fat is pathognomonic of elastofibroma. A differential diagnosis for lesions that are relatively hypocellular
and contain abundant collagen would include elastofibroma,
extra-abdominal desmoid-type fibromatosis, neurofibroma,
and MFH/fibrosarcoma.
MRI of soft-tissue masses
281
sequences it is most often high signal intensity (greater than
subcutaneous fat), but may demonstrate intermediate signal
intensity.50 Lesions are frequently homogeneous on T1W sequences and heterogeneous on longer TR acquisitions.52
These lesions, as well as ancient schwannomas, are one of the
few benign lesions that may demonstrate central necrosis,
which may contribute to lesion heterogeneity.23 Contrast enhancement was present in all cases in a series of 8 patients
with a diffuse enhancement pattern in 67% of cases and
peripheral enhancement in approximately 25%.50 Linear extension along the fascia (“fascial tail sign”) may suggest the
diagnosis, and mild surrounding edema may also be
present.23
Dermatofibrosarcoma
Protuberans
Figure 3 Elastofibroma. A 53-year-old woman with slowly growing
mass at her right scapula. (A) Axial T1-weighted (TR/TE; 500/20)
and (B) T2-weighted (TR/TE; 3500/96) without fat suppression
demonstrate a lenticular mass (white arrow) with signal similar to
skeletal muscle and hyperintense linear streaks of entrapped fat.
Nodular Fasciitis
Nodular fasciitis is a benign soft-tissue lesion of unknown
cause composed of proliferating fibroblasts. The lesion may
grow rapidly and show high mitotic activity, simulating a
more aggressive lesion. It is the most common benign tumor
or tumorlike condition of fibrous tissue. It typically affects
patients aged 20-40 years with no sex predilection.37,46,47
Lesions typically present as a rapidly growing painless mass,
although mild pain or tenderness may be present in approximately 50% of cases.48 The upper extremity is involved in
46% of cases, particularly the volar forearm. Nodular fasciitis
has 3 common locations: subcutaneous, fascial, and intramuscular. Lesions are subcutaneous between 3 and 10 times
more frequently than other sites. The fascial form is the second most common and least frequent is the intramuscular
type. The deeper intramuscular form is usually larger and is
the most likely to be mistaken for sarcoma.47,49,50 Most lesions show a maximal diameter of 2 cm or less.51 On T1W
images, nodular fasciitis has a signal intensity similar to or
slightly higher than skeletal muscle (Fig. 4).49 With T2W
Dermatofibrosarcoma protuberans constitutes approximately 6% of soft-tissue sarcomas.53 The lesion is an intermediate grade malignancy, but fibrosarcomatous transformation may occur in 17%-27%.54-56 Dermatofibrosarcoma
protuberans most commonly occurs in the third to fifth decades of life.57 Males are affected more frequently than females. The lesion presents as a slowly growing reddish brown
to bluish superficial skin nodule. Large lesions may become
painful.58 The trunk is affected in up to 50% of cases followed
up in frequency by the proximal upper and lower extremities.59 MR demonstrates a lesion involving the skin and subcutaneous adipose tissue with a nodular or lobular architecture. The signal characteristics of the lesion are nonspecific,
with signal similar to skeletal muscle on T1W images and
similar to or greater than fat on T2W sequences (Fig. 5).
Moderate enhancement is seen after gadolinium enhancement. The lesion may show heterogeneous signal if hemorrhage or necrosis are present. Satellite nodules in the adjacent
subcutaneous tissue may be present, and linear extensions
along the skin are also often detected.
A differential diagnosis for a subcutaneous lesion would
include cutaneous MFH/fibrosarcoma, dermatofibrosarcoma
protuberans, skin adnexal/appendage tumor, and metastasis.
MFH/Fibrosarcoma
The World Heath Organization significantly reorganized the
nomenclature of malignant fibrous lesions of the soft tissue in
April 2002. The term MFH has been replaced by undifferentiated high-grade pleomorphic sarcoma. Giant cell MFH and
inflammatory MFH are now called undifferentiated highgrade pleomorphic sarcoma with giant cells and undifferentiated high-grade pleomorphic sarcoma with prominent
inflammation. Myxoid MFH is now called myxofibrosarcoma.60 Having said this, most of our colleagues continue to use
the term MFH either out of familiarity or because of the
cumbersome new designations.
Fibrosarcoma is a low-to-intermediate grade malignant tumor of fibroblasts composing 5% of soft-tissue sarcomas.23,61
It occurs primarily in adults with 60% of patients aged 40-70
E.A. Walker, A.J. Song, and M.D. Murphey
282
Figure 4 Nodular Fasciitis. Nodular fasciitis in a man aged 43 years who presented with a palpable hand mass. (A)
Sagittal T1-weighted (TR/TE; 730/10) MR image demonstrates a subcutaneous soft-tissue mass, which is isointense to
mildly hyperintense compared with muscle. This mass is hyperintense on (B) Sagittal STIR (TR/TE; 3985/70) MR image
with a small area of central cystic change (white arrow) representing necrosis. Also, note the mild surrounding edema.
There is relatively homogenous diffuse enhancement on (C) sagittal T1-weighted, postcontrast, fat-suppressed (TR/TE;
325/10) MR image. Mild linear fascial extension (“fascial tail sign,” white arrowhead) is demonstrated best on postcontrast imaging in this case.
years.62,63 There is a male predilection (61% of cases).64 It
most commonly involves the deep soft tissues of the
trunk.62,63,65 Patients usually present with a painless mass
slowly enlarging over several months duration and 30% of
patients may have dull aching pain or tenderness.62
MFH/undifferentiated high-grade pleomorphic sarcoma is
a high-grade lesion of fibroblasts, myofibroblasts, or undifferentiated mesenchymal cells.61 Subtypes include storiform
and/or pleomorphic (50%-60%), myxoid (25%), giant cell
(5%-10%), and inflammatory (⬍5%) types.60 MFH is the
most common soft-tissue sarcoma of adults accounting for
20%-30% of soft-tissue sarcomas and is the most frequent
post radiation sarcoma. Peak incidence is in the fifth decade.
There is a male predilection (70% of lesions). Patients usually
present with an enlarging, painless soft-tissue mass with an
average size of 5-10 cm.61 Most common locations are the
lower extremity (50%), upper extremity (25%), and retroperitoneum (15%). Lesions are most commonly in a deep
intramuscular location (70%) with 5%-10% being subcutaneous.66
Imaging features of adult fibrosarcoma and MFH are indistinguishable and described together. Lesions are typically
seen as an intramuscular mass with intermediate intensity on
T1W and intermediate-to-high (greater than fat) signal on
T2W images (Fig. 6). The lesions are heterogeneous on all
pulse sequences reflecting variable amounts of collagen,
myxoid tissue, necrosis, and hemorrhage. Low signal regions
on T2W sequences presumably represent areas of high collagen content. The lesion margin is usually well defined because of a fibrous pseudocapsule. MFH and/or fibrosarcoma
typically show enhancement, which may be heterogeneous if
areas of necrosis or hemorrhage are present. Destruction of
adjacent cortical bone may be present, similar to synovial
sarcoma.66-69 When there is history of a spontaneous hematoma, be suspicious of an underlying neoplasm (particularly
MFH or synovial sarcoma) and look for solid or nodular
enhancing components, usually in the periphery. Hematomas reveal thick non-nodular walls often containing hemosiderin. Edema is often seen surrounding a hematoma secondary to irritation from the blood, but a tumor that
hemorrhages typically retains the blood within the pseudocapsule and edema is not a prominent feature.60,66
Lipoma
Lipoma is the most common soft-tissue neoplasm and represents about 50% of all soft-tissue tumors. The incidence is
approximately 2.1 per 100 people.21,70 Lipoma is more common than liposarcoma by a ratio of 100:1.21,71,72
Most lipomas are discrete masses categorized by anatomic
location as superficial (subcutaneous) or deep. Deep lipomas
are much less common and account for approximately 1% of
lipomas.73
Superficial lipoma typically present in the fifth and sixth
decades with 80% of lesions in patients aged 26-65 years.72
Both males and females have been reported as more commonly affected, but there is no clear-cut sex predilection.71,74,75 Lesions are typically small with 80% less than 5
cm.71 Superficial lipomas are most commonly located in the
trunk, shoulders, upper arm, and neck.71 Superficial lipoma
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283
with a painless, slow-growing soft-tissue mass.75 Lipomas
may be multiple in 5%-15% of patients.21,23,71,74 Weiss and
Goldblum separate deep lipomas from the intramuscular and
intermuscular lipomatous tumors,76 but we group all lipomatous lesions found beneath the superficial fascia together as
deep lipomas. Deep lipoma involving the extremity is most
commonly intramuscular.77
Lipomas most commonly demonstrate signal characteristics identical to subcutaneous fat on all pulse sequences with
high signal on T1W and T2W sequences with minimal (⬍2
mm) septations, however 28%-30% may have thick septa or
nodularity similar to liposarcoma (Fig. 7).78 Intramuscular
lipomas may have irregular margins, which interdigitate with
the adjacent skeletal muscle referred to as “infiltrating lipoma.” There should be no significant enhancement of the
lesion after contrast administration.23
Differential diagnosis for a lipomatous lesion with mild
complexity includes lipoma, angiolipoma, myolipoma,
chondroid lipoma, lipoblastoma, spindle cell/pleomorphic
lipoma, hibernoma, and well-differentiated liposarcoma.
Liposarcoma
The World Heath Organization has reorganized the nomenclature of malignant lipomatous lesions of soft tissue in April
2002. Current subtypes of liposarcoma include well-differentiated liposarcoma, dedifferentiated liposarcoma, myxoid
liposarcoma, pleomorphic liposarcoma, and mixed-type liposarcoma. The previous lesion referred to as round cell
liposarcoma has been incorporated into the category of myxoid liposarcoma.60 Liposarcoma is the second most common
soft-tissue sarcoma after MFH.53 The estimated annual incidence is 2.5 per million population.79
Well-Differentiated Liposarcoma
Figure 5 DFSP Dermatofibrosarcoma protuberans (DFSP) in a
woman aged 32 years who presented with a slow-growing anterior
calf mass. (A) Sagittal T1-weighted (TR/TE; 600/22) MR image demonstrates a superficial subcutaneous protuberant soft tissue mass
arising from the skin of the anterior proximal lower leg. (B) Axial
proton density (TR/TE; 2083/30) MR image with fat saturation demonstrates linear extension along the skin (white arrows).
is often difficult to distinguish from the surrounding cutaneous tissue, particularly if the lesion is “nonencapsulated.”
Therefore, we prefer to place a fiducial marker over superficial lesions, position the patient so the lesion is not compressed, and compare the area to the contralateral side.
Deep lipomas (including the intramuscular and intermuscular lipomatous tumors) occur most commonly in patients
aged 20-60 years. Men are affected more frequently than
women, and lesions commonly affect the large muscles of the
lower extremity (45%), trunk (17%), and shoulder (12%).
Lipomas of the retroperitoneum are rare and a lipomatous
lesion in this location should be treated as a liposarcoma.53,72
The size range of lipoma is large and lesions can measure up
to 20 cm.21,71,72 Superficial and deep lipoma often present
Well-differentiated liposarcoma is a low-grade malignancy,
which recurs locally, but does not metastasize.78 It is the most
common subtype representing about 50% of all liposarcomas.79 There is an equal sex distribution. This lesion is not
seen in patients aged less than 10 years and the peak prevalence is in the sixth and seventh decades.78 Common lesion
locations include the lower extremities (50%), retroperitoneum (20%-33%), upper extremity (14%), and trunk
(12%).78,80 Retroperitoneal lesions have up to a 91% local
recurrence rate after resection. Lesions are most frequently
intramuscular, but they can occur in intermuscular and subcutaneous locations.78,81 With MR, well-differentiated liposarcoma is a mass composed of greater than 75% adipose
tissue, but with significant nonadipose components seen as
prominent thick septa and focal nodular regions usually less
than 2 cm in size (Fig. 8).82-86 Nodular nonlipomatous components of size greater than 3 cm suggest dedifferentiated
liposarcoma.78 Moderate to marked enhancement may be
seen in the nonlipomatous thickened septa and nodular areas.82 The lesion can be difficult to distinguish from lipoma.
Statistical factors favoring the diagnosis of well-differentiated
liposarcoma as opposed to lipoma include male sex, age
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284
Figure 6 Malignant fibrous histiocytoma (MFH). A 78-year-old black woman with a 4 – 6-week history of developing
thigh pain. (A) Sagittal T1-weighted and (B) T1-weighted postcontrast (TR/TE; 882/20) images demonstrate a large
thigh lesion with intramuscular location, cystic spaces (*) and hemorrhage (arrows). A large enhancing component is
noted at the dorsal aspect of the lesion (arrowheads). (C) T2-weighted fat saturation axial image (TR/TE; 3340/77)
demonstrates a heterogeneous lesion with multiple fluid levels (arrows).
greater than 66 years, lower percentage of fat in the lesion,
mineralization, size greater than 10 cm, greater than 2 mm
thick septa, or nonlipomatous nodular or globular foci.86
A differential diagnosis for soft-tissue lesions with components of relatively high signal intensity on T1W images may
include lipoma/well-differentiated liposarcoma, clear cell
sarcoma, melanotic melanoma, alveolar soft part sarcoma,
hemangioma, and subacute hemorrhage.
Myxoid Liposarcoma
Myxoid liposarcoma is an intermediate to high-grade malignancy depending on the percentage of round cell component. It is the second most common type of liposarcoma
representing 20%-50% of all liposarcomas.78,87-89 Myxoid liposarcomas account for 10% of all soft-tissue sarcomas.90
Peak prevalence is from the forth to fifth decades of life.
These lesions show no gender predilection78 and predominantly affect the lower extremity (75%-80% of cases), partic-
ularly the popliteal region and medial thigh. Extremity myxoid liposarcoma are most frequently intermuscular (70%80% of cases). Intramuscular and subcutaneous lesions are
less common.23,79,81,87-89 Clinical presentation of myxoid liposarcoma is that of a painless soft-tissue mass. On MR, these
lesions are typically large, well-defined, and multilobulated
(Fig. 9). Low signal intensity T1W images and marked high
signal T2W sequences reflect the high water content of the
lesion and these features may mimic a cyst. Adipose tissue
with high T1W signal typically constitutes a small volume of
the lesion (⬍10%) with a lacy or linear pattern. In our experience, approximately 90% of myxoid liposarcomas demonstrate fat on an MR image. Identification of the subtle fat
component may require comparison of T1W and T2W images in the same plane.78,91,92 Areas of intermediate T1W and
T2W signal may represent foci of a round cell component.
Myxoid liposarcoma may demonstrate enhancement in a peripheral nodular (61% of cases), central nodular (44% of
cases), or diffuse pattern (17% of cases) allowing differentia-
MRI of soft-tissue masses
285
Figure 7 Lipoma. A 62-year-old man with firm arm nodule for 10 years. (A) Axial T1-weighted (TR/TE; 500/15) image
demonstrates a well-encapsulated superficial (subcutaneous) lesion with signal isointense to subcutaneous fat beneath
the fiducial marker. A 38-year-old woman with slowly growing thigh mass for 6 years, now with pain on sitting.
(B) Axial T1-weighted (TR/TE; 633/11) and (C) T2-weighted fat saturation (TR/TE; 4540/72) images demonstrate an
intramuscular lesion (*) with signal identical to subcutaneous fat and thin fibrous septa. (D) Sagittal T1-weighted fat
saturation post (TR/TE; 631/11) demonstrates mild peripheral and septal enhancement. Note the similar septations
present in the adjacent subcutaneous fat.
tion from a cystic lesion. Round cell components may reveal
more marked diffuse enhancement.93
Differential diagnosis for a predominantly myxoid appearing soft-tissue lesion includes; myxoid liposarcoma, myxofibrosarcoma (or myxoid MFH), myxoid chondrosarcoma,
myxoma, ganglion cyst, synovial cyst/bursa, and peripheral
nerve sheath tumor.
Benign Peripheral
Nerve Sheath Tumor
Benign peripheral nerve sheath tumors (BPNSTs) are typically divided into schwannoma (neurilemoma) and neurofi-
broma.61 Both lesions contain cells closely related to the normal Schwann cell.
Schwannoma is slightly less common than neurofibroma
and comprises approximately 5% of all benign soft-tissue
tumors.72 Schwannoma is most commonly seen in patients
aged 20-50 years with an equal sex distribution.61,94 Schwannoma is usually a slow growing, nonaggressive lesion that
presents as a painless mass of size less than 5 cm. Pain may be
associated with larger lesions.23 Common sites of involvement include the cutaneous nerves of the head, neck, and
flexor surface of the extremities. Posterior mediastinum and
retroperitoneum are frequent locations for deep-seated lesions.61 Schwannoma may be plexiform or multiple in ap-
E.A. Walker, A.J. Song, and M.D. Murphey
286
Figure 8 Well-differentiated Liposarcoma. A 31-year-old woman with thigh pain status post fall. (A) Axial T1-weighted
(TR/TE; 500/12), (B) short tau inversion recovery (STIR) (TR/TE; 7688/18), (C) T1-weighted fat saturation postcontrast
(TR/TE; 468/12), and (D) sagittal T2-weighted (TR/TE; 4303/120) images demonstrate a high-signal intensity intramuscular lipomatous lesion with predominantly fatty signal, but thickened septa (arrows) and mild nodularity (arrowheads).
proximately 5% of cases.95 Lesions are sporadic in 90% of
cases; 3% occur with neurofibromatosis type 2 (NF2) and 2%
occur with schwannomatosis.96 The lesion is typically separable from the adjacent nerve after incising the epineurium
and nerve function is thus preserved after resection.23
Neurofibroma constitutes slightly more than 5% of benign
soft-tissue tumors.72 Neurofibroma is most commonly seen
in patients aged between 20 and 30 years and demonstrates
no sex predilection.61,94 Three types of neurofibroma are classically described, including localized (90%), diffuse, and
plexiform.23,72 Superficial cutaneous or deep-seated nerves
may be involved. Localized neurofibromas are usually a slow-
growing, painless masses measuring less than 5 cm. The diffuse type primarily affects children and young adults and
most frequently involves the subcutaneous tissue of the head
and neck and only 10% are associated with neurofibromatosis type 1 (NF1).23,72 Neurofibroma, unlike schwannoma,
cannot be separated from the nerve and complete excision of
the neoplasm requires sacrifice of the nerve.97
NF1 is seen in 1 of every 2500-3000 births.98,99 Males are
more commonly affected.61 NF1 demonstrates multiple local
neurofibromas and frequently plexiform lesions. These lesions occur anywhere in the body, both superficial and deep.
Plexiform neurofibroma represents diffuse involvement of a
MRI of soft-tissue masses
287
Figure 9 Myxoid liposarcoma. Myxoid liposarcoma in a 61-year-old man with a history of a slow-growing thigh mass
presented with worsening thigh pain. (A) T1-weighted (TR/TE; 566.664/10.776) MR image demonstrates septal areas
of high signal (white arrows). These regions correspond to areas of intermediate to low signal on both (B) proton density
T2-weighted, fat-suppressed (TR/TE; 3350/46.176), and (C) T1-weighted postcontrast fat-suppressed (TR/TE; 550/
10.776) images following the signal characteristics of fat, which is less than 5%-10% of the total tumor volume. The
pattern of enhancement can help differentiate myxomatous tumors from truly cystic lesions, which they can mimic on
T2-weighted/fluid-sensitive MR images.
long segment of nerve giving a “ropelike” or “bag of worms”
appearance and is pathognomonic of NF1. The incidence of
malignant transformation to malignant peripheral nerve
sheath tumor (MPNST) is between 2% and 29% in patients
with NF1.
On MR, the signal intensity of localized lesions is nonspecific and will be similar to or lower than muscle on T1weighted images and higher than fat on T2-weighted images
(Fig. 10). Recognition of the well-defined, fusiform shape of
the lesion can be very helpful to identify the lesion as BPNST,
which is caused by the tubular entering and exiting nerve.
With schwannoma, the entering and exiting nerve may be
eccentric to the soft-tissue mass. Diffuse neurofibroma may
show predominant low T2W signal, which may be related to
the high collagen content. Heterogeneity of BPNST is variable, particularly with hemorrhage, necrosis, and areas of
degeneration seen in the ancient schwannomas.23 The “target
sign” is almost pathognomonic for neurofibroma (70% of
cases), but can be seen with schwannoma. It refers to low-tointermediate T2W signal centrally secondary to more fibrous
tissue and high T2W signal peripherally likely related to
myxoid tissue (Fig. 10D).100 The central fibrous areas have
marked contrast enhancement.100-103 The “fascicular sign”
manifests as multiple ringlike structures seen on T2W or
proton density–weighted images and is seen in superficial
and deep-seated lesions.23 A rim of fat (split fat sign) is often
seen with deep-seated BPNSTs, but is nonspecific and can be
seen in many intermuscular lesions.104
Malignant Peripheral
Nerve Sheath Tumor
MPNST accounts for 5%-10% of soft-tissue sarcomas. It usually affects patients aged 20-50 years, with a slight female
predilection. It is associated with NF1 in 25%-70% of cases,
where it presents about a decade earlier with a male predilection (80%).61 Patients present with pain and neurologic
symptoms of motor weakness more frequently than those
with BPNST. A sudden increase in size of a previously stable
lesion should also raise suspicion for MPNST. MPNST usually affects medium to large deep-seated nerves with the sciatic nerve, brachial plexus, and sacral plexus most commonly
involved.105 These lesions are typically greater than 5 cm in
size, whereas BPNSTs are frequently less than 5 cm. Distinguishing MPNST and BPNST by imaging can be challenging
as the lesions can appear very similar. There are some imaging features that may be helpful. The “target sign” and “fascicular sign” are uncommon in MPNST (Fig. 11). Margins of
MPNST may be ill-defined. Central necrosis is more common
in the malignant lesion, but can be seen with ancient schwannoma.23 One study suggests that MPNST and PNST cannot
be adequately separated by evaluation of lesion heterogeneity.106 Enhancement of the benign lesion is variable and
prominent enhancement is noted in the malignant lesion.23
More recently PET imaging, including the use of 11C methionine has been suggested as useful in this distinction as
well.107-109
E.A. Walker, A.J. Song, and M.D. Murphey
288
Figure 10 Neural lesions. A 31-year-old woman with popliteal mass enlarging and becoming painful. (A) Sagittal proton
density (TR/TE; 1700/25), (B) T2-weighted fat saturation (TR/TE; 4889/70) and (C) T1-weighted fat saturation
postcontrast images (TR/TE; 560/10) demonstrate an eccentrically entering and exiting nerve (arrows) consistent with
schwannoma. Higher T2 signal intensity is noted in the periphery (arrowheads) and avid central enhancement (*).
(D) Axial T2-weighted image with fat saturation (TR/TE; 4889/70) in a 16-year-old male with calf mass demonstrates
2 lesions with high T2 signal in the lesion periphery secondary to myxoid region (target sign) (arrows). An 18-year-old
female with a history of neurofibromatosis type I. (E) Coronal T2-weighted fat saturation sequence (TR/TE; 4889/70)
with plexiform neurofibroma of the sciatic nerves (arrowheads). These can be described as ropelike or moniliform.
Note the central necrosis (arrow) of the MPNST in the upper right thigh. A 64-year-old man with neurofibromatosis
and diffuse neurofibroma involving the skin of the anterior left thigh. (F) Axial T1-weighted image (TR/TE; 425/07)
demonstrates replacement of the subcutaneous fat with diffuse intermediate signal lesion (arrows).
Synovial Sarcoma
Synovial sarcoma is an intermediate to high-grade neoplasm
with extensive metastatic potential.110 This lesion accounts
for about 5%-10% of soft-tissue sarcomas. It is typically seen
in young adults aged between 15 and 35 years with the mean
patient age of 32, although there is a wide age range, including newborns. Males and females are affected equally.53,111,112
Patients with synovial sarcoma may initially present with
a palpable slow-growing mass, which can simulate a benign
process.113 In contrast to most other soft-tissue malignancies,
pain is often present. The duration of symptom may vary
from days to as long as 20 years before initial diagnosis.114
Synovial sarcomas are most commonly located in the lower
extremities (60%-70%) and 80%-95% are in the extremities
(often occurring near a joint).111,114 The popliteal fossa is the
most frequent location.110 Most synovial sarcomas are centered in an intermuscular location. It is the most common
malignancy of the foot and ankle in patients aged 6-45
years.53 Despite the name, the tumor does not arise from the
synovium, and fewer than 10% of cases are intra-articular.
Lesions demonstrate calcification, often in the periphery of
the tumor, on radiographs in up to 30% of cases. These
calcifications are difficult to appreciate on MR. Other softtissue lesions, which commonly demonstrate calcification
include soft-tissue osteosarcoma/chondrosarcoma, chondroma, myositis ossificans, and leiomyosarcoma. Synovial
sarcomas are typically heterogeneous, with signal similar to
skeletal muscle on T1W sequences and equal to or greater
than subcutaneous fat on T2W images (Fig. 12). The heterogeneity of these lesions is depicted as the “triple sign” in
30%-50% of cases, with areas that are hyperintense, isointense, and hypointense to fat on T2W sequences.115 This
finding is presumably the result of a mixture of solid cellular
elements, hemorrhage or necrosis, and calcified or fibrotic
collagenized areas.116,117 A multiloculated appearance with
internal septations may also be present.117 Hemorrhage is
present in more than 40% of patients with fluid levels in
MRI of soft-tissue masses
289
Figure 11 Malignant Peripheral Nerve Sheath Tumor (MPNST). An 18-year-old female with history of neurofibromatosis type 1 and pain in the right groin. Prior MPNST was resected from the calf 4 years prior. (A) Sagittal T1-weighted
(TR/TE; 548/12) and (B) Sagittal T2-weighted with fat saturation (TR/TE; 1500/15) images demonstrate a heterogeneous intermuscular lesion with entering and exiting nerves (arrows). Axial T1-weighted fat saturation (C) pre and (D)
postcontrast images (TR/TE; 566/12) reveals a large lesion with hemorrhage (arrowhead) and central necrosis (*).
10%-25% of lesions on MR imaging.115-117 A combination of
hemorrhage, fluid levels and septa may also cause the “bowl
of grapes” sign.110 Cortical erosion or marrow invasion may
be seen on MR in up to 21% of cases.115,117 Contrast enhancement is usually prominent and heterogeneous, and can be
very important to demonstrate small areas of nodular enhancement in a predominantly cystic lesion that may otherwise be mistaken for a benign cyst. Serpentine vascular channels can be noted in approximately 30% of cases.110
Differential diagnosis for soft-tissue lesions with fluid levels
includes synovial sarcoma, hemangioma, myositis ossificans,
hematoma, and lymphangioma.
Pigmented
Villonodular Synovitis and GCTTS
Pigmented villonodular synovitis (PVNS) and GCTTS are benign synovial proliferative lesions of the joint and tendon
sheath, respectively. These lesions are believed to be neoplas-
E.A. Walker, A.J. Song, and M.D. Murphey
290
Figure 12 Synovial Sarcoma. A 42-year-old Hispanic female presents with an enlarging extraarticular mass over her
superomedial right knee during 6 months. (A) Sagittal proton-density–weighted (TR/TE; 2200/25.6), (B) axial T2weighted image with fat saturation (TR/TE; 4266.7/105.3), and (C) coronal T2-weighted (TR/TE; 4950/104.1) MR
images demonstrate a large, heterogeneous lesion in the superomedial right knee with solid and cystic components.
Sagittal MR image demonstrates heterogeneous lesion adjacent to the suprapatellar bursa (arrows). Coronal T2 reveals
marked heterogeneity with the “triple sign,” including areas of high (H), intermediate (I) and low (L) signal within the
mass.
tic rather than reactive.111,118 They are divided according to
their location (intra-articular vs extra-articular) and their pattern of growth (localized or diffuse).23
Localized disease, both extraarticular and intraarticular,
represents 77% of cases (the tenosynovial form being
the most common), compared with diffuse intraarticular
involvement, which accounts for 23%. Patients are typically adult, with the peak incidence in the third to fifth
decades and there is a slight female predominance.119-122
Clinical symptoms include soft-tissue swelling or a slowly
enlarging, painless soft-tissue mass, which is freely mobile.72,119,120,122 Pain may be aggravated by activity.121 Most
of these lesions occur in the hand and wrist (65%-89%). It
is one of the most common soft-tissue masses in the hand,
second in frequency only to ganglion.120,123 In the hand,
the lesion more commonly affects the volar aspect of the
digits. The foot and ankle location accounts for 5%-15% of
lesions. MR frequently demonstrates a nonspecific welldefined soft-tissue mass adjacent to and partially surrounding the tendon. Lesions are approximately equal to
or less than skeletal muscle on T1W. On T2W images,
lesions are heterogeneous with signal intensity equal to or
less than fat.124 Marked enhancement is noted in most
cases.125 Osseous pressure erosions may be present in
15%-20% of cases.
Pigmented villonodular synovitis is most common in
the third and fourth decades. It has equal frequency in
men and women, with an annual incidence of approximately 2 per million.126 Symptoms include mechanical
pain aggravated by motion and improves with rest. Swell-
MRI of soft-tissue masses
ing and limited range of motion may also be experienced.127 PVNS most frequently affects the large joints,
with about 75%-80% occurring in the knee. Other joints
involved in decreasing order of frequency are the hip,
ankle, shoulder, and elbow.128-130 Tumor recurrence after
surgery is common. Geographic, lytic osseous erosions
with sclerotic borders are most common in the hip (93%)
and shoulder (75%) because of their smaller capacity.
Bone marrow edema may be noted at sites of osseous
erosion, but the joint space is usually preserved.128,129 MR
shows a diffuse, multinodular intra-articular synovialbased mass (Fig. 13). Lesions are approximately equal to
or less than skeletal muscle on T1W. There is predominantly decreased signal intensity on T2W images resulting
from the hemosiderin with scattered areas of high
T2W signal.126,131,132 PVNS reveals susceptibility artifact
291
(“blooming”) on gradient echo sequences, which may help
to distinguish the lesion from other causes of diffuse synovial thickening.133 Intense contrast enhancement is typical, but may vary depending on the amount of fibrosis and
hemosiderin in the lesion.134,135 There is typically an associated joint effusion, which may be prominent.131
Hemangioma and/or
Vascular Malformations
We tend to combine hemangiomas and vascular malformations into one category for discussion. Hemangiomas
and/or vascular malformations are among the most frequent tumors to involve the soft tissue and comprise 7% of
all benign tumors. Hemangioma is the most common tu-
Figure 13 Diffuse PVNS. A 68-year-old white female with a history of knee pain and swelling. (A) Sagittal proton
density–weighted (TR/TE; 2000/18), (B) T2-weighted image with fat saturation (TR/TE; 3000/70) and (C) T1-weighted
fat saturation postcontrast images (TR/TE; 550/18) show a heterogeneous lesion filling the posterior knee joint (arrows)
with intermediate to decreased signal. Postcontrast image demonstrates diffuse enhancement of the lesion (small arrow)
and synovitis in the suprapatellar bursa (arrowheads). A 36-year-old woman with knee pain and swelling shows (D) a
large intra-articular lesion with “blooming” artifact (arrows) on gradient echo sequence (TR/TE; 58.2/05).
E.A. Walker, A.J. Song, and M.D. Murphey
292
Figure 14 Hemangioma. Hemangioma in a 28-year-old man with a history of a palpable triceps mass for the past 4-5
months. (A) Sagittal T1-weighted (TR/TE; 13/550) MR image demonstrates an intramuscular triceps mass with predominately peripheral lacelike strands of fat. (B) Coronal STIR (TR/TE; 14/1400) image demonstrates areas of high
signal corresponding to low flow vascularity. (C) Axial T1-weighted postcontrast image with fat suppression (TR/TE;
17/1371.83) shows diffuse mildly heterogeneous enhancement and peripheral circular vessels seen en face (white
arrowheads).
mor in infancy and childhood.61,94,136 It is estimated
1%-2% of the general population and 10% of Caucasians
are affected.137 Hemangiomas are more common in
women with a 3:1 ratio.23 Lesions may increase dramatically in size during pregnancy. Soft-tissue hemangioma
may be superficial or deep, with the deep lesions most
frequently intramuscular. Clinical presentation is often a
painful lesion that intermittently changes in size. Pain associated with intramuscular hemangioma is often vague
and related to exercise. Hemangioma are frequently subdivided based on the predominant type of vascular channel (capillary, cavernous, arteriovenous, or venous).61
Cavernous hemangiomas frequently calcify with dystrophic mineralization and organizing thrombus (phlebolith)
best seen on radiographs or CT. On T1W images, intra-
muscular hemangioma may be defined or a poorly marginated mass of low-to-intermediate signal intensity with areas of high signal intensity related to fat or slow-flowing
blood (Fig. 14). These high signal intensity areas vary from
fine lacelike strands to thick course bands. The fat may be
so extensive as to simulate lipoma.138-143 On T2W sequences, the lesion may be a well-marginated or infiltrative mass with very high signal intensity owing to slow
blood flow in vascular components in most lesions and
intermediate signal corresponding to adipose tissue. The
circular vessels seen en face and linear vessels seen longitudinally with adjacent fat overgrowth have a characteristic appearance. These lesions tend to be heterogeneous on
all pulse sequences and they frequently infiltrate rather
than displace adjacent tissues.144
MRI of soft-tissue masses
Hemangioendothelioma,
Hemangiopericytoma,
and Angiosarcoma
Hemangioendothelioma is a vascular neoplasm of intermediate
aggressiveness between hemangioma and angiosarcoma. Hemangioendothelioma occurs in young patients and involves soft
tissue more often than bone. Soft-tissue hemangioendothelioma
usually involves the deep tissues of the extremities, with approx-
293
imately 50% of the cases being closely related to a vessel from
which they may have arisen.144
Hemangiopericytoma is a vascular neoplasm of intermediate
aggressiveness with benign and malignant forms. The highest
incidence is in middle-aged adults.61 Hemangiopericytoma
commonly involves the lower extremity (35% of cases), most
often the soft tissue of the thigh. The pelvis and retroperitoneum
are involved in 25% of cases. The tumor often demonstrates
large vessels, predominantly in the periphery.144
Figure 15 Hemangiopericytoma. Hemangiopericytoma is suggested by the presence of high-flow peripheral vessels
depicted by serpentine flow voids (white arrows). (A) Coronal T1-weighted (TR/TE; 500/10), (B) Sagittal T1-weighted
postcontrast with fat saturation (TR/TE; 600/10), and (C) axial T2-weighted (TR/TE; 4000/84) MR images demonstrate
a mildly heterogeneous T1 intermediate, T2 hyperintense, and diffusely enhancing mass in the posterior compartment
of the mid thigh.
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294
Figure 16 Leiomyosarcoma. A 57-year-old man with 1-yr history of enlarging supraclavicular soft tissue mass with
subcutaneous location and protuberant morphology. (A) Sagittal T1-weighted (TR/TE; 400/16) and (B) axial T2weighted image with fat saturation (TR/TE; 3000/70) demonstrate a large, heterogeneous lesion with intermediate
signal. (C) Sagittal T1-weighted image with fat saturation post gadolinium (TR/TE; 400/16) shows intense heterogeneous enhancement with prominent central nonenhancing area (*).
Angiosarcoma is an aggressive, vascular malignancy with
high local recurrence and distant metastases. Male to female
predilection is 2:1. Angiosarcomas involve the skin (33%), soft
tissues (24%), and bone (6%). Angiosarcoma is related to
chronic lymphedema in 10% of cases.61,144
It is usually not possible to differentiate hemangioendothelioma, hemangiopericytoma, and angiosarcoma radiologically.
The MR signal characteristics are intermediate signal on T1 and
high signal on long TR sequences (Fig. 15). These lesions demonstrate aggressive infiltration of the adjacent tissues. Areas of
hemorrhage with high T1W signal may be seen. Prominent serpentine vascular channels in the periphery of the lesion can
suggest the diagnosis and are seen most frequently with hemangiopericytoma. The signal intensity of these vascular structures
may reflect high flow (low signal on all pulse sequences) or low
flow (high signal on T2W images).144
Differential diagnosis for a soft-tissue mass with prominent
vascular channels includes alveolar soft part sarcoma, metastatic renal cell carcinoma, hemangiopericytoma, heman-
gioendothelioma, rhabdomyosarcoma, extraskeletal Ewing
sarcoma, and synovial sarcoma.
Leiomyosarcoma
Leiomyosarcoma is a high-grade malignancy, which represents approximately 9% of all soft-tissue sarcomas.53,145 Patients with soft-tissue leiomyosarcoma have a median age in
the fifth to sixth decades.146-148 Retroperitoneal lesions (20%
of cases) are more common in females 2:1 to 7:1, and there is
a male predilection for peripheral lesions (12% of cases).148
Retroperitoneal lesions present clinically as an abdominal
mass and swelling with pain in less than 10%.147 It is the
second most common retroperitoneal tumor after liposarcoma.149 Extremity lesions present with a painless slowly enlarging mass most commonly affecting the thigh.146 Imaging of
leiomyosarcoma is typically nonspecific. Mineralization on
radiograph has been reported in 17% of cases.150 Lesions are
typically isointense to muscle on T1-weighted images and
MRI of soft-tissue masses
variably hyperintense relative to muscle on T2-weighted images, with prominent contrast enhancement (Fig. 16).150
Large lesions are usually more heterogeneous secondary to
hemorrhage, necrosis, and cystic change.149
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