The evaluation of patients with soft-tissue masses must be done in a
systematic fashion to prevent management errors. Although most soft-tissue
masses (approximately 99%) are benign, an error in the management of a
soft-tissue sarcoma can lead to limb loss or adversely affect
survival1. Before
magnetic resonance imaging became easily available, physicians relied on the
patient's history, physical examination, conventional radiographs, and
computed tomography scans for decision-making. These modalities often were
insufficient for establishing a definitive diagnosis. The patient's history
alone cannot provide enough information for a diagnosis and, in fact, may be
misleading. For example, lesions identified after a traumatic episode are not
necessarily traumatic in origin; only half of soft-tissue sarcomas are painful
at presentation2,
and the growth rate may not assist in the diagnosis (slow-growing lesions can
be malignant or benign). Similarly, although a patient may present with
systemic symptoms, the lack of systemic symptoms does not exclude malignancy.
Physical examination may provide some clues that may suggest malignancy, but
none are pathognomonic. Conventional radiography and computed tomography are
not specific enough in differentiating benign and malignant soft-tissue
masses. If one relies solely on these modalities, biopsy often is necessary
for diagnosis and management. Biopsy is associated with several hazards,
including neurovascular injury, hematoma formation, and delayed
wound-healing.
The use of magnetic resonance imaging to identify soft-tissue lesions has
markedly altered the treatment algorithm for a number of
lesions3,4.
In contrast to conventional radiography and computed tomography, magnetic
resonance imaging provides clear advantages in terms of diagnosis: the spatial
resolution of the images is excellent; the images can be reconstructed in
multiple planes; lesions can be identified more readily, and the lesion's
signal characteristics can help to narrow the differential diagnosis; areas of
hemorrhage, cysts, and vascular structures are better seen; and boundaries
between the lesion and unaffected bordering tissues can be evaluated readily,
facilitating the planning of surgical approaches. In addition, magnetic
resonance imaging used for preoperative planning can help to minimize
violation and subsequent contamination of crucial neurovascular
structures.
The purposes of this report were (1) to provide a diagnostic and treatment
algorithm for soft-tissue lesions based on the concept of determinate and
indeterminate categorization, and (2) to assist the orthopaedic surgeon in
developing the skills necessary to categorize a lesion as determinate or
indeterminate in nature and to be able to recognize the commonly occurring
determinate lesions. With this classification system, surgeons can plan
treatment for determinate lesions without a biopsy and can recommend biopsy
for indeterminate lesions to establish a diagnosis before planning
treatment.
The algorithm presented relies on the physician's ability to characterize a
lesion as determinate or indeterminate. A determinate lesion is one that can
be diagnosed definitively by means of the history and physical examination,
and with appropriate imaging modalities such as magnetic resonance imaging or
conventional radiographs—or, in simple terms, a lesion for which a
diagnosis can be given without biopsy. An indeterminate lesion is one that
must be biopsied to ensure an accurate diagnosis. Each individual physician
has a particular degree of confidence in his or her own ability to diagnose a
soft-tissue lesion that will guide the clinical management of the patient. It
is important to note also that discussion with other specialists, such as
musculoskeletal radiologists and pathologists, can provide much needed
information and often proves to be crucial in making the correct diagnosis. A
multidisciplinary approach to soft-tissue lesions is
essential8.
Determinate lesions include lipoma, hemangioma, ganglion and Baker cysts,
hematoma, myositis ossificans, myonerosis, neurofibroma, muscle tear,
pigmented villonodular synovitis, bursitis, and aneurysm. Indeterminate
lesions include the lesions that cannot be diagnosed without biopsy, such as
various sarcomas (e.g., liposarcoma, synovial sarcoma, epithelioid sarcoma,
and malignant fibrous histiocytoma).
Lipoma
The lipoma is the most common of all soft-tissue tumors and is composed of
mature adipose tissue. It has a characteristic firm, fatty feel and typically
confers no symptoms. Nevertheless, some lipomas can cause pain through
compression of adjacent neurovascular structures and, accordingly, lesions
arising in the deep tissues more commonly cause symptoms than those in more
superficial areas.
Lipomas have a characteristic appearance on magnetic resonance imaging
corresponding to that of adipose tissue. These benign tumors appear bright on
T1-weighted imaging (Fig. 1-A)
and moderate to bright on T2-weighted images
(Fig. 1-B). In all sequences,
the lesion appears isointense compared with the subcutaneous fat. The use of
fat-suppressed T2-weighted or short tau inversion recovery images, or both,
confirms the
diagnosis9. The
diagnosis of lipoma can be made with authority when the signal intensity of
the lesion matches that of subcutaneous fat on all pulse sequences, including
fat-suppression pulse sequences. The image may show fibrous septations, which
may not enhance with
gadolinium10,11.
These lesions do not penetrate surrounding structures. When a lesion shows
areas with fibrous or myxoid degeneration, the physician should consider
liposarcoma in the differential diagnosis. In such cases, biopsy is warranted.
Similarly, broad septations or septations with nodularity make the lesion more
consistent with liposarcoma.
Hemangioma
Although a hemangioma is most commonly a cutaneous lesion found in
children, the orthopaedic surgeon may be consulted on deep, intramuscular
lesions for which physical examination findings are nonspecific. Overall,
these lesions have a female predominance as high as
3:112. Fifty
percent of patients describe a history of pain, which is theorized to arise as
a result of the lesion causing ischemia in the surrounding soft tissues
through a vascular steal
phenomenon13.
Superficial lesions may feel soft and may increase in size when placed in a
dependent position, but it may be difficult to detect this posture-related
change with deep
lesions14.
Although conventional radiographs often show phleboliths, the magnetic
resonance imaging findings typically prove diagnostic and show lipomatous
tissue (most of which is contained in the margins of the lesion), vascular
formations, hemosiderin deposits, and fibrosis. Overall, the lesion has a
heterogeneous appearance, bright on T1-weighted images
(Fig. 2-A) secondary to the
adipose tissue of the lesion and bright on T2-weighted
(Fig. 2-B) and short tau
inversion recovery imaging, corresponding with the vascularity of the lesion.
The lesion may have a serpentine appearance secondary to the multiple vessels
in the lesion. Lobules and septations also are found within the
lesion4,13.
Areas of high-velocity blood flow corresponding to feeding vessels appear as
signal voids. Gadolinium administration results in bright enhancement of the
lesion15.
Ultrasound can also prove useful in the diagnosis of this
lesion13,16.
Ganglion Cyst
Ganglion cysts that involve the dorsal or volar aspect of the wrist are one
of the few types of soft-tissue lesions for which a physical examination is
characteristic enough to label the lesion as determinate. These lesions need
no imaging other than conventional radiography and can be treated as the
patient and physician prefer. Some investigators have suggested that these
lesions form when repeated stress causes mucoid degeneration of associated
periarticular tissues or tendon sheaths, whereas others hypothesize that
lining cells cause production of a hyaluronic-acid-rich substance, which
causes the formation of a cystic
lesion17-19.
Ganglion cysts also commonly occur in the foot and ankle, although they can
be associated with any tendon sheath, labrum, or capsule. Unlike a Baker cyst,
a ganglion cyst does not communicate with the joint. When such a lesion is
found in a location other than the wrist, additional imaging should be
performed. On magnetic resonance imaging, the lesion appears smooth and round
or ovular, and it may have septations. The wall of the cyst is
well-circumscribed and forms a distinct border against the adjacent tissues.
Although the septations may enhance with gadolinium administration, the lesion
itself should not. The lesion appears with a signal intensity similar to that
of water—bright on T2-weighted imaging or short tau inversion
recovery4,9,20
(Fig. 3-A) and dark on
T1-weighted imaging (Fig.
3-B).
Baker Cyst
Originally described by
Baker21, the
synovial cyst (now known as the Baker cyst) forms when synovial fluid
insinuates from the knee joint into communicating bursae or by causing
herniation of the synovial membrane itself. This lesion occurs most commonly
under the medial head of the gastrocnemius muscle. The lesion is often
asymptomatic, but it can cause pain. In addition, the cyst may rupture or
leak, causing resultant swelling and/or pain in the affected limb;
thrombophlebitis, compartment syndrome, and claudication can
occur22,23.
The cause of the lesion is intra-articular and can include abnormalities
ranging from anterior cruciate ligament damage to osteoarthritis, although
meniscal tears are the most common
cause24,25.
Ultrasound may be useful for diagnosis, but magnetic resonance imaging is
the study of choice because it can delineate underlying abnormalities such as
meniscal or anterior cruciate ligament tears. Magnetic resonance imaging
findings of a Baker cyst are similar to those of a ganglion cyst. The Baker
cyst is an ovular, well-defined mass found posterior to the knee joint. The
fluid appears dark on T1-weighted images and bright on T2-weighted and short
tau inversion recovery imaging (Figs. 4-A
and 4-B). The signal intensity of the lesion matches that of joint
fluid on all pulse sequences.
Hematoma
Although most patients with a hematoma do not present to an orthopaedist,
it is important to keep this lesion in the differential diagnosis of
soft-tissue lesions. The patient often relates a history of trauma, and
residual ecchymosis can sometimes be seen during the physical examination.
When a history of trauma is not present, it is important to ask the patient
about systemic anticoagulation or clotting deficiencies because these
conditions can be associated with chronic expanding
hematomas26. Most
such lesions will resolve on their own, but the natural history of the lesion
may also follow two other courses: the hematoma may begin to calcify on the
periphery (eventually becoming myositis ossificans) or it may continue to
expand, which may be related to continual irritation caused by hemosiderin
breakdown products. In such instances, the lesion does not heal, and it
chronically expands secondary to continued capillary
bleeding27,28.
Continued expansion of the lesion may cause compression of neurovascular
structures or pressure erosion of nearby osseous
structures27.
T1-weighted imaging shows a heterogeneous pattern. Areas of high signal
intensity represent areas of continuing hemorrhage. Overall, the lesion is
well defined and does not invade other muscle compartments
(Fig. 5-A). T2-weighted images
show heterogeneity (Fig. 5-B).
Areas of low signal intensity, i.e., signal dropout, occur in areas of
hemosiderin deposition. Areas of high signal intensity represent granulation
tissue. A low-signal pseudocapsule often is seen. Fluid-fluid levels have also
been described29.
Gradient-echo imaging can be used to investigate further the areas of
hemosiderin
deposition26,27
and will show the profound signal dropout (dark areas) that is
characteristically seen on gradient-echo imaging in the presence of
hemosiderin or other ferromagnetic materials such as metallic implants.
Gadolinium-enhanced images can be used to confirm the identity of the lesion.
When there is no enhancement with gadolinium contrast, the lesion can be
considered determinate. Although Liu et
al.26 reported
cases of gadolinium enhancement of chronic hematomas, the increased chance of
malignancy makes diagnosis uncertain, and these lesions cannot be considered
determinate26,30.
Myositis Ossificans
Some injuries progress from a simple hematoma to myositis ossificans. The
exact mechanism for this progression is unknown, although it develops most
often during the third decade of
life31,32.
The most commonly affected muscles are the quadriceps and
brachialis31,32.
It is thought that these lesions occur more commonly after severe injuries.
Diagnosis of this lesion can often be made with conventional radiography. The
lesion appears in the pattern of mature, lamellar bone and is well
defined33. For
early lesions, when calcification is absent, magnetic resonance imaging
provides an additional imaging option. On T1-weighted imaging, the lesion most
often resides inside the same compartment as the traumatized muscle, and the
lesion is isointense or slightly hypointense relative to skeletal muscle. In
some instances, the lesion may be subtle, so that it may be recognized only by
alteration of the fascial
planes32
(Fig. 6-A). On T2-weighted and
short tau inversion recovery imaging, the lesion appears hyperintense compared
with muscle (Fig. 6-B).
Surrounding edema may or may not be present. The periphery of the lesion may
have decreased signal intensity, showing the zonal pattern of growth; when
this pattern is recognized, it is diagnostic.
Myonecrosis (Diabetic and Idiopathic)
Myonecrosis may present as a soft-tissue lesion. This condition is
associated most commonly with diabetes, but other predisposing factors include
alcohol consumption. Diabetic myonecrosis can even occur as the initial event
in a patient's history, although most patients have severe neuropathy or other
more severe sequelae in the disease
process34,35.
This painful lesion develops quickly with or without a history of trauma. It
is thought that the lesion develops secondary to endothelial damage from
diabetic microangiopathy, combined with activated coagulation factors and the
continued presence of fibrin degradation
products36. The
only laboratory abnormality associated with the disease is an elevated
creatinine serum kinase, but even this finding is not always
present35,37.
Biopsy should be avoided because these patients are at high risk for
wound-healing
complications38.
Magnetic resonance imaging is the diagnostic modality of choice. Swelling of
the muscle occurs and can be visualized best on T1-weighted imaging, although
fascial layers and muscle fiber patterns are maintained
(Fig. 7-A). T2-weighted imaging
shows the lesion more clearly, with diffuse hyperintensity. The overall
picture is mixed, with areas of necrosis and muscle regeneration
(Fig. 7-B). The lack of
invasion of surrounding structures differentiates this lesion from sarcomas.
Gadolinium contrast may be used, with enhancing areas corresponding to healing
or viable tissue, whereas nonenhancing areas correspond to loci of tissue
necrosis35,37.
Neurofibroma
Patients with a history of neurofibromatosis Type 1 present with
soft-tissue neurofibromas that can be mistaken for sarcomas. These patients
often do not have any associated neurologic
deficit39. The
masses occur superficially and in the deep tissues, and they may or may not
cause pain. Because patients with neurofibromatosis Type 1 are at high risk
for malignancy, magnetic resonance imaging can be useful in determining the
nature of the lesion and in ruling out dedifferentiation of the lesion into a
neurofibrosarcoma.
On T1-weighted imaging, the lesion appears darker than skeletal muscle and
often has a nodular appearance (Fig.
8-A). T2-weighted imaging shows areas of high signal intensity
(corresponding with myxoid areas) and areas of low signal intensity
(corresponding with compressed nerve fibers)
(Fig. 8-B). Commonly, a target
sign is seen, with an area of low signal intensity within a larger,
high-signal-intensity
area40,41.
It should be noted that continued observation with serial magnetic resonance
imaging can rule out dedifferentiation to neurofibrosarcoma.
Muscle Tear
A patient with a muscle tear often can recall the exact moment when the
injury occurred. There is a feeling of sudden weakness, and a snapping sound
may or may not be heard. The muscle in question often swells and becomes quite
tender. Other signs, including ecchymosis and edema, occur, although none is
specific for muscle tear. Over time, the swelling subsides, but the patient
may be left with a lump, i.e., soft-tissue fullness, in the area that
corresponds to scarring from the previous lesion and may be mistaken for a
soft-tissue
tumor42,43.
Although this presentation is the most common one, it should be noted that
muscle tears can also occur insidiously. One series of muscle tears presenting
as soft-tissue masses showed that six of seven occurred without a traumatic
event and that only 50% caused
pain44.
Magnetic resonance imaging is the best imaging modality for making the
diagnosis of a muscle tear. T1-weighted imaging shows the ruptured muscle or
the formation of scar, or both. Care should be taken to evaluate the course of
the involved muscle in the axial, coronal, and sagittal planes and to confirm
that the morphology of the injury suggests the presence of a muscle tear. Most
frequently, the deformity is clear, and there is no evidence of invasion of
the surrounding structures (Fig.
9-A). The time relative to the injury dictates the muscle's
appearance on T2-weighted imaging. Acute injuries show hyperintense lesions
with surrounding edema (Fig.
9-B). Chronic injuries show low to intermediate signal
intensity.
Pigmented Villonodular Synovitis
Another lesion that might be mistaken for a soft-tissue mass, pigmented
villonodular synovitis, occurs infrequently, but it can be diagnosed with
magnetic resonance imaging. Patients typically complain of pain in or around
the involved joint, with associated swelling. Warmth and effusion of the joint
also may
occur43,45.
The most common location is the knee, followed by the hip, ankle, and elbow.
The disease has two different forms: one that affects the entire joint in a
diffuse pattern and another that presents in a nodular form. The nodular form
is more easily resected, but treatment for either form should be attempted
because secondary arthritis will develop if the abnormal tissue is not
excised46.
Conventional radiographs show a joint effusion with joint erosion after
continued disease, although most of the joint space is maintained. Narrowing
of the joint occurs concentrically. The lesion has a characteristic appearance
on magnetic resonance imaging: low signal intensity on both T1-weighted and
T2-weighted imaging secondary to the high hemosiderin content of the lesion
(Figs. 10-A and 10-B).
Gradient-echo images, which are particularly sensitive to ferromagnetic
materials such as hemosiderin, show profound signal dropout in patients with
pigmented villonodular synovitis and may help to differentiate this lesion
from synovial chondromatosis. Thus, the lesion can be described as
"blooming" from the joint
capsule45. Although
gradient-echo and fast-field-echo imaging may show hemosiderin content better
than T1-weighted or T2-weighted
imaging47 does,
hemosiderin deposition may not occur if the lesion is imaged too early, i.e.,
before
maturation46,48.
If a mass is noted, it is usually indicative of nodular disease.
Bursitis
When a mass develops near a joint, the physician should consider bursitis
among the potential diagnoses. The inflamed bursa can present acutely,
subacutely, or chronically; the last presentation may mimic a tumor. The cause
of the bursitis may vary, but most commonly it is associated with trauma,
infection, gout, or rheumatoid
arthritis49-51.
Similarly, the affected area varies, and almost any joint can be involved. The
most common locations include the prepatellar area and the greater trochanter.
In these locations, the physician can make the diagnosis without magnetic
resonance imaging. Magnetic resonance imaging is most useful in assisting the
physician to make the diagnosis of bursitis in other locations (e.g., about
the olecranon, ankle, and pes anserinus
insertion)49,51,52.
On T1-weighted imaging, the inflamed bursa appears as an ovular or cystic
structure that is hypointense compared with muscle
(Fig. 11-A). T2-weighted
imaging shows the high signal intensity common to all fluid-filled lesions
(Fig. 11-B), and the periphery
of the lesion may also appear bright. Gadolinium enhancement occurs in
infectious or inflammatory cases (e.g., rheumatoid arthritis or
gout)49,51,53.
Aneurysm and/or Pseudoaneurysm
Although the formation of an aneurysm or pseudoaneurysm in an extremity is
uncommon, it may mimic a malignant soft-tissue lesion. The most common cause
of such a lesion is trauma, although there are other causes (e.g., congenital
disease, atherosclerosis, and mycotic aneurysms). The incidence approaches its
peak in individuals who are sixty-five years of age or older, and men are
affected more often than
women54. The
formation of a pseudoaneurysm occurs more commonly than does a true aneurysm
in the extremities, and aneurysms rarely form below the
knee55. Popliteal
artery aneurysms, the most common aneurysm in the lower extremity, can affect
nearby neurovascular
structures56-58.
Symptoms such as paresthesias or painful claudication secondary to compression
of adjacent neurovascular structures can occur, although the mass itself may
be non-painful. Palpation of the lesion often reveals a pulse.
On both T1-weighted and T2-weighted imaging, the size of the associated
vessel is at least 50% larger than that of neighboring sections
(Fig. 12). With gadolinium
enhancement, the aneurysm appears bright (as does the entire vessel). Mural
thrombus may or may not exist and has imaging characteristics similar to those
of a hematoma.
When the physician cannot reach a diagnosis on the basis of the patient
history, physical examination, and advanced imaging, the lesion is considered
indeterminate and possibly malignant. Lesions that are hypointense compared
with muscle on T1-weighted imaging and hyperintense on T2-weighted imaging are
suspicious for soft-tissue sarcomas. Similarly, certain elements of the
physical examination, such as a size of >5 cm, a firm mass, subfascial
location, and a matted lesion adherent to neighboring tissues, are
characteristic of soft-tissue sarcomas. Although suggestive of malignancy,
these characteristics are not
diagnostic59.
If the lesion is indeterminate, a tissue sample must be obtained for
diagnosis. Given the consequences of misdiagnosis or failure to diagnose a
soft-tissue lesion, the importance of obtaining a biopsy cannot be
overemphasized. The three primary techniques include open biopsy, core needle
biopsy, and excisional biopsy.
The standard in obtaining diagnostic samples of tissue is the open biopsy
technique. The technique allows direct visualization of the lesion. Frozen
sections obtained at the time of the procedure ensure that the surgeon has
obtained a diagnostic section of tissue. When performing an open biopsy, the
surgeon must meticulously plan the approach because subsequent procedures will
require excision of the tract of the biopsy. Transverse incisions must be
avoided, and care should be taken to avoid exposing (and thus contaminating)
neurovascular structures during the procedure. At all times, meticulous
hemostasis must be maintained to prevent hematoma formation. Hematomas that
track under subcutaneous tissue or through intermuscular spaces carry tumor
cells and may contaminate these
areas9.
The core needle biopsy, especially when performed at centers that
specialize in musculoskeletal tumors, is an alternative to open biopsy. Some
investigators have questioned the sensitivity of core biopsy
alone60, but
numerous studies have shown that it provides an accurate diagnosis in >80%
of
cases61-64.
The numerous advantages of core needle biopsy include decreased patient
morbidity, less subcutaneous hematoma formation, and avoidance of the need for
open biopsy. The procedure often is performed on an outpatient basis and
without the use of general anesthesia. Advanced techniques such as cytogenetic
studies and electron microscopy also can be used with this
technique9. When
available, core needle biopsy often is preferred to open biopsy.
In general, excisional biopsy should be avoided, but when used, it should
be reserved for lesions measuring <2 cm or lesions for which the surgeon
already has a definitive diagnosis. It should not be used for large lesions or
lesions that do not have a diagnosis because the consequences of inadequate
resection are severe. If excisional biopsy must be repeated, the revision
procedure becomes markedly more difficult than the index procedure because of
the disruption of soft-tissue planes and because hematoma formation
contaminates the wound bed. In addition, repeat excision results in lower
rates of successful tumor
removal65,66.
?