Magnetic resonance imaging is the mainstay of diagnostic imaging for soft tissue masses, but plain film, ultrasound, and computed tomography all have roles. A subset of lesions has specific imaging features that enable a confident radiological diagnosis with appropriate clinical correlation. Many soft tissue masses have nonspecific appearances and should be considered for biopsy in a specialist center. When a biopsy is required for definitive diagnosis, careful multidisciplinary planning is essential to avoid contamination of unaffected tissue, leading to recurrence and unnecessary amputations. This article discusses radiological diagnosis, biopsy, and management of the soft tissue mass.
Key points
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Magnetic resonance imaging is the mainstay of diagnostic imaging for soft tissue masses, but plain film, ultrasonography, and computed tomography have roles. Nuclear medicine contributes to staging and detection of recurrence.
- •
A subset of lesions has specific imaging features that enable a confident radiological diagnosis with appropriate clinical correlation.
- •
Many soft tissue masses have nonspecific appearances and should be considered for biopsy in a specialist center.
- •
When a biopsy is required for definitive diagnosis, careful multidisciplinary planning is essential to avoid contamination of unaffected tissue, leading to recurrence and unnecessary amputations.
Introduction
Background
The soft tissue mass is a common complaint that raises concern and anxiety for malignancy in patients and physicians alike. However, incidence of benign tumors is estimated at 3000 per million population and a benign cause is found in 95% of patients presenting to primary care with a soft tissue mass. It is important to establish a good clinical history and perform careful examination before imaging, as such masses may have a nonpathological explanation or nonsoft tissue etiology. These include the following:
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Normal anatomy
- ○
Ribs
- ○
The sternoclavicular joint, particularly after age-related degenerative hypertrophy
- ○
Subcutaneous fat irregularity in larger patients
- ○
The subcutaneous fat pad overlying the cervicothoracic junction
- ○
- •
Masses arising from a bone or abdominal organ
- ○
Old fractures
- ○
Bone tumors
- ○
Hepato/splenomegaly, gallbladder masses, and hernias
- ○
- •
Imaginary masses
- ○
Overanxious patient
- ○
Obesity
- ○
Family history of cancer
- ○
Important factors to note in the history are summarized in Table 1 . In addition to these, the patient’s age and the location of the lesion can further reduce the differential diagnosis. For example, many mesenchymal tumor types occur in adults, angiomas occur in all ages, and dermatofibrosarcoma protuberans (DFSP) and epithelioid sarcoma peak in the 20 to 40 age range. DFSP often involves the skin, malignant fibrous histiocytoma is often deep, liposarcomas are usually found in the extremities and retroperitoneum, and epithelioid sarcoma is most common in the fingers, hands, and forearms.
| History Says… | Could Be |
|---|---|
| Previous or known primary malignancy | Metastasis or recurrence Radiation-induced sarcomas |
| Previous trauma or on anticoagulation | Hematoma or myositis ossificans |
| Painful lesion | Inflammatory or neural origin |
| Rapid increase in size | May be malignant |
| Stable size over long period | Likely benign |
| Variation in size | Hemangioma or ganglia |
| Multiple lesions | Lipomatosis or neurofibromatosis Metastases |
These features help the referring physician decide on the necessity for imaging and the best initial modality to request (eg, a radiograph for a suspected bony mass or an ultrasound for soft tissue). This information allows the radiologist to appropriately protocol the requested studies to expedite patient care; for example, changing a modality or arranging the most appropriate sequences and orthogonal planes on magnetic resonance imaging (MRI). Furthermore, the information provides valuable clues as to the likely pathology, to correlate with the imaging. This can be particularly useful when faced with nonspecific imaging appearances.
All physicians should be wary of a history of trauma; although this is a common cause for a mass, sometimes the event has drawn the patient’s attention to the affected area for the first time and can result in a misleading diagnosis.
Sarcomas
A rare, but perhaps the most feared, cause of a soft tissue mass is the soft tissue sarcoma. They are tumors of mesenchymal origin that histologically resemble, but do not necessarily arise from, the tissue they are named for. More than 50 histologically distinct subtypes exist. The major categories are summarized in Table 2 .
| Tumor Resembles | Tumor Name |
|---|---|
| Fat | Liposarcoma |
| Skeletal muscle | Rhabdomyosarcoma |
| Peripheral nerves | (Malignant) peripheral nerve sheath tumor (M)PNST |
| Blood vessels | Angiosarcoma |
| Fibrous tissue | Fibrosarcoma |
| Bone | Osteosarcoma |
| Cartilage | Chondrosarcoma |
Sarcomas account for fewer than 1% of solid adult tumors. They were estimated to have caused 3490 deaths in the United States in 2005, with an international incidence of 1.8 to 5.0 per 100,000 people per year. The vast majority are soft tissue tumors, with just more than 10% occurring in bone. Two-thirds of soft tissue sarcomas occur within the limbs.
The risk factors are not well understood and are dependent on subtype. They are often sporadic but associated with familial cancer syndromes and previous radiation exposure. Sarcomas have traditionally been associated with poor survival because of vague, nonspecific, early symptoms, leading to delayed presentation, delayed diagnosis, and metastases. They occur more frequently in adolescents and young adults than do other cancers, leading to substantial loss of years of life and morbidity from limb loss.
Role of the Radiologist
The radiologist has several roles in the diagnosis and management of soft tissue masses:
- •
Detection of the mass and confirmation of the existence of the mass.
- •
Characterizing the mass: size, location, related structures, and likely composition and giving a differential diagnosis.
- •
Staging, in the case of malignancy.
- •
Image-guided biopsy to establish/confirm the histologic diagnosis.
- •
Follow-up to assess treatment response, recurrence, and posttreatment complications.
In this article, we discuss appearances of the soft tissue mass, both benign and malignant, from the common lipoma through to rare malignancies; the strengths and limitations of the various imaging modalities; and the basic principles of guided biopsy and subsequent surgical management.
Introduction
Background
The soft tissue mass is a common complaint that raises concern and anxiety for malignancy in patients and physicians alike. However, incidence of benign tumors is estimated at 3000 per million population and a benign cause is found in 95% of patients presenting to primary care with a soft tissue mass. It is important to establish a good clinical history and perform careful examination before imaging, as such masses may have a nonpathological explanation or nonsoft tissue etiology. These include the following:
- •
Normal anatomy
- ○
Ribs
- ○
The sternoclavicular joint, particularly after age-related degenerative hypertrophy
- ○
Subcutaneous fat irregularity in larger patients
- ○
The subcutaneous fat pad overlying the cervicothoracic junction
- ○
- •
Masses arising from a bone or abdominal organ
- ○
Old fractures
- ○
Bone tumors
- ○
Hepato/splenomegaly, gallbladder masses, and hernias
- ○
- •
Imaginary masses
- ○
Overanxious patient
- ○
Obesity
- ○
Family history of cancer
- ○
Important factors to note in the history are summarized in Table 1 . In addition to these, the patient’s age and the location of the lesion can further reduce the differential diagnosis. For example, many mesenchymal tumor types occur in adults, angiomas occur in all ages, and dermatofibrosarcoma protuberans (DFSP) and epithelioid sarcoma peak in the 20 to 40 age range. DFSP often involves the skin, malignant fibrous histiocytoma is often deep, liposarcomas are usually found in the extremities and retroperitoneum, and epithelioid sarcoma is most common in the fingers, hands, and forearms.
| History Says… | Could Be |
|---|---|
| Previous or known primary malignancy | Metastasis or recurrence Radiation-induced sarcomas |
| Previous trauma or on anticoagulation | Hematoma or myositis ossificans |
| Painful lesion | Inflammatory or neural origin |
| Rapid increase in size | May be malignant |
| Stable size over long period | Likely benign |
| Variation in size | Hemangioma or ganglia |
| Multiple lesions | Lipomatosis or neurofibromatosis Metastases |
These features help the referring physician decide on the necessity for imaging and the best initial modality to request (eg, a radiograph for a suspected bony mass or an ultrasound for soft tissue). This information allows the radiologist to appropriately protocol the requested studies to expedite patient care; for example, changing a modality or arranging the most appropriate sequences and orthogonal planes on magnetic resonance imaging (MRI). Furthermore, the information provides valuable clues as to the likely pathology, to correlate with the imaging. This can be particularly useful when faced with nonspecific imaging appearances.
All physicians should be wary of a history of trauma; although this is a common cause for a mass, sometimes the event has drawn the patient’s attention to the affected area for the first time and can result in a misleading diagnosis.
Sarcomas
A rare, but perhaps the most feared, cause of a soft tissue mass is the soft tissue sarcoma. They are tumors of mesenchymal origin that histologically resemble, but do not necessarily arise from, the tissue they are named for. More than 50 histologically distinct subtypes exist. The major categories are summarized in Table 2 .
| Tumor Resembles | Tumor Name |
|---|---|
| Fat | Liposarcoma |
| Skeletal muscle | Rhabdomyosarcoma |
| Peripheral nerves | (Malignant) peripheral nerve sheath tumor (M)PNST |
| Blood vessels | Angiosarcoma |
| Fibrous tissue | Fibrosarcoma |
| Bone | Osteosarcoma |
| Cartilage | Chondrosarcoma |
Sarcomas account for fewer than 1% of solid adult tumors. They were estimated to have caused 3490 deaths in the United States in 2005, with an international incidence of 1.8 to 5.0 per 100,000 people per year. The vast majority are soft tissue tumors, with just more than 10% occurring in bone. Two-thirds of soft tissue sarcomas occur within the limbs.
The risk factors are not well understood and are dependent on subtype. They are often sporadic but associated with familial cancer syndromes and previous radiation exposure. Sarcomas have traditionally been associated with poor survival because of vague, nonspecific, early symptoms, leading to delayed presentation, delayed diagnosis, and metastases. They occur more frequently in adolescents and young adults than do other cancers, leading to substantial loss of years of life and morbidity from limb loss.
Role of the Radiologist
The radiologist has several roles in the diagnosis and management of soft tissue masses:
- •
Detection of the mass and confirmation of the existence of the mass.
- •
Characterizing the mass: size, location, related structures, and likely composition and giving a differential diagnosis.
- •
Staging, in the case of malignancy.
- •
Image-guided biopsy to establish/confirm the histologic diagnosis.
- •
Follow-up to assess treatment response, recurrence, and posttreatment complications.
In this article, we discuss appearances of the soft tissue mass, both benign and malignant, from the common lipoma through to rare malignancies; the strengths and limitations of the various imaging modalities; and the basic principles of guided biopsy and subsequent surgical management.
Preimaging planning
Following the discovery and clinical evaluation of a suspected soft tissue mass, a variety of imaging modalities are available to the referring clinician. Each has its advantages and limitations. MRI is widely acknowledged to be the gold standard for soft tissue imaging, but plain films, ultrasound, computed tomography (CT), and nucleotide imaging can all serve a purpose. The attributes of each modality are summarized in Table 3 .
| Modality | Advantages | Disadvantages |
|---|---|---|
| Plain film |
|
|
| Ultrasound |
|
|
| MRI |
|
|
| CT |
|
|
| PET |
|
|
| Angiography |
|
|
Although MRI is usually the most informative imaging modality, ultrasound may be preferable as an initial screening test that is well tolerated by patients, can confirm the presence and size of a lesion, give an indication of benign or malignant nature, and evaluate the need for further investigation. It provides dynamic evaluation of hernia and is diagnostic for simple lipoma. Accurate definitive diagnosis of many lesions is not possible however.
Radiographs are often unrewarding in the context of soft tissue mass, but give added information on calcium and are therefore a useful adjunct to an MRI. Disrupted tissue planes, lucent fatty lesions, and evidence of erosions suggesting the possibility of tophi also may be seen.
CT provides excellent calcium detail and is very useful where osteoid/chondroid matrix and/or bone involvement is suspected. Positron emission tomography (PET) CT is reserved for staging malignancy and detecting recurrence. Angiography may provide useful images for preoperative planning and embolization of tumors before resection or for palliative pain management.
Diagnostic imaging technique
A few simple principles will optimize image quality for soft tissue imaging.
- •
Plain films: Always obtain at least 2 orthogonal plains. They are recommended as a routine adjunct to MRI when evaluating limbs and pelvic or shoulder girdle lesions.
- •
Ultrasound: In general, start with the highest-frequency probe available and then reduce as required. Linear probes of approximately 17 MHz are ideal for superficial lesions, but curvilinear probes in the 5-MHz range may be necessary for deeper lesions and larger patients. Evaluate any internal vascular flow with color Doppler. Acoustic shadowing may represent calcification, whereas posterior acoustic enhancement suggests a cystic lesion. Check for peristalsis in suspected bowel herniae.
- •
MRI
- ○
Skin markers are strongly advised for subtle, doubtful, or diffuse lesions. These should be placed over small lesions, or at the outer limits of ill-defined ones.
- ○
At least 2 orthogonal planes should be used, with the choice tailored to the location and orientation of the lesion.
- ○
Field of view should be kept focused of the lesion. A wider field of view may be used for initial detection and where multiple lesions are suspected, but avoid trying to characterize 2 or more widely spaced lesions in a single broad field, or imaging both limbs together. A full-length view of the bone on one sequence is advised to identify any skip lesions.
- ○
Sequences: We recommend our tumor protocol consisting of axial T1, axial T2, axial T2 Fat Saturated (FS), sagittal gradient echo (GRE), and a coronal short-tau inversion recovery (STIR) sequence.
- ▪
T1 and T2 Turbo spin echo (SE) are performed to ascertain basic signal characteristics, define the location, and begin substance characterization.
- ▪
T2 FS confirms the presence of fat and increases conspicuity of nonfat and fluid, such as edema.
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STIR is similar to T2 FS in revealing lesions with a high water content and edema and confirming fat content.
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T2* GRE sequence is useful for identification of hemosiderin as low signal with blooming artifact, therefore useful in diagnosing hemangiomas, pigmented villonodular synovitis (PVNS), and mature hematomas.
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- ○
Routine use of Gadolinium is controversial. It is advocated in some centers, but in others it is reserved purely for follow-up and problem solving, for example identifying areas of recurrence postoperatively or targeting of solid components during biopsy.
Pearls and Pitfalls
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When contrast is selected, it is vital to have a similar fat-saturated sequence, preferably T1 FS, for comparison.
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The previous protocol should be modified to take into account the orientation of the lesion. Review of the localizer images before formal sequence acquisition is useful where the lesion topography is uncertain, before acquiring the formal sequences.
Interpretation/assessment of clinical images
Interpretation begins with a description of the lesion, which should attempt to answer the following questions:
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What is it the composition? Including fat, calcification, hemosiderin, and fluid.
- •
What is the shape and structure? Presence of lobulation, septation, cystic/solid, fluid levels, and lesion dimensions.
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Where is it? The report should include the location, adjacent structures, and any invasion. The relationship to neurovascular bundles, muscle compartments, bones, and joints must be included.
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Where is the nodal/metastatic disease?
The radiologist must then try to determine what is it? Some lesions have specific appearances. Recognition of these can spare the patient unnecessary biopsy, anxiety, and, in the worse cases, surgery due to misdiagnosis. Box 1 lists the lesions that may be recognized by their imaging features alone.
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