Certain soft-tissue tumors seem to be specific to the upper extremity; most are benign. Knowledge of key magnetic resonance features, with clinical history and epidemiologic knowledge, can assist the radiologist in establishing optimal diagnosis. Indeterminate lesions require biopsy to exclude malignancy.
Key points
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Magnetic resonance (MR) imaging can definitively diagnose lipomas, neural fibrolipomas, palmar fibromatosis, benign peripheral nerve sheath tumors, and glomus tumors.
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In most benign soft-tissue tumors of the upper extremity, characteristic MR imaging features combined with clinical history and epidemiologic knowledge can predict specific diagnoses.
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Epithelioid sarcomas are rare malignant soft-tissue tumors that usually occur in the hand or forearm with lymphadenopathy.
Introduction
The most frequently encountered tumors of the upper extremity often appear elsewhere in the body. There are some lesions, however, that appear primarily in the upper extremity.
MR imaging has become the technique of choice for detecting and characterizing soft-tissue masses. Its improved soft-tissue contrast has provided significant advantages for assessing lesion conspicuity as well as characterizing the lesions and local staging. Tumors involving the upper extremity are often benign, and MR imaging can be fairly specific in diagnoses. This report provides an MR imaging review and pictorial for common soft-tissue tumors of the upper extremity.
Introduction
The most frequently encountered tumors of the upper extremity often appear elsewhere in the body. There are some lesions, however, that appear primarily in the upper extremity.
MR imaging has become the technique of choice for detecting and characterizing soft-tissue masses. Its improved soft-tissue contrast has provided significant advantages for assessing lesion conspicuity as well as characterizing the lesions and local staging. Tumors involving the upper extremity are often benign, and MR imaging can be fairly specific in diagnoses. This report provides an MR imaging review and pictorial for common soft-tissue tumors of the upper extremity.
Imaging protocol
Evaluation of the upper extremity with MR imaging begins with proper patient positioning to maximize comfort and thereby minimize motion. The patient’s arms should be placed at the isocenter of the magnet to avoid degrading signal to noise and field homogeneity, which affects image quality. It may be useful to place a marker over the area of clinical concern, particularly with subcutaneous lipomas or small soft-tissue tumors. All efforts should be made to maximize signal to noise ratios, regardless of system design.
The field of view should be tailored to the size of both the patient and the suspected mass. Lesion size also dictates whether use of a local surface or cylindrical coil is appropriate, particularly for small lesions. Proper coil use makes it possible to image small or superficially located soft-tissue masses. Slice thickness can also vary based on the lesion.
Lesions should be imaged in at least 2 orthogonal planes, using conventional T1-weighted (T1W) and T2-weighted (T2W) spin-echo MR imaging in at least 1 plane. Because radiologists are most familiar with conventional axial anatomy, axial T1W and T2W imaging should be obtained in almost all cases. The choice of additional imaging planes vary based on the involved body part, lesion location, and relationship of the lesion to crucial structures.
Fat-suppressed T2W imaging increases lesion to background signal intensity differences. It is also useful for decreasing or eliminating the MR signal from fat, allowing increased conspicuity of lesions containing paramagnetic substances, such as methemoglobin, on T1W images, and identifying contrast enhancement. Gradient-echo imaging may be a useful supplement in demonstrating hemosiderin because of its greater magnetic susceptibility. Intravenous contrast is often not required. However, it is helpful to differentiate cysts from solid masses and soft-tissue sarcomas from peripheral nonneoplastic areas of edema. Diffusion-weighted images (DWIs) provide molecular information regarding fluid motion in tissues. Apparent diffusion coefficient values calculated quantitatively from DWIs have been explored to improve lesion characterization and evaluate response to therapy. They can be performed quickly, do not require administration of exogenous contrast medium, and do not involve a significant increase in examination time.
Benign soft-tissue tumors
Lipoma
Lipomas are the most common soft-tissue neoplasm and represent about 50% of all soft-tissue tumors. They can occur superficially or deeply in subcutaneous fat, muscles, synovium, or parosteal areas. Although intramuscular lipomas arise within muscle, they may involve both muscular and intermuscular tissue rather than the intermuscular region only. Intramuscular lipomas occur in patients of all ages, with most presenting between 30 and 60 years of age. There is a slight male predominance. Lesions commonly affect large muscles of the lower extremity (45%), trunk (17%), shoulder (12%), and upper extremity (10%).
Depending on the size and location of the intramuscular lipoma, radiography may reveal an intramuscular mass of fat density. Murphey and colleagues reported that radiologic evaluation is diagnostic in up to 71% of cases. The lesion may be identified on MR images as a predominantly fatty mass with signal intensity equal to that of subcutaneous fat ( Fig. 1 ). Although the mass is usually well defined and sharply circumscribed, it may have irregular margins that interdigitate with adjacent skeletal muscle. Such lesions are referred to as infiltrating lipomas.
Neural Fibrolipoma
Neural fibrolipomas are also known as fibrolipomatous hamartomas of the nerve, perineural lipomas, fatty infiltration of the nerve, and intraneural lipomas. Patients with neural fibromas typically present during early adulthood with a soft, slowly enlarging mass in the volar aspect of the hand, wrist, or forearm. Approximately 80% of upper extremity lesions originate in the median nerve. The lower extremity is involved less frequently. The lesion is typically present at birth or presents within the first 2 years of life. Neural fibrolipomas associated with macrodactyly are known as macrodystrophia lipomatosa ( Fig. 2 ).
The affected nerve is diffusely enlarged, with the epineurium and perineurium infiltrated by fibroadipose tissue that surrounds and separates normal-appearing fascicles. The MR appearance of neural fibrolipomas is pathognomonic. Low signal intensity nerve bundles surrounded by increased signal intensity related to fat appear cablelike on axial T1W images and spaghettilike on coronal T1W images.
Angiolipoma
Angiolipomas are typically subcutaneous nodules consisting of mature fat cells intermingled with small, thin-walled capillary-type vessels, several of which contain fibrin thrombi. They most commonly affect young male patients between 10 and 30 years of age. The most frequent site of involvement is the forearm, followed by the trunk and upper arm. Multiple lesions are seen in approximately 70% of cases.
Areas of low signal intensity on T1W images and high signal intensity on T2W images represent vascular components enhanced with intravenous contrast material. MR imaging helps discriminate between lipomas and angiolipomas that show intense enhancement on contrast-enhanced T1W images ( Fig. 3 ).
Nodular Fasciitis
Nodular fasciitis is a benign proliferative lesion of fibroblasts that most commonly develops at the superficial fascia in subcutaneous tissue. It is also frequently seen in intramuscular or intermuscular regions ( Fig. 4 ). Lesions tend to occur between 20 and 40 years of age, growing rather rapidly with slight tenderness. They appear most often in the forearm, followed by the thigh and upper arm.
Nodular fasciitis appears round or oval and is usually well circumscribed. The lesion may be categorized as myxoid, cellular, or fibrous, according to predominant histologic features. This histologic diversity accounts for the variable MR images of the lesions. The signal of cellular lesions appears nearly isointense to skeletal muscle on T1W images and hyperintense to that of adipose tissue on T2W images. Highly fibrous lesions have a hypointense signal on all types of MR images. The inverted target sign of a central high T2 signal with corresponding secondary to internal cystic change or necrosis is often seen. Contrast enhancement is typically diffuse but may be peripheral in lesions with a greater extracellular myxoid matrix and central fluid-filled spaces. An important diagnostic feature on MR imaging is linear extension of the lesion along the fascia (fascial tail appearance), which may also be enhanced with contrast.
Pigmented Villonodular Synovitis
Pigmented villonodular synovitis (PVNS) represents a benign, hypertrophic synovial process characterized by villous, nodular, and villonodular proliferation and pigmentation from hemosiderin. The localized extra-articular form of PVNS is frequently referred to as giant cell tumor of tendon sheath (GCTTS). Localized disease affecting an intra-articular location is referred to as the localized PVNS.
Diffuse types include conventional (or diffuse) PVNS and diffuse-type giant cell tumor ( Table 1 ).
| Diagnosis | Predilection Sites | Peak Age | Sex | Imaging Findings |
|---|---|---|---|---|
| Intramuscular lipoma | Extremity, trunk, shoulder | 30–60 y | M > F | Interdigitate with the adjacent skeletal muscle |
| Neural fibrolipoma | Median nerve | 10–40 y | M > F, with macrodactyly; M < F, without macrodactyly | Cablelike and spaghettilike appearance on T1WI |
| Angiolipoma | Forearm, trunk, upper arm | 10–30 y | M > F | High signal intensity on T2WI represents vascular components enhanced on contrast-enhanced T1WI |
| Nodular fasciitis | Forearm, thigh, upper arm | 20–40 y | M = F | Inverted target or fascial tail appearance on T2WI |
| GCTTS | Finger | 20–40 y | M = F | Blooming artifact on gradient-echo sequences |
| FTS | Finger | Any age | M > F | Not markedly low signal intensity on gradient-echo sequences; lack or mild enhancement |
| Palmar fibromatosis | Palmar | Older than 65 y | M > F | Well-defined or ill-defined superficial mass occurring along the deep palmar aponeurosis |
| Neurofibroma | Skin, where the tumors are associated with small nerves | 20–30 y | M = F | Target sign, centrally entering and exiting nerve signs are more common than in schwannoma |
| Schwannoma | Skin and subcutaneous tissue of the head, neck, and extremity | 30–60 y | M = F | Peripherally entering and exiting nerve signs and cystic area are more common than in neurofibroma |
| Extraskeletal chondroma | Finger, hand, toe, foot | 30–60 y | M > F | Mineralization characteristic of cartilaginous tumors |
| Glomus tumor | Finger nail bed | 20–40 y | M < F | A small mass related to the nail bed with prominent and diffuse enhancement |
| Angioleiomyoma | Extremity | 30–60 y | M < F | Either homogeneous or heterogeneous isointensity compared on T1WI and hyperintensity with few low-signal-intensity foci on T2WI, flow voids |
| Pilomatoricoma | Subcutaneous tissue of the head, neck, and upper extremity | <20 y | M = F | Well-circumscribed lesion with sandlike calcifications on radiography |
| Synovial sarcoma | Lower extremity | 15–35 y | M = F | Calcification, fluid-fluid levels, triple signal intensity |
| Epithelioid sarcoma | Hand, forearm | 10–35 y | M > F | Spread along tendon sheaths and aponeuroses |
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