Hypoechoic Muscle Mass

DIFFERENTIAL DIAGNOSIS

Common

• Hematoma
• Muscle Tear
• Nerve Sheath Tumor

Less Common

• Soft Tissue Sarcoma
• Myxoma
• Fibromatosis
• Abscess
• Metastases
• Lymphangioma
• Intramuscular Extension of Baker Cyst
• Vascular Malformation
• Local Recurrence
• Intramuscular Ganglion Cyst
• Granuloma
• Diabetic Muscle Infarction

Rare but Important

• Parasitic Infection

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

• Clinical history is important for differentiating any muscle mass
• Acute hematoma and infection are usually readily distinguishable from other muscle masses
• Make every effort to reach diagnosis before resorting to percutaneous biopsy or aspiration

Often percutaneous biopsy is not necessary

However, if unsure regarding nature of mass, arrange either follow-up or biopsy or request alternative investigation (usually MR)

Helpful Clues for Common Diagnoses

• Hematoma

Due to trauma, anticoagulation, or vascular malformation

Anterior thigh is common location because it is susceptible to compression injury against femoral shaft and muscle contraction injury

Initially hyperechoic or isoechoic

– Becomes more hypoechoic with increasing liquefaction after several days to weeks

– ± layering or whorled pattern due to sequential episodes of bleeding (expanding hematoma)

Mild intramuscular hemorrhage may not be apparent on US, since ill-defined hyperechoic areas of blood blend with hyperechoic muscle

– No disturbance of muscle architecture with minor bleeding

– MR is more sensitive than US at detection of tumor hemorrhage
• Muscle Tear

Discontinuity ± retraction of muscle fibers within muscle bulk or at myofascial junction

– Myofascial junction most common site of tear

± tear filled with hematoma or fluid

± surrounding muscle and subcutaneous edema

Do not confuse with muscle contusion

– Contusion shows no fiber discontinuity

– May cross muscle fascial boundaries

– Ill-defined hyperechogenicity of muscle due to edema ± blood

– Hyperemia during reparative stage
• Nerve S heath Tumor

Arises along course of peripheral nerve

Well-defined, fusiform-shaped, hypoechoic mass

– Anechoic areas due to myxoid accumulation (common)

– ± additional areas of hyperechogenicity due to hemorrhage, calcification, or fibrosis

Posterior acoustic enhancement (mild to moderate)

Thickened entering or exiting nerve (very common)

– Entering or exiting nerve may not be visible if tumor arises from small peripheral nerve

Split-fat sign due to separation of muscle fibers with enhanced visibility of fat at edge of tumor

– Do not confuse with thickened nerve at edge of tumor

Mild to moderate hyperemia on color Doppler

– Very occasionally, minimal demonstrable vascularity

Cannot differentiate between schwannoma and neurofibroma based on US findings alone

Try, however, to determine whether nerve is centrically or eccentrically placed relative to parent nerve

Helpful Clues for Less Common Diagnoses

• Soft Tissue Sarcoma

Usually seen as large, well-defined, hypoechoic mass within muscle layer

– Moderately to highly vascular

– Occasionally hypovascular or even avascular on color Doppler imaging

– Hypovascularity does not exclude malignancy

Any large (> 5 cm), solid, nonfatty soft tissue tumor should be considered sarcoma unless proven otherwise by biopsy

– Most large intramuscular masses require biopsy

– Biopsy not very helpful in distinguishing well-differentiated liposarcoma from lipoma

– Better to decide likelihood of liposarcoma by clinical and MR criteria as well as histological analysis of full tumor following excision
• Myxoma

Composed of few spindle-shaped cells within mucoid material supported by loose collagen framework

– Derived from modified fibroblasts with increased proteoglycan production

Hypoechoic, cystic-type, intramuscular mass ± comet-tail artifacts

– Peripheral rim of increased echogenicity (bright rim sign), corresponding to perilesional muscle edema

– Triangular hyperechoic area adjacent to mass (bright cap sign), corresponding to muscle atrophy

– No communication with adjacent joint

– Main differential diagnosis is myxoid liposarcoma
• Fibromatosis

Also known as desmoid tumor

Locally aggressive overgrowth of fibrous tissue with well-defined or infiltrative border

– Typically absent or minimal vascularity on color Doppler imaging
• Abscess

More frequent in immunosuppressed patients

Many variable appearances

Thick-walled, irregular hypervascular outline with hypoechoic, avascular necrotic center (typical)

– + edema and hyperemia of adjacent inflamed tissues

– ± intralesional gas locules seen to move on real-time imaging

– ± enlarged regional lymph nodes

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Tags: Diagnostic Ultrasound Musculoskeletal

Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

DIFFERENTIAL DIAGNOSIS

Common

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

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Hypoechoic Muscle Mass

Hypoechoic Muscle Mass

Less Common

Rare but Important

Helpful Clues for Common Diagnoses

Helpful Clues for Less Common Diagnoses

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Hypoechoic Muscle Mass

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