Hypoechoic Subcutaneous Mass

DIFFERENTIAL DIAGNOSIS

Common

• Lipoma
• Vascular Anomaly
• Epidermoid Cyst
• Peripheral Nerve Sheath Tumor

Less Common

• Vascular Leiomyoma
• Pilomatricoma
• Fibroma
• Glomus Tumor
• Lymph Node
• Hematoma
• Abscess
• Fat Necrosis
• Rheumatoid Nodule
• Foreign Body Granuloma
• Sweat Gland Tumor
• Metastasis
• Lymphoma
• Sarcoma

Dermatofibrosarcoma Protuberans

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

• Ensure lesion is confined to subcutaneous tissues

Lesion location has important implications for diagnosis and treatment
• Use minimal transducer pressure to avoid distorting lesion

Copious skin gel will allow stand-off effect for superficial lesions

– This is better than using gel pad, which will exert pressure on subcutaneous tissues
• Compressibility assessed by transducer pressure

Gives indication of firmness of mass, which is useful when distinguishing fatty from nonfatty tissue or inflammatory from noninflammatory tissue

Helpful Clues for Common Diagnoses

• Lipoma

Variable echogenicity depending on cellularity and fat-water content

– Usually are mildly hyperechoic or isoechoic to subcutaneous fat

– Subcutaneous fat usually hypoechoic but this echogenicity can vary for different locations

Diagnosis (as always) depends on constellation of findings rather than 1 single feature

– Well-marginated, encapsulated, compressible mass with multiple fine distinctive echogenic lines parallel to skin surface

– Usually no vascularity on color Doppler imaging
• Vascular Anomaly

Comprises both vascular tumor (hemangioma) and vascular malformation

– Differentiation based on cellular turnover, histologic features, and natural history

Variable US appearances

– Mixed echogenicity depending on relative amount of fatty stroma or dilated vascular channels

– Dilated vascular or lymphatic spaces may appear as hypoechoic vascular channels or cystic spaces

– Vascular anomalies with prominent vascular components appear hypoechoic

– Vascularity varies from no detectable flow to very hypervascular depending on vessel type, size, and flow

Slow venous flow best seen on real-time grayscale imaging

– Moderately compressible ± phleboliths
• Epidermoid Cyst

Appearances depend on degree of cyst maturation and compactness of keratin ± presence of cyst rupture

Well-circumscribed, ovoid or lobulated mass with increased acoustic transmission

Most are heterogeneous

– Layered keratin aggregates ± cholesterol deposition → linear, hyperreflective, disc-like areas

– Areas lacking keratin → cleft-like or filiform anechoic or hypoechoic areas

– Less compact keratin → increased hypoechogenicity

Most epidermoid cysts are avascular

– Peripheral and pericystic vascularity is feature of cyst rupture with pericystic inflammation
• Peripheral Nerve Sheath Tumor

Well-defined homogeneous hypoechoic mass

Occasionally heterogeneous

– Heterogenicity due to areas of myxoid tissue, hemorrhage, fibrosis, or calcification

Fusiform or oblong-shaped along course of nerve

– Entering or exiting nerve seen in majority of cases

– Entering/exiting nerves may not be seen if arising from small nerve

Posterior acoustic enhancement is common

Usually mild to moderate vascularity

Helpful Clues for Less Common Diagnoses

• Vascular L eiomyoma

Benign, solitary smooth muscle neoplasm most commonly occurs in subcutaneous soft tissues of lower limb

Usually round or ovoid in shape with long axis parallel to extremity axis

Smooth-bordered, homogeneous, hypoechoic mass without perceivable capsule

Occurs in close proximity to artery or vein

Often hypervascular ± vascular convergence
• Pilomatricoma

Benign skin tumor arising from cells of hair matrix; more commonly seen in children

Well-circumscribed, ovoid, heterogeneous, solid subdermal mass containing matrix calcification, intrinsic vascularity, and peripheral hypoechoic rim (due to connective tissue capsule)

Intrinsic vascularity may be peripheral, central, or mixed
• Fibroma

Localized tumorous collection of collagen with sparse number of fibroblasts

Well-defined to irregular hypoechoic mass

Minimal to mild intrinsic vascularity
• Glomus Tumor

Arises from glomus body, which is arteriovenous shunt in dermis that contributes to temperature regulation

Most common location: Distal extremities, especially subungual areas

Small, well-defined, hypoechoic, hypervascular mass

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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 Subcutaneous Mass

Hypoechoic Subcutaneous Mass

Less Common

Helpful Clues for Common Diagnoses

Helpful Clues for Less Common Diagnoses

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Hypoechoic Subcutaneous Mass

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