Soft Tissue Mass Clinical and Imaging Approach

An approach to soft tissue masses.

Clinical examination and ultrasound review of soft tissue masses may lead to:

1. A specific diagnosis
2. A mass like lesion
3. No sonographic abnormality

Specific diagnosis include a foreign body, henia, ganglion cyst, lymph node, Bone and calcifications, epidermal cysts, abscess and hematoma.

Mass like lesions may either be superficial and less than 5cm

• Characteristic of a lipoma; consider clinical follow up or MRI
• Not characteristic of a lipoma; consider excision, needle biopsy, or MRI.

Mass like lesions may be deep or greater than 5cm in depth. 

• Please consider an MRI of the extremity in question or a CT of the CHEST and ABDOMEN.

In the event of a suspicious clinical examination, but No sonographic abnormality; consider MRI or CT.

Specific diagnosis on US: 

• a foreign body: including wood, glass and metal may be visualised on US. Wood usually has a echogenic focus with abnormal shadowing deep to the foreign body. Glass as an echogenic focus with reverberation artifact. Metal may have either shadowing or reverberation artifact. A metal foreign body may show a twinkle artifact.
• henia: Heanias change in size, with shadowing at the edge or neck of the hernia. It is important to differentiate a lipoma from a peritoneal hernia, as the treatment is different. A lipoma does not have edge shadowing. Remember besides peritoneal hernias there are muscle hernia. The tibialis anterior muscle hernia is amongst the most common muscle hernia, and herniates through the deep fascia, through to the subcutaneous tissue, on dynamic imaging (that is exercise).
• ganglion cyst: anechoic lesion, with predominant through transmission, no internal doppler signal to indicate blood flow, may have partial septations and internal debris. The cyst connects and should be traced to a joint or a tendon sheath.  Be careful of lymphoma, that may appear as a cyst but has increased doppler signal. 
• lymph node: lymph node has a fatty hilum with doppler signal. The absence of a fatty hilum is concerning for metastasis.
• Bone and calcifications: Please correlate with a radiograph. If there is a osteochondroma measure the cartilaginous cap. Fractures, bony protuberances may also be detected.
• Fat necrosis: Subcutaneous location, may have some degree of shadowing. Altered subcutaneous fat.
• epidermal inclusion cysts: Dermal attachment, deep acoustic enhancement, No internal flow. Chronic non-painful lesion. Should touch the dermis. These may rupture with pain.
• abscess: need differential compression, hyperechoic to anechoic making the echogenicity of the lesion less sensitive. Expect thickening of the overlying dermis and subcutaneous tissue. Cellulitis has  dermal thickening, expansion and increased echogenicity of the subcutaneous fat, without a defined or loculated fluid collection. Melanoma - no thickening of the dermis or subcutaneous tissue. 
• Hematoma - Acute echogenic, Chronic hypoechoic. If there is doubt must consider MRI to exclude sarcoma, that may have arterial blood flow. 

abscess, angiomyolipoma, color Doppler, epidermal cyst, epidermal inclusion cyst, extended field of view, fat necrosis, fibrolipoma, foreign body, ganglion cyst, hemangioma, hematoma, hernia, intramuscular squamous cell carcinoma, lipoma, liposarcoma, lymph node, metastatic melanoma, neurofibroma, non-Hodgkin lymphoma, pilomaticooma, schwannoma