Many patients come to the emergency department with complaints related to the soft tissues, e.g., infection, injury, and abnormal masses. Traditionally, computed tomography and magnetic resonance have been used when imaging studies are needed in these patients; however, ultrasound is generally more readily available and in some instances is the preferred imaging study.
The most common use of bedside ultrasound in patients with soft-tissue abnormalities is in the evaluation of infections, including cellulitis, abscess, and necrotizing fasciitis. Other soft-tissue indications include the evaluation of cysts and lymph nodes. Ultrasound is also used to locate foreign bodies.
Although the majority of abscesses are treated with incision and drainage, in certain cases, usually because of cosmesis, treatment with needle aspiration and antibiotics may be an option. Ozseker and colleagues found that ultrasound-guided aspiration and irrigation of breast abscesses was preferred to surgical drainage for abscesses with a diameter less than 3 cm. Ultrasound provides dynamic real-time guidance for needle aspiration, resulting in increased success.
Anatomy
The structures that are imaged in soft-tissue bedside ultrasound are primarily the skin, subcutaneous tissue, fascia, and muscle.
The skin consists of two layers: the superficial epidermis and the deeper, thicker dermis. The subcutaneous tissue, located beneath the dermis, consists of connective tissue septa and fat lobules. Fascia, a deeper structure, is a dense, fibrous membrane. Muscle consists of long muscle fibers grouped together into fascicles. Various layers of connective tissue surround the individual muscle fibers, fascicles, and entire muscles.
Scanning Technique, Normal Findings and Common Variants
To image deep structures such as the thigh muscles as shown here,
a low frequency curvilinear transducer may be used.
Normal skin, subcutaneous tissue, and fascia.
Longitudinal image of muscle.
Transverse image of muscle.
Early cellulitis.
Cobblestone appearance of advanced cellulitis.
Small ganglion cyst.
Equipment
Selection of the appropriate transducer is an important aspect of soft-tissue bedside ultrasonography. Because most structures to be imaged are relatively superficial, a high-frequency (7–12 MHz) linear transducer is most useful and provides a good balance between imaging depth and resolution. On occasion, deeper structures need to be visualized; in these cases, a lower-frequency transducer is required. If a lower-frequency linear transducer is not available, then a curvilinear transducer may be used .
Scanning Technique
The sonographer’s grip on the transducer is especially important in soft-tissue ultrasound because fine, controlled movements of the transducer are often required. The transducer should be held such that part of the hand, such as the small finger or ulnar aspect, rests against the patient’s body to stabilize the transducer.
In many cases, it is helpful to begin scanning a short distance away from the area of interest to gain an appreciation of the appearance of the normal, uninvolved anatomy. Then the transducer can be slid toward the area of interest. It can be helpful for the sonographer to place a finger of the hand not holding the transducer on the area of interest and then slide the transducer until it contacts the finger.
Images should be obtained in both longitudinal and transverse planes, which will provide the most information and allow accurate localization. It may be helpful to view the contralateral side of the patient’s body to obtain information about the normal appearance of structures.
Normal Findings
With the equipment that is typically used for bedside ultrasound , the epidermis and dermis cannot be differentiated. They appear together as a thin, hyperechoic layer. The subcutaneous layer appears hypoechoic on ultrasound, with two components: hypoechoic fat interspersed with hyperechoic linear echoes running mostly parallel to the skin, which represent connective tissue septa .Veins and nerves may be visualized within the subcutaneous layer.
Fascia appears as a linear hyperechoic layer. Its thickness may vary depending on the location.
Muscle fascicles can be visualized as hypoechoic cylindrical structures, with hyperechoic connective tissue (perimysium) surrounding them. A characteristic feature of muscle is that its appearance on ultrasound can change with contraction; it appears thicker and more echoic on short-axis planes when contracted.
Lymph nodes are hypoechoic and generally oval.
Pathology
Cellulitis
Cellulitis is the pathologic condition most frequently encountered during soft-tissue bedside ultrasonography.
The ultrasound appearance of cellulite varies depending on the stage and severity. The initial appearance may be generalized swelling and increased echogenicity of the skin and subcutaneous tissues As cellulitis progresses and the amount of subcutaneous fluid increases, hyperechoic fat lobules become separated by hypoechoic fluid-filled areas. This later stage of cellulitis is most typical and has been described as having a cobblestone appearance.
The appearance of fluid-filled interlobar septae is not specific for cellulitis but rather of generalized subcutaneous edema, which may result from other conditions such as congestive heart failure.
Picture above; Abscess , shows hyperemia , patient had pain and mild fever , wbc was increased.
Color and power Doppler are advanced ultrasound modalities that can help determine whether the inflammation characteristic of cellulitis is present. However, their use in the emergency department is beyond the skills of most emergency practitioners, who will instead rely on the physical examination for clinical correlation.
Tayal and colleagues studied the use of bedside ultrasound in emergency department patients with signs of cutaneous soft-tissue infection but no signs of obvious abscess. The use of ultrasound was found to change the management of a significant percentage of the study group. By routinely utilizing ultrasound in the evaluation of these patients, the physicians were able to avoid unnecessary drainage procedures as well as detect occult abscesses. This research supports the use of ultrasound in the evaluation of most patients with cellulitis.
Necrotizing Fasciitis
Necrotizing fasciitis is an uncommon, severe, life-threatening infection that involves the subcutaneous tissue, fascia, and muscle. On ultrasound it appears as thickened distorted fascia with adjacent hypoechoic fluid collection, along with swelling of the subcutaneous tissue and muscle. Small foci of gas can appear as bright echogenic areas with posterior acoustic shadowing.
Morrison et al used ultrasound to evaluate emergency department patients with Fournier’s gangrene and found subcutaneous scrotal gas in all cases. The authors concluded that bedside ultrasound was very useful in the evaluation of these patients.
Cysts
Ultrasound can help differentiate solid from cystic masses. Ganglion cysts are a common cystic mass that arises from tendon sheaths and joints (Figure7). They are filled with a gelatinous material. On ultrasound they appear anechoic and may cause posterior acoustic enhancement. It may be possible to trace the cyst to its origin from the tendon sheath or joint space.
ganglion cyst.
Lymph Nodes
Normal and reactive lymph nodes have the same ultrasound appearance: they are hypoechoic, with an echogenic hilus, and are generally oval. [hyperlink to ENT-Lymphadenitis] Malignant lymph nodes are usually hypoechoic, without an echogenic hilus, and round. This distinction is beyond the skill and experience of most emergency physicians, who should not attempt to differentiate these two entities. However, they can use ultrasound to identify a mass as a probable lymph node.
lymph node with normal flow.
Foreign Bodies
Ultrasound is useful in the evaluation of wounds and other soft tissue that may contain foreign bodies. [hyperlink to Foreign Bodies] It is especially useful in the search for radiolucent foreign bodies, which are difficult or impossible to detect by plain radiography or computed tomography.
AV MALFORMATION.
Bladder mass with flow, Had hematuria.
-Transitional cell carcinoma
Achilles Retro calc Bursitis; hyperemia.
Calcification .4th MCP dorsal. hand.
soft tissue edema .
Muscular hematoma.
muscular hematoma.
LIPOMA;
MUSCULAR TEAR.
MUSCLE WALL DEFECT; hernia.
sebaceous cyst .
Soft tissue Cancer .
Calf tear.
muscular tears , always compare with the other side.
Supraspinatus tear.
For trigger fingers ; Always check the flexor tendons of the hand, start from the dip, pip , MC areas and look at the tendon sheath thickness, fluid, ganglion cyst, calcifications, hyperemia and pain. Compare with other side. do sagittal and transverse section. Make sure to measures the depth without too much pressure so the Dr can have true depth for the injection. If you see a nerve or blood vescel in the area mark the image and inform the Radiologist so he can make note of it to the Doctor to be careful with the injection.
Thank you for reading.
Steve Ramsey; PhD- Public Health. MSc – Medical Ultrasound
BSC – Diagnostic Imaging; Calgary- Alberta- Canada.