Soft tissue, musculoskeletal system, and miscellaneous targets

Overview

Besides encompassing specific focused techniques, the holistic approach (HOLA) ultrasound concept, introduced in Chapter 1 , promotes generic scanning of any body part (head-to-toe ultrasound imaging) as modulated by current clinical indications. Any ultrasound view obtained through the skin contains some information about soft tissues. While serving as an imaging window and as anatomic reference structures in focused techniques (e.g., the chest wall in lung scanning), soft tissues per se are often a primary target (e.g., in extremity crush injury). Therefore mastery of fine anatomy is essential for the HOLA-level ultrasound operator, both in terms of tissue type (e.g., fascia, tendon, peritoneum), and in terms of named structures (e.g., basilic vein, gracilis muscle, median nerve). This chapter reviews nonspecific (generic) soft tissue and musculoskeletal (MSK) imaging and miscellaneous intensive care unit (ICU)-relevant HOLA targets.

Soft tissue and skeletal scanning may be indicated in many clinical situations, including the following:

• Visible bruising, swelling, deformity, redness, pulsation, or asymmetry

• Palpable mass, warmth, pulsation, crepitus, or other focal abnormality

• Known or suspected foreign body, including indwelling access devices

• Known or suspected MSK injury or history of a relevant event, such as a fall

• Traumatic or surgical wounds

• Spontaneous, traumatic, surgically placed, or postsurgical fistulas

• Ruling out pathologic lymph nodes

• Planning interventional procedures (e.g., vascular access)

• Known or suspected vascular pathology or access devices, including status post difficult vascular access

Equipment and technique

Any modern multipurpose system with a high-frequency (7-15 MHz) transducer is appropriate for most superficial targets. Lower frequencies (2-5 MHz) are used for deeper tissues in large subjects or large body parts (e.g., the thigh). More than one transducer can be used on the same region of interest (ROI) to exploit advantages of each. Some experts recommend broadband microconvex transducers (usually 5-8 MHz) for most soft tissue targets because they offer a good balance of resolution and penetration in a wide-angle view through a small footprint. With any transducer, both B-mode and color Doppler mode are often used. Although elastography , an emerging method to map elasticity of tissues, currently has limited use in the ICU, every superficial tissue scanning procedure includes elements of “visual elastography” (see Pathology section later).

Commercially available gel pads or a thick layer of gel (probe “floating” technique) are used for imaging the most superficial tissues or lesions, especially when an adequately high-frequency probe is not available.