Soft Tissues
fies the extension of the necrosis [1]. Ultrasound may theoretically allow early diagnosis by showing deep areas of emphysema before they become clin- ically accessible. Ultrasound may also distinguish between gangrenous cellulitis (which preserves the muscle) and necrotizing fasciitis (with myonecro- sis). Hypoechoic areas dissociating the muscle fibers would then be observed.
Deep Hematoma
A hematoma gives well-limited mass that is ane- choic at the first stage and can quickly become echoic and heterogeneous (Fig. 22.2). In case of doubt, ultrasound-guided investigation can give the diagnosis.
A hematoma can develop anywhere and give distinctive signs. At the rectus abdominis muscle, its extraperitoneal nature will be recognized since the peritoneal sliding will be preserved, posterior to the mass. In severe forms, it can be the source of compression (bowel, bladder, etc.) [2].
Soft tissues are accessible to ultrasound. They can be of interest in several instances.
Soft Tissue Abscess
The ultrasound signs include hypoechoic, heteroge- neous mass and inconstant punctiform hyperechoic areas indicating bacterial gas (Fig. 22.1), signs indi- cating a fluid nature such as posterior enhancement (which is inconstant) or changes in dimensions under probe pressure (but such maneuvers can be very harmful, not to say risky). In fact, abscess and hematoma often have similar patterns, and the ultra- sound-guided tap will make a definite diagnosis.
Necrotizing Cellulitis
The role that ultrasound can play is not well known in necrotizing cellulitis. The diagnosis is usually clinical. Surgical exploration alone speci- CHAPTER 22
Fig. 22.1. Huge heterogeneous collection in the gluteal area. With ultrasound guidance, the tap withdrew pus, thus confirming the abscess. Young patient with trauma
Fig. 22.2. Thigh collection in another traumatized pa- tient. The pattern is not far from that described in Fig. 22.1 but here is a partially solid hematoma
Parietal Emphysema
Parietal emphysema generates air comet-tail-type artifacts. They usually conceal the deeper struc- tures (Fig. 22.3). The presence of parietal emphyse- ma is certainly one of the rare indications to cancel ultrasound examination. However, it is sometimes possible to hide the masses of gas by gentle pressure. At the thoracic level, this is facili- tated by the ribs, which remain solid under pres- sure. Lung sliding can then sometimes be analyzed (see Chap. 16). Note that pneumothorax is not always present.
Let us recall that comet-tail artifacts generated by parietal emphysema can be a dangerous pitfall for the beginner when they appear as E lines. This pattern may be erroneously interpreted as B lines or lung rockets, and genuine pneumothorax can be missed (see Fig. 16.11, p 113). The search for the bat sign in this setting prevents this pitfall.
Edematous Syndromes
In cases of major hydric retention, the soft tissues are enlarged by edema, with hypoechoic zones dis- sociating the muscles. The analysis of the deeper structures is not hindered, as water is a good con- ductor for ultrasound beams.
In situations such as nephrotic syndrome with massive hypoalbuminemia, more or less substan- tial effusions can affect all of the anatomical com- partments.
Parietal Vessels
Ultrasound can be useful to accurately locate the epigastric or internal mammary vessels if a local tap is considered (see Fig. 5.12, p 32).
Undernutrition
The nutritional status of a patient is usually moni- tored by weighing the patient. This is a simple parameter. However, the maneuver is demanding for the paramedical team, and above all, the data obtained is a rough result of inverse trends: in a critically ill patient, the muscles and fat compart- ments decrease whereas the water compartment increases. Once more, ultrasound can potentially
provide logic-based assistance.A differential analy- sis of the fat [3], muscle and interstitial compart- ments can in fact be carried out (Fig. 22.4). Accept- ing that these variations are the same in any part of the body, only one standardized area should be investigated. An easy-to-access and reliable area is, for instance, a transverse, paraumbilical scan of the rectus abdominis muscle (Fig. 22.4) or, perhaps better, a transverse scan of the crural muscle at mid-thigh. Ultrasound may also detect interstitial edema before clinical evidence, but this precise issue has not yet been investigated.
158 Chapter 22 Soft Tissues
Fig. 22.3. Parietal emphysema. The deep structures in this thoracic view are unrecognizable since they are hidden by numerous comet-tail artifacts. This aspect is unusable. These are W lines, defined as comet-tail arti- facts arising from different levels in the soft tissues
Fig. 22.4. Transverse scan of the paraumbilical abdomi- nal wall. The white arrows sharply delimit the fat com- partment (17 mm), the black arrows the muscular com- partment (9 mm for the muscle). These measures can easily be repeated during the stay of the patient. Probe with 7.5-MHz frequency
Miscellaneous
Multiple disorders such as cysts, arterial aneurysms, osteomas, etc. not related to the acute illness can be detected in the soft tissues.
Traumatic Rhabdomyolysis
The muscular loges have increased volume, with- out abscess or hematoma to explain the clinical swelling. A hypoechoic pattern of the muscles with disorganization of the normal muscular architec- ture has been described [4]. Another advantage of ultrasound is ruling out associated venous throm- bosis (with here a possible place for Doppler if the compression maneuver is harmful).
Malignant Hyperthermia
A heterogeneous and grainy pattern of the mus- cles, with a hypoechoic pattern of the septa and fascia is described by some [5], not found by others [6]. The rarity of this syndrome in our ICU has until now prevented us from forming an opinion.
References
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3. Armellini F, Zamboni M, Rigo L, Todesco T, Bergamo- Andreis IA, Procacci C, Bosello O (1990) The contri- bution of sonography to the measurement of intra- abdominal fat. J Clin Ultrasound 18:563–567 4. Lamminen AE, Hekali PE, Tiula E, Suramo I, Korhola
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