2.2. Necrotizing and Non-Necrotizing Fascitiis

Infective fasciitis is an infection of the fascia and can be non-necrotizing (NNF) or necrotizing. Necrotizing fasciitis (NF), as a part of necrotizing soft-tissue infections (NSTI), is a rare but rapidly progressive infection of the deep soft tissue and fascia. If not treated promptly, it can lead to high morbidity and mortality ^[10][17][10,17]. Early surgical intervention is an important prognostic factor [10]. This infection is commonly presented as type 1, which is polymicrobial with common organisms that include aerobes and anaerobes. It commonly affects the perineum and trunk and is common in patients of advanced ages who have decreased immunity from preexisting diseases. Type 2 disease is monomicobial with Group A Streptococcus (most common) or staphylococcus aureus (including methicillin-resistant Staphylococcus aureus) being the common organisms. Patients are usually younger with trauma being a common method of inoculation. Vibrio and Clostridium species (type 3) and fungi (type 4) are additional causative organisms ^[10][18][10,18]. Predisposing factors include diabetes, obesity, immunosuppressed states, trauma (which can be minor, such as insect bites), intravenous drug use, venous insufficiency, and peripheral vascular disease. Common sites of infection include the extremities, perineum, trunk, and head and neck. NF has been given specific names when affecting certain regions—Ludwig angina when it affects the submandibular region and Fournier gangrene when it affects the perineum [19]. This infection commonly follows a penetrating injury or surgery, but can also occur without a history of trauma ^[17][19][17,19]. Following inoculation, there is a rapid growth of bacteria with production of exotoxins and activation of cytokines. Blood vessels are thrombosed and damaged with resultant ischemia and necrosis. The infection spreads along the fascia, far and wide, and can affect all tissues from skin to muscles ^[2][10][19][2,10,19]. Necrotizing soft-tissue infection (NSTI) is an advocated terminology to encompass all necrotizing infections deep to the skin, including the fascia ^[2][11][20][2,11,20].

2.3. Soft-Tissue Foreign Body

Each year, more than 11 million patients present to emergency departments with traumatic wounds and lacerations, with approximately 10% of these cases having a retained foreign body ^[21][42]. These retained foreign bodies are most commonly found in the extremities, with nearly one third involving the wrist, hand, or fingers ^[22][43]. The most common retained foreign bodies include wood, glass, and metal ^[23][44]. Soft tissue foreign bodies may also be the result of self-inflicted penetrating trauma, also known as self-embedding behavior ^[24][45]. Foreign bodies may also result from medical procedures, due to retained sponges or instruments or broken fragments of drains, implants, or surgical devices ^[25][46]. Metallic foreign bodies are common after gun-related injuries. Most foreign bodies are recognized at the time of injury, but more than one third may be missed at initial physical evaluation and can remain asymptomatic ^[26][47]. Although most foreign bodies can be removed by the injured patient without a problem, some cannot and are presented to the care of a physician. One series of foreign bodies in the hand reported a wide range of time anywhere from the day of injury to 20 years later for the removal of the retained foreign body (mean of seven months), with 43% being removed within one week and 11% being retained for more than one year ^[26][47]. Retained foreign bodies can result in a granulomatous immune response as the surrounding tissues attempt to wall off the foreign body from the patient, also known as foreign body reaction ^[27][48]. This starts with an aggregation of macrophages, lymphocytes, plasma cells, and fibroblasts that surround the foreign body. As most foreign bodies are too large to phagocytose, the macrophages undergo epithelioid transformation and fuse to form multinucleated giant cells and produce cytokines that stimulate fibroblasts to encapsulate the foreign body in a collagen matrix ^[28][49]. For organic foreign bodies, such as wood or animal parts, the foreign body reaction will continue until degradation; however, for nondegradable foreign bodies, the reaction continues until a well-formed capsule separates the foreign body from the immune system and may become asymptomatic for years or until trauma disrupts this capsule ^[29][50]. The first-line imaging modality for suspected foreign body should be conventional radiography, which is capable of detecting 80% of all foreign bodies ^[30][31][51,52]. This mostly depends on the atomic number and density of the foreign body; lower-density objects are radiolucent, but up to 98% of higher-density radiopaque objects are also depicted on conventional radiographs ^[23][31][44,52]. Metal, glass, stone, graphite, and calcified biologics (e.g., sea urchin spines) are all radiopaque, whereas wood, plastic, acrylics, and non-calcified biologics (e.g., larvae) are radiolucent ^[22][23][43,44]. Ultrasound is the best imaging modality for the evaluation of suspected radiolucent foreign bodies, with all foreign bodies demonstrating hyperechogenicity on ultrasound with posterior acoustic shadowing; foreign bodies with an irregular or curved surface demonstrate a “clean” shadow, and those with a flat or smooth surface, such as metal, glass, or plastic, demonstrate a “dirty” shadow with posterior reverberation (comet tail artifact) (Figure 3) ^[32][33][34][53,54,55].