RadioGraphics
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

DOI: 10.1148/rg.276075033
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow CME Test (opens in a new window)
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Fayad, L. M.
Right arrow Articles by Fishman, E. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Fayad, L. M.
Right arrow Articles by Fishman, E. K.
Related Collections
Right arrow Musculoskeletal Radiology
Right arrow Computed Tomography
Right arrow Emergency Radiology
RadioGraphics 2007;27:1723-1736
© RSNA, 2007

EDUCATION EXHIBIT

Musculoskeletal Infection: Role of CT in the Emergency Department1

Laura M. Fayad, MD, John A. Carrino, MD, and Elliot K. Fishman, MD

1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Medical Institutions, 601 N Wolfe St, Baltimore, MD 21287. Presented as an education exhibit at the 2006 RSNA Annual Meeting. Received February 27, 2007; revision requested March 27 and received April 20; accepted April 27. E.K.F. received a research grant from Siemens, is a member of the Siemens and GE Healthcare advisory boards, and is a cofounder of Hip Graphics; remaining authors have no financial relationships to disclose. Address correspondence to L.M.F. (e-mail: lfayad1{at}jhmi.edu).


   Abstract
Top
 Abstract
LEARNING OBJECTIVES
 Introduction
 Materials and Methods
 Results and Discussion
 Conclusions
 References
 
Musculoskeletal infection is commonly encountered in the emergency department and can take many forms, depending on the involvement of the various soft-tissue layers, bones, and joints. Infection may manifest as superficial cellulitis, necrotizing or nonnecrotizing fasciitis, myositis, a soft-tissue abscess, osteomyelitis, or septic arthritis. Because clinical parameters for the detection of musculoskeletal infection generally lack sensitivity and specificity, computed tomography (CT) plays an important role in the assessment of potential musculoskeletal infections in the emergency department. CT provides an analysis of compartmental anatomy, thereby helping to distinguish among the various types of musculoskeletal infection and to guide treatment options. Specific imaging features exist that help identify the numerous forms of infection in the bones and soft tissues, and CT is invaluable for detecting deep complications of cellulitis and pinpointing the anatomic compartment that is involved by an infection. Although all patients with musculoskeletal infection will require treatment with antibiotics, CT helps guide therapy toward emergency surgical débridement in cases of necrotizing fasciitis and toward percutaneous drainage in cases of abscess formation.

© RSNA, 2007


   LEARNING OBJECTIVES
Top
 Abstract
 LEARNING OBJECTIVES
Introduction
 Materials and Methods
 Results and Discussion
 Conclusions
 References
 
After reading this article and taking the test, the reader will be able to:


   Introduction
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
Materials and Methods
 Results and Discussion
 Conclusions
 References
 
Each year, the diagnosis of musculoskeletal infection is made in approximately 1.98 million patients in the emergency department, most of whom are afflicted with cellulitis or a soft-tissue abscess (1). In a large inner-city hospital, however, musculoskeletal infection is more commonly encountered in the emergency department and is generally more severe than in the community at large, given the high number of intravenous drug abuse patients and human immunodeficiency virus (HIV)–infected individuals who frequent the emergency department and are susceptible to these infections (2–5). For example, in one inner-city hospital, soft-tissue infections accounted for 18.3% of all intravenous drug abuse–related visits to the emergency department (5), and, in another setting, osteomyelitis and septic arthritis were seen in 38.7% of HIV-infected patients (4). Other patients who are especially at risk for musculoskeletal infection include those with sickle cell disease, in whom one study found osteomyelitis in 17.8% of cases (6); diabetic patients, 25% of whom experience foot ulcers and are at high risk for osteomyelitis (7); patients with peripheral vascular disease; and immunocompromised patients.

Musculoskeletal infection can take many forms, depending on what tissues are involved (Fig 1). Infection may manifest as superficial cellulitis, necrotizing or nonnecrotizing fasciitis, myositis, a soft-tissue abscess, osteomyelitis, or septic arthritis. Numerous noninvasive techniques are currently being used to evaluate cases of suspected musculoskeletal infection. However, because clinical parameters such as white blood cell count, C-reactive protein level, and erythrocyte sedimentation rate generally lack sensitivity and specificity, particularly in bone infections (8), computed tomography (CT) plays an important role in the assessment of potential musculoskeletal infections in the emergency department. CT provides an analysis of compartmental anatomy, thereby helping to distinguish the various patterns of musculoskeletal infection and guide treatment options. Another cross-sectional imaging modality for the assessment of musculoskeletal infection is magnetic resonance (MR) imaging, which provides superior contrast resolution compared with CT. Consequently, MR imaging may provide a superior analysis of compartmental anatomy and is more sensitive to the presence of soft-tissue abnormalities and acute osteomyelitis than is CT. However, MR imaging is not usually the first cross-sectional test available in the emergency department and is more time consuming and more expensive than CT in the diagnosis of musculoskeletal infection.


Figure 1
View larger version (72K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1.  Drawings illustrate the normal soft-tissue and bone compartments that may be affected by musculoskeletal infection.

 
In this article, we examine the role of CT in the evaluation of musculoskeletal infections in the emergency department of a large inner-city hospital. In so doing, we discuss and illustrate the spectrum of musculoskeletal infections that may be encountered and specific imaging features that help distinguish among these disorders.


   Materials and Methods
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Materials and Methods
Results and Discussion
 Conclusions
 References
 
Using an imaging database with ICD-9 codes, we retrospectively identified patients who had undergone CT in the emergency department for suspected musculoskeletal infection between September 19, 2002, and September 12, 2006. The medical charts of these patients were reviewed for clinical history, including signs and symptoms; the results of laboratory work-up; and CT findings. Specific cases were then selected to highlight characteristic features of musculoskeletal infection. In these cases, CT had been performed on four-, 16-, and 64-detector CT scanners, with the latter being introduced in November 2004. CT was performed on a 64-detector CT scanner (Siemens Sensation 64; Siemens Medical Solutions, Malvern, Pa) in approximately 50% of cases.

Because a 64-detector CT scanner provides a spatial resolution greater than that of its predecessors, it is expected to produce scans on which subtle details are enhanced and possibly more easily identified than on scans obtained with scanners with fewer detectors, although research to support this hypothesis is lacking. With 64-detector CT, isotropic data sets are produced that can be manipulated to create multiplanar reformatted (MPR) and three-dimensional (3D) volume-rendered (VR) CT images at the same resolution as that of axial CT scans; this capacity represents a distinct advantage over earlier technology, which did not allow the acquisition of isotropic data sets. Other advantages of 64-detector CT include (a) shorter scanning times in emergency department patients who may not be able to cooperate for an extended period of time, and (b) ease of concurrent performance of CT angiography.

The imaging parameters were guided by the clinical application. Skeletal disease was imaged without the intravenous administration of contrast material and with the following parameters: 120 kVp, 200–225 effective mAs, 0.5-second rotation time, and 0.6-mm detector collimation. For soft-tissue disease, scanning parameters were 120 kVp, 200 effective mAs, 0.5-second rotation time, and 0.6-mm detector collimation. In all cases of suspected soft-tissue infection, 120 mL of iohexol (Omnipaque 350; Nycomed Amersham, Princeton, NJ) was administered intravenously. All scanning data obtained in these cases were sent to a workstation (Leonardo, Siemens), and two-dimensional MPR and 3D VR CT images were created by a radiologist at the workstation using InSpace software (Siemens). In addition, traditional axial images were reconstructed in all cases, with a section thickness of 3 mm.

It should be noted that in the elderly population and in persons who cannot receive intravenous contrast material, MR imaging may be a more effective means of imaging for potential soft-tissue infection, given that the diagnosis can generally be made with the use of noncontrast fluid-sensitive sequences.


   Results and Discussion
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Materials and Methods
 Results and Discussion
Conclusions
 References
 
Between September 19, 2002, and September 12, 2006, a total of 1196 emergency department patients underwent CT for suspected musculoskeletal infection. Of these patients, 1122 (93.8%) had a suspected soft-tissue infection, whereas only 74 (6.2%) had a suspected bone infection; 783 patients (65.5%) had an underlying history of HIV infection. An upper-extremity infection was seen in 134 cases (11.2%) and a lower-extremity infection in 172 cases (14.4%); the chest, pelvis, or spine was involved in the remaining cases. Certain cases in which 64-detector CT was performed were chosen to highlight the characteristic features of the spectrum of musculoskeletal infections discussed in the following sections.

Cellulitis
Cellulitis represents an acute infection of the dermis and subcutaneous tissues that results in pain, erythema, edema, and warmth. Because the epidermis is not involved, cellulitis is not transmitted by person-to-person contact (Fig 2). Cellulitis occurs following disruption of the skin and invasion by microorganisms that may be indigenous flora, such as Staphylococcus aureus, or exogenous bacteria. Patients with peripheral vascular disease or diabetes are particularly susceptible to this type of infection, since minor injuries to the skin or cracked skin in the feet or toes can serve as a point of entry for infection. Other patients who are susceptible to cellulitis include those in whom foreign bodies such as intravenous catheters and orthopedic hardware penetrate the skin (9).


Figure 2
View larger version (67K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2.  Cellulitis. Drawings illustrate the pathophysiologic changes of cellulitis. The dermis and subcutaneous tissues are involved, with occasional thickening of the superficial fascia. The epidermis is not involved, thereby prohibiting the person-to-person spread of disease.

 
Uncomplicated cellulitis is a clinical diagnosis and is treated conservatively with antibiotics and locally supportive measures. However, there is a risk for serious and rapid spread of infection in patients with diabetes, immunodeficiency, impaired peripheral circulation, or a history of lymphadenectomy (10). In such patients who present to the emergency department, CT is used to accurately differentiate between superficial cellulitis and cellulitis associated with a deep-seated infection. In uncomplicated cellulitis, CT demonstrates skin thickening, septation of the subcutaneous fat, and thickening of the underlying superficial fascia (Fig 3), although it should be noted that bland edema due to heart failure or stasis will have a similar appearance, and clinical correlation is required. If present, a radiopaque foreign body associated with cellulitis can be detected at CT (Fig 4).


Figure 3A
View larger version (59K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3a.  Cellulitis in a 50-year-old man with a history of intravenous drug abuse who presented with swelling of the right hand and forearm. Sagittal oblique (a) and coronal oblique (b) VR CT images show an ulceration of the skin with extensive underlying subcutaneous stranding and septation, findings that are characteristic of cellulitis.

 

Figure 3B
View larger version (77K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3b.  Cellulitis in a 50-year-old man with a history of intravenous drug abuse who presented with swelling of the right hand and forearm. Sagittal oblique (a) and coronal oblique (b) VR CT images show an ulceration of the skin with extensive underlying subcutaneous stranding and septation, findings that are characteristic of cellulitis.

 

Figure 4
View larger version (99K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 4.  Cellulitis in a 31-year-old woman with a history of HIV infection and intravenous drug abuse who presented with a skin infection on the right side of the groin. CT scan shows a broken needle fragment in the right inguinal region (arrow) with associated minimal skin thickening.

 
If the infection spreads to deeper tissues, deep cellulitis, myositis, necrotizing fasciitis, or osteomyelitis can occur, all of which can be excluded with CT. A soft-tissue abscess is a well-recognized complication of cellulitis.

Special consideration should be given to geriatric patients, in whom cellulitis of the lower extremities is more likely to develop into thrombophlebitis. In the latter setting, contrast material–enhanced CT can help identify the extent of thrombus.

Necrotizing Fasciitis
Necrotizing fasciitis is a progressive, rapidly spreading infection of the deep fascia, with secondary necrosis of the subcutaneous tissues (Fig 5). The speed with which the infection spreads is directly proportional to the thickness of the subcutaneous layer (11). Necrotizing fasciitis is relatively rare, although its prevalence is on the rise because of an increase in the number of immunocompromised patients with HIV infection, diabetes mellitus, cancer, alcoholism, vascular insufficiencies, and organ transplants. It can occur after trauma or around foreign bodies in surgical wounds, although it can also be idiopathic, as in scrotal or penile necrotizing fasciitis (Fournier gangrene). Necrotizing soft-tissue infections are often accompanied by gas-forming anaerobic bacteria, usually in combination with aerobic gram-negative organisms (12).


Figure 5
View larger version (68K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 5.  Necrotizing fasciitis. Drawings illustrate the pathophysiologic changes of necrotizing fasciitis, including liquefactive necrosis of the subcutaneous fat, air tracking along deep fascial planes, and vascular thrombosis with resultant skin changes.

 
Necrotizing fasciitis constitutes a life-threatening surgical emergency. Unfortunately, this infection can be difficult to recognize in its early stages and progresses rapidly. The overall morbidity and mortality rate is 70%–80%, and one of the most important predictors of mortality is a delay in the diagnosis of necrosis (13). Hence, CT can play a vital role in suggesting the diagnosis early and initiating rapid and successful treatment.

The imaging findings in necrotizing fasciitis are similar to those in cellulitis but are more severe and show involvement of deeper structures. One specific distinguishing sign of necrotizing fasciitis is the presence of gas in the subcutaneous tissues caused by gas-forming anaerobic organisms (Fig 6), although gas is not observed in all cases. Other CT features include thickening of the affected fascia, fluid collections along the deep fascial sheaths, and extension of edema into the inter-muscular septa and the muscles (Figs 7, 8) (14,15). At contrast-enhanced CT, there is no demonstrable enhancement of the fascia, a finding that confirms the presence of necrosis and helps distinguish nonnecrotizing fasciitis from necrotizing fasciitis. Nonnecrotizing fasciitis does not require emergency surgery, but affected patients should be followed up because of the potential for necrosis.


Figure 6
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 6.  Necrotizing fasciitis. CT scan obtained in a 45-year-old man with a history of intravenous drug abuse, who presented with swelling and pain in the left upper extremity, shows subcutaneous fluid and gas with underlying muscle edema, with gas dissecting along nonenhancing fascia, findings that are indicative of necrotizing fasciitis.

 

Figure 7
View larger version (52K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 7.  Necrotizing fasciitis. CT scan obtained in a 61-year-old woman with a history of underlying diabetes, who presented with altered mental status and sepsis, shows subcutaneous fat stranding and gas dissecting along fascial planes. The patient had a small vulvar abnormality that had rapidly developed into necrotizing fasciitis involving both lower extremities.

 

Figure 8
View larger version (125K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 8.  Necrotizing fasciitis. CT scan of the pelvis obtained in a 69-year-old man with a history of diabetes, who presented to the emergency department with delirium and sepsis, shows gas dissecting along the gluteus fascial plane, a finding that is indicative of necrotizing fasciitis. The patient underwent extensive débridement but subsequently died.

 
Treatment of necrotizing fasciitis involves aggressive surgical débridement and the administration of antibiotics (Fig 9).


Figure 9
View larger version (112K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 9.  Necrotizing fasciitis. Sagittal oblique 3D VR CT image obtained in a 35-year-old man with a history of intravenous drug abuse and necrotizing fasciitis of the right upper extremity shows extensive débridement of the upper-extremity skin, subcutaneous tissues, and underlying muscles. The patient had undergone multiple débridements and a 6-week course of intravenous antibiotics. The area showed eventual healing by secondary intention, and a skin graft was not required.

 
Soft-Tissue Abscess
Although most bacterial infections in the soft tissues stay localized, an abscess may form, particularly in immunocompromised patients. The most commonly isolated pathogen is S aureus (16), although in an urban emergency department population, methicillin-resistant S aureus is cultured in 51% of patients with a soft-tissue infection (17), and these patients are more likely to have a soft-tissue abscess than are patients in whom other bacteria are cultured (18). At CT, a well-demarcated fluid collection with a peripheral pseudo-capsule showing rim enhancement is characteristic of an abscess and helps differentiate an abscess from simple cellulitis or fasciitis (Fig 10) (19–21). Treatment of a soft-tissue abscess consists of appropriate antibiotics and percutaneous drainage.


Figure 10
View larger version (105K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 10.  Soft-tissue abscess in a 46-year-old man with HIV infection who presented with right axillary pain and redness. The patient had a history of cat scratches. CT scan shows right axillary lymphadenopathy and a small rim-enhancing abscess (arrow). The patient tested positive for Bartonella henselae at serologic analysis.

 
Infectious Myositis
Infectious myositis is an acute, subacute, or chronic infection of skeletal muscle that is most often seen in young adults. Although viruses, bacteria (including mycobacteria), fungi, and parasites can cause myositis, the most common infectious agent is a bacterium, S aureus (77% of cases) (22). Pyomyositis (Fig 11), or bacterial myositis, was once considered a tropical disease but is now seen in temperate climates, particularly with the emergence of HIV infection (23). In one study, 17% of North American patients with pyomyositis had underlying HIV infection (24). Some authors report pyomyositis as the most common musculoskeletal complication of AIDS (4), but other risk factors abound, including strenuous activity or rhabdomyolysis (Fig 12) and muscle trauma, in which cases a hematoma may form and act as a nidus for infection (Fig 13). Skin infections, infected insect bites, injection of illicit drugs, and underlying diabetes mellitus can also lead to pyomyositis.


Figure 11
View larger version (76K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 11.  Pyomyositis. Drawings illustrate the pathophysiologic changes of the second phase of pyomyositis. The first phase results in muscle edema, whereas the second phase is characterized by muscle enlargement and edema with an organized muscle abscess.

 

Figure 12
View larger version (97K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 12.  Pyomyositis. CT scan obtained in a 33-year-old man with a history of cocaine abuse, who presented to the emergency department with rhabdomyolysis, shows marked enlargement and low attenuation in the left pectoralis muscle, findings that are suggestive of superimposed pyomyositis. The patient was subsequently treated with intravenous antibiotics.

 

Figure 13
View larger version (106K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 13.  Pyomyositis. CT scan obtained in a 48-year-old man with a history of HIV infection and intravenous drug abuse, who presented with a hematoma in the right thigh following a fall, shows a large mass with a fluid-fluid level (arrow), a finding that represents the hematoma. The hematoma was aspirated, revealing a superinfection with Escherichia coli.

 
Primary pyomyositis can involve any muscle group in the body. Typically, only a single muscle is affected, although 11%–43% of patients with pyomyositis have involvement of multiple sites (22). The most common site of infection is the quadriceps muscle, followed by the gluteal and iliopsoas muscles, with upper-extremity muscles being affected less frequently (22). In the past, it was shown that iliopsoas pyomyositis affected up to 20% of patients with spinal tuberculosis, so that the diagnosis of an iliopsoas abscess most frequently implied an underlying tuberculous infection of the spine. Today, however, iliopsoas pyomyositis most commonly occurs secondary to gastrointestinal or urinary tract infection (Figs 14, 15) (25–27).


Figure 14
Figure 14
View larger version (275K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 14.  Iliopsoas pyomyositis in a 56-year-old man with a history of methicillin-resistant S aureus bacteremia and back pain. Coronal 3D VR CT images show bilateral psoas abscesses (arrows) associated with diskitis or osteomyelitis.

 

Figure 15
View larger version (106K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 15.  Iliopsoas pyomyositis in a 52-year-old woman with a history of HIV infection and intravenous drug abuse who presented with back pain. CT scan shows a rim-enhancing paraspinal abscess with epidural extension (arrows) that required drainage. In HIV-infected patients with paravertebral abscess, atypical pathogens such as tuberculosis should be sought; in this case, no pathogen was cultured.

 
Findings of pyomyositis can be subtle in immunocompromised persons; thus, a high degree of suspicion is required for diagnosis. Pyomyositis is characterized by three stages: (a) the invasive stage, in which edema in the affected muscle leads to pain; (b) the suppurative phase, in which the patient develops a fever and, if not treated, an abscess; and (c) the late stage, which is potentially life threatening and leads to toxicity and sepsis (22).

At CT, there is enlargement and decreased attenuation of the affected muscle with effacement of surrounding fat planes. Involvement of a muscle group that is disproportionate to the involvement of subcutaneous tissue helps distinguish myositis from primary cellulitis. Intramuscular fluid collections may be observed, and contrast material is administered to help differentiate necrotic from viable musculature and to demonstrate a rim-enhancing abscess if present (Figs 16, 17).


Figure 16A
View larger version (143K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 16a.  Pyomyositis. Coronal oblique 3D VR CT image (a) and axial CT scan (b) obtained in an afebrile 49-year-old man with a history of HIV infection and intravenous drug abuse, who presented to the emergency department with increasing redness, warmth, and swelling of the left upper extremity, show a large rim-enhancing abscess within the deltoid muscle, with overlying skin thickening and enhancement. The underlying vessels were patent, with no evidence of venous thrombosis or osteomyelitis. Note the axillary lymphadenopathy.

 

Figure 16B
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 16b.  Pyomyositis. Coronal oblique 3D VR CT image (a) and axial CT scan (b) obtained in an afebrile 49-year-old man with a history of HIV infection and intravenous drug abuse, who presented to the emergency department with increasing redness, warmth, and swelling of the left upper extremity, show a large rim-enhancing abscess within the deltoid muscle, with overlying skin thickening and enhancement. The underlying vessels were patent, with no evidence of venous thrombosis or osteomyelitis. Note the axillary lymphadenopathy.

 

Figure 17
View larger version (126K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 17.  Pyomyositis. Sagittal MPR CT image of the left shoulder obtained in a 60-year-old man with a history of immunosuppression from prior liver transplantation, who presented with febrile neutropenia and left shoulder pain, shows enlargement of the left teres major muscle with a small rim-enhancing abscess (short arrow), a finding that indicates pyomyositis. Myositis of the teres minor muscle is also seen, with enlargement of the muscle belly and edema (long arrow).

 
CT can help guide treatment toward aspiration and is useful for surgical planning, since drainage of the muscle abscess followed by administration of appropriate antibiotics remains the mainstay of treatment and usually leads to complete recovery. Complications of untreated pyomyositis may include a compartment syndrome, progression of infection to osteomyelitis and septic arthritis, and even death. In the long term, patients may experience muscle scarring, weakness, and dysfunction (22).

Osteomyelitis
Osteomyelitis is a bone infection that can result from hematogenous spread or can be secondary to direct or contiguous inoculation (Fig 18). In young adults, it is most commonly associated with an open fracture or direct trauma, whereas in elderly and pediatric patients, the cause of osteomyelitis is typically bacteremia. As with other musculoskeletal infections, disease states known to predispose patients to osteomyelitis include immunosuppression, diabetes mellitus, sickle cell disease, intravenous drug abuse, and alcoholism.


Figure 18
View larger version (76K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 18.  Osteomyelitis. Drawings illustrate the pathophysiologic changes of osteomyelitis due to contiguous spread. Bone infection results from the spread of disease in the adjacent soft-tissue structures.

 
Hematogenous osteomyelitis usually manifests with a slow, insidious progression of symptoms; in contrast, osteomyelitis due to direct inoculation is localized, with prominent local signs and symptoms. The most frequently involved bones are the tibia, wrist, femur, ribs, and thoracolumbar spine (15). The most commonly cultured pathogen is S aureus (28), although in HIV-infected patients, 30% of cases of osteomyelitis are due to atypical mycobacteria (29). It should be noted that blood culture results are positive in only 50% of patients with hematogenous osteomyelitis.

Imaging can play a vital role in the diagnosis of osteomyelitis, since the diagnosis requires fulfillment of two of the following four criteria, one of which is positive imaging findings: (a) purulent material draining from the site of acute osteomyelitis, (b) positive findings at bone tissue or blood culture, (c) localized classic physical findings of bone tenderness and edema, and, as mentioned, (d) positive radiologic findings. Unfortunately, conventional radiographic evaluation of acute osteomyelitis is insufficient because bone changes are not evident for 14–21 days after the onset of infection. In fact, radiographs are typically normal at presentation in 95% of cases, and it is not until 28 days after the onset of infection that 90% of patients demonstrate some abnormality at conventional radiography (30). Therefore, although MR imaging is the accepted modality of choice for the early detection and surgical localization of osteomyelitis, in the emergency department, CT is usually more readily available for establishing the diagnosis (31).

At CT, features of bacterial osteomyelitis include overlying soft-tissue swelling, periosteal reaction, medullary low-attenuation areas or trabecular coarsening, and focal cortical erosions (Figs 19, 20). In addition, an extramedullary fat-fluid level is a rare but specific sign for osteomyelitis. This sign is an indication of cortical breach and, thus, in the absence of trauma, helps confirm the presence of osteomyelitis (32). CT is considered superior to MR imaging in the setting of chronic osteomyelitis for the demonstration of cortical destruction and gas (Fig 21) (33). Sequestra may be detected with CT, although the viability of sequestered bone is more reliably determined with MR imaging.


Figure 19A
View larger version (78K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 19a.  Osteomyelitis in a 45-year-old man with a history of diabetes and foot ulceration who presented to the emergency department with drainage of pus from the ulcer site. Coronal MPR CT images show a small ulceration on the medial foot at the level of the first metatarsal head (arrow in a), with associated extensive skin and subcutaneous edema. Air is identified in the subcutaneous tissues, a finding that suggests necrotizing fasciitis. In this case, however, air was shown tracking from the ulcer to the subcutaneous tissues, and then through a sinus tract into the first metatarsal head (arrow in b), a finding that indicates osteomyelitis. The patient required trans-metatarsal amputation to control the infection.

 

Figure 19B
View larger version (73K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 19b.  Osteomyelitis in a 45-year-old man with a history of diabetes and foot ulceration who presented to the emergency department with drainage of pus from the ulcer site. Coronal MPR CT images show a small ulceration on the medial foot at the level of the first metatarsal head (arrow in a), with associated extensive skin and subcutaneous edema. Air is identified in the subcutaneous tissues, a finding that suggests necrotizing fasciitis. In this case, however, air was shown tracking from the ulcer to the subcutaneous tissues, and then through a sinus tract into the first metatarsal head (arrow in b), a finding that indicates osteomyelitis. The patient required trans-metatarsal amputation to control the infection.

 

Figure 20A
View larger version (86K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 20a.  Osteomyelitis in an 84-year-old man with a history of coronary artery disease, aortic aneurysm, and peripheral vascular disease who presented with pain in the left great toe. Sagittal MPR (a) and axial 3D VR (b) CT images show fractures of the first metatarsal head and sesamoid bone. In addition, there is periosteal reaction and erosion of the first metatarsal head, findings that indicate superimposed osteomyelitis. Note the extensive overlying skin and subcutaneous edema.

 

Figure 20B
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 20b.  Osteomyelitis in an 84-year-old man with a history of coronary artery disease, aortic aneurysm, and peripheral vascular disease who presented with pain in the left great toe. Sagittal MPR (a) and axial 3D VR (b) CT images show fractures of the first metatarsal head and sesamoid bone. In addition, there is periosteal reaction and erosion of the first metatarsal head, findings that indicate superimposed osteomyelitis. Note the extensive overlying skin and subcutaneous edema.

 

Figure 21
Figure 21
View larger version (138K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 21.  Chronic osteomyelitis in a 43-year-old woman with a history of HIV infection, intravenous drug abuse, diabetes, and endocarditis. A diagnosis of left femoral osteomyelitis had been made. CT scans show a subperiosteal abscess associated with endosteal erosions, periosteal reaction, and an adjacent soft-tissue abscess in the left femur. Note the medullary area of low attenuation, a finding that represents necrotic bone and was proved surgically.

 
As stated earlier, the pathogen most commonly associated with osteomyelitis is S aureus. However, mycobacterial infections are of great concern in the emergency department of a large inner-city hospital. The patient group at greatest risk for developing tuberculosis is the HIV-infected population (34). In long bones, tuberculous osteomyelitis usually begins in the metaphysis and spreads to the epiphysis. Eventually, cortical erosion into the joint occurs. Typically, skeletal tuberculosis manifests with distinct bone margins without evidence of periosteal reaction (unless occurring in children). The most common osseous site of disease is the spine (50% of cases) (31)—in particular, the thoracic spine. CT findings of early infection include vertebral osteopenia, followed by slight disk space narrowing and characteristic anterior corner bone destruction. Skip lesions can occur and can spread to the posterior elements, a rare but specific sign for tuberculosis. Paravertebral soft-tissue edema and abscess formation occurs, and, in chronic cases, calcification in the wall of these abscesses can be detected with CT (Fig 22).


Figure 22
View larger version (121K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 22.  Osteomyelitis in a 44-year-old man with a history of intravenous drug abuse, HIV infection, and chronic back pain. CT scan of the lumbar spine reveals a tuberculous abscess with paravertebral calcification in the wall (arrow).

 
In addition to tuberculosis, the HIV-infected population is susceptible to bacillary angiomatosis, an unusual form of osteomyelitis that is associated with fever, anemia, hepatosplenomegaly, and well-defined nonsclerotic lytic lesions that are demonstrated at CT. This diagnosis requires biopsy and characteristic histologic analysis, without which the required specific antibiotic may not be prescribed.

In the emergency department, osteomyelitis rarely requires emergent stabilization or resuscitation. The primary challenge for the emergency department physician is to consider the diagnosis in the presence of subtle signs or symptoms and to initiate appropriate treatment. Therapy for osteomyelitis involves (a) the intravenous administration of antibiotics and (b) referral of the patient to a surgeon and, possibly, to a medical infectious disease expert. Without the initiation of proper treatment, complications of osteomyelitis may ensue, and morbidity can be significant as the infection spreads to adjacent soft tissues or joints. Complications include the formation of a bone abscess, fracture, septic arthritis, and secondary cellulitis with draining soft-tissue sinus tracts. If acute osteomyelitis evolves into a chronic infection, significant pain and disability may result. In the spine, complications can be devastating, with up to 10%–15% of patients developing neurologic findings, frank spinal cord compression, and lower-extremity paralysis (Fig 23).


Figure 23
View larger version (99K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 23.  Osteomyelitis with spinal complications in a 64-year-old man who initially had degenerative disk disease requiring lumbosacral fusion and laminectomies. The patient subsequently developed urosepsis followed by infection of the surgical site. Surgical hardware was removed, but attempts at treatment failed, leading to further destruction of the vertebral bodies, lumbosacral subluxation, and paraplegia. Sagittal 3D VR CT image of the lumbosacral spine shows severe retrolisthesis with disk space narrowing, irregularity of the vertebral end plates, and sclerosis, findings that are consistent with diskitis-osteomyelitis at L5-S1. Note the calcifications, which are related to the presence of bone graft and prior surgery.

 
Septic Arthritis
In the absence of trauma to or recent instrumentation of the joint, septic arthritis is usually secondary to hematogenous seeding. Hence, large joints with abundant blood supply to the metaphyses are most prone to bacterial infection, with the most commonly affected joints theoretically being the shoulder, hip, and knee. However, in intravenous drug abusers, the sternoclavicular joint is more frequently affected, for unclear reasons (Fig 24).


Figure 24
View larger version (95K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 24.  Septic arthritis in a 43-year-old woman with a history of intravenous drug abuse and HIV infection. A diagnosis of right sternoclavicular joint infection had been made. A blood culture revealed methicillin-resistant S aureus. Coronal 3D VR CT image shows widening of the sternoclavicular joint with subchondral erosions.

 
If unrecognized and left untreated, septic arthritis can result in irreversible joint damage within 48 hours of the onset of infection due to the proteolytic enzymes of the white blood cells that flood the infected synovial space (35). Therefore, timely diagnosis and treatment are critical.

Risk factors for septic arthritis include advanced age, an immunocompromised state, rheumatoid arthritis, intraarticular injections, and prosthetic joints. Most important, patients who are bacteremic for whatever reason are at high risk. Hence, in the emergency department of an inner-city hospital, septic arthritis is encountered most frequently in intravenous drug abusers and HIV-infected patients. S aureus is the most commonly isolated agent (31.3% of cases), although numerous atypical pathogens have also been identified as causes of septic arthritis (36).

The diagnosis of joint sepsis is often considered straightforward. The patient presents with a painful joint, fever, and purulent synovial fluid. Imaging generally plays an adjunct role to arthrocentesis in the diagnosis of joint sepsis; if synovial fluid cannot be retrieved, however, radiologic studies become of the utmost importance. CT features of septic arthritis include a joint effusion and bone erosions around the joint. A fat-fluid level can be a specific sign in the absence of trauma (37). In a study by Major and Tehranzadeh (38), approximately 90% of patients with septic arthritis recovered with appropriate antibiotic treatment (Fig 25).


Figure 25
View larger version (121K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 25.  Septic arthritis in a 37-year-old man with a history of sickle cell disease who presented with an infected left hip. CT scan shows a left hip abscess containing air, with marked destruction of the left hip joint. Note the fat-fluid level (arrow), which is a specific sign of infection in the absence of trauma.

 
Septic Bursitis
Septic bursitis occurs in the same population as does septic arthritis, particularly in immunocompromised patients (38). It typically results from extension of an infection from the joint space into one of the surrounding bursae (Fig 26).


Figure 26
View larger version (87K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 26.  Septic bursitis in a 51-year-old man with a history of leukemia who presented with swelling, redness, and pain about the left elbow. Sagittal MPR CT image shows skin and subcutaneous thickening—findings that are indicative of cellulitis—as well as olecranon bursitis (arrow), which was proved to be infected at aspiration.

 

   Conclusions
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Materials and Methods
 Results and Discussion
 Conclusions
References
 
In the evaluation of potential musculoskeletal infection, CT is invaluable for detecting deep complications of cellulitis and pinpointing the anatomic compartment that is involved by an infection. Although all patients with musculoskeletal infection will require treatment with antibiotics, CT helps guide therapy toward emergency surgical débridement in cases of necrotizing fasciitis and toward percutaneous treatment in cases of abscess formation. In a large inner-city hospital, where intravenous drug abusers and HIV-infected individuals are encountered with greater frequency, infection by atypical pathogens should be sought.


   Footnotes
 

Abbreviations: HIV = human immunodeficiency virus, MPR = multiplanar reformatted, VR = volume-rendered, 3D = three-dimensional


   References
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Materials and Methods
 Results and Discussion
 Conclusions
 References
 

  1. McCaig LF, Nawar EW. National Hospital Ambulatory Medical Care Survey: 2004 emergency department summary. Adv Data 2006;372:1–30.[Medline]
  2. Kelen GD, Fleetwood D. HIV infection and intravenous drug users: implications for emergency services. Emerg Med Clin North Am 1990;8:653–664.[Medline]
  3. Restrepo CS, Lemos DF, Gordillo H, et al. Imaging findings in musculoskeletal complications of AIDS. RadioGraphics 2004;24:1029–1049.[Abstract/Free Full Text]
  4. Bahebeck J, Bedimo R, Eyenga V, et al. The management of musculoskeletal infection in HIV carriers. Acta Orthop Belg 2004;70:355–360.[Medline]
  5. Kerr T, Wood E, Grafstein E, et al. High rates of primary care and emergency department use among injection drug users in Vancouver. J Public Health (Oxf) 2005;27:62–66.[CrossRef][Medline]
  6. Bahebeck J, Atangana R, Techa A, Monny-Lobe M, Sosso M, Hoffmeyer P. Relative rates and features of musculoskeletal complications in adult sicklers. Acta Orthop Belg 2004;70:107–111.[Medline]
  7. Singh N, Armstrong DG, Lipsky BA. Preventing foot ulcers in patients with diabetes. JAMA 2005; 293:217.[Abstract/Free Full Text]
  8. Perry M. Erythrocyte sedimentation rate and C reactive protein in the assessment of suspected bone infection: are they reliable indices? J R Coll Surg Edinb 1996;41:116–118.[Medline]
  9. Baddour LM. Cellulitis syndromes: an update. Int J Antimicrob Agents 2000;14:113–116.[CrossRef][Medline]
  10. Biviji AA, Paiement GD, Steinbach LS. Musculoskeletal manifestations of human immunodeficiency virus infection. J Am Acad Orthop Surg 2002;10:312–320.[Abstract/Free Full Text]
  11. Anaya DA, Dellinger EP. Necrotizing soft-tissue infection: diagnosis and management. Clin Infect Dis 2007;44:705–710.[CrossRef][Medline]
  12. Ozalay M, Ozkoc G, Akpinar S, Hersekli MA, Tandogan RN. Necrotizing soft-tissue infection of a limb: clinical presentation and factors related to mortality. Foot Ankle Int 2006;27:598–605.[Medline]
  13. Brothers TE. Magnetic resonance imaging differences between necrotizing and nonnecrotizing fasciitis. J Am Coll Surg 1998;187:416.[CrossRef][Medline]
  14. Schmid MR, Kossmann T, Duewell S. Differentiation of necrotizing fasciitis and cellulitis using MR imaging. AJR Am J Roentgenol 1998;170: 615–620.[Abstract/Free Full Text]
  15. Wu CM, Davis F, Fishman EK. Musculoskeletal complications of the patient with acquired immunodeficiency syndrome (AIDS): CT evaluation. Semin Ultrasound CT MR 1998;19:200–208.[CrossRef][Medline]
  16. Paydar KZ, Hansen SL, Charlebois ED, Harris HW, Young DM. Inappropriate antibiotic use in soft tissue infections. Arch Surg 2006;141:850–856.[Abstract/Free Full Text]
  17. Frazee BW, Lynn J, Charlebois ED, Lambert L, Lowery D, Perdreau-Remington F. High prevalence of methicillin-resistant Staphylococcus aureus in emergency department skin and soft tissue infections. Ann Emerg Med 2005;45:311–320.[CrossRef][Medline]
  18. Moran GJ, Krishnadasan A, Gorwitz RJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. N Engl J Med 2006;355:666–674.[Abstract/Free Full Text]
  19. Lee DJ, Sartoris DJ. Musculoskeletal manifestation of human immunodeficiency virus infection: review of imaging characteristics. Radiol Clin North Am 1994;32:399–411.[Medline]
  20. Beltran J. MR imaging of soft-tissue infection. Magn Reson Imaging Clin N Am 1995;3:743–751.[Medline]
  21. Struk DW, Munk PL, Lee MJ, Ho SG, Worsley DF. Imaging of soft tissue infections. Radiol Clin North Am 2001;39:277–303.[CrossRef][Medline]
  22. Bickels J, Ben-Sira L, Kessler A, Wientroub S. Primary pyomyositis. J Bone Joint Surg Am 2002; 84:2277–2286.[Free Full Text]
  23. Fleckenstein JL, Burns DK. Differential diagnosis of bacterial myositis in AIDS: evaluation with MR imaging. Radiology 1991;179:653–658.[Abstract/Free Full Text]
  24. Christin L, Sarosi GA. Pyomyositis in North America: case reports and review. Clin Infect Dis 1992;15:668–677.[Medline]
  25. Ricci MA, Rose FB, Meyer KK. Pyogenic psoas abscess: worldwide variation in etiology. World J Surg 1986;10:834–843.[CrossRef][Medline]
  26. Jayoussi R, Bialik V, Eyal A, Shehadeh N, Etzioni A. Pyomyositis caused by vigorous exercise in a boy. Acta Paediatr 1995;84:226–227.[Medline]
  27. Kao PF, Tsui KH, Leu HS, Tsai MF, Tzen KY. Diagnosis and treatment of pyogenic psoas abscess in diabetic patients: usefulness of computed tomography and gallium-67 scanning. Urology 2001;57:246–251.[CrossRef][Medline]
  28. Kao HC, Huang YC, Chiu CH, et al. Acute hematogenous osteomyelitis and septic arthritis in children. J Microbiol Immunol Infect 2003;36: 260–265.[Medline]
  29. Vassilopoulos D, Chalasani P, Jurado RL, Workowski K, Agudelo CA. Musculoskeletal infections in patients with human immunodeficiency virus infection. Medicine (Baltimore) 1997;76: 284–294.[CrossRef][Medline]
  30. Wheat J. Diagnostic strategies in osteomyelitis. Am J Med 1985;78:218–224.[CrossRef][Medline]
  31. De Vuyst D, Vanhoenacker F, Gielen J, Bernaerts A, De Schepper AM. Imaging features of musculoskeletal tuberculosis. Eur Radiol 2003;13:1809–1819.[CrossRef][Medline]
  32. Hui CL, Naidoo P. Extramedullary fat fluid level on MRI as a specific sign for osteomyelitis. Australas Radiol 2003;47:443–446.[CrossRef][Medline]
  33. Hernandez RJ. Visualization of small sequestra by computerized tomography: report of 6 cases. Pediatr Radiol 1985;15:238–241.[CrossRef][Medline]
  34. Moore SL, Rafii M. Imaging of musculoskeletal and spinal tuberculosis. Radiol Clin North Am 2001;39:329–342.[CrossRef][Medline]
  35. Hammel JM, Kwon N. Septic arthritis of the acromioclavicular joint. J Emerg Med 2005;29:425–427.[CrossRef][Medline]
  36. Yuan HC, Wu KG, Chen CJ, Tang RB, Hwang BT. Characteristics and outcome of septic arthritis in children. J Microbiol Immunol Infect 2006;39: 342–347.[Medline]
  37. Kumar J, Bandhu S, Kumar A, Alam S. Extraosseous fat fluid level: a specific sign for osteomyelitis. Skeletal Radiol 2007;36(suppl 1):101–104.[CrossRef]
  38. Major NM, Tehranzadeh J. Musculoskeletal manifestations of AIDS. Radiol Clin North Am 1997;35:1167–1189.[Medline]




This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow CME Test (opens in a new window)
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions