Osteomyelitis Imaging

Osteomyelitis is a multifaceted disease characterized by inflammation of bone and marrow. While various etiologies of osteomyelitis have been documented, it is almost always secondary to infection. Osteomyelitis may occur through direct inoculation of bacteria into the bone, hematogenous spread from distant sites of infection, or the contiguous spread from nearby soft tissues, termed nonhematogenous infection. Common causative organisms of osteomyelitis include , spp., and . In patients with specific comorbidities, such as sickle cell disease, other etiologic infectious agents, such as  spp. and , are more common. In the pediatric population, osteomyelitis typically affects the long bones and results from hematogenous spread. In adults, however, osteomyelitis is more commonly due to nonhematogenous contiguous spread from surgery, trauma, soft tissue infection, or prosthetic material. Patients with diabetes are at an increased risk of osteomyelitis, particularly if vascular function is compromised. Osteomyelitis may be acute, subacute, or chronic. Patients with acute osteomyelitis typically present within 2 weeks of disease onset with local symptoms of progressive erythema, edema, and warmth. Constitutional symptoms such as fever, chills, irritability, decreased appetite, lethargy, or malaise may also occur. Pediatric patients with acute osteomyelitis may present with localized symptoms but frequently present with a refusal to bear weight or limited motion of the affected extremity. Patients with subacute osteomyelitis present after the initial 2 weeks of symptoms, often with mild pain and minimal fever. Septic arthritis can occur if the joint capsule is involved. Brodie abscess is a subacute form of osteomyelitis typically arising through hematogenous spread but may occur secondary to trauma. The classic presentation of Brodie abscess is a cavity in the metaphysis of a long bone, filled with suppurative or granulation material and surrounded by dense fibrous tissue and sclerotic bone. Chronic osteomyelitis develops when acute osteomyelitis is inadequately treated, or the infection does not respond to standard therapies. Symptoms of chronic osteomyelitis include edema, pain, and erythema at the site of infection; fever is less common. The defining characteristic of chronic osteomyelitis is the presence of necrotic bone, known as a sequestrum. Other typical features of chronic osteomyelitis include reactive bony encasement of the sequestrum, called an involucrum, and localized bone loss. In chronic osteomyelitis, there is potential for the development of sinus tracts if the infection extends through the infected cortical bone. Chronic recurrent multifocal osteomyelitis (CRMO) is not a subtype of chronic osteomyelitis but a unique inflammatory condition primarily affecting the pediatric population. CRMO is not an infectious process but an autoinflammatory disorder in which the immune system mistakenly targets the bone. The characteristic feature of CRMO is the presence of multiple bony lesions in various anatomical locations, typically long bones, clavicles, or vertebrae. Patients with CRMO experience recurrent episodes of bone pain, swelling, and tenderness. However, systemic symptoms like fever and weight loss are usually absent. Diagnosing CRMO can be challenging due to intermittent and nonspecific symptoms. Imaging modalities such as magnetic resonance imaging (MRI) are crucial in identifying the bone marrow edema and inflammatory patterns associated with CRMO. MRI also aids in distinguishing the bony abnormalities of CRMO from bony metastases. The adult counterpart of CRMO is SAPHO syndrome, defined as the combined occurrence of synovitis, acne, pustulosis, hyperostosis, and osteitis. Compared to patients with CRMO, patients with SAPHO syndrome have a significantly higher prevalence of skin lesions, particularly palmoplantar pustulosis. The bony lesions of SAPHO syndrome are primarily seen in the chest wall and pelvis, while CRMO typically targets the long bones. This contrast is believed to be secondary to age-related metaphyseal development; open growth plates in children increase the likelihood of metaphyseal lesions. The involvement of the sternoclavicular and first sternocostal joint and ossification of the costoclavicular ligaments is frequently observed in SAPHO syndrome but not reported in CRMO. Diagnosing osteomyelitis relies on clinical evaluation, laboratory testing, and imaging studies. Imaging techniques, including x-rays, MRI, computed tomography (CT), and nuclear medicine studies such as bone scintigraphy, gallium scanning, and 18F-fluorodeoxyglucose positron emission tomography-CT (18F-FDG PET-CT), play a crucial role in identifying the early and chronic changes of osteomyelitis. Imaging findings may aid the diagnosis of osteomyelitis and play a role in determining disease complications and guiding treatment strategies. Osteomyelitis is a complicated and potentially devastating clinical condition. Advances in understanding its pathogenesis, antibiotic development, and improved imaging techniques have revolutionized the management of osteomyelitis. The early recognition of osteomyelitis promotes rapid intervention, minimizing morbidity and optimizing patient outcomes.