Osteomyelitis and Beyond

R. Paul Guillerman, MD Associate Professor of Radiology Baylor College of Medicine Department of Pediatric Radiology Texas Children’s Hospital Houston, Texas Disclosure of Commercial Interest

Neither I or a member of my immediate family have a financial relationship with a commercial organization that may have an interest in the content of this educational activity Objectives

Review the characteristic imaging findings of pediatric musculoskeletal infections

Focus particularly on MRI and invasive community- acquired (CA-SA) infections

Present the differentiating features of potential mimics of infection Pediatric

Classic clinical signs of fever, pain, swelling, and decreased mobility present in only a slight majority

↑ wbc count in 30-65%

Blood cultures + in 30-75%

Organism isolated by tissue biopsy in 50-85%

↑ ESR or fever in 70-90%

↑ CRP in 98% Conventional Approach to Imaging Acute Pediatric Musculoskeletal Infections

Obtain scan if XR negative

Reserve MRI for suspected spinal or pelvic osteomyelitis or lack of treatment response

No longer optimal with advent of community-acquired Staphylococcus aureus (CA-SA)

Community-Acquired Staphylococcus aureus (CA-SA)

Distinctions from traditional Staphylococcus aureus: Community-acquired Affects otherwise healthy, immunocompetent children Can have rapid, invasive course Can be methicillin-resistant (MRSA) or sensitive (MSSA)

Surgical debridement and drainage of associated and effusions is the mainstay of therapy

Gadolinium-enhanced MRI is the imaging modality of choice, particularly for detection of early osteomyelitis and associated soft-tissue disease Clinical Spectrum of Invasive CA-SA MSK Infections

Osteomyelitis Septic arthritis Pyomyositis Deep Clinical Spectrum of Invasive CA-SA MSK Infections

Osteomyelitis Septic arthritis Pyomyositis Deep abscess

Infants at higher risk CA-SA MSK Infection

T1-W STIR Gad T1-W FS

Osteomyelitis with subperiosteal abscess CA-SA MSK Infection

Gad T1-W FS

Gad T1-W FS

Readily breaches musculoskeletal tissue barriers

Browne Pediatr Radiol 2008 CA-SA MSK Infection

Gad T1-W FS Gad T1-W FS

Involvement often multifocal CA-SA MSK Infection

Gad T1-W FS

Associated with septic thrombophlebitis near osteomyelitis site

Browne Pediatr Radiol 2008 CA-SA MSK Infection

STIR

Septic pulmonary emboli associated with higher mortality

Browne Pediatr Radiol 2008 8-year-old with left hip pain, fever, elevated ESR and CRP “Cold” Osteomyelitis

Gad T1-W FS Toddler with “normal” bone scan Toddler with “normal” bone scan

T1-W Gad T1-W FS Tibial Osteomyelitis with Intra-Osseous Abscess

T1-W Gad T1-W FS 5-month-old not moving right arm Epiphyseal and Metaphyseal Osteomyelitis

Gad T1-W FS 1-month-old with suspected septic arthritis of the right hip

T1-W STIR

STIR Epiphyseal Involvement Occult on Pre- Contrast MRI Sequences

T1-W STIR Gad T1-W FS

STIR Gad T1-W FS Age-Dependence of Osteomyelitis Location

Childhood Infancy

Marin Curr Prob Diagn Radiol 2004 Growth Cartilage “Osteomyelitis”

May relate to septic thrombosis or necrosis of cartilage

Applies to the epiphyses and apophyses 7-Week-Old with Multifocal Epimetaphyseal Involvement Dynamic Contrast-Enhanced MRA 7-Week-Old with Multifocal Epimetaphyseal Involvement Delayed Post-Contrast MRI

Gad T1-W FS Gad T1-W FS Skeletal Extremity CA-SA Infection in Infants

Involves growth cartilage of epiphyses or epiphyseal- equivalents in 50% of cases and exclusively in 25% Occult on non-enhanced MRI sequences in 80% Manifests as hypo-enhancing foci in the growth cartilage on contrast-enhanced MRI sequences Not excluded by the absence of joint effusion Skeletal Extremity CA-SA Infection in Infants

Follow-up XR reveals growth disturbances in 80% of those with growth cartilage involvement

Gad T1-W FS

17-days-old 3-years-old

Browne AJR 2012 Imaging of Pediatric MSK Infections in CA-SA Endemic Areas

MRI preferred over bone scan as primary imaging test

High incidence (2/3) of extra-osseous complications Abscess, septic thrombophlebitis Preoperative MRI reduces operative time and exposure

High incidence (1/2) of “cold” or occult osteomyelitis or on bone scan, particularly in infants 20-month-old, limping for 3 weeks, afebrile, normal ESR/CRP 20-month-old, limping for 3 weeks, afebrile, normal ESR/CRP

T1-W STIR Gad T1-W FS

Subacute osteomyelitis

Central abscess fluid Penumbra of enhancing high T1-W signal granulation tissue Very low T1-W signal sclerotic rim Low T1-W signal peri-lesional edema

T1-W Brodie Abscess

Subacute osteomyelitis

Central abscess fluid Penumbra of enhancing high T1-W signal granulation tissue Very low T1-W signal sclerotic rim Low T1-W signal peri-lesional edema

May be afebrile with normal T1-W inflammatory marker levels 13-year-old male with acute CA-SA osteomyelitis

STIR T1-W 4 months later…

Gad T1-W Gad T1-W , , Cloaca

Gad T1-W Gad T1-W Chronic Osteomyelitis

Persistence of symptoms for > 1 month after appropriate antibiotic therapy, or infection > 1 month after inadequately treated osteomyelitis

Sequestrum – necrotic bone fragment

Involucrum – thick periosteal new bone

Cloaca – draining tract through defect in cortex and involucrum

Marin Curr Prob Diag Rad 2004 Indications for Follow-Up MRI of Pediatric MSK Infection

Routine follow-up MRI not warranted

Only 10-20% of follow-up MRI exams provide information that affects patient management (e.g., invasive procedure, change in antibiotic therapy)

Indications include failure to show clinical improvement or persistent CRP elevation 11-month-old non-weight-bearing, elevated CRP; septic hip arthritis or osteomyelitis suspected by ER MD and orthopedist

STIR STIR CA-SA Septic Arthritis of the Knee

Gad T1-W FS Gad T1-W FS

Difficult to localize infection in infants by clinical exam CA-SA Septic Arthritis of the Knee

Gad T1-W FS Gad T1-W FS

Important to survey large FOV initially Septic Arthritis

Most common in hip or knee

Staphylococcus or Streptococcus most common

Kingella kingae increasingly recognized in young children and associated with milder disease

Poor outcome associated with delay in diagnosis Articular cartilage destruction Osteonecrosis Growth deformity Osteomyelitis, abscess, sepsis 8-year-old with left hip pain, elevated wbc count and CRP Septic Arthritis Persisting fever and high CRP after hip drainage and normal left femur biopsy

T1-W STIR Gad T1-W FS Acetabular Osteomyelitis and Obturator Pyomyositis

T1-W STIR Gad T1-W FS Suspected Septic Arthritis US vs. MRI

2/3 of patients with septic arthritis have adjacent abscess (subperiosteal or intramuscular) or osteomyelitis

Reliable predictors needed to guide management – US and immediate joint drainage vs. pre-operative MRI to define drainable fluid collections and bone biopsy site(s)

Age > 4 yr, symptom duration > 3 days, fever > 2 days, elevated CRP, elevated ANC, low platelet count, and bacteremia identified as independent predictors 10-year-old fell on left hip, next day developed right hip pain, fever, high CRP Intolerance to sitting, refusal to walk, pain radiating down back of thigh and leg

Gad T1-W FS

Gad T1-W FS Piriformis Pyomyositis

Gad T1-W FS

Gad T1-W FS Pyomyositis

Increased incidence related to CA-SA emergence

Most common of the lower extremity and pelvis

CRP and ESR usually elevated, while CK usually normal

Preceded by skin penetration (bug bite, laceration) in 50% and by trauma or vigorous activity in 25% Teenager with right hip pain and fever

STIR Gad T1-W FS Teenager with right hip pain and fever

Gad T1-W FS Crohn Ileitis with Sinus Tract to Iliopsoas

Gad T1-W FS

Iliopsoas pyomyositis often secondary to GI, GU, or spinal infection Infectious Osteomyelitis Mimics 16-year-old with acne, elevated ESR/CRP, left shoulder pain then right thigh pain

T2-W FS Chronic Recurrent Multifocal Osteomyelitis (CRMO)

Auto-inflammatory disorder

Personal or family history of dermatologic (psoriasis, pustulosis) or gastrointestinal disorders (IBD) common

Treated with NSAIDs, TNF inhibitors, bisphosphonates

Protracted clinical course with recurrences 15-year-old with Crohn disease, CRMO

STIR

Most commonly affects the extremity long , clavicles, spine, and pelvis Usually multifocal, asymmetric, metachronous CRMO

T1-W T2-W FS Gad T1-W FS

Lysis, followed by sclerosis and No abscess, fistula or soft tissue mass 4-month-old with forearm swelling, elevated ESR/CRP

Gad T1-W FS STIR 4-month-old with forearm swelling, elevated ESR/CRP Caffey Disease 6-year-old with thigh pain

T1-W STIR Acute Leukemia

T1-W STIR 12-year-old with elbow pain, elevated ESR, CRP, and LDH

T1-W STIR Gad T1-W FS Lymphoblastic Lymphoma

T1-W STIR Gad T1-W FS 3-year-old with left thigh pain, fever, elevated ESR

STIR Gad T1-W FS 3-year-old with left thigh pain, fever, elevated ESR

STIR Gad T1-W FS Langerhans Cell Histiocytosis (LCH)

STIR Gad T1-W FS

Fever and elevated ESR common in LCH, Ewing sarcoma, and non-Hodgkin lymphoma of bone Limping febrile toddler, normal knee XR Tibia/fibula radiograph 3 weeks later Toddler’s Fracture 15-year-old football player with knee pain, elevated ESR

T1-W 15-year-old football player with knee pain, elevated ESR

STIR Gad T1-W FS

STIR Gad T1-W FS Septic Arthritis Mimics 5-year-old with left hip pain, joint effusion, T 38 C, normal WBC/ESR/CRP 5-year-old with left hip pain, joint effusion, T 38 C, normal WBC/ESR/CRP

Jung J Pediatr Ortho 2003 2.9% probability of septic arthritis, presumed transient synovitis

Jung J Pediatr Ortho 2003 No need for further imaging or arthrocentesis

Jung J Pediatr Ortho 2003 Transient Synovitis of the Hip (Toxic Synovitis)

Most common cause of acute hip pain in the 3-10 year- old age group

1/2 of cases preceded by recent upper respiratory tract infection

Usually recover within 2 weeks with rest and NSAID’s, but recurrent in 4-17%

1-2% later develop Legg-Calve-Perthe disease MRI Distinction of Transient Synovitis and Septic Arthritis in Clinically Equivocal Cases

Transient Finding Septic Arthritis Synovitis Signal intensity alterations of bone marrow on non- 33-56% 0% contrast sequencesq Juxta-articular soft tissue 66-89% 31-36% signal intensity alterations Bilateral joint effusion 17% 63% Synovial thickening 83% 55%

Decreased enhancement 22-89% 6-18% of femoral capital epiphysis 4-year-old with left hip pain and elevated wbc count, ESR and CRP

T1-W STIR Left hip joint effusion, normal marrow signal intensity

T1-W STIR Decreased enhancement of left capital femoral epiphysis

Gad T1-W FS Gad T1-W FS

Suggests need for further evaluation with arthrocentesis for septic arthritis, but … Decreased enhancement of left capital femoral epiphysis

Gad T1-W FS Gad T1-W FS

…does not correlate with effusion size …is not predictive of subsequent Pyomyositis Mimics 18-year-old male with sickle cell disease, severe foot pain

STIR T1-W T1-W FS Sickle Cell Vaso-Occlusive Myonecrosis

STIR T1-W T1-W FS 15-year-old with ALL in remission, leg swelling, fever, elevated CRP

STIR

T1-WI PD FS 15-year-old with ALL in remission, leg swelling, fever, elevated CRP

Gad T1-WI Infrapopliteal Deep Venous Thrombosis

Gad T1-WI Gad T1-WI Gad T1-WI 15-month-old, non-weight-bearing with elevated ESR and CRP Additional history of elevated CK and recent rhinitis Viral Myositis with Rhabdomyolysis Pediatric Rhabdomyolysis

Viral myositis causes majority of cases in the first decade of life

Trauma, exercise and drug-related causes more frequent in second decade of life

“Classic triad” of myalgia, dark urine, weakness in < 1% 17-year-old with left leg pain after football practice, elevated CRP and CK

T1-WI STIR 17-year-old with left leg pain after football practice, elevated CRP and CK

Gad T1-WI

Gad T1-WI Exertional Compartment Syndrome

Gad T1-WI

Gad T1-WI 15-year-old with right thigh pain and swelling

Gad T1-W FS T1-W STIR Pain of onset sudden playing soccer

Gad T1-W FS T1-W STIR Tear of Deep Myotendinous Junction of Rectus Femoris

Gad T1-W FS T1-W STIR Conclusion MRI preferred over bone scan for imaging of MSK infection, particularly in CA-SA endemic locales “Cold” osteomyelitis, abscess, and septic thrombophlebitis are common Large FOV survey and Gadolinium-enhanced sequences crucial in infants

MRI can help differentiate septic arthritis from transient synovitis in clinically equivocal cases

Clinical history is often key in differentiating mimics