Musculoskeletal Infection Extremities • Pathophysiology Nuttaya Pattamapaspong M.D

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Topics

• Role of imaging in extremity infection Musculoskeletal Infection Extremities • Pathophysiology Nuttaya Pattamapaspong M.D. Department of Radiology, Faculty of • Imaging features Medicine, Chiang Mai University, Chiang Mai, Thailand

Detection of Infection Role of Imaging in Extremity Infection Challenges • Detection of infection • Musculoskeletal infections have multiple patterns of presentation.

• Variability of the host immune response and • Determination the disease extent virulence of pathogen. • Clinical presentation & radiological features may • Guidance for intervention procedure similar to those of non-infectious process. • 50% of children having musculoskeletal infection are misdiagnosed as tumors or other conditions.*

* Rasool MN, JBJS(Br) 2001

Detection of Infection Anatomy & infection

Challenges • Superficial soft tissue • Increased immunocompromised patients infection (AIDs, chemotherapy, steroid, - Skin immunosupressive drugs) - Subcutaneous tissue • If untreated, musculoskeletal infection leads to - Superficial fascia fatal outcome or amputation. (Cellulitis)

• Infectious diseases are common problems of the tropical region.

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Anatomy & infection Detection of Infection Imaging of choices • Deep soft tissue infection • Radiographs - Deep/inter-compartment fascia (fasciitis) - Muscle (pyomyositis) • CT - Bursitis/tenosynovitis - Arthritis • US - Osteomyelitis

• MRI

Detection of Infection: Radiographs Detection of Infection: Radiographs

• Osseous lesions: • Osseous lesions: • Radio opaque Bone destruction, periosteal Bone destruction, Metal foreign bodies reaction, osteosclerosis, periosteal reaction, sequestra, involucrum osteosclerosis, sequestra involucrum • Radio-opaque foreign bodies • Radio-opaque foreign bodies

• Soft tissue gas • Soft tissue gas A 54 yo man post traumatic chronic osteomyelitis

Detection of Infection: Radiographs Detection of Infection: CT • Gas/ necrotizing fasciitis • Osseous lesions: • Improve detection Bone destruction, comparing to periosteal reaction, radiographs osteosclerosis, sequestra • Osseous lesions: involucrum Bone destruction, periosteal reaction, • Radio-opaque foreign osteosclerosis, sequestra bodies • Soft tissue gas, abscesses • Soft tissue gas • Foreign bodies Left iliopsoas abscesses with gas bubbles

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Detection of Infection: CT Detection of Infection: CT

• Improve detection • Improve detection Wooden foreign body comparing to comparing to radiographs radiographs • Osseous lesions: • Osseous lesions: Bone destruction, periosteal Bone destruction, periosteal reaction, osteosclerosis, reaction, osteosclerosis, sequestra sequestra • Soft tissue gas, abscesses • Soft tissue gas, abscesses • Radio-opaque foreign A 65 yo man with retained • Radio-opaque foreign Swelling of the foot for 2 wks bodies pieces of glass for 20 years bodies History of penetrating injury last 5 years.

Detection of Infection: US Detection of Infection: US

Wooden foreign body • Distinguish superficial/ • Distinguish superficial/ Thrombophlebitis deep soft tissue deep soft tissue US infection. infection. • Soft tissue abscesses • Soft tissue abscesses • Foreign bodies • Joint effusion • Joint effusion • Subperiosteal abscess/ cortical bone • Subperiosteal abscess/ destruction cortical bone Penetrating injury with compressed destruction abscess in the dorsum of

hand

Detection of Infection & Guide of Treatment Detection of Infection: US

• Distinguish superficial/ Post surgical infection deep soft tissue infection. • Soft tissue abscesses • Joint effusion • Subperiosteal abscess/ cortical bone destruction • Foreign bodies • Guide of aspiration Abscess, real time scan

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Detection of Infection: US Detection of Infection: US

• Distinguish superficial/ • Cortical bone destruction deep soft tissue of the femur infection. • Soft tissue abscesses Plate • Joint effusion • Subperiosteal abscess/ cortical bone destruction • Foreign bodies Transverse US of the thigh • Guide of aspiration Longitudinal scan of the thigh Underlying multiple myeloma with post operative thigh pain and fever

Pathophysiology & Imaging Features

Sources of infection US T1 fat sat+Gd - Hematogenous spread - Contiguous infection - Penetrating injury

Skin, Subcutaneous tissue, Muscles, Joints, Bursa, Tendon sheaths, Bones Inflammatory response and tissue damage

Abscess formation Surrounding tissue reaction & reparative process

Imaging Features : Imaging Features Hematogenous spread infection Contiguous infection Single lesion in high vascular Multiple lesions area • A 72-year-old woman • Shoulder pain with a mass for 1 year. • Tuberculous arthritis with subacromion A 24 yo/F, leukemia, subdeltoid bursitis Shoulder coronal T1 +Gd A 4 yo boy acute osteomyelitis disseminated fungal in the metaphysis infection (Fusarium spp.)

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Imaging Features Imaging Features Penetrating injury Cellulitis A bed sore with osteomyelitis Axial Arm • Subcutaneous tissue STIR infection

• Edema and enhancement of the subcutaneous tissue T1+Gd and superficial fascia

Imaging Findings Imaging Features Cellulitis cellulitis & superficial soft tissue abscess

fibula

Transverse scan of the left mid thigh Transverse scan of the calf Thickened subcutaneous tissue and interlobular septal fat

Imaging Features Imaging Features cellulitis & superficial soft tissue abscess Necrotizing Fasciitis

• A 42 yo woman with HIV infection and S. epidermidis soft tissue abscess

Necrotizing Fasciitis with skin necrosis

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Imaging Findings Imaging Features Necrotizing Fasciitis Necrotizing Fasciitis Necrotizing vs non- • Thickened T2- necrotizing fasciitis hyperintense • Presence of gas • Non-enhancing fascia • Significant thickening of the

abnormal signal intensity of STIR the fascia on T2-weighted images (> 3 mm) • Non-enhancing fascia • Multiple compartment

T1+Gd Kim KT, Radiology 2011, 259 :816-24

Imaging Features Imaging Features Pyomyositis Pyomyositis

T1WI T2WI with fat T1WI +Gd Early stage suppression • Hyperintense signal on T2WIs • Muscle enhancement

Pyomysitis Pyomyositis: Abscess wall Bleeding Fibrosis Inflammatory cells

Fibrosis+Inflammatory cells + blood vessels Bleeding T1WI T2WI with fat H&E Iron in bacteria or macrophage suppression Free radical

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Imaging Features Imaging Features Osteomyelitis Osteomyelitis Stages : no-clear distinction • Acute osteomyelitis • Subacute osteomyelitis > 2-3 Weeks • Chronic osteomyelitis >3 months

Bone destruction Abscess formation Reactive bone Tissue necrosis formation 4-year-old boy - bone Axial T2WIs with fat saturation - bone marrow

Imaging Features Imaging Features Osteomyelitis Osteomyelitis • Moth-eaten osteolytic lesion in • Extensive bone marrow the metaphysis with cortical edema destruction and laminated periosteal reaction • Subperiosteal abscess DDx 1. Osteomyelitis 2. Ewing sarcoma • Formation of abscesses 3. Other small round cell is the hallmark of tumors : lymphoma leukemia infection Sagittal T1+Gd

Imaging Features Imaging Features Osteomyelitis Osteomyelitis Periosteum in children is loosely attached to the • Acute osteomyelitis in bone adult

• A 31-year- old woman Extensive subperiosteal with pathologic fracture reaction & Infarction of of the distal femur bone

Involucrum & sequestrum

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Acute osteomyelitis in adult Imaging Features Osteomyelitis Periosteum in adult is firmly attached to the bone

Increased intraosseous pressure Axial T1+Gd Abscess Fracture

Imaging Features Osteomyelitis • Brodie’s abscess A 44- year-old woman Tuberculous osteomyelitis/arthritis Coronal MRI of the wrist T1-weighted image

T1WI T2WI T1+Gd

MRI Features of Osteomyelitis

Brodie’s abscess Tuberculous arthritis & osteomyelitis Abscess: T1, T2 • “ penumbra zone” T1- Granulation tissue: hyperintense rim due T1, T2 to fibrovascular tissue with hemorrhage • Sensitivity 73.3%* Fibrosis: T1, T2 Specificity 99.1% Bone edema: * Shimose S. Acta Radiologica, 2008 T1, T2

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Vascular channels & Osteomyelitis Vascular channels & Osteomyelitis • Transphyseal spread/transphyseal tunneling

Neonate-18 mo >16 yrs 18 mo-16 yrs T1WI GRE Infection begins in medullary cavity of metaphysis or near the A 10 month-old girl with osteomyelitis of the distal tibia physis of flat bones.

Osteomyelitis Osteomyelitis Axial view of the foot Osteomyelitis in the diabetic foot is almost always associated with skin ulcer or soft tissue infection Commonly associated with bone prominences: metatarsal head, T1 signal T2 signal Enhanced on post calcaneus, malleoli, and intensity intensity contrast study toes. : A 52 yo M, DM & ulcer lateral malleolus

Imaging Features Role of Imaging in Septic Arthritis Septic arthritis • Diagnosis made by presence of painful joint, fever, purulent synovial fluid • Helpful in the diagnosis if synovial fluid cannot be obtained • Distinguish septic arthritis from contiguous infection (most common- osteomyelitis)

A 4 yo girl with septic arthritis of the right hip

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Imaging Features Imaging Features Septic arthritis Septic arthritis Gouty arthritis Septic arthritis of the ankle 33/M

effusion

synovium+capsule

tibia A 4 yo girl with septic arthritis of the right hip f Knee transverse scan Ankle transverse scan

Imaging Features Imaging Features Septic arthritis Septic arthritis Findings 23/F Regional osteoporosis 57/M septic arthritis • Joint effusion • Synovial hypertrophy & enhancement • Bone marrow edema • Bone erosions

MRI of infected and noninfected joints Complication of Septic Arthritis Infected (%) Non-infected(%) -Joint effusion 79 82 -Inhomogeneous 21 27 effusion -Synovial thickening 68 55 - Synovial enhancement 94 88 - Bone erosion 79 38 - Bone edema 74 38 Erosions and bone edema Graif M. Skeletal Radiolo 1999 Paraarticular abscesses (indicate disruption of joint capsule)

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Complication of Septic Arthritis Complication of Septic Arthritis

• Tenosynovitis • Tenosynovitis Synovial hypertrophy& enhancement Tendon sheath effusion Tendon rupture

Axial T1+Gd of the hand

T2WI with fat sat T1WI+Gd

Complication of Septic Arthritis Conclusion

• Synovial hypertrophy& enhancement Roles of imaging studies are • Tendon sheath effusion • Detection of infection • Define the extension (superficial/deep infection) • Tendon rupture

Imaging patterns of extremity infection are the results of • Source of infection : hematogeneous spread, contiguous sources, penetrating injuries Sagittal T1+Gd of the ankle • Affected compartments • Tissue destruction, abscess formation • Tissue responses

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