Approach to Lower Extremity Osteomyelitis. A radiologic tour of a patient encounter

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1 Approach to Lower Extremity Osteomyelitis A radiologic tour of a patient encounter David Guo,, HMS III Gillian Lieberman, MD BIDMC, October 2009

2 Our learning goals Review lower extremity anatomy Discuss menu of available of tests Demonstrate classic findings of osteomyelitis on plain film and MRI Develop and refine the differential diagnosis for osteomyelitis

classic findings of osteomyelitis on plain film and

3 Meet our patient, Mr. J 39 year-old homeless male with history of HIV, ETOH abuse, and traumatic R ankle fracture s/p ORIF 3 years ago Arrives in ED with a painful, swollen right ankle

$fracture s/p ORIF 3 years ago Arrives in ED$

4 Our patient: HPI First noticed pain 3 weeks ago in his right ankle while walking 5 days ago, medial right ankle became red and swollen with burning sensation

5 Our patient: differential diagnosis #1 Cellulitis Osteomyelitis Fracture Septic arthritis Osteoarthritis Rheumatoid arthritis Gout Tumor What radiologic test should we order first?

6 Menu of tests Plain Film MRI CT Ultrasound Nuclear medicine Three-phase bone scan WBC scan FDG PET Gallium

7 Anatomy: review Before we continue to the plain film findings, we will review the anatomy of the ankle region

8 Anatomy: bones of the foot

9 Anatomy: the mortise joint Fibula Tibia Lateral Malleolus Medial Malleolus Talus Mortise joint Tibial plafond Normal Ankle Xray, Mortise View Talar dome

Tibial plafond Normal Ankle Xray, Mortise View

10 Our patient: plain film Now back to our patient We will start with earlier images for baseline comparison

11 Our patient: ankle plain film, 3 months prior AP Mortise Lateral BIDMC PACS

12 Our patient: plain film highlights, 3 months prior Disruption of trabecular lines Metallic washer Increased sclerosis Narrowing joint space Osteoarthritis, secondary to infection or fracture Ankle X-ray, X Mortise View BIDMC PACS

$to infection or fracture Ankle X-ray, X Mortise View$

13 Our patient: ankle plain film, current AP Mortise Lateral BIDMC PACS

14 Our patient: plain film highlights, current Area of increased lucency in medial aspect of distal tibial metaphysis Area of increased sclerosis in distal tibia Increased soft tissue swelling Cortical erosion Periosteal new bone formation Ankle X-ray, Mortise View BIDMC PACS

increased sclerosis in distal tibia Increased soft tissue swelling

15 Our patient: summary from plain films There is a process occurring in the Soft tissue: Swollen Bone: Chronic process: causing sclerosis Acute process: causing lucency Joint: Narrowingloss of cartilagearthritis arthritis

Chronic process: causing sclerosis Acute process:

16 Our patient: differential diagnosis #2 Cellulitis Osteomyelitis Fracture Septic arthritis Osteoarthritis Rheumatoid arthritis Gout Tumor What test should we order next?

17 Menu of Tests Plain Film MRI CT Ultrasound Nuclear medicine Three-phase bone scan WBC scan FDG PET Gallium

18 Our patient: normal anatomy on T1 MRI Fat Tendons Ligaments Cortex Bone marrow Muscle Axial T1 MRI, distal R lower extremity BIDMC PACS

19 Our patient: T1 MRI findings On T1 Fluid is dark, fat is bright Gives the broad anatomy view Abnormalities Bone: lesion that is hypointense to marrow Soft tissue: lesion that is isointense to muscle Axial T1 MRI, distal R lower extremity BIDMC PACS

lesion that is hypointense to marrow Soft tissue: lesion that

20 Our patient: T2 MRI findings On T2 Fluid is bright, fat is dark. Gives pathology view Abnormalities Soft tissue: improved view of loculated fluid collection Axial T2 MRI, distal R lower extremity BIDMC PACS

21 Our patient: STIR MRI findings Axial STIR (normal) Axial STIR (at lesion) On STIR (Short Tau Inversion Recovery) Fat is subtracted out, leaving fluid bright We show normal STIR for comparison Abnormalities Diffusely increased signal in tibia bone marrow edema Cortical erosion Periosteal edema BIDMC PACS

22 Our patient: T1 post-gad MRI findings Axial T1 pre-gad Axial T1 post-gad On T1 post-gad gad IV contrast (gadolinium) shows disruption of tissue boundary We show T1 pre-gad shown for comparison Abnormalities Decreased signal in marrow necrotic bone Sinus tract and abscess BIDMC PACS

23 Our patient: summary from MRI Soft tissue: Loculated abscess Sinus tract to bone Bone: Diffuse tibial bone marrow edema Cortical erosion and periosteal edema inflammatory process Necrotic bone sequestrum Diagnosis?

24 Our patient: diagnosis of osteomyelitis Definition: infection of the bone marrow Acute: : evolves over days to weeks Chronic: : evolves over months to years,, with relapses Bacteria remain in sequestra,, where antibiotics cannot reach Route of spread Contiguous spread Trauma, bone surgery, foreign body implant Vascular insufficiency Diabetic foot ulcer Hematogenous spread Nidus of infection, more often in children Risk factors Drug abuse,, trauma, HIV, transplant, diabetes, foreign bodies Source: Lew, Daniel and Francis Waldvogel. Lancet Approach to imaging modalities in setting of suspected osteomyelitis. Up To Date, accessed Applies to Mr. R

25 Our patient: treatment summary Orthopedics performed drainage and debridement twice and got bone biopsy Bone biopsy returned positive for Pseudomonas Received 6 weeks of IV Cefepime Prognosis: Mr. R will likely return with acute exacerbations of chronic osteomyelitis

26 Review of imaging approach Plain Film: good MRI: the good first step,, but limited sensitivity (14%)* the preferred modality, showing extent of soft tissue and bone marrow inflammation 91% sensitivity, 82% specificity** CT: modality of choice when MRI is unavailable Ultrasound: limited use, sometimes for pediatrics and sickle cell Nuclear medicine: similar sensitivity to MRI, but bone turnover can be non-specific Three-phase bone scan WBC scan FDG PET Gallium *Tumeh et al. Disease activity in osteomyelitis: role of radiography. Radiology 1987 Dec;165(3):781-4 **Matowe, L. and F. Gilbert. How to synthesize evidence for imaging guidelines. Clinical Radiology (59): 63-68

27 Fake-outs on MRI Findings on MRI can be non-specific Fracture Postsurgical changes Osteonecrosis Adjacent arthritis Neoplasm The following examples demonstrate the importance of considering clinical history with imaging findings

28 Companion Pt 2: Lesion on MRI 64 yo M with CML and lung cancer presenting with ankle pain MRI shows distal fibular lesion,, but biopsy needed to distinguish among Osteomyelitis Inflammatory arthritis Tumor Lung cancer metastasis! Axial T2 MRI, distal L fibula BIDMC PACS

29 Companion Pt 3: Lesion on MRI 22 yo M with left anterior leg pain MRI shows mid-tibial lesion with cortical erosion and soft tissue involvement: tumor or infection? Axial T2 MRI, L mid-tibia Ewing s s sarcoma! BIDMC PACS

30 Selected examples of alternative modalities Plain Film MRI CT Ultrasound Nuclear medicine Three-phase bone scan WBC scan FDG PET Gallium Most commonly used first-line Other available approaches

31 Companion Pt 4: Osteomyelitis Gallium/Bone Scan Anterior Posterior 37 yo M with history of IV drug use presents with fevers, chills, rigors and back pain Gallium/bone scan shows increased uptake at right sacroiliac joint Posterior Posterior-Oblique Acute osteomyelitis Gallium/Bone Scan Courtesy of Dr. Donohoe

32 Companion Pt 5: Osteomyelitis on FDG PET/Bone scan Sagittal View 69 yo M with HTN, IV drug use presented with 10/10 back pain Received PET scan following incidental lung mass found on CT Increased uptake in vertebra! FDG PET CT (C-) Fusion L1-T12 vertebral osteomyelitis (confirmed with MRI) Courtesy of Dr. Donohoe

33 Conclusion Plain film and MRI are the modalities of choice for suspected osteomyelitis Classic findings for chronic osteomyelitis include: Plain film: lucent or sclerotic change, cortical erosion, periosteal reaction MRI: bone marrow edema, abscess or sinus tract, sequestra Differential diagnosis of osteomyelitis should include tumor and inflammatory arthritis Imaging findings can be non-specific, so clinical history is paramount to diagnosis

34 Acknowledgments Erica Gupta Mary Hochman Kevin Donohoe Jim Wu Corrie Yablon Gillian Lieberman Maria Levantakis

35 References Tumeh et al. Disease activity in osteomyelitis: role of radiography. Radiology 1987 Dec;165(3):781-4 Matowe, L. and F. Gilbert. How to synthesize evidence for imaging guidelines. Clinical Radiology (59): Pineda et al. Imaging of osteomyelitis: current concepts. Infect Dis Clin North Am Dec;20(4): Lew, Daniel and Francis Waldvogel. Lancet Approach to imaging modalities in setting of suspected osteomyelitis. Up-To-Date, accessed 10/14/09 Websites

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