The Spectrum of Imaging Findings in Children with MRSA

The Spectrum of Imaging
Findings in Children with
MRSA
1Leann
E. Linam, M.D.
Nicholas Cajacob, MS 3
1Janet Strife, M.D.
1Department
of Radiology
Cincinnati Children’s Hospital Medical Center
University of Cincinnati College of Medicine
Goals and objectives
• OBJECTIVE: To describe the imaging findings and
utilization in children with MRSA
• STUDY DESIGN: Retrospective review of imaging in
children with postive cultures of MRSA
• CONCLUSION:
• Imaging helps evaluate the site, extent of infections and
helps guide surgical or medical management options.
• Imaging characteristics suggest MRSA is a virulent
infections and associated with fluid collections.
• Cellulitis is the most common manifestation of this
bacteria, but all areas imaged demonstrate an
aggressive appearance of infection.
Introduction
Community-acquired methicillin resistant
staph aureus (MRSA) is seen with
increasing frequency in pediatric patients
throughout the United States. Many of
these patients undergo imaging and are
admitted to the hospital for treatment and
imaging of their infections. To our
knowledge, imaging findings in children
have not been described.
Background
• First recognized in early 1960’s after
introduction of Methicillin1
• MRSA is a misnomer as methicillin has not
been used since 1960’s
• Resistance mediated by mecA gene -encodes altered penicillin-binding protein
with low affinity or susceptibility to
methicillin, cephalosporins, and all betalactam antibiotics2
• Hospital-Acquired and Community-Acquired
forms
• Can cause a wide array of infections
including: skin, pneumonia, osteomyelitis,
arthritis, endocarditis, and sepsis
CDC/ Jim Biddle
Hospital Acquired
MRSA
Community Acquired
MRSA
Criteria include:
• Recent hospitalization
• Chronic illness requiring
frequent hospital visits
• Nursing home admission
• IV drug use
• Contact with a person
with a risk factor3
• Genetically distinct
Criteria include:
• No risk factors
• No Infection prior to
hospital admission
• Most involve skin and
soft tissues4
• Most strains contain
virulence factor PantonValentine leukocidin5
• Necrotizing pneumonia
and skin infections
• Genetically distinct
Clinical Aspects of MRSA
• Present as a “suspected
bug bite”
• Brown recluse spider bite
has a similar clinical
appearance with rapid
progressive skin changes.
• Brown recluse spider is
native to Kansas, Texas,
Oklahoma, and
Mississippi
CDC
• In other areas, one should
be highly suspicious of
MRSA6
CDC/Harold G. Scott
Clinical Picture of MRSA
Cutaneous abscess located on the hip of a prison inmate, which had begun to
spontaneously drain, releasing its purulent contents. The abscess was caused by
MRSA.
CDC/ Bruno Coignard, M.D.; Jeff Hageman, M.H.S.
Clinical Picture of MRSA
MRSA cutaneous abscess on the knee
CDC/ Bruno Coignard, M.D.; Jeff Hageman, M.H.S.
MATERIALS AND METHODS:
• A retrospective review was performed of
all MRSA culture positive inpatients and
outpatients, over 4.5 years. Charts were
reviewed to identify infection related
imaging and the imaging findings were
assessed.
RESULTS
• 365 children had MRSA positive cultures
from 1/1/03 to 6/8/07.
• Imaging was performed in 251 patients
• Figure 1 demonstrates the distribution of
imaging
• Figure 2 demonstrates anatomic
distribution of infection
Distribution Of Imaging In Patients
With MRSA
140
120
100
number of
patients
radiograph
only
80
ultrasound
60
MRI
40
CT
20
0
1
imaging modality
nuclear
medicine
Distribution Of Area Of Infection In
Patients With MRSA
250
200
150
cellulitis
Number of
patients
abscess and
cellulitis
osteomyelitis
100
50
pneumonia
0
1
Area of infection
other
diagnosis
Results Summary
• Radiographs
– extensive soft tissue swelling.
• Ultrasounds
– diffuse soft tissue edema
– multiple tiny fluid collections consistent with aggressive cellulitis.
• MRI imaging
– Differentiated cellulitis versus osteomyelitis
– Osteomyelitis showed subperiosteal elevation
– Localized abscesses
• In patients with pneumonia, pleural effusions were
always present on radiographs.
• Abscesses were seen in unusual places, including
kidneys, paraspinal muscles, labia, and scrotum.
Soft Tissue Infection/Cellulitis
History: suspected bug bite; culture yielded MRSA
Cellulitis with Abscess
Ultrasound of rt
forearm shows
diffuse cellulitis with
small fluid collections
Images from scrotal
ultrasound showing
extensive cellulitis and
small phlegmon (bottom
image
3.5 year old with labial
swelling. Ultrasound
shows extensive
cellulitis of the rt labia
compared to the left
(upper image). There
are enlarged lymph
nodes in the rt groin.
Same patient returned 3 days
later, now with labial abscess
Cellulitis/Osteomyelitis
Initial Radiograph “normal”
Osteo radiograph, MRI
Initial radiograph in a patient with left shoulder pain
shows no abnormality
Osteomyelitis: 3 days later
aggressive bony changes
Same patient 3 days later now demonstrating extensive destruction
of proximal humerus.
MRI Findings
• T2 weighted images
• Extensive abnormal
signal in the marrow
• Subperiosteal fluid
• Soft tissue induration
• Small micro abscesses
within cellulitis
MRI Findings
• Post contrast T1 imaging
• Enhancement in the soft
tissues
• Necrotic bone (arrow)
Initial chest radiograph in 10 month old
presenting with cough and fever
pneumonia
Chest radiograph – 2 days later
Pneumonia/Pleural Effusion/Abscess
CT Findings
• Consolidation
• Necrotic lung
• No pleural
enhancement
CT of the chest (same patient)
demonstrating consolidation,
necrotic lung.
CT Findings
• Consolidation
• Necrotic lung
• No pleural
enhancement
CT Paraspinal
Abscess
• 13 year old with
paraspinal mass
• Initially questioned
by imaging to be
lymphatic
malformation
• Biopsy and culture
grew MRSA
Patient with pyelonephritis,
persistent fevers and left
flank pain. Ultrasound
demonstrates hypoechoic
peripheral area in lower
pole of left kidney with
decreased flow, consistent
with a renal abscess.
CT scan on the
same patient
confirms the
renal abscess,
as well as
demonstrating
pyelonephritis
more inferiorly.
Conclusions
• MRSA is a virulent infection often requiring
imaging to evaluate the site and type of infection
and to help guide surgical or medical treatment
options.
• Cellulitis is the most common manifestation of
this bacteria, but all areas imaged demonstrate
an aggressive appearance of infection.
• With the exception of extremity radiographs,
imaging of MRSA uniformly demonstrated fluid
collections.
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