utility of mri in the follow-up of pyogenic spinal infection

8/6/2019 Utility of MRI in the Follow-up of Pyogenic Spinal Infection

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ORIGINAL ARTICLE

Utility of MRI in the follow-up of pyogenic spinal infection

in children

Qiuyan Wang & Paul Babyn & Helen Branson &

Dat Tran & Jorge Davila & Edrise L. Mueller

Received: 5 June 2009 /Revised: 6 August 2009 /Accepted: 27 August 2009 /Published online: 10 September 2009# Springer-Verlag 2009

Abstract

Background MRI is used at an increasing rate in evaluationof pediatric spinal infections both at the time of diagnosis

and in follow-up. However, the impact of MRI in follow-up

has been rarely evaluated to date.

Objective To evaluate serial follow-up spinal MRI changes

compared to clinical outcome and assess their impact on

clinical management.

Materials and methods All pediatric (


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reduced diagnostic delay, aided recovery and helped

avoid lengthy hospitalizations [4].

With the shift in contemporary management from

surgical therapy to primary medical therapy [57], MRI

is increasingly used in follow-up to assess treatment

response. However, the value of MRI in the follow-up of

pediatric spinal infection has not been fully established.

Several adult studies have shown that no single MRIfinding correlates well with clinical status and that some

MRI features may persist or even worsen initially despite

clinical improvement on antibiotic treatment [810]. Given

the differences in vascular supply and immaturity of the

pediatric spine, we wished to determine the utility of

follow-up MRI in children. Our objectives were to assess

the correlation between serial MRI features of spinal

infection with clinical outcome and the impact of follow-

up MRI on clinical management for children with

pyogenic spinal infection.

Materials and methods

This is a single-center retrospective cohort study. Institu-

tional Review Board approval was obtained and waiver of

consent was granted.

Patient population

All children diagnosed with pyogenic spinal infection,

spondylodiscitis, or localized vertebral osteomyelitis during

a 9-year period (January 2000 to September 2008) were

identified from a search of our radiology reporting database

and health record database using the international classifi-

cation of disease coding (ICD). Ninety-seven cases of

spinal infection were identified. All children with pyogenic

spinal infection and available baseline MRI exam before

treatment and at least 1 follow-up MRI after initiation of

treatment were included in this study. Children with

atypical infections including tuberculous or blastomycotic

spondylodiscitis, and spondylodiscitis secondary to direct

spinal trauma, spinal surgery or instrumentation were

excluded. A total of 17 children met our criteria.

Clinical information including childrens age, gender,

initial presentation and length of symptoms prior to

diagnosis was collected. Main laboratory tests included

erythrocyte sedimentation rate (ESR), white blood cell

(WBC), polymorphonuclear leukocytes (PMN) and

C-reactive protein (CRP). The treatment used and

response to therapy were recorded. The impact of

follow-up MRI on clinical decision making was assessed

retrospectively through review of the medical records by

an infectious disease physician using a pre-designed data

collection form.

Image acquisition

All MRI exams were acquired on a GE Signa 1.5-T MRI

scanner at software level 9.1 (GE Medical Systems,

Milwaukee, WI, USA) except for one case with an outside

hospital baseline MRI. The scan protocol at baseline and

follow-up MRI consisted of: sagittal T1-W, sagittal FSE

T2-W images with fat saturation, axial T1-W and T2-Wimages of the region of interest, and post-contrast T1-W

sagittal, axial and coronal scans with fat saturation.

Image review

All available MR imaging was reviewed electronically on

PACS by two staff radiologists one with more than

20 years of experience in musculoskeletal diseases and a

neuroradiologist both blinded to all patients clinical

information. MRI features were recorded, specifically bone

marrow edema, bone enhancement, bone destruction and

vertebral body height loss, abnormal T2-W disc signal andenhancement, epidural enhancement and abscess, canal

compromise, and paraspinal soft-tissue enhancement and

abscess.

Qualitative assessment of interval changes of individual

MRI findings on the first follow-up compared with baseline

MRI was rated independently by the two radiologists as

normal, better, same or worse. The time and anatomic

extent of all follow-up exams were recorded. MRIs done

less than 4 months after baseline were considered short-

term follow-up, while those conducted after 4 months were

considered long-term follow-up.

Statistical analysis

Inter-observer agreement on interval changes for each MRI

feature was evaluated by kappa value.

Results

Clinical and laboratory characteristics

Pyogenic spinal infection was found in nine girls and eight

boys, ranging in age from 2 months to 16 years. Seven of

the 17 children were younger than 3 years, median

16 months. The remaining 10 children were between 9

and 16 years of age, median 12 years. Back or neck pain

was the predominant clinical presentation in 13/17 cases,

with fever in 11/17 cases. Torticollis, buttock/hip pain, and

constipation were encountered in one case each. In the

younger age group, the presentation was more nonspecific

and included fever, tachypnea, abdominal distension,

irritability with movement, and refusal to bear weight.

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Sixteen cases (94%) had elevated ESR, with 10 cases

(59%) showing leukocytosis. Blood cultures were positive

in 9/17 cases, including six with Staphylococcus aureus and

one case each of Streptococcus pyogenes group A,

Salmonella typhimurium, and Pseudomonas species. No

other causative infectious lesions for these children were

found. Bone biopsies were available in two cases and grew

S. aureus and Salmonella typhimurium. Two of three paraspinal soft-tissue biopsies were positive (both for S.

aureus). Predisposing conditions were seen in four patients

(24%), including one case each of patent ductus arteriosus,

hereditary spherocytosis, trisomy 6, and psoriasis.

Management

All children were treated with intravenous antibiotics based

on susceptibility profiles when available. Two underwent

laminectomy for extensive epidural abscess.

All children except one had satisfactory clinical im-

provement within 1 month of initiating treatment.

Follow-up MRI data

Fifty-one follow-up MRIs were done, ranging from 2 weeks

to nearly 5 years after the baseline MRI. Mean follow-up

number of exams was three per patient, range 17 exams

(Fig. 1). The first follow-up MRI exams were completed 2

17 weeks after baseline MRI, mean 8 weeks. Thirty-five

whole spine scans and 16 localized spine scans were

performed in follow-up. In those seven patients younger than

3 years, 33 follow-up MRIs were performed, in which 17

exams utilized general anesthesia and 10 required sedation.

Short-term follow-up MRIs were performed in all

children, while long-term follow-up was done in 10 patients. Stated clinical indications for follow-up MRI

exams included: routine follow-up in 37 exams (73%),

assess response to antibiotic treatment in six exams (12%),

assess spinal cord compression in two exams (4%), assess

residual back pain in two exams (4%), assess potential

differential diagnosis in two exams (4%), establish length

of antibiotic treatment in one exam and evaluate necessity

for urgent surgery in one exam.

Initial and follow-up MRI features

Location

The distribution of affected vertebral segments in our

patients was as follows: two cervical, five thoracic, five

lumbar, three sacral and one each with thoracolumbar and

lumbrosacral segment involvement. Specific MRI features

noted at baseline and follow-up are tabulated in Table 1.

MRI features Baseline MRI

(n=17 patients)

Short-term follow-up

(n=17 patients)aLong-term follow-up

(n=10 patients)

2 vertebra involvement 12 13 1

Marrow edema 17 16 7

Bony enhancement 17 16 7

Body height loss 3 5 3

Disc T2-W signalb 9 10 7

Disc enhancementb 4 8 4

Epidural enhancement 13 9 3

Epidural abscess 5 1 1

Canal compromise 11 6 3

Paraspinal enhancement 15 12 7

Paraspinal abscess 7 4 1

Table 1 Comparison of MRI

findings at baseline and short-

term or long-term follow-up

a1 follow-up MRI without

contrastb There is no disc applicable in a

C1-2 case

0 10

20

30

40

50

60

Time (month)

1 2 3 4 5 6 7 8 9 1011 121314151617Cases

Time and frequency of follow-up MRI in 17 cases

1st F/U

2nd F/U

3rd F/U

4th F/U

5th F/U

6th F/U

7th F/U

Fig. 1 Time and frequency of

follow-up MRI

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Bone abnormalities

At baseline MRI, bone marrow edema (hypointense on T1-

W and hyperintense on STIR/T2-W images) appeared in all

17 children. Single vertebra involvement was seen initially

in five children, while involvement of two or more

vertebrae was found in 12 children. No skip lesions were

seen. Bone marrow edema affected the vertebral body in 14

children, while involvement of the posterior elements alone

without vertebral body involvement was seen in three

children (Fig. 2). The causative organisms were S. aureus in

two cases and Pseudomonas species in the other.

On follow-up MRI for the five children with single

vertebra involvement, bone marrow edema completely

resolved in one child, remained as single vertebra involve-ment in two children and progressed to involve adjacent

disc and vertebra in the two other children (Fig. 3). For the

12 children with two or more vertebrae involvement,

marrow edema improved in seven, remained static in three,

and extended to involve more of the spine in two.

Bone enhancement was seen in all 17 children at

baseline. On follow-up, abnormal enhancement resolved

completely in one child, improved in three and remained

static in eight. Worsening of bone enhancement was seen in

four cases. The remaining one had no contrast agent study

available.

Loss of vertebral body height was seen in 3/17 children(17%) on baseline and 5/17 (29%) on follow-up. Sagittal

view showed irregularity or erosion of low T2-W signal

vertebral end plate (Fig. 4). Bone destruction and near-

complete collapse of the vertebra was seen in one child on

baseline and two on follow-up MRI.

At baseline, facet joint involvement was noted in three

children, including one with unilateral and two with

bilateral involvement. On T2-W images, the affected joints

appeared hyperintense with adjacent paraspinal soft-tissue

abnormality and slight joint effusion (Fig. 5). There was

obvious enhancement after contrast administration.

Fig. 2 A 2-month-old girl with blood culture positive for Staphylo-

coccus aureus. Sagittal T2-W image shows hyperintense T7 spinal

process (arrow) with epidural abscess extending from C7 to T11 level.

Normal signal intensity is preserved in vertebral bodies and discs

Fig. 3 A 13-year-old boy. a Diffuse L4 vertebral body shows

increased signal intensity on sagittal T2-W image and b enhancement

after contrast administration. Normal high signal disc and linear low

signal central cleft is preserved in the L4-5 disc. c Two months later

there is improvement in the degree of vertebral body marrow edema in

the L4 body with new involvement of the L5 and L4-5 discs. The boy

was clinically improved at the time of this follow-up

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Disc abnormalities

At baseline, discs adjacent to the affected bone were normal

on T2-W images in 10 children (59%). Seven children

(41%) showed abnormal signal intensity on T2-W imaging,

including four cases that were hypointense, two with mixed

signal intensity and one with complete destruction of the

interval disc. Among the seven children with abnormal T2-

Fig. 4 A 2-month-old girl with

biopsy positive culture of

Staphylococcus aureus. a Sagit-

tal T2-W image shows destruc-

tion of T8, T9 and intervertebral

disc with loss of vertebral body

height, more so on T9. There is

absence of the normal linear

hypointensity of the adjacent

endplates of T8 and T9. Lobu-lated paravertebral soft-tissue

abscess is present anteriorly. b

One month later sagittal T2-W

image shows more extensive

bone destruction with almost

complete vertebral height loss in

T8 and T9. Retrolisthesis and

kyphosis caused canal compro-

mise and cord compression. The

girl was clinically improved at

the time

Fig. 5 A 3-year-old girl with blood positive culture of a Pseudomo-

nas species. a Axial T2-W image shows marrow edema involving the

left L5 pedicle, lamina and facet joint. Joint shows irregularity. b Post-

contrast axial T1-W image of the baseline MRI shows enhancement in

the left posterior element of L5 and paravertebral soft tissue. There is

an epidural abscess with thick-walled peripheral enhancement and

right deviation of the dural sac. c Follow-up at 2 months. Post-contrast

axial T1-W image shows improvement of paraspinal and epidural

enhancement without abscess. d Axial post-contrast T1-W image

scanned 18 months after baseline MRI shows persistent epidural

enhancement with a possible small abscess (arrow). The girl was

symptom-free at the follow-up MRI

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W signal intensity, five cases showed enhancement after

administration of contrast agent. New disc involvement was

seen in two children on follow-up MRI (Fig. 6). Disc

abscess formation was seen in one child on baseline and

two on follow-up MRI; they appeared as a fluid-like T2-W

hyperintensity without enhancement (Fig. 7).

Epidural involvement

At baseline, 13/17 children (76%) had epidural thickening

or mass-like soft-tissue intensity on T1-W/T2-W imaging.

Avid enhancement with thickening after contrast adminis-

tration measured 219.8 mm, mean 6.1 mm. Eight children

Fig. 6 A 2-year-old girl with spondylodiscitis at L1-2 level. a Initial

sagittal T2-W imaging shows diffuse marrow edema of L1-2 vertebral

bodies and heterogeneity in disc signal with overall loss of disc

hyperintensity and joint space. b There is no disc enhancement post-

contrast administration. c six weeks later T2-W image shows

increased endplate and disc destruction with new central disc

enhancement d. The girl was clinically improved at the time of

follow-up

Fig. 7 A 12-year-old girl with negative blood culture. a Sagittal T2-

W image shows decreased T7-8 disc space and signal intensity

accompanied by adjacent endplate irregularity. b One month later

sagittal T2-W image shows interruption of low signal end plates of

T7-8 and minimal body height loss. c T7-8 disc abscess appears

hyperintense without enhancement on post-contrast image. The girl

was clinically improved at the time. Note a syrinx at the same level of

thoracic spinal cord posteriorly

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had varying degrees of spinal canal compression. Five

children had epidural abscess formation ranging from 3 mmto 11.8 mm, mean 9.2 mm; they were centrally hypointense

with rim enhancement on post-contrast sequences (Fig. 5).

On short-term follow-up, only a 4-mm epidural abscess

remained, in one child. Extent of epidural enhancement

decreased, range 212.9 mm, mean 3.8 mm.

Paraspinal soft-tissue involvement

At baseline, 15/17 children (88%) had paraspinal soft-tissue

involvement. The thickness of enhancing paraspinal soft

tissue ranged from 4 mm to 60 mm, mean 16.2 mm, which

enhanced intensely after contrast administration. Sevenchildren had paraspinal abscess formation, range 2

43 mm, mean 15.6 mm (Fig. 8). Three paraspinal abscesses

remained on short-term follow-up MRI; two were smaller

while the other enlarged. Paraspinal soft-tissue enhance-

ment on follow-up MRI improved in all but one case, range1.420 mm, mean 6.7 mm.

Overall follow-up changes compared with baseline MRI

Short-term (


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appearance; (2) improvement of soft-tissue appearance but

more extensive involvement of bone and/or disc; and (3)

worsening of bone, disc and soft-tissue appearance.

1. Improvement of bone, disc and soft-tissue appearance

In follow-up MRI, 8/17 (47%) children showed improve-

ment including decrease in or disappearance of: (1) abnormal

signal intensity and enhancement within bone marrow and

disc, (2) epidural thickening and/or (3) paraspinal soft-tissue

infective changes. Clinical and laboratory results were also

improved in these children. Two of these eight children had

initial laminectomy for extensive epidural abscess.

2. Improvement of soft-tissue appearance but more exten-

sive involvement of bone and/or disc

In follow-up MRI, 8/17 (47%) children showed more

bone and/or disc abnormalities such as increased bone

marrow edema, vertebral segment involvement, end plate

n=17a Better Same Worse Kappa

Rater1 Rater2 Rater1 Rater2 Rater1 Rater2

Involved segment 4 3 11 12 2 2 0.64

Marrow edema 8 10 5 3 4 4 0.71

Bony enhancement 5 8 8 4 4 4 0.53

Body height loss 0 0 14 14 3 3 1

Disc T2-W abnormal signal 1 0 10 12 6 5 0.53

Disc enhancement 0 1 8 9 8 6 0.76

Epidural enhancement 12 10 3 5 1 1 0.73

Epidural abscess 5 5 12 12 0 0 1

Canal compromise 7 7 8 9 2 1 0.49

Paraspinal enhancement 13 12 2 3 1 1 0.83

Paraspinal abscess 6 8 10 7 1 2 0.69

Table 3 Inter-rater comparison

about changes on follow-up MR

compared with baseline MR

a1 follow-up MRI without con-

trast so n=16 for bony, disc,

epidural and paraspinal en-

hancement

Fig. 9 A 14-year-old girl with

Staphylococcus aureus septice-

mia. Axial and sagittal post-

contrast T1-W images with fat

saturation in baseline MRI (a, b)and follow-up 2.5 months later

(c, d) show interval improve-

ment of paravertebral soft tissue

(black arrows in a) and epidural

involvement (white arrow in a).

Interval irregularity of the L1-2

end plates and L1-2 disc

changes are noted at follow-up

with new disc enhancement

(arrow in d). Clinically the girl

was asymptomatic at this time

Pediatr Radiol (2010) 40:118130 125


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destruction, vertebral body height loss, disc destruction, and

bone and/or disc enhancement after administration of

contrast agent. The epidural and paraspinal soft-tissue

involvement showed variable improvement with either

disappearance or decrease of epidural and/or paraspinal

abscesses (Fig. 9). Clinical and laboratory results (WBC,

PMN, ESR and CRP) demonstrated improvement in these

children.

Fig. 10 A 16-year-old boy with biopsy culture of Salmonella

typhimurium. Sagittal T2-W and post-contrast axial T1-W images

from baseline MRI (a, b) and short-term follow-up 1 month later (c, d)

show progressive vertebral end plates of L3 and L4, and L3-4 disc

destruction (c). d Increased epidural and paravertebral soft-tissue

involvement with paraspinal abscess formation is present at 1-month

follow-up. The boy was still febrile and had severe back pain

necessitating analgesics at the time. e At 6-month follow-up, sagittal

T1-W image shows hyperintense L3-4 vertebral bodies, isointense on

T2-W fat-saturation imaging (f), suggesting healing fat deposit. g

Post-contrast axial T1-W image at 6 months post-treatment shows

residual paraspinal soft-tissue enhancement (arrow) but complete

resolution of epidural infection. The boy was asymptomatic at that

time

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3. Worsening of bone, disc and soft-tissue appearance

There was progression in epidural and paraspinal soft-

tissue infection along with further bone and disc destruction

in one child (Fig. 10). The interval time of follow-up for

this child was 1 month after baseline MRI. Clinically there

was no improvement, as the child remained febrile with

severe back pain, necessitating analgesics at follow-upMRI. Laboratory results showed increased WBC, PMN and

ESR.

Long-term (>4 months) follow-up after starting antibiotic

treatment

Ten children (59%) had follow-up MRI greater than

4 months after baseline. In long-term follow-up, there

was overall improvement in bone and soft-tissue

involvement in all children. However, some residual

bone, disc or soft-tissue changes were evident in some

children.Marrow edema, bone enhancement and T2-W disc

a bn orma l sig na l were p ersisten tly see n in sev en

children, range 733 months, mean 15 months, after

baseline MRI. Four of these seven children demon-

strated persistent disc enhancement. Loss of vertebral

body height was seen in three children at 12, 15 and

33 months after baseline MRI. The near-complete

destruction of vertebrae in two children with long-

lasting spinal misalignment required internal fixation.

Three children showed patchy hyperintensity around

the reg io n o f forme r b on e d estruc tion o n T 1-W

imaging and isointensity on T2-W fat saturated imag-

ing, suggestive of healing fat deposits (Fig. 10).

Epidural enhancement was seen in three children,

ranging from 6 to 18 months after baseline MRI. A possible

small abscess and slight canal compromise was seen in one

child by the time of his last follow-up MRI at 18 months

after baseline (Fig. 5). The child was symptom-free at that

time.

Paraspinal soft-tissue enhancement was seen in seven

children between 6 and 33 months, mean 14 months, after

baseline MRI. A small possible abscess remained in a

symptom-free child at 6 months after baseline MRI

(Fig. 10).

Impact on clinical treatment

Extension of antibiotic treatment occurred in 8/17 (47%)

children, based in part on abnormal findings on follow-up

MRI including prolonged bone, disc or soft-tissue enhance-

ment, despite the children being clinically asymptomatic.

The elongation of antibiotic treatment ranged from 2 weeks

to 8 months, mean 3.6 months.

Discussion

Spondylodiscitis accounts for 24% of all infectious bone

diseases [11, 12]. It is even less common in children.

However, pediatric pyogenic spinal infection can cause

severe and long-lasting neurologic complications. Tubercu-

losis used to be the predominant form of spondylodiscitis,

but nontuberculous pyogenic spine infections have beenincreasingly noted [13] and are responsible for approxi-

mately 2% of all juvenile bone infections [14].

Our study demonstrated a bimodal age distribution for

spinal infection (


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Epidural and/or paraspinal soft-tissue involvement

Follow-up MRI can help in monitoring the response to

treatment. Our study showed that reduction of epidural and/

or paraspinal soft-tissue inflammation is the earliest sign of

improvement compared to bone and/or disc changes after

initiation of antibiotic treatment. This concurs with adult

studies. Veillard et al. [20] pointed out in a prospectivestudy of 16 cases that the reduction in paravertebral and in

epidural abscesses were the only two features that improved

on follow-up MRI 1 month after the start of antimicrobial

therapy. Similarly, Kowalski et al.s study [9] used

associated soft-tissue changes only as the single grading

scale to assess the risk of treatment failure on follow-up

MRI for patients with spinal infection. Further, epidural

and/or paraspinal soft-tissue infection correlated better with

our patients clinical status than with bone and/or disc

destruction.

Most of our patients demonstrated quick reduction of

epidural and paraspinal soft-tissue change. However, threechildren had residual epidural enhancement and seven

children had prolonged residual paraspinal soft-tissue

enhancement ranging from 6 to 33 months after baseline

MRI. Chart review at the time of MRI follow-up showed no

fever, pain or any movement limitation. This suggests

granulation tissue formation post-infection rather than an

active infectious process.

Our only case with clinical deterioration at the time of 1-

month follow-up MRI demonstrated worsening of soft-tissue

infection, with abscess formation and further destruction of

the vertebral body and intervertebral disc. His subsequent

follow-up MRIs at 12 and 14 months showed overall

improvement although marrow edema, bone enhancement

and abnormal T2-W disc signal were still present. The

epidural and paraspinal soft-tissue infection had disappeared

and the child was asymptomatic.

Bone and disc involvement

Our study showed that bone and disc MRI abnormalities

can persist or show short-term worsening despite clinical

and laboratory improvement in response to antibiotics. This

is supported by Zarrouk et al.s [21] prospective study in

adults wherein 94% of follow-up MRIs at 3 months after

onset of disease had vertebral destruction, with 39%

showing worse vertebral destruction compared to baseline

MRI. Bone destruction was still present in all of their 22

cases at 6-month follow-up MRI.

Where follow-up MRI is not necessary

Although MRI is essential for initial diagnosis, our study

demonstrates that serial routine follow-up MRIs to assess

treatment response are not necessary for the vast majority

of cases. Follow-up MRI is not needed for patients with

good clinical response. These patients should be followed

clinically and/or with laboratory tests. Ultimately, decisions

about treatment should be based on clinical status and not

MRI findings.

A potential negative impact of follow-up MRI on

management in our study was the extension of antibiotictreatment. In 47% of our cases, antibiotic treatment was

extended at least in part because the follow-up MRI showed

prolonged bone, disc or soft-tissue enhancement despite the

patients being clinically symptom free. Roblot et al. [7]

reported that short-duration ( 6 weeks) antibiotic therapy

does not enhance the risk of spinal infection relapse

compared to 3 months or longer duration. In other words,

the patients clinical presentation and illness course, rather

than the follow-up MRI, should be considered when

deciding the length of antibiotic treatment.

Indications for follow-up MRI

For patients with unsatisfactory clinical response to anti-

biotics, MRI can help reevaluate the extent of infection, in

particular to delineate the presence and extent of epidural

abscess and spinal cord or canal compression (Fig. 4).

Prompt diagnosis and combined antibiotic and/or surgical

treatment help to prevent adverse outcomes, so follow-up

MRI is essential in cases with poor clinical response.

In the pediatric population, especially for younger

children, MRI often needs to be done under general

anesthesia or sedation. In our study, 33 of the 51 follow-

up MRI exams were performed on seven children younger

than 3 years with multiple general anesthesia and/or

sedation. Except for one follow-up MRI exam requested

to evaluate spinal cord compression caused by misalign-

ment of the spine, the remaining MRIs were routine follow-

ups to assess the response to treatment. Therefore, 41% of

our patients accounted for 65% of the follow-up MRIs. This

disproportionate number of follow-up MRIs performed on

children


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MRI for the only child in our study with clinical

deterioration also had deteriorating bone involvement.

However, he also had deteriorating disc and soft-tissue

involvement at 1 month after baseline MRI. His subsequent

long-term follow-up MRIs showed continuous improve-

ment in bone, disc and soft-tissue changes.

Our study shows that long-term (>4 months) follow-up

MRI should not be used to determine response to treatment. Neither residual bone nor soft-tissue changes correlated

with clinical symptoms in long-term follow-up.

The most useful follow-up MRI is conducted between

1 and 4 months, with emphasis on soft-tissue involve-

ment. One should be cautious not to over-interpret

progressive bone changes with improving soft-tissue

involvement as disease progression. Such inappropriate

interpretation of follow-up MRI findings can cause

overestimation of the severity of the disease and

precipitate unnecessary treatment.

Limited follow-up MRI

Whole spine MRI can rule out multifocal spinal involve-

ment, which is helpful to distinguish other infectious or

inflammatory spondylitis, and should be performed at

baseline. For follow-up, however, the value of whole spine

MRI is less certain. None of the 35 whole spine scans in

our follow-up study showed any additional lesions. There-

fore, limited spine MRI is recommended at follow-up to the

region of interest, when indicated, to reduce the time of

scan and general anesthesia, unless disease progression is

suspected.

Limitations of our study

The main limitations of this study are its retrospective

nature and small sample size. The imaging analysis was

based on the data available at the time of study. The time of

follow-up MRI exam was variable based on access to MR

imaging and decision making of the treating physicians.

The inter-observer agreement was calculated by means

of kappa statistics. The interpretation of kappa value for

individual MRI features varied from 0.49 to 1, or from

moderate agreement, substantial agreement to almost

perfect agreement according to Landis and Koch [22].

Assessment for vertebral body height loss and epidural

abscess had perfect agreement while assessment for canal

compromise had moderate agreement. Although the median

kappa value was acceptable, our inter-observer agreement

could have likely been improved if readers had a pretest to

reach consensus before independent case review.

Although the sample size of our study is small, it reflects

the largest single institution sample to date. Further

prospective and multidisciplinary studies can be undertaken

to examine the value, indications, timing and frequency of

follow-up MRI in the management of children with spinal

infection.

Conclusion

Epidural and paravertebral soft-tissue changes on short-term follow-up MRI correlated better with patients clinical

symptoms compared to bone and disc destruction. Bone

and disc changes can appear to progress more so than soft-

tissue infection despite adequate clinical response to

therapy. Although MRI is essential for initial diagnosis,

serial routine follow-up MRIs were not necessary for the

vast majority of cases. Follow-up MRI is not needed for

patients with good clinical response; these patients should

be followed clinically and/or with laboratory markers of

inflammation. The segment of the pediatric population that

might benefit from follow-up MRI includes those who

deteriorate clinically and those too young for clinicalresponse to be accurately assessed. If follow-up MRI is

indicated, localized spine rather than whole spine scan is

recommended unless disease extension beyond the original

focus is suspected. Further, for follow-up MRIs conducted

between 1 and 4 months, soft-tissue involvement should be

the focus rather than bone changes. Long-term follow-up

MRI is not necessary. Treatment decisions, including

elongation of antibiotic course, should be made based on

initial presentation and clinical response rather than on

long-term follow-up MRI findings.

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