1. Sentinel sign for ipsilateral pelvic and hip disorders
Iliac Wing Sign
Sentinel sign for ipsilateral pelvic and hip disorders
Thank you
Dr Antoine MARCHAND
Dr Raphaël GUILLIN
Department of Radiology and Medical Imaging, CHRU of Rennes, FRANCE

2. Iliac Wing Sign (IWS) ?
High Intensity linear image on fat-suppressed T2 sequence
On the interface between the deeper aspect of the iliacus muscle and the iliac bone
First of all, an IWS is a High Intensity linear image on fat-suppressed MRI T2 sequence.
It is located on the interface between the deeper aspect of the iliacus muscle and the iliac bone.
You can see an example on this picture, white arrows representing IWS.

3. IWS: why indirect radiologic signs are important
Mme B, 26 years old, suspicion of septic spondylodiscitis
MRI of spine :
Through this coming situation, we will be able to acknowledge the role played by IWS as a sentinel sign: a young woman came in for an MRI as her GP was suspecting a septic spondylodiscitis. Spine MRI was normal but the radiologist noticed  that the oedema  was present in the deeper  aspect of the iliacus muscle, and was even predominant on the left hand side  of the pelvis. This sign drew the radiologist's attention who decided to complete an MRI examination with another sequence focused on pelvis.
He diagnosed a sacro iliitis. So IWS was in that case an indirect radiologic sign that helped the radiologist to elaborate the final diagnosis.
Additional pelvis MRI :

4. Precedent studies But no correlation between IWS and
Age, weight, gender, status
No distinction between:
Actually, IWS has already been described in precedent studies but in these previous ones, it has never been correlated  with patient’s clinical data such as his age, weight, gender or status. Furthermore, there has never been a distinction between unilateral, bilateral symmetrical and bilateral asymmetrical patterns.
Unilateral (U-IWS)
Bilateral and Asymmetrical (BA-IWS)
Bilateral Symmetrical (B-IWS)
Kakigi, Eur J Radiol, 2012 
Eshed, Acta Radiol, 2013 

5. Iliac Wing Sign Study Retrospective study
Review of pelvis MRI examination realised between 2010 and 2012
Inclusion criteria: at least 1 coronal T2 with FS No hip prosthesis or other orthopaedic device, initial sacro iliitis suspicion
304 MRI included
Average Age of patients : 44 years old (0,5-87)
172 men and 132 women
For these reasons, we implemented a new retrospective study, in which we reviewed 304 pelvis MRI examinations including at least 1 coronal T2 with FS. Exclusion criteria were hip prosthesis or other orthopaedic devices, and initial suspicion of sacro iliitis that need specific protocol.
The average Age of patients was 44 years old and our study included 172 men and 132 women.

6. Clinical data Presence and IWS type
independent review by 2 radiologists
Presence of pathologies by consensus
With histological proofs if present
Associated findings
Coxofemoral joint effusion? Ilio psoas bursitis ?
Hip pain?
Posterior to lumbar spine soft tissue oedema (PLSTE)
Depending on patient age or heart/kidney insufficiency but not on spine pathology
Presence and IWS type were recorded independently by 2 radiologists. Presence and type of pathology on MR examination were assessed by consensus with histological proof when present.
Presence of coxofemoral joint effusion, hip pain and posterior to lumbar spine soft tissue oedema were also recorded independently.
Shi, AJR, 2003 
Genu, Diag Interv Imagin, 2014 

7. IWS : RESULTS Inter reader reliability:
IWS : prevalence : 27%, PPV 96%, NPV 35%
U-IWS and BA-IWS: PPV=100% (84% for B-IWS)
Ipsilateral pathology : U-IWS: 90% (low rate for other IWS types)
rare enhancement of IWS in case of gadolinium injection (4/27)
Inter reader reliability:
Kappa > 0.9
In our study, prevalence of IWS was 27 percent with a good positive predictive value and in contrast with a low negative predictive value. More interestingly, U-IWS and BA-IWS presented a tremendous PPV of 100%. Furthermore in U-IWS, ipsilateral pathology was observed in 90% of the MR examinations. We have also noticed a rare enhancement of IWS and an excellent inter reader reliability (up to 0.9)

8. Results : IWS and clinical data
Association
Age
Posterior to lumbar spine soft tissue oedema
Coxofemoral joint effusion
U-IWS
+ (OR=1,5) NS
+ (OR=1,98)
BA-IWS
+ (OR=2,4)
++ (OR=15,7)
+ (OR=2,45)
B-IWS
+ (OR=2,05)
+++ (OR=20,6)
Considering clinical data, all types of IWS were associated with age, especially B-IWS types. These ones were strongly associated with posterior to lumbar spine oedema contrary to Unilateral IWS. Interestingly enough, precedent authors had already showed   that posterior to lumbar spine oedema was depending on age, kidney and heart insufficiency but not on spine pathology.
Coxo femoral effusion was associated with Unilateral and BA type but not with Bilateral Symmetrical IWS.
No association was demonstrated between IWS and Hip pain, ilio psoas bursitis, gender, weight and status.
OR : odds ratio ; NS : non significant
No statistical association between IWS (all IWS type) and :
Ilio psoas bursitis
Hip Pain
Gender, weight, status

9. P < 0.05 OR=6.2; range, 1.77-25.85, p<0.001
8/2
12/11
The important point of this graph is that it shows how IWS is significantly more common in case of fracture and malignant bone tumor.
Furthermore, when bone tumor was diagnosed, IWS presence led to an increase by a factor of 6 to the risk of the tumor to be malignant.
9/21
3/9
5/16
6/19
0/15
OR=6.2; range, , p<0.001

10. IWS prevalence given main anatomical localizations of pathologies
Concerning Main anatomical localization, no significant association was found with IWS prevalence.
5/13
23/63
4/15

11. Vasogenic Oedema >> inflammatory tissue
What is IWS ?
Layer of like water High intensity on T2 weighted sequence with fat suppression
Enhancement was unusual
Eshed
But what is truly IWS ? Regarding the nature of IWS, its high T2 signal with unusual enhancement suggests more a vasogenic oedema than an inflammatory tissue; but unfortunately we were missing histological proof and this represents one of the limit of our study.
Vasogenic Oedema >> inflammatory tissue

12. Physiopathology ? Kakigi Eshed 8% Arthro MRI (total 50)
The second question is how IWS is being formed? One precedent author suggested that in case of a fracture , stretching strengths would be more concentrated on iliacus muscle, resulting in oedema synthesis. But this cannot  explain IWS formation in case of a malignant  tumor.
On another hand, another author suggested a communication between deep aspect of iliacus muscle and coxofemoral joint. However this communication was found in only 8% in Eshed MRI arthrography study. What’s more in our study, we proved a notable association between coxofemoral joint effusion and Unilateral and BA IWS. This association was noteworthy in case of B symmetrical IWS. 
8% Arthro MRI (total 50)
Kakigi
Eshed

13. Conclusion IWS is correlated with age
Mainly in bilateral type (B-IWS)
IWS is an ipsilateral sentinel sign
Especially in U-IWS et BA-IWS types: PPV of pathology = 100% and good localization skill
Excellent inter reader reliability
IWS is more often seen
In case of fracture
In case of malignant bone tumor: indirect sign of neoplasia
TO CONCLUDE, Firstly : IWS is significantly associated with age, mainly in bilateral type.
Secondly, IWS is an ipsilateral sentinel sign of pathology, especially in U-IWS and BA-IWS with excellent inter reader reliability.
Finally, we are able to ascertain that IWS is more often found in case of fractures or malignant bone tumors.

14. Thanks for your attention