Magnetic resonance imaging of the healthy pediatric knee and wrist: defining normal values for synovial thickness.

Juvenile idiopathic arthritis (JIA) is not a single disease, but a term that
includes all chronic rheumatic diseases of childhood, beginning for the age of
16, persistent for more than 6 weeks and of unknown etiology and
pathophysiology. It is characterized by prolonged synovial inflammation that
can lead to the destruction of joints, pain and loss of function. The
prevalence in developed countries varies between 16 and 150 per 100.000, making
JIA one of the leading causes of pediatric acquired disability4. The evidence
that early therapeutic intervention improves long-term outcome increases. If
patients need to be treated in an earlier stage, complete comprehension of
disease status by means of objective disease activity parameters is necessary.
Besides a complete work-up of clinical history, physical examination and
laboratory tests, imaging studies are very important in the assessment of
disease status. Synovial hypertrophy, a critical hallmark of disease activity
and present in early stages of JIA, is most accurately depicted by MRI after IV
Gd contrast injection, because the enhancement after Gd differentiates between
joint effusion, fibrous tissue and inflamed synovium. To optimize the objective
assessment of disease activity and increase utility of MRI as the superior
imaging technique in JIA, a standardized protocol like a MRI scoring system is
expedient. As JIA concerns children and their growing skeleton, some MRI
findings are part of maturation process in children and should not be mistaken
for joint pathologies. Therefore a complete comprehension of the normal anatomy
of the growing skeleton is required for the development of a MRI scoring system.
Müller et al. (2011) reports about the pediatric wrist of healthy subjects and
MRI features like joint fluid, bony depressions and medullary signal changes.
Yet on the synovium, as primary target of disease, no cut-off values to
differentiate between low-grade arthritis and normal have been determined.
Semi-quantitative terms describing the extend of synovial hypertrophy do not
suffice as objective disease activity parameters. A proper and objective
distinction between pathologic and normal synovium can only be made with the
measurement of synovial thickness after enhancement. Therefore it is necessary
to gain knowledge on the normal values for synovial thickness on MRI in healthy
children. There exist several studies reporting about mild enhancement of
synovial tissue in the wrists of healthy adults. To the best of our knowledge,
no reports on synovial enhancement or thickness on MRI after IV Gd contrast in
children have been published.
As MRI with IV Gd contrast is considered as an invasive imaging technique in
children, we chose to conduct this study with a negligible additional burden in
patients who are already scheduled for MRI with IV Gd contrast and had an
acceptable disease load.

Primary Objective
To define normal values for synovial thickness in the healthy pediatric knee
and wrist on MRI after intravenous gadolinium contrast administration.

Secondary Objective
To evaluate possible age-dependent variations in normal values for synovial
thickness on MRI after intravenous gadolinium contrast administration in
children.

Prospective observational

Patients who are already scheduled for an MR Enterography with IV Gd contrast
are asked to participate in this study.
1. Patient will be physically examined for any signs of inflammation of the
joints before MR Enterography (additional examination time: 10 minutes)
2. Patient has to change position in the MRI scanner to get the knee or wrist
positioned in a dedicated knee or wrist coil (additional time to change
position: 3 minutes).
3. One additional MRI sequence will be added at the end of the regular MRI scan
(additional scan time: 5 minutes).