Synovium

For Medical Students

What It Shows

The synovium lines the joint and produces its fluid, and when normal it is too thin to see. 5.5.12 covers the bursa.

It becomes visible when it thickens, which is what synovitis is. 5.14.1 covers synovitis.

It matters because it is the one knee tissue whose assessment regularly needs intravenous contrast, and the routine protocol does not include it. 5.2.21 covers advanced magnetic resonance techniques.

How It Is Acquired

Assess for synovial thickening on the fluid sensitive sequences, where thickened synovium is distinguishable from fluid with difficulty. 5.2.16 covers fat suppression.

Give intravenous contrast where the distinction matters, because synovium enhances and fluid does not. 5.2.21 covers advanced magnetic resonance techniques.

Assess the recesses, since synovial proliferation collects in them. 5.5.12 covers the bursa.

Look for a mass like synovial process, which is a different diagnosis from diffuse thickening. 5.14.5 covers PVNS and TGCT.

Assess for loose bodies, which synovial processes generate. 5.14.6 covers synovial chondromatosis.

What Normal Looks Like

No visible synovium, because a normal lining is too thin to resolve.

A small amount of physiological joint fluid without surrounding thickening. 5.5.12 covers the bursa.

Clean recesses without proliferative tissue. 5.5.12 covers the bursa.

No enhancement where contrast was given. 5.2.21 covers advanced magnetic resonance techniques.

MRCS Level

How It Is Acquired

In a viva this is the tissue to name when asked when a knee study needs contrast.

The expected points are the fluid sensitive sequences, the contrast, the recesses, the mass like process, and the loose bodies.

Say that contrast separates synovium from fluid. 5.2.21 covers advanced magnetic resonance techniques.

Say that diffuse thickening and a mass like process are different diagnoses. 5.14.5 covers PVNS and TGCT.

Say that the routine protocol does not include contrast. 5.5.1 covers the standard protocol.

What Normal Looks Like

The reasoning expected is that synovium is a thin vascular membrane, so it is below the resolution of a routine study when normal and becomes resolvable only when it proliferates. 5.14.1 covers synovitis.

Being vascular is what makes it enhance, and fluid being avascular is what makes contrast the discriminator. 5.2.21 covers advanced magnetic resonance techniques.

Proliferative synovium collects where the capsule is redundant, which is why the recesses are where it is found. 5.5.12 covers the bursa.

A haemosiderin containing synovial process has its own signal characteristics, which is why a mass like lesion is approached differently from diffuse thickening. 5.14.5 covers PVNS and TGCT.

How Good It Is

Magnetic resonance imaging detects synovial thickening and characterises it only with contrast.

Its best contribution is detecting proliferative synovium and loose bodies, which changes the diagnostic direction. 5.14.6 covers synovial chondromatosis.

It is limited without contrast, because thickened synovium and joint fluid have similar signal on the routine sequences. 5.2.16 covers fat suppression.

No figures appear for accuracy on this page, under decision 028, and no synovial thickness or enhancement values appear either: those are published quantities and this environment cannot check them.

FRCS Level

How Good It Is

At decision level synovial assessment redirects a knee from a mechanical pathway to an inflammatory or neoplastic one.

Diffuse synovial thickening with an effusion suggests an inflammatory process rather than a mechanical one, which is a referral. 5.14.2 covers rheumatoid arthritis.

A mass like synovial process is a surgical diagnosis with its own operation. 5.14.5 covers PVNS and TGCT.

Loose bodies from a synovial process are a mechanical finding within a synovial diagnosis. 5.14.6 covers synovial chondromatosis.

A contrast study is the one to request when the distinction matters, and it has to be requested. 5.2.21 covers advanced magnetic resonance techniques.

Where It Misleads

The commonest error is reading an effusion as synovial thickening without contrast. 5.2.21 covers advanced magnetic resonance techniques.

Normal recess fluid is reported as synovitis. 5.5.12 covers the bursa.

A mass like process is reported as diffuse thickening. 5.14.5 covers PVNS and TGCT.

A synovial process is found and the loose bodies are not sought. 5.14.6 covers synovial chondromatosis.

Contrast is not requested where the question needed it. 5.5.1 covers the standard protocol.

Fellowship Level

Where It Misleads

At fellowship level the synovium is the knee tissue whose assessment most often fails for a reason outside the imaging.

The study that would answer the question needs contrast, the routine protocol does not include it, and the request rarely says that a synovial question is being asked, so the wrong study is performed. 5.20.1 covers structured reporting.

Synovitis is also found in mechanically driven arthritis, so its presence does not by itself indicate an inflammatory arthropathy, and the report often implies that it does. 5.14.1 covers synovitis.

Quantitative synovial volume measurement exists in research and is not routine, so a diffuse process is graded by impression. 5.18.1 covers quantitative magnetic resonance imaging.

Ultrasound with Doppler assesses synovial activity directly and is rarely used alongside, which leaves two partial answers rather than one complete one. 5.2.11 covers Doppler imaging.

The useful practice is to name the synovial question on the request so that contrast is given, and to report thickening without implying its cause. 5.1.3 covers choosing the correct investigation.