Synovitis

For Medical Students

What It Shows

Synovitis is thickening and inflammation of the joint lining, usually with an effusion. 5.5.11 covers the synovium.

Magnetic resonance imaging shows the thickened lining and the fluid, and separates them reliably only with contrast. 5.2.13 covers the T1 imaging.

It matters because it is the common end appearance of every condition in this chapter and of mechanical irritation too, so the finding names nothing by itself. 5.20.8 covers common reporting errors.

How It Is Acquired

Use fluid sensitive sequences to show the effusion and its distribution. 5.2.17 covers the STIR imaging.

Add contrast when the question is how much of what you see is thickened lining. 5.2.13 covers the T1 imaging.

Use a gradient echo sequence where a blood product is suspected. 5.2.18 covers the gradient echo imaging.

Record the distribution, since uniform and nodular behave differently. 5.14.5 covers the PVNS and TGCT.

Record the bone and the cartilage, because erosion separates the inflammatory causes. 5.5.6 covers the bones.

What Normal Looks Like

A thin synovial lining not separately visible on most sequences. 5.5.11 covers the synovium.

A small physiological amount of joint fluid. 4.3.8 covers swelling.

No erosion at the bare areas of bone inside the capsule. 5.5.6 covers the bones.

No signal loss suggesting haemosiderin. 5.2.18 covers the gradient echo imaging.

What Abnormal Looks Like

Uniform thickening of the lining with an effusion. 5.14.2 covers rheumatoid arthritis.

Nodular thickening, which narrows the differential sharply. 5.14.5 covers the PVNS and TGCT.

Signal loss on gradient echo images, which points at blood products. 5.2.18 covers the gradient echo imaging.

Bodies within the fluid, which point at cartilage or at loose fragments. 5.14.6 covers synovial chondromatosis.

Erosion at a bare area, which marks an inflammatory arthropathy rather than irritation. 5.14.3 covers psoriatic arthritis.

MRCS Level

How It Is Acquired

In a viva the expected answer uses the distribution and the company the finding keeps.

The expected points are the fluid sensitive sequences, contrast where it helps, the gradient echo sequence, the distribution, and the bone.

Say that the finding is a sign rather than a diagnosis. 5.20.1 covers structured reporting.

Say that mechanical irritation produces the same appearance as early inflammatory disease. 5.1.2 covers clinical examination versus imaging.

Say that aspiration answers questions no sequence can. 5.4.17 covers the aspiration.

What Abnormal Looks Like

The reasoning expected is that the synovium has a limited repertoire, so a wide range of insults produce thickening, effusion and hyperaemia, and the discriminating features are what else is present. 5.5.11 covers the synovium.

Four substances carry their own signal and are therefore diagnostic when seen: haemosiderin, cartilage, crystal and gas. 5.14.4 covers crystal arthropathy.

Erosion and new bone separate the inflammatory arthropathies from each other on pattern. 5.14.3 covers psoriatic arthritis.

Infection shares the appearance with all of them and is excluded by aspiration rather than by imaging. 5.14.7 covers septic arthritis.

How Good It Is

Magnetic resonance imaging shows synovitis better than any other modality and identifies its cause only when a second feature is present.

Its best contribution is the extent and the distribution, with the state of bone and cartilage alongside. 5.5.6 covers the bones.

It is limited because thickening is non specific, because separating lining from fluid needs contrast, and because infection cannot be excluded. 5.14.7 covers septic arthritis.

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

FRCS Level

How Good It Is

At decision level the finding changes a plan once a cause is attached, and until then it generates investigations rather than decisions. 5.1.3 covers choosing the correct investigation.

A nodular pattern with signal loss is an operative diagnosis. 5.14.5 covers the PVNS and TGCT.

Uniform thickening with erosion belongs to rheumatology before surgery. 5.14.2 covers rheumatoid arthritis.

Synovitis with established joint space loss is part of the arthritis rather than a separate problem. 5.20.6 covers reporting osteoarthritis.

An acute hot knee is aspirated whatever the scan shows. 5.4.17 covers the aspiration.

Where It Misleads

The commonest error is reporting synovitis as a diagnosis. 5.20.8 covers common reporting errors.

A large effusion is read as severe disease, when volume and activity differ. 4.3.8 covers swelling.

Thickened lining is read as fluid on sequences without contrast. 5.2.13 covers the T1 imaging.

Post-operative synovial thickening is read as recurrent disease. 5.20.7 covers reporting the post-operative knee.

A popliteal cyst is reported as a separate finding rather than as a sign of the joint's pressure. 5.4.4 covers the posterior knee.

Fellowship Level

Where It Misleads

At fellowship level the scan usually arrives reported as synovitis and the referral asks for an arthroscopy. 5.1.2 covers clinical examination versus imaging.

A diagnostic arthroscopy for an undiagnosed synovitis is rarely the right next step, because the fluid and a biopsy can be obtained with less. 5.4.17 covers the aspiration.

Treated inflammatory disease looks unlike the textbook, so the appearance is partly a record of the treatment. 5.14.2 covers rheumatoid arthritis.

Quantifying synovial volume has been proposed as an outcome measure and carries the standardisation problem of every quantitative measure. 5.18.1 covers the quantitative MRI.

Automated detection reports thickening reliably and inherits the same differential. 5.18.8 covers artificial intelligence in imaging.

The useful report gives the distribution, the second feature if there is one, the bone and cartilage, and the statement that infection is not excluded. 5.20.1 covers structured reporting.