Ganglion Cysts

For Medical Students

What It Shows

A cruciate ganglion cyst is a fluid filled collection arising within or adjacent to the ligament, with a thin wall and no solid component. 5.7.1 covers the normal cruciate.

They are described as fusiform when they run along the ligament's fibres and lobulated when they sit beside it. 2.7.1 covers the gross anatomy.

It matters because most are incidental and a minority cause mechanical symptoms, so the decision rests on the pattern of symptoms rather than on the finding. 5.1.6 covers imaging pitfalls.

How It Is Acquired

Confirm the lesion follows fluid signal on every sequence, which is what makes it a cyst. 5.2.14 covers T2 imaging.

Establish its relationship to the ligament, since a cyst within the fibres differs from one displacing them. 5.5.9 covers the ligaments.

Look for an intraosseous component at the attachments, which accompanies these and is a separate observation. 5.7.6 covers mucoid degeneration.

Look for a neck connecting it to the joint, which indicates where it arose. 5.14.1 covers synovitis.

Assess the ligament itself, because mucoid change and a cyst frequently coexist. 5.7.6 covers mucoid degeneration.

What Abnormal Looks Like

A well defined collection following fluid signal on all sequences, thin walled and without solid tissue.

A fusiform shape running along the ligament's fibres, or a lobulated collection beside it.

An intraosseous cystic focus at the femoral or tibial attachment. 5.7.6 covers mucoid degeneration.

A ligament that is otherwise continuous, with no secondary signs of injury. 5.11.7 covers bone marrow lesions.

MRCS Level

How It Is Acquired

In a viva the expected answer confirms the lesion is a cyst before discussing what to do about it.

The expected points are the fluid signal on all sequences, the relationship to the ligament, the intraosseous component, the neck, and the state of the ligament.

Say that most of these are incidental findings. 5.1.6 covers imaging pitfalls.

Say that the symptomatic ones cause mechanical symptoms rather than instability. 3.7.8 covers anterior stability.

Say that a solid component takes the lesion out of this category entirely. 5.14.6 covers synovial chondromatosis.

What Abnormal Looks Like

The reasoning expected is that a lesion following fluid signal on every sequence has no cellular content, which is what separates a cyst from a tumour and makes the diagnosis an imaging one. 5.2.13 covers T1 imaging.

A cyst within the ligament's fibres separates them without tearing them, which is why the ligament's function is preserved. 2.7.3 covers the histology.

A cyst large enough to occupy the notch can limit extension mechanically, which is the presentation that makes it symptomatic. 2.7.12 covers the surgical anatomy.

The intraosseous component shares the process with mucoid degeneration, which is why the two are found together and are probably one entity. 5.7.6 covers mucoid degeneration.

How Good It Is

Magnetic resonance imaging characterises these lesions well and says nothing about whether they are causing symptoms.

Its best contribution is the confident exclusion of a solid lesion, which is the question that matters when the appearance is unfamiliar. 5.14.6 covers synovial chondromatosis.

It is limited by being unable to connect the finding to the complaint, which is the only clinically useful question here. 5.1.6 covers imaging pitfalls.

No figures appear for accuracy on this page, under decision 028, and the comparison is the claim: characterisation is reliable and attribution of symptoms is not, which is a comparison rather than a number.

FRCS Level

How Good It Is

At decision level the finding is almost always a reason to do nothing, and the exceptions are defined clinically.

An incidental cyst in a knee with unrelated symptoms is reported and left, because intervention offers nothing. 5.1.6 covers imaging pitfalls.

A large notch cyst with mechanical loss of terminal extension is the case in which aspiration or excision is discussed. 2.7.12 covers the surgical anatomy.

A cyst with coexisting mucoid change is the same process, and treating it means treating a ligament that is still working. 5.7.6 covers mucoid degeneration.

A lesion that does not follow fluid signal on every sequence is a different problem and needs characterising rather than treating. 5.13.7 covers bone tumours.

Where It Misleads

The commonest error is attributing a patient's knee pain to an incidental cyst. 5.1.6 covers imaging pitfalls.

A cyst between the fibres is reported as a partial tear. 5.7.2 covers the partial tears.

An intraosseous component is reported as a separate bone lesion. 5.13.7 covers bone tumours.

The lesion is called a cyst without checking every sequence, so a solid lesion is dismissed. 5.2.13 covers T1 imaging.

The coexisting mucoid change is not mentioned, so two reports describe one process. 5.7.6 covers mucoid degeneration.

Fellowship Level

Where It Misleads

At fellowship level the cruciate ganglion is a small problem that illustrates a large one: imaging finds things whose relationship to symptoms it cannot test.

The prevalence in asymptomatic knees means the pre-test probability that any given cyst explains a complaint is low, and the report rarely says so. 5.1.6 covers imaging pitfalls.

Whether these and mucoid degeneration are one entity is unsettled, and the literature reports them separately while describing overlapping findings. 5.21.2 covers the cruciate imaging literature.

The published series on treatment are small, uncontrolled and selected on imaging, which is the weakest basis for an intervention on an intact ligament. 3.7.8 covers anterior stability.

Size thresholds for significance are quoted and none is established, which is why no measurement appears on this page. 5.21.2 covers the cruciate imaging literature.

A report that states the finding is probably incidental does more for the patient than one that describes it precisely, and the convention does not ask for that sentence. 5.20.1 covers structured reporting.