(Baker's cyst)

Very rare in children. Expansion of the bursa located between the tendons of the medial head of the gastrocnemius and the semimembranosus muscle. Synovial cyst communicates generally with the articular cavity of the knee and its content is thick.

Different types:

-        idiopathic (95%): between 2 and 14 years old, most common in boys, usually asymptomatic but can cause discomfort during movement or local discomfort

-        secondary to an intra-articular (meniscal lesion or a ligament) injury, inflammatory origin (juvenile arthritis: synovial proliferation, thick membrane) or systemic origin (hemophilia: appearance in two layers, disseminated lupus erythematosus).

It seems that the origin of the cyst is the presence of a joint effusion that is "pumped" into the bursa via a small orifice during movement and that a mechanism of poppet valve prevents the fluid to flew back into the joint cavity. Part of the fluid is absorbed, but the fibrin remains trapped in the cavity, which explains the sticky consistency of the cystic fluid.

The cyst disappears spontaneously in a few weeks or months in the majority of cases. Otherwise, it must be surgically resected. Risk of rupture in the popliteal fossa.

Differential diagnosis: arterial aneurysm, venous thrombosis, ganglion

Anesthetic implications :

contraindication to the realization of a nerve block around the popliteal fossa.

References:

-        Alessi S, Depaoli R, Canepari M, Bartolucci F, Zacchino M, Draghu F.
Baker’s cyst in pediatric patients: ultrasonographic characteristics.
J Ultrasound 2012; 15: 76-81

Updated: August 2016