Complicated parameniscal giant cyst with distal dissection and regional infection.

We present the case of an 80-year-old woman with obesity (BMI: 32.4), who had Kellgren–Lawrence stage IV osteoarthritis of the right knee. She had a history of an anterolateral mass on her right knee for the past 6 years which was round, fluctuating in consistency, non-painful and with no associated erythema, and did not impede movement (Fig. 1A). No prior trauma had been documented. She had recently undergone a Magnetic Resonance Imaging study (MRI) which described the presence of a cyst in the lateral region of the knee and which came into contact with the joint space at the meniscal space level (Fig. 1B–D). This parameniscal cyst had been drained on several occasions obtaining mucoid, aseptic material, with no complications. The most recent drainage had been performed 2 months prior to the hospitalization date. The patient came to the clinic due to enlargement of the parameniscal cyst and due to the appearance of a second mass on the same leg, distal and lateral to the original. This new mass had developed over the past 30 days, was accompanied by pain upon light touch and showed unequivocal local signs of inflammation. In the 2 days prior there had been spontaneous drainage of pus from the new mass which coincided with the appearance of fever. X-rays showed an ovoid, well limited structure with an air–liquid level 8 cm distal from the parameniscal cyst, on the upper, lateral third of the leg, as well as an increase in the opacity of soft tissue at that level (Fig. 2). The culture of the fluid obtained from this newer collection isolated methicillin-sensitive Staphylococcus aureus. Faced with the possibility of a macroscopic communication