In case of a cyst, ultrasound in many cases can show a relation between the lesion and the different anatomical structures, as in this case the medial meniscus.
A meniscal cyst is usually associated with a miscal tear. Articular fluid is dispersed through the meniscal tear.
It is possible to do an ultrasound guided puncture of a meniscal cyst. Injection of corticosteroids can sometimes be helpful. Since the underlying cause is usually a pathological meniscus, it is better to treat the cause especially in younger patients
Another common fluid filled structure on the medial aspect of the knee is the pes anserinus bursa. In this case the typical location underneath the pes anserinus tendons makes it possible to differentiate it from a medial meniscal cyst.
In a case of a liquefied hematoma the patient history should be helpful
In case of a solid lesion, ultrasound is less reliable in determining the nature of the mass. Ultrasound however is helpful in performing guided punctures or biopsies
Although it is possible to detect meniscal tears with ultrasound, MRI is the modality of choice for examining the menisci and other intra-articular structures.
For more examples of meniscal cysts visit http://www.ultrasoundcases.info