A 39-year-old man underwent MR imaging of his left knee for evaluation of a painless mass arising just lateral to the patellar tendon.
A 39-year-old man presented with a slowly enlarging, painless mass in the anterior aspect of his left knee, which was situated just lateral to the patellar tendon. Examination revealed a firm, non-mobile, 2 centimetre mass. The overlying skin appeared normal. The lesion was non-tender. An MRI was performed. Sagittal imaging (fig 1) showed a horizontal tear of the anterior and posterior horns of the lateral meniscus. In addition, a large (5 centimetre), lobulated high-signal lesion was demonstrated anterior to the torn meniscus, occupying much of Hoffa’s fat pat, and consistent with a parameniscal cyst. Coronal FSE T2 fat-saturated imaging showed multiple thin septations within this high signal structure (fig 2). On transverse, proton density fat-saturated imagin (fig 3), the cyst was identified extending through the lateral patellar retinaculum, immediately adjacent to the patellar tendon, into the subcutaneous fat of the anterior knee.
Parameniscal cysts were first described in 1904 [1] and are considered to develop due to extrusion of synovial fluid through micro- and macroscopic meniscal tears, which are present in every case [2]. They are commonly identified, with a reported incidence of 4%, at MR investigation of the knee, and are not infrequently asympomatic [3]. The patient may present with a palpable mass rather than symptoms of internal derangement of the joint. Earlier literature suggested that the incidence of lateral parameniscal cysts was 3 to 7 times higher than that of medial cysts, however more recent studies indicate that medial meniscal cysts are more common [4]. One theory for the explanation of this contradictory data suggests that patients with lateral parameniscal cysts are more likely to undergo imaging, as the relative paucity of soft tissue along the lateral aspect of the knee means that the cysts are more easily palpated, both by the patient and the physician [3]. MRI delineates the size and origin of parameniscal cysts well [5]. It allows distinction of these lesions from other para-articular cystic lesions such as ganglions and bursae. On MRI, parameniscal cysts typically appear as well-defined collections of fluid, often with internal septations, adjacent to a horizontal cleavage tear of a meniscus. Occasionally, haemorrhage into a parameniscal cyst may alter the signal characteristics of the lesion.The cyst may dissect through tissue planes to distant locations, and in these cases a connecting stalk needs to be identified in order to differentiate the lesion from other cystic abnormalities [5]. Parameniscal cysts related to the lateral meniscus most commonly arise from its anterior aspect while medial cysts tend to arise from the body and posterior horn [5]. Surgical management of parameniscal cysts may be necessary when patients present with swelling or pain. The accepted standard intervention is arthroscopic partial meniscectomy with intra-articular cyst drainage [1].
Parameniscal cyst.
Based on the provided MRI images of the left knee joint, the following key features are observed:
Based on the above imaging findings and the patient's medical history, the possible diagnoses or differential diagnoses include:
Considering the patient's age (39 years old), clinical presentation (painless lateral knee swelling), imaging evidence of lateral meniscus tear, and a communicating cystic lesion, the most likely diagnosis is:
Lateral Meniscus Tear with Parameniscal Cyst
For further confirmation, arthroscopic evaluation can be considered to directly assess the meniscal damage and the cyst, and partial meniscectomy with cyst management could be performed during surgery to obtain a definitive pathological diagnosis.
Primary treatment strategies can be divided into conservative treatment and surgical treatment:
Note: Lateral meniscal cysts have a tendency to recur. If the underlying meniscal tear is not addressed during surgery, the recurrence rate is higher.
During postoperative or conservative treatment, exercise intensity should progress gradually and be individualized:
Example training plan:
This report is a reference-based analysis derived from the provided information and cannot replace in-person consultation or professional medical advice. If you have any concerns or your symptoms worsen, please consult an orthopedic or sports medicine specialist promptly.
Parameniscal cyst.
