Pathognomic Discoid Medial Meniscus with a Parameniscal Cyst: A Case Report and Literature Review of Anomalous Medial Meniscus Variants

Abstract

Discoid medial meniscus is an extremely rare anomaly with an incidence of 0.1-0.3%. Only 35 cases have been reported in literature so far. The association of a Parameniscal cyst with a discoid medial meniscus has been not described in literature to our knowledge. The cyst related to the discoid medial meniscus was anteromedial in location as compared to the lateral discoid meniscus cyst which usually is in lateral or postero-lateral in position. We present a case report of a complete discoid medial meniscus with a parameniscal cyst which was treated successfully by excision of the central anomalous part of the meniscus and cyst decompression. The presentation differs drastically as compared to a discoid lateral meniscus and the age of presentation is also not defined due to rarity of such cases. The discoid medial meniscus developed a horizontal cleavage tear and consequently a parameniscal cyst which became symptomatic insidiously. Physical examination revealed medial joint line tenderness with Thessaly test and Steinman II tests positive (Figure 1). Controversy exists with regards to the etiology of discoid medial meniscus wherein Kaplan in 1974 stated that congenital alteration in the attachment of posterior horn of the meniscus by the meniscofemoral ligament which becomes hypermobile and Smillie postulated that menisci exist as cartilaginous disc at an early stage in development and congenital discoid meniscus is attributable to persistence of the disc shape at varying stages of embryonic development. Various anomalies reported include anterior horn hypoplasia, anomalous posterior horn attachment to lateral femoral condyle, anomalous insertion of anterior horn to ACL, anterior transportation of the anterior medial meniscus below the anterior edge of the tibial plateau and the anterior horn contiguous with the ACL, increased tibial plateau concavity with elongated medial tibial spine and lastly bilateral occurance.