Lateral discoid flounce meniscus

Clinical History

A 14-year-old male patient was referred to our hospital because of trauma during football. He claimed medial knee pain following a moderate valgus injury 1 week before imaging. The physical examination showed tenderness in keeping with medial collateral ligament strain. The lateral compartment was asymptomatic. MRI examination was suggested.

Imaging Findings

MRI examination was performed with a 1.5 Tesla scanner (Vision Hybrid, Siemens Erlagen, Germany) using a phased-array knee coil. The examination protocol included axial and sagittal fat-saturated turbo spin echo PD-w (TR/TE, 3500/14 ms), sagittal T2*-w MEDIC (TR/TE 520/26) and coronal T1-w spin echo (TR/TE, 500/14 ms) MR sequences. Mild bone bruise was demonstrated in the medial tibial condyle (Fig. 1). In addition, a discoid-like lateral meniscus with flounce appearance and an elongated lower pole of the patella were found (Fig. 1-4).

Discussion

A. The discoid meniscus is a thickened, disc-like meniscus and is referred as a normal anatomical variant in 3% of general population mostly seen on the lateral side [1]. Pathogenetically, the discoid meniscus may result from failure of the central resorption during the embryologic development [2]. Others believe that discoid appearance of the meniscus may result from failure of the meniscotibial ligamentous attachment of the posterior horn [3]. A flounce appearance on the other hand is a normal variant characterised by a single symmetric fold at the free edge of the meniscus. It is being seen most commonly at the medial side in 0.2-6% of patients [4, 5]. The meniscal flounce seen in a lateral discoid meniscus has not been previously reported to the best of our knowledge.

B. The discoid meniscus is either asymptomatic or presents with non-specific pain and functional limitation. It is also reported that discoid meniscus is a predisposing factor for meniscal tear and it might be associated with various musculoskeletal abnormalities [1]. In the case presented, an elongated lower pole of the patella was found. In contrast, meniscal flounce is considered to be of no clinical significance and indeed it may represent a positional-related finding. Meniscal flounce should not be misdiagnosed as a meniscal tear and thus arthroscopy of the knee is unnecessary.

C. Discoid meniscus is characterised by width of more than 15 mm in coronal slices or when the meniscal bow-tie is present in at least 3 consecutive 4 mm thick slices in the sagittal plane. Meniscal flounce is a wave or S-shaped deformity along the free edge of meniscal body on sagittal images without any high MR signal, to suggest a tear.
D. Our patient was treated conservatively regarding the bone bruise by ceasing the sports activities for 1 month and in the clinical follow-up there were no complaints.
E. Treatment is not required because both the discoid and flounce meniscus are normal variants.

Differential Diagnosis List

Final Diagnosis

Meniscal flounce seen in a discoid lateral meniscus

URL:	https://eurorad.org/case/10033
DOI:	10.1594/EURORAD/CASE.10033
ISSN:	1563-4086