Discoid meniscus in children: magnetic resonance imaging characteristics.

OBJECTIVE: To describe the magnetic resonance imaging (MRI) appearance and associated abnormalities of discoid menisci in children. PATIENTS AND METHODS: The MRI findings for a total of 30 knees (in 20 children ranging in age from 4.5 to 16 [mean 9] years) in which discoid meniscus had been diagnosed were reviewed and correlated with clinical symptoms and arthroscopy findings. RESULTS: The symptoms, bilateral in 5 patients and unilateral in 15, included pain in 15 knees, snapping or clunking in 8, reduced mobility in 8, locking in 2 and "giving-way" in 2; there were flexion contractures in 2 patients. Five patients had unilateral symptoms but bilateral discoid menisci. The transverse diameter of the meniscus ranged from 18 to 37 mm and the depth from 14 to 36 mm. The lateral meniscal height was significantly greater than the medial meniscal height (p = 0.0001). On T1-weighted and T2-weighted images the meniscal signal was increased heterogeneously in 11 knees, in a central, horizontal, linear fashion in 9, diffusely in 6 and in a partly linear, partly diffuse fashion in 3. Thirteen joint effusions, 10 lateral meniscal tears and 4 meniscal cysts were identified. Eight arthroscopy procedures were performed in six of the children (for seven knees). Discoid meniscus was confirmed in six knees (with one initial false-negative result), tears were confirmed in four, and an additional tear was identified in one; in addition, one meniscus was characterized as Wrisberg type. CONCLUSIONS: Discoid meniscus commonly occurs bilaterally. High intrameniscal signal is found, especially in symptomatic patients. The size criteria for diagnosing this condition in children are similar to those for adults.