Characterization of the "red zone" of knee meniscus: MR imaging and histologic correlation

PURPOSE: To determine the extent and vascularity of knee menisci with conve ntional and gadolinium-enhanced magnetic resonance (MR) imaging in cadaveri c specimens, with histologic findings as the reference standard, and to inv estigate signal intensity changes in menisci and perimeniscal soft tissues in symptomatic patients. MATERIALS AND METHODS: Radial dimensions and enhancement patterns of menisc i were recorded and compared in (a) 12 cadaveric menisci examined with conv entional and gadolinium-enhanced intermediate-weighted and fat-suppressed T 1-weighted spin-echo MR imaging, high-spatial-resolution T1-weighted and fa st low-angle shot MR imaging, and gross anatomic and histologic specimens a nd (b) 18 patients examined with conventional and gadolinium-enhanced fat-s uppressed T1-weighted spin-echo MR imaging. RESULTS: No differences in radial measurements of the meniscus were found f or different MR techniques (P = .551). Despite the presence of vessels in t he peripheral 10%-15% of the menisci, no enhancement of menisci was detecte d in specimens or patients. Perimeniscal soft-tissue enhancement adjacent t o the posterior horn was greater than that adjacent to the anterior horn (P < .05), and enhancement of the lateral meniscal body was greater than that of the medial meniscal body (P < .05). CONCLUSION: The wedge-shaped low-signal-intensity structure seen on MR imag es represents the entire meniscus. Intravenous injection of contrast materi al does not appear to be useful for differentiation of the vascularized fro m the nonvascularized zone of the meniscus.