The absent bow tie sign represents the loss of the normal appearance of the menisci on parasagittal MRI images and is suggestive of meniscal injury.

Normally the medial and lateral menisci appear as low signal triangular structures linked by a thin body located between the femoral condyles and tibial plateau. The appearance of the menisci has been likened to a bow tie.

As the normal meniscus laterally measures 9-12 mm in width, it should be seen on a number of adjacent images (2-3 images if imaged with 3 mm thick slices with a 1 mm skip).

An absent bow tie sign is therefore when less than two sagittal slices demonstrate a normal body of the meniscus and is suggestive of meniscal pathology, including:

bucket handle tear with displacement (often with a double PCL sign)
flap tear with displacement (i.e. bucket handle, but the handle at one end has come loose)
free fragment with displacement (i.e. bucket handle, but the handle at both ends has come loose)

Other meniscal changes can, however, appear similar, including:

prior resection of a meniscal tear
degenerative maceration of the inner edge of the meniscus
small patients (children / small adults)

Related pathology

In contrast, if there are more 2 or 3 sagittal images with a visible bow-tie this implies a discoid meniscus; obviously, this depends on the slice thickness and skip width.