Sonography of intramuscular myxomas: the bright rim and bright cap signs

The objective of this study was to retrospectively review sonographic images of pathologically proven soft tissue myxomas to determine whether a sonographic correlate to the bright rim and bright cap signs described in the magnetic resonance imaging literature is present.

The study group consisted of 6 patients with pathologically proven soft tissue myxomas (1 man and 5 women; age range, 41-72 years; mean, 56.5 years). The available sonographic images for each subject were retrospectively reviewed by 2 authors (L.F. and K.F.), with agreement reached by consensus. Among other findings, images were also reviewed for a peripheral rim of increased echogenicity (termed the "bright rim sign") and for the presence of a triangular hyperechoic area adjacent to at least one of the poles of the mass (termed the "bright cap sign").

The bright rim and bright cap signs were seen in 5 (83%) of the 6 myxomas. The single case without the bright cap sign was not the same case as the one lacking the bright rim sign.

The sonographic bright rim and bright cap signs were associated with 5 (83%) of the 6 intramuscular myxomas. These findings correlate with their magnetic resonance imaging equivalents, which are well documented in the literature, due to muscle atrophy and adjacent fatty infiltration. Recognition of these features may assist in a more accurate sonographic diagnosis before biopsy.