Delineation of the levator palpebrae superioris muscle: a magnetic resonance imaging study

To the best of our knowledge, the levator palpebrae superioris muscle (LM) has not been previously evaluated radiologically. This study aimed to explore the LM using magnetic resonance imaging (MRI).

A total of 109 patients underwent thin-section coronal T2-weighted MRI. For comparison, the orbits were dissected on four sides of two cadaver heads.

On cadaveric specimens, the LMs partially overlapped the superior rectus muscles (SRMs) at the orbital apex. Additionally, an oculomotor branch was observed to initially course along the inferior aspect of the SRM, then bridge the medial margin of the muscle and finally distribute over the LM. On MRI, intermuscular separations were identified in 79% between the LM and SRM. They were open at the medial edges and closed at the lateral edges and demonstrated signal intensity similar to that of the orbital fat. The widths and heights of the separations were highly variable but more distinct towards anteriorly. In 20%, the separations were symmetrical, while they were right-side-predominant in 28% and left-side-predominant in 31%. Similarly, the widths of both LMs were considerably variable. In 33%, they were symmetrical, while right-side-predominant in 23% and left-side-predominant in 25%.

The LM and SRM are separated by intervening fat tissue with open medial and closed lateral edges, not uniformly attached with each other. The LM may be more easily separated from the SRM when approached from the medial side.