Bilateral supernumerary rectus muscles of the orbit

Abstract

A bilateral anomaly of the rectus muscles and a unilateral variation of the levator palpebrae muscle were found in the right and left orbits of an 84‐year‐old man. The anomaly was in the form of a supernumerary rectus muscle lying on a sagittal orientation between the optic nerve and lateral rectus muscle (in the right orbit) and adjacent to the inferior rectus muscle (in the left orbit). In each orbit the anomalous muscle originated occipitally from the common tendinous ring and frontally—near the eyeball—joined the terminal part of the inferior rectus. On its superior margin the anomalous muscle had, in the right orbit, a broad (4 mm), and in the left orbit a slender (2 mm) muscular bridge to the superior rectus muscle. Because of their connection to the superior rectus and their innervation by N.III the accessory orbital muscles are not deemed to be vestiges of the retractor bulbi muscle which, with the exception of the primates, is a typical occurrence in vertebrates and is always innervated by N.VI. Our anomalous orbital muscle must be explained as a supernumerary rectus muscle. A further variation occurred in the right orbit: an isolated medial part or belly of the levator palpebrae muscle (the so‐called M. gracillimus). In primates this variation is known as a remnant of the membrana nictitans (third eyelid of the amniotes). Ignorance of anomalies in the orbital muscles may lead to confusion and error in diagnostic identification and surgical exposure. Clin. Anat. 11:271–277, 1998. © 1998 Wiley‐Liss, Inc.

An anomalous muscle linking superior and inferior rectus muscles in the orbit

“…Such muscles have been divided into two groups (Whitnall, 1921;Von Lüdinghausen, 1998;Lueder, 2002): (i) accessory or supernumerary rectus muscles (Aubaret, 1909(cited in Whitnall, 1921; Von Lüdinghausen, 1998;Lueder, 2002); and (ii) retractor bulbi muscles (Whitnall, 1911(Whitnall, , 1921Von Lüdinghausen, 1998;Lueder, 2002). The accessory or supernumerary rectus muscles are rarely described in the literature (Aubaret, 1909;Whitnall, 1921;Von Lüdinghausen, 1998).…”

“…Accessory or supernumerary rectus muscles are rarely described (Aubaret, 1909;Whitnall, 1921;Von Lüdinghausen, 1998) and, to our knowledge, there have only been three cases in reported Caucasians. Because the two orbital structures that Whitnall pointed out as vestiges of the retractor bulbi muscles (Whitnall, 1911) seem to be accessory or supernumerary rectus muscles, there could, indeed, be a total of five cases reported in Caucasians including these two, although this cannot be determined correctly from the type of innervation because these muscles are innervated by either the oculomotor nerve or the abducent nerve.…”

Fibrotic superior oblique and superior rectus muscles with an accessory tissue band

“…The supernumerary rectus muscles as well as the levator palpebrae superioris muscle have been reported previously in humans. 4 The fibrous band may be a misdirected accessory part of the levator palpebrae superioris muscle.…”

Anomalous Extraocular Muscles with Strabismus

“…5 The described atavistic retractor bulbi muscles have either a cone shape or multiple tendon slips that surround the optic nerve region. 6 Our patient lacked these findings. We believe that this accessory muscle resulted from a disturbance of the mesodermal development of the extraocular muscles.…”