Anat Cell Biol.  2023 Mar;56(1):145-149. 10.5115/acb.22.139.

Untrapped: bilateral hypoplasia of the trapezius muscle

• Rounds BR
• Rasey MF
• Kulesza R

• KMID: 2540994
• DOI: http://doi.org/10.5115/acb.22.139

Abstract

Agenesis or congenital hypoplasia of skeletal muscles occurs infrequently but may occur with specific conditions such as Poland syndrome. The trapezius muscle can vary in the extent of its bony attachments or may have additional slips, however congenital absence or hypoplasia is extremely rare. There are only a few reports of partial or complete absence of the trapezius muscle. Two cases of bilateral absence of the trapezius were both in males and were accompanied by the absence of additional muscle in the pectoral girdle. Herein, we describe a case of a 56-year-old male cadaver with bilateral hypoplasia of the trapezius. The muscle was largely represented by atrophied muscle fibers with an abundance of fibrotic or fatty connective tissue. This subject had very minor hypoplasia of the left pectoralis major muscle, but the remaining muscles of the pectoral girdle were normal. The spinal accessory nerve terminated in the sternocleidomastoid muscle on both sides, failing to reach the trapezius. We interpret these findings to be consistent with a minor variant of Poland syndrome.

Keyword

Anatomy; Poland syndrome; Cranial nerve

Figure

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  Fig. 1 Dissection of T muscles. Shown in (A) is a superficial dissection of the hypoplastic T (outlined with black dashed line). The only muscle fibers present are indicated by black arrows. The regions indicated by the red boxes were removed for histological study (Fig. 2). The region indicated by the green box was a defect revealing the underlying rhomboid muscle. The blue box indicates the region of a deeper dissection shown in B. (B) shows the underside of the S and T. The spinal accessory nerve (black wire/arrowhead) terminates within the S. The greater occipital nerve is indicated by the red wire and red arrowhead. Branches from the cervical plexus (yellow wire/yellow arrowheads) were found along the deep surface of the hypoplastic T. (C) shows the anterior neck and shoulder region from the subject. The S muscles were symmetric and appeared of normal bulk. The right PM muscle appeared normal, the left PM appeared to be missing the inferiormost fibers (arrowheads). D: deltoid, ES: erector spinae, L: latissimus dorsi, LS: levator scapulae, PM: pectoralis major, R: rhomboid major, S: sternocleidomastoid, SH: sternohyoid, Sp: splenius, SS: semispinalis, T: trapezius.

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  Fig. 2 Histological examination. Shown in (A, B) are H&E-stained sections from the left trapezius. There were few characteristic skeletal muscle fascicles present (black arrows), but there was an abundance of collagen fibers (asterisk). The region indicated by the box is shown at higher magnification in B. The muscles fibers were pale, irregular and indistinct (black arrow), There was infiltration with adipose (white arrow). Shown in (C, D) are H&E-stained sections from the right trapezius. There were very few muscle fibers, although when present there had characteristic morphology. There was an abundance of connective tissue fibers (asterisks). The region in the box is shown at higher magnification in (D). Muscle fibers (black arrow) were surrounded by adipose (white arrowheads) and collagen. The scale bar in A is 400 microns and corresponds to C also. The scale bar in B is equal to 100 microns and corresponds to D also.

Reference

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