# Ipsilateral Supernumerary Heads of the Sternocleidomastoid and Flat Fibers of the Omohyoid Muscle: A Cadaveric Case Report

## TL;DR

A rare anatomical variation in neck muscles is reported, highlighting potential surgical risks and the need for anatomical awareness.

## Contribution

This is the first report of a combined variation in the sternocleidomastoid and omohyoid muscles in a single cadaver.

## Key findings

- The sternocleidomastoid had four heads merging into a common belly.
- The omohyoid appeared as flat fibers with a fused superior belly and sternohyoid.
- These variations may increase surgical risks in the neck region.

## Abstract

This case report presents an ipsilateral anatomical variation in the right neck of an 80-year-old male cadaver. The Sternocleidomastoid muscle exhibited four heads, one sternal and three clavicular heads. All the heads are merging into a common belly and inserting normally into the mastoid process. The right omohyoid muscle appeared as flat fibers, lacking an intermediate tendon and having its superior belly fused with the sternohyoid muscle. Abnormal development of the embryonic branchial arch mesoderm and occipital myotome leads to these variations. The Sternocleidomastoid and omohyoid are critical surgical landmarks in the neck. Their aberrant morphology can distort normal anatomical planes, increasing risks of neurovascular injury during neck dissections, central venous catheterization, or reconstructive surgeries. These variations are distinct and previously unreported in this specific combination. Hence, this report underscores the critical need for comprehensive anatomical awareness among clinicians, particularly head and neck surgeons, to navigate these variations safely, improving patient outcomes.