Unilateral Rectus Capitis Posterior Major Muscle Duplication: Clinical Implications

Abstract

Here, we present an anomaly of the rectus capitis posterior major (RCPM) muscle, found during routine cadaver dissection in a gross anatomy course. The RCPM is one of four muscles in the suboccipital region, the superior portion of the posterior neck, inferior to the occipital region of the head. The suboccipital muscles, including the RCPM, maintains posture of the neck to support the head and facilitate flexion, extension and lateral bending of the neck and rotation of the head at the atlanto‐occipital joint. We observed a unilateral, right‐sided duplication of the RCPM. This anomaly has several clinical implications: (1) Contraction of this duplicate muscle may cause postural instability or shift toward the right side, leading to improper weight bearing of the head. This may also cause loss of range of motion in the head of neck. This may lead to chronic neck pain and cervicogenic headache. (2) The greater occipital nerve passes through the suboccipital triangle, as it relays cutaneous innervation from the occipital scalp. We observed the greater occipital nerve passing between the two RCPM muscles, suggesting a potential for compression and sensory deficits. (3) The vertebral artery also passes inferior to the suboccipital muscles on its course to the brain stem, and compression of the vertebral artery by the RCPM may reduce blood supply to the brain stem, leading to dizziness or other neurovascular symptoms. Overall, this anomalous muscle, though likely rare, may be identified as a potential cause of the aforementioned symptoms, and surgical intervention may be warranted in severe cases.Support or Funding InformationN/AThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.