The neck is made up of many different muscles and ligaments which support the weight of the head and allow for its wide range of movement. These muscles also form a layer of protection for neurovascular structures that exit and enter the skull.
The deepest region of the back of the neck is the suboccipital region lying underneath the trapezius, splenius capitis, and semispinalis capitis muscles. It is a pyramidal-shaped muscle compartment inferior to the external occipital protuberance of the occipital bone to the posterior aspect of the atlas (C1) and axis (C2) cervical vertebrae. Inside the suboccipital region is the suboccipital triangle and its neurovascular contents: the vertebral artery, suboccipital nerve (C1), and suboccipital venous plexus.
Floor - posterior atlanto-occipital membrane and posterior arch of C1 vertebra
Roof - semispinalis capitis muscle
Superomedial border - rectus capitis posterior major muscle
Superolateral border - obliquus capitis superior muscle
Inferolateral border - obliquus capitis inferior muscle
|Contents||Vertebral artery (third part), suboccipital nerve (C1), and suboccipital venous plexus|
|Clinical relations||Occipital neuralgia|
This article will discuss the borders and contents of the suboccipital triangle and the condition occipital neuralgia.
The suboccipital triangle is contained within a space bordered by muscles and ligaments deep to the nuchal region (posterior neck).
The suboccipital triangle has three boundaries contained between a floor and roof.
- Floor - posterior arch of atlas and posterior atlantooccipital membrane (ligament). This ligament is broad and extends from the posterior margin of the foramen magnum to the posterior arch of atlas. It aids in preventing excessive movement of the atlantooccipital joints (two lateral, one median).
- Roof - semispinalis capitis muscle. This flat muscle forms a sheet over the back of the neck covering all suboccipital muscles
The four suboccipital muscles lie deep to semispinalis capitis muscle: Two rectus capitis posterior muscles (major and minor) and two obliquus capitis muscles (superior and inferior). Three of these make up the boundaries of the suboccipital triangle. They originate from processes of atlas or axis. Most insert near the inferior nuchal line of the occipital bone except obliquus capitis inferior which inserts onto C1. Contraction of these muscles extend the head at the atlantooccipital joint and rotate the face to the same side.
The suboccipital triangle contains the vertebral artery, suboccipital nerve (C1), and suboccipital venous plexus.
The atlantic part of the vertebral artery (V3 segment) leaves the transverse foramen of the atlas C1 vertebra, courses through the suboccipital triangle, pierces through the posterior atlantooccipital membrane, and then enters the skull through the foramen magnum. The left and right vertebral arteries then merge at the brainstem to form the basilar artery.
The suboccipital nerve is the posterior ramus of C1 spinal nerve. It courses between the posterior arch of atlas and the vertebral artery to innervate the four suboccipital muscles.
Deoxygenated blood from the back of the scalp drains into the occipital vein. It pierces through trapezius muscle to drain into the suboccipital venous plexus. Blood then drains into the deep cervical vein, vertebral vein, and brachiocephalic vein.
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Occipital neuralgia is intermittent stabbing or throbbing pain in the occipital region because of compression, demyelination, or damage of an occipital nerve (greater (C2), lesser (C2-C3), or third (C3)). This could be from tight muscles, impinging arteries, posterior head trauma, whiplash, or other head and neck injuries. The occipital nerves course near the suboccipital triangle and hence can cause pain in that area. Patients typically present with severe pain in the occipital region radiating towards the top of the skull and tenderness along the course of the affected nerve.
Treatment for occipital neuralgia initially includes rest, warm or cold compress, physical therapy, and anti-inflammatory medications. An occipital nerve block can be performed as a direct intervention and to confirm the diagnosis. In this procedure, anesthetic is injected into the occipital region to temporarily alleviate pain in the area.