Scalenovertebral triangle
This important anatomical region of the deep neck has a geometric triangular shape and is known as the trigonum scalenovertebrale.
Topographic boundaries:
- The base of the triangle is formed directly by the cervical pleura (cupula of the pleura).
- The apex points upward, reaching the level of the transverse process of the sixth cervical vertebra (C6).
- The medial boundary is reliably formed by the longus colli muscle (m. longus colli).
- The lateral boundary is represented by the anterior scalene muscle (m. scalenus anterior).
Contents of the triangle: The medial section of the axillary artery lies directly upon the dome of the pleura here. Between the muscular structures, hidden beneath the 5th cervical fascia, lie the sympathetic trunk and the cervicothoracic ganglion, which is often referred to clinically as the stellate ganglion. The branches of the subclavian artery also pass through this zone. The thoracic duct (ductus thoracicus) deserves special attention — it is an unpaired structure and is found in this triangle only on the left side.
Antescalene space
The antescalene space (spatium antescalenum) is located anterior to the scalene muscles and serves as a receptacle for major veins.
Boundaries of the space:
- Anteriorly, it is bounded by the outer part of the lower section of the sternocleidomastoid muscle.
- Posteriorly, the wall is formed by the anterior scalene muscle, down the anterior surface of which the phrenic nerve descends.
Topography and vessels: In the deep layers of the neck, positioned between the 3rd and 5th fascia, runs the medial neurovascular bundle. It is tightly enclosed within its own fascial sheath, which is formed by the parietal layer of the 4th cervical fascia.
A key feature of this zone is the renowned Pirogov's venous angle. This is the confluence point of the internal jugular vein (v. jugularis interna) with the subclavian vein. The internal jugular vein itself exhibits a characteristic inferior dilation in this region — the jugular bulb (bulbus venae jugularis inferior). Immediately lateral to the venous angle, the external jugular vein (v. jugularis externa) drains into the subclavian trunk.
Interscalene space and nerves
The interscalene space (spatium interscalenum) is a cleft located strictly between the anterior and middle scalene muscles. Externally, this region is covered by the prevertebral layer — the 5th cervical fascia.
Contents of the space: Inside this narrow muscular cleft, a crucial stage of major nerve trunk formation takes place: the cervical plexus (plexus cervicalis) and brachial plexus (plexus brachialis) are formed here.
Speaking of the innervation of the neck muscles that bound these spaces, the accessory nerve (n. accessorius) must be mentioned. It is responsible for the motor innervation of the sternocleidomastoid muscle (which forms the anterior wall of the antescalene space) and also innervates the adjacent trapezius muscle.
Briefly: answers to topical questions
Which branches arise from the subclavian artery within the scalenovertebral triangle?
Four branches arise from the first part of the subclavian artery within the scalenovertebral triangle.
- Vertebral artery (a. vertebralis) — enters the transverse foramina of the cervical vertebrae, forms a loop between the 1st and 2nd vertebrae, and enters the cranial cavity.
- Internal thoracic artery (a. thoracica interna).
- Thyrocervical trunk (truncus thyrocervicalis).
- Costocervical trunk (truncus costocervicalis).
What are the topographic and anatomical relationships between the subclavian vein and subclavian artery in the antescalene space?
In the antescalene space, the subclavian vein lies anterior to the anterior scalene muscle and arches over the 1st rib medial to the subclavian artery. The lower edge of the subclavian vein overlaps the artery. At the same time, the vein is separated from the subclavian artery by the scalene tubercle (tuberculum musculi scaleni anterioris) and the anterior scalene muscle itself, behind which the artery runs.
What clinical symptoms occur in scalene muscle syndrome (compression of the brachial plexus and subclavian artery)?
Scalene muscle syndrome presents with symptoms related to the compression of the trunks of the brachial plexus and the subclavian artery.
- Pain — localized in the shoulder region and the upper medial border of the scapula.
- Radiating pain — extends down the shoulder to the radial aspect of the forearm, radiating to the 1st (thumb) and 2nd (index) fingers of the hand.
- Objective symptoms — tension and tenderness upon palpation of the scalene muscles, as well as limited lateroflexion (bending) of the cervical spine in the opposite direction.
To memorize the boundaries of the scalenovertebral triangle: Longus (colli muscle) — Inside, Anterior (scalene) — Outside, Cupula (of the pleura) — Below.
Class and exam questions
Where is Pirogov's venous angle located topographically?
It is located in the antescalene space. This is the anatomical site where the internal jugular vein merges with the subclavian vein.
Which muscles bound the interscalene space?
It lies between the anterior scalene muscle anteriorly and the middle scalene muscle posteriorly. Externally, it is covered by the 5th fascia.
Where does the thoracic duct run in the neck?
In the scalenovertebral triangle, where it is located exclusively on the left side.
What does the accessory nerve innervate?
The accessory nerve (n. accessorius) innervates the sternocleidomastoid and trapezius muscles.
What else to study on this topic
- Topography of the phrenic nerve on the anterior scalene muscle
- Structure and functions of the cervicothoracic (stellate) sympathetic ganglion
- Branches of the subclavian artery in the scalenovertebral triangle
- Formation of the neurovascular bundle sheath from the 4th cervical fascia
- Anatomy of the cervical and brachial plexuses in the interscalene space
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