The investing (superficial) layer of deep cervical fascia is the outermost layer of the deep cervical fascia encircling the neck as a complete cylinder deep to the platysma. It splits to enclose the sternocleidomastoid and trapezius muscles and to form the roof of the anterior and posterior cervical triangles. Superiorly it attaches to the mandible, mastoid, and occiput; inferiorly to the clavicle and manubrium.
Forms the outermost circumferential investing layer of the neck, enclosing the cervical viscera and muscles, providing structural integrity to the neck, and forming the roof of the anterior and posterior cervical triangles through which access is gained in neck surgery.
The investing cervical fascia is the first deep fascial layer encountered in neck dissection and in approaches to the cervical spine, carotid artery, and thyroid. It defines the deep boundary of cervical lymph node groups for nodal dissection planning. The deep cervical fascia system (investing, pretracheal, prevertebral layers with the alar fascia) defines the distinct spaces of the neck and their infection spread patterns. Incision through this layer in the anterior cervical triangle exposes the strap muscles below.
Tonsillar or dental infections may penetrate the investing cervical fascia and spread between fascial layers into the parapharyngeal or retropharyngeal space, tracking along the danger space to the posterior mediastinum, producing descending necrotising mediastinitis requiring emergency surgical drainage through the neck and chest.
