Alar fascia
The alar fascia is a thin fibroareolar membrane separating the (anterior) true retropharyngeal space from the (posterior) danger space.
Notably, in the well patient, the alar fascia is not usually visible on cross-sectional imaging, and the two spaces are typically identified as a single space. The alar fascia may however become apparent on contrast-enhanced CT or MRI as a thin membrane in the retropharyngeal space in patients presenting with extensive regional edema or a collection.
On this page:
Summary
- location: between the visceral and prevertebral fascia, dividing radiological retropharyngeal space in a coronal plane
-
boundaries:
- superior: level of C1, where it may fuse posteriorly with the prevertebral fascia 1 or transition to loose areolar tissue 2
- inferior: level of T2, where it fuses anteriorly with visceral fascia
- lateral: carotid sheaths bilaterally
Gross anatomy
Boundaries
Superiorly, the prevertebral fascia extends until the level just above the C1 anterior tubercle, where it either fuses with prevertebral fascia posteriorly1, or narrowed to a median raphe before transitioning to loose areolar tissue 2. It does not connect to the skull base as a distinct layer.
Inferiorly, there is progressive fusion anteriorly with the visceral (buccopharyngeal) fascia between the T2 and T4 vertebral levels.
Laterally, the alar fascia fuses with the lateral wall of each carotid sheath. Additionally, some fibers are contributed by the medial raphe extensions of the posterior middle pharyngeal constrictor 2.
Relations
Anteriorly, the alar fascia delimits the posterior margin of the true retropharyngeal space.
Posteriorly, the alar fascia delimits the anterior margin of the danger space.
Contents
The alar fascia is made of loose areolar tissue. Some authors state that, in addition, the substance of the alar fascia contains the sympathetic chain, superior cervical ganglion, and superior laryngeal nerve 3.
Radiographic features
Alar fascia is not usually resolved on imaging; however, it may be visible on contrast-enhanced CT as a thin membrane in the retropharyngeal space in patients with extensive regional edema e.g. post-radiation therapy 2.
Related pathology
-
retropharyngeal abscess
- alar fascia represents the anterior boundary of the danger space, itself a potential space through which an infective process from the pharyngeal region can extend into the mediastinum
Related Radiopaedia articles
Anatomy: Head and neck
- skeleton of the head and neck
-
cranial vault
- scalp (mnemonic)
-
sutures
- calvarial
- facial
- frontozygomatic suture
- frontomaxillary suture
- frontolacrimal suture
- frontonasal suture
- temporozygomatic suture
- zygomaticomaxillary suture
- parietotemporal suture (parietomastoid suture)
- occipitotemporal suture (occipitomastoid suture)
- sphenofrontal suture
- sphenozygomatic suture
- spheno-occipital suture (not a true suture)
- lacrimomaxillary suture
- nasomaxillary suture
- internasal suture
- basal/internal
- skull landmarks
- frontal bone
- temporal bone
- parietal bone
- occipital bone
- skull base (foramina)
-
facial bones
- midline single bones
- paired bilateral bones
- cervical spine
- hyoid bone
- laryngeal cartilages
-
cranial vault
- muscles of the head and neck
- muscles of the tongue (mnemonic)
- muscles of mastication
- muscles of facial expression
- muscles of the middle ear
- orbital muscles
- muscles of the soft palate
- pharyngeal muscles
- suprahyoid muscles
- infrahyoid muscles
- intrinsic muscles of the larynx
- muscles of the neck
-
deep spaces of the neck
- anterior cervical space
- buccal space
- carotid space
- danger space
- deep cervical fascia
- infratemporal fossa
- masticator space
- parapharyngeal space
- parotid space
- pharyngeal (superficial) mucosal space
- perivertebral space
- posterior cervical space
- pterygopalatine fossa
- retropharyngeal space
- suprasternal space (of Burns)
- visceral space
- surgical triangles of the neck
- orbit
- ear
- paranasal sinuses
- nose
- oral cavity
- pharynx
- larynx
- viscera of the neck
- blood supply of the head and neck
-
arterial supply
-
common carotid artery
- carotid body
- carotid bifurcation
- subclavian artery
- variants
-
common carotid artery
- venous drainage
-
arterial supply
- innervation of the head and neck
-
cranial nerves
- olfactory nerve (CN I)
- optic nerve (CN II)
- oculomotor nerve (CN III)
- trochlear nerve (CN IV)
-
trigeminal nerve (CN V) (mnemonic)
- trigeminal ganglion
- ophthalmic division
- maxillary division
- mandibular division
- abducens nerve (CN VI)
- facial nerve (CN VII)
- vestibulocochlear nerve (CN VIII)
- glossopharyngeal nerve (CN IX)
-
vagus nerve (CN X)
- superior laryngeal nerve
- recurrent laryngeal nerve (inferior laryngeal nerve)
- (spinal) accessory nerve (CN XI)
- hypoglossal nerve (CN XII)
- parasympathetic ganglia of the head and neck
- greater occipital nerve
-
cervical plexus
- muscular branches
- longus capitis
- longus colli
- scalenes
- geniohyoid
- thyrohyoid
-
ansa cervicalis
- omohyoid (superior and inferior bellies separately)
- sternothyroid
- sternohyoid
- phrenic nerve
- contribution to the accessory nerve (CN XI)
- cutaneous branches
- muscular branches
- brachial plexus
- pharyngeal plexus
-
cranial nerves
- lymphatic drainage of the head and neck
Unable to process the form. Check for errors and try again.