Aberrant internal carotid artery is a variant of the internal carotid artery (ICA) and represents a collateral pathway resulting from involution of the normal cervical portion (first embryonic segment) of the ICA 5.
There is consequent enlargement of the usually small collaterals which course t...
The accessory meningeal artery is a branch of the maxillary artery but can also branch from the middle meningeal artery.
The artery passes upwards through the foramen ovale to supply the trigeminal ganglion and the dura mater of Meckel's cave and the middle cranial fossa. It also usually suppli...
Accessory parotid glands are a normal variant and represent ectopic salivary tissue separate from, but usually in close proximity to, the main parotid glands.
Accessory parotid glands are commonly picked up incidentally on ultrasound; seen in ~20% of the general population 2.
The parietal and occipital bones in particular are common regions for accessory sutures because of their multiple ossification centres.
It is important to know these anatomic variations, mainly on the head trauma image studies in children, where it could be difficult to differentiate non-depres...
Agger nasi air cells are the most anterior ethmoidal air cells lying anterolateral and inferior to the frontal recess and anterior and above the attachment of the middle turbinate. They are located within the lacrimal bone and therefore have as lateral relations the orbit, the lacrimal sac and t...
The anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge for radiologists and imaging specialists.
Head and neck anatomy
Abdominal and pelvic anatomy
The angular vein drains the anterior region of the scalp 1. It is formed by the union of the supratrochlear and supraorbital veins and becomes the facial vein 1,2,3.
The angular vein is formed at the medial canthus as the supratrochlear vein and supraorbital vein unite 1,2. The a...
The annular ligament (or ligamentum anulare stapedis) of the stapes attaches the rim of the footplate of the stapes to the rim of the oval window. This forms the stapediovestibular joint; a fully-functional articulation is vital for transmission of sound vibrations in the middle ear to the fluid...
The ansa cervicalis (or ansa hypoglossi, an archaic synonym) is a component of the cervical plexus which gives muscular branches to the geniohyoid muscle of the suprahyoid group and all four of the infrahyoid (strap) muscles.
superior root: derived from the anterior prima...
The anterior cervical space is a small infrahyoid compartment of the head and neck. It is a fat containing space and is not enclosed by fascia 1.
posterior: carotid space
medial: visceral space
superior: submandibular space
The anterior commissure of the larynx is the anterior junction point of the true vocal cords. It is bounded anteriorly by the thyroid cartilage and is part of the laryngeal glottis.
The anterior cranial fossa constitutes the floor of cranial vault which houses the frontal lobes of the brain.
Structures present in the midline of anterior cranial fossa from anterior to posterior are:
groove for superior sagittal sinus
groove for anterior meningeal vessels
The anterior division of the mandibular division of the trigeminal nerve has four branches, which are all motor branches except one. The four branches are:
deep temporal nerves
lateral pterygoid nerves
The anterior epitympanic recess, also known as the supratubal recess, is a small discrete space in the epitympanum anterior to the malleus. It is separated from the epitympanum proper by the anterior attic bony plate, also known as the cog, which has its orientation in the coronal anatomical pla...
The anterior ethmoid artery is a branch of the ophthalmic artery. It supplies the anterior and middle ethmoidal sinuses, frontal sinus, the lateral nasal wall and the nasal septum (see nasal cavity).
It traverses the anterior ethmoidal foramen with the anterior ethmoidal nerve (w...
The anterior ethmoidal nerve is an extraconal branch of the nasociliary nerve, a branch of ophthalmic division of the trigeminal nerve. Some authors describe it as either the terminal branch or a direct continuation of the nasociliary nerve. It branches off distal to the infratrochlear nerve an...
The anterior jugular vein is a paired tributary of the external jugular vein.
It arises beneath the chin in the region of the hyoid bone or suprahyoid neck.
Origin and course
The anterior jugular vein has its origin as the confluence of several small superficial subma...
The anterior lacrimal crest is a bony projection on the frontal process of the maxilla continuous with the orbital rim which creates the lateral margin of the lacrimal sac fossa. The medial palpebral ligament is attached to anterior lacrimal crest.
Immediately anterior to the anterior lacrimal ...
The anterior nares (singular: naris) (or nostrils) form the entrance to the nose. Each naris is formed by a ring of structures:
medially the columella (soft tissue anteroinferior portion of the nasal septum)
laterally and superiorly the nasal ala
inferiorly the nasal sill
The anterior superior alveolar canal courses through the anterior wall of the maxillary sinus, and contains the anterior superior alveolar nerve, artery and vein. Usually, it shares a common channel with the infraorbital canal but when seen separately should not be confused for a fracture.
The anterior superior alveolar nerve, also known as the anterior superior dental nerve, is the third branch of the infra-orbital nerve, from the maxillary division of the trigeminal nerve. It is the largest of the superior alveolar nerves and contributes to the superior dental plexus.
The anterior triangle forms the anterior compartment of the neck and is separated from the posterior triangle by the sternocleidomastoid muscle. The triangles of the neck are surgically focussed, first described from early dissection-based anatomical studies which predated cross-sectional anatom...
The anterior tympanic artery is the second named branch of the first part of the maxillary artery. The vessel passes through the petrotympanic fissure to supply the lining of the middle ear and accompanies the chorda tympani in its course.
Arnold's nerve is the auricular branch, also known as the mastoid branch, of the vagus nerve (CN X).
Origin and course
Arnold's nerve originates from the superior ganglion of the vagus nerve and also has a small contribution from the inferior ganglion of the glossopharyngeal nerve. It ascends ...
The arteries of the head and neck are branches of the common carotid and subclavian arteries.
common carotid artery
internal carotid artery (segments)
persistent stapedial artery
The aryepiglottic folds are two ligamentomuscular structures within the supraglottic larynx that function to protect the airway when swallowing.
Each aryepiglottic fold is comprised of the superior ligamentous edge of the quadrangular membrane and covering mucous membrane 1, the ...
The arytenoid cartilages are paired hyaline cartilages that articulate with the sloping upper border of the lamina of the cricoid cartilage by the cricoarytenoid joint. This joint allows movement of the arytenoid cartilages, which is vital in approximating, tensing and relaxing the vocal folds.
The ascending cervical artery is 1 of the 4 branches of the thyrocervical trunk (off the first part of the subclavian artery).
It is a small artery that ascends medial to the phrenic nerve on the prevertebral fascia. It contributes many small spinal branches into the intervertebral foramina of ...
The ascending pharyngeal artery, the smallest branch of the external carotid artery, is a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid and under the stylopharyngeus.
origin: a branch of the external carotid artery
The asterion is the junction on the side of the posteroinferior calvarium where three sutures meet:
It represents the site of the closed mastoid fontanelle. It is located at the posterior end of the parietotemporal suture, whereas ...
Asymmetric pneumatisation of petrous apex results in asymmetric fatty bone marrow within the petrous apex. It is a common incidental finding on brain and skull base MRI.
Asymmetric pneumatisation of the petrous apex results in the presence of bon...
The auriculotemporal nerve is a sensory branch of the posterior division of the mandibular division of the trigeminal nerve.
The auriculotemporal nerve divides posteriorly from the posterior division of the mandibular division before dividing into two roots separate to encircle t...
The basal lamella, also known as basal lamella of the middle turbinate, is an osseous lamella that separates the anterior from the posterior ethmoid sinuses 1.
Internal anterior to posterior partitions of the ethmoid sinuses are called basal lamellae. According to a concept propose...
The base of the skull (or skull base) forms the floor of the cranial cavity and separates the brain from the structures of the neck and face.
The base of the skull is a bony diaphragm composed of a number of bones - from anterior to posterior:
The basion is the median (midline) point of the anterior margin of the foramen magnum. The apical ligament attaches to it.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
Various lines and measurements using the ...
Bill bar is a bony anatomical landmark that divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment. Anterior to Bill's bar, in the anterior superior quadrant, are the facial nerve (CN VII) and nervus intermedius, and posterior to it, in the po...
The body of the sphenoid bone is the midline cubical portion of the sphenoid bone, hollowed by the sphenoid air sinuses.
The body has superior, inferior, anterior, posterior, and lateral surfaces.
The superior surface features:
ethmoidal spine: prominent spine that articulates...
The bony orbit refers to the bones that constitute the margins of the orbits, that is the roof, medial and lateral walls and floor. The orbital margin or rim refers to the anterior circular margin of the orbit. The orbital apex refers to the posterior confluence of the orbit, where the optic can...
Bouthillier et al. described (in 1996) 1 a seven segment internal carotid artery (ICA) classification system. It remains the most widely used system for describing ICA segments at the time of writing (mid-2016).
There are a few other classifications systems including those proposed by Fisher (1...
A mnemonic for remembering the branches of the maxillary artery is:
DAM I AM Piss Drunk But Stupid Drunk I Prefer, Must Phone Alcoholics Anonymous
D: deep auricular artery
A: anterior tympanic artery
M: middle meningeal artery
I: inferior alveolar artery
A: accessory meningeal ar...
Useful mnemonics to remember the four branches of the thoracoacromial artery are:
CAlifornia Police Department
Cadavers Are Dead People
B: breast (pectoral)
CAlifornia Police Department
The bregma is the midline bony landmark where the coronal and sagittal sutures meet, between the frontal and two parietal bones.
It is the anterior fontanelle in the neonate and closes in the second 2 (typically around 18 months after birth).
It is one of the skull landmarks, craniometric poin...
The buccal nerve is the only purely sensory branch of the anterior division of the mandibular division of the trigeminal nerve. It is not to be confused with the buccal branch of the facial nerve.
The buccal nerve divides off the anterior division and passes with the paired nerve...
The buccal space (or buccinator space) is one of the seven suprahyoid deep compartments of the head and neck.
The buccal spaces are paired fat contained spaces on each side of the face forming cheeks. Each space is enveloped by the superficial (investing) layer of the deep cervi...
The buccinator artery is a small branch from the second part of the maxillary artery. It runs obliquely forward, between the medial pterygoid and the insertion of the temporalis, to the outer surface of the buccinator, to which it is distributed, anastomosing with branches of the facial artery a...
The bulla lamella is a structure that, when intact, forms the posterior boundary of the frontal recess. When pneumatised, it forms the ethmoid bulla.
It is frequently incomplete and often does not reach the roof of the ethmoid at the skull base. Under these circumstances, the fro...
The carina is part of the trachea and is an important reference point in chest imaging.
The carina is found at the base of the trachea and it is formed as the main bronchi divide into right and left branches.
The carina usually sits in the T4/T5 plane and is at the level of the ...
The caroticotympanic branch (tympanic branch) is a small branch from the C2 segment of the internal carotid artery. It is a vestigial remnant of the hyoid artery.
It passes posterolaterally into the middle ear cavity and anastomoses with the inferior tympanic artery (a branch of the external ca...
The carotid bifurcation is the point at which the common carotid artery terminates. As it does so, it forms the internal and external carotid arteries which go on to supply the head and neck.
It is closely related anatomically to the carotid body, a small group of chemoreceptors and supporting ...
The carotid body is located within the neck, and in close proximity to the carotid bifurcation. It is composed of a number of chemoreceptor cells and supporting matrix and detects changes in the composition of blood in the common carotid as it forms the internal and external carotid arteries.
The carotid canal is a passage within the petrous temporal bone and transmits the internal carotid artery and sympathetic plexus. Its inferior opening is called the carotid foramen and is situated anteriorly to the jugular fossa and medially to the tympanic plate. The carotid canal is initially ...
The carotid space (also known as the post-styloid parapharyngeal space) is one of the seven deep compartments of the head and neck.
The carotid space is a roughly cylindrical space that extends from the skull base through to the aortic arch. It is circumscribed by all three laye...
The carotid triangle is one of the paired triangles in the anterior triangle of the neck. The triangles of the neck are surgically focussed, first described from early dissection-based anatomical studies which predated cross-sectional anatomical description based on imaging (see deep spaces of t...
The central artery of the retina or central retinal artery (CRA) arises from the ophthalmic artery.
The central artery of the retina courses anteriorly and inferior to the optic nerve, It then pierces the dura and the arachnoid of the optic nerve. It then runs in the centre of t...
The central base of skull is a region of the skull base centred on the pituitary fossa and includes surrounding structures.
Despite no single universally accepted definition of this region, it is frequently used clinically and is conceptually useful particularly when considering tumours of the ...
Cervical lymph node groups describe the anatomic position of the nodes. It differs from cervical lymph node levels, covering all lymph nodes not just those relevant to head and neck surgery.
Groups described in the literature include but are not limited to:
The cervical plexus is formed by the ventral (anterior) rami of the C1 to C5 nerve roots and innervates the diaphragm, provides motor supply to some neck muscles and cutaneous sensation to the skin of the head, neck and chest.
anterior rami of C1 to C5 nerves
The Chorda tympani is a nerve that arises from the mastoid segment of the facial nerve, carrying afferent special sensation from the anterior two-thirds of the tongue via the lingual nerve, as well as efferent parasympathetic secretomotor innervation to the submandibular and sublingual glands.
The ciliary ganglion is one of four parasympathetic ganglia of the head and neck. It receives parasympathetic fibres from the oculomotor nerve.
smallest of the ganglia (2mm in size)
located posterolaterally in the intraconal space of the orbit (towards the orbital apex) between ...
The clivus is the sloping midline surface of the occipital bone anterior to the foramen magnum. Specifically it is located in the basiocciput. At the clivus, the occipital bone has articulations with the sphenoid and petrous part of temporal bone1.
Inferiorly the clivus is flanked be the rounde...
Cloquet's canal, also known as the hyaloid canal or Stilling's canal, is a transparent canal that runs from the optic nerve disc to the lens traversing the vitreous body. It serves as a perivascular sheath surrounding the hyaloid artery in the embryonic eye.
The cochlea is part of the inner ear osseous labyrinth found in the petrous temporal bone.
The cochlea is a shell-shaped spiral that turns between two-and-a-half and two-and-three-quarters times around the modiolus (a central column of porous bone).
The spiral of the cochlea is...
The cochlear duct (also known as the scala media) is housed centrally in the cochlea which is part of the inner ear along with the vestibular apparatus 1,4. The cochlea is located in the bony labyrinth, which is found in the temporal bone 2.
The cochlear duct is a cavity filled w...
Thin osseous septum separating the semicanal for tensor tympani and the bony Eustachian tube.
The cochlear promontory is the name given to the bone that overlies the basal turn of the cochlea protruding into the middle ear cavity.
glomus tympanicum paragangliomas typically arise in the region of the cochlear promonotory
The colliscalene triangle is an important anatomical region of the neck, situated medial to the scalenus anterior muscle.
medial: lateral border of longus colli
lateral: medial border of scalenus anterior
inferior: first part of the subclavian artery
apex: carotid ...
The columella is the most anteroinferior portion of the nasal septum. It is a single midline structure composed of cartilage and overlying skin, extending posteriorly from the tip of the nose. The lateral aspects form the medial wall of each nostril.
History and etymology
From the Latin word f...
The common carotid artery is a paired structure that supplies blood to the head and neck.
left: branch of the aortic arch
right: branch of the brachiocephalic trunk
course: posterior to sternoclavicular joint, lateral to thyroid and trachea
supply: head and neck
The common facial vein is formed by the joining of the facial vein and anterior branch of the retromandibular vein. It is part of the venous drainage system of the face.
origin and termination: the facial vein (along with the facial artery) pierces the deep investing fascia of the neck...
Concha bullosa (plural: conchae bullosae) (also known as middle turbinate pneumatisation) is a common finding and although associated with deviation of the nasal septum, it is usually of little clinical importance.
Concha bullosa is a normal variant and is one of the most common v...
The condylar canal, or canalis condylaris, is a skull base canal in the posterior cranial fossa, located in the condylar fossa.
location: in the condylar fossa of the posterior cranial fossa, posterior to the occipital condyles
emissary veins, connecting the sigmoid sinus to...
Congenital absence of the internal carotid artery (ICA) is a rare anomaly that occurs in less than 0.01% of the population. It encompasses agenesis, aplasia, and hypoplasia 1.
The most common type of collateral flow is through the circle of Willis, through the anterior communicating artery (ACO...
The conjunctiva is a transparent membrane is attached at the margins of the cornea. It is loosely attached to the sclera and thence reflected over the inner surface of the eyelids. It is firmly attached to the tarsal plates and blends with the skin at the margins of the lids.
The corniculate cartilages are paired, elastic and accessory cartilages of the larynx that lie superior to and articulate with the apices of the arytenoid cartilages. They are components of the laryngeal cartilages. The word 'corniculate' comes from the latin word 'cornu' meaning horn-like.
The coronal suture is the cranial suture formed between the two parietal bones and the frontal bone. At the junction of coronal, sagittal and frontal sutures is the anterior fontanelle which is open at birth and usually fuses at around 18-24 months after birth.
Fusion of the coronal suture occu...
The corrugator supercilii are two small, triangular muscles that allow facial expression through movement of the eyebrows, including frowning. They originate from the medial end of the supraorbital margins and insert deep to and can cause traction on the skin over the middle of the supraorbital ...
The costocervical trunk is one of the branches of the second part of the subclavian artery. It arises from the posterior wall of the subclavian artery, posterior or medial to the anterior scalene muscle and courses posterosuperiorly across the suprapleural membrane where it divides into 2 branc...
The cranial vault, also known as the skull vault, skullcap or calvaria, is the cranial space that encases and protects the brain together with the base of the skull (chondrocranium). The cranial vault and the base of skull together form the neurocranium.
Although commonly seen in r...
The cribriform plate is a sieve-like structure between the anterior cranial fossa and the nasal cavity. It is a part of ethmoid bone and supports the olfactory bulb, which lies in the olfactory fossa. It is perforated by foramina for the passage of the olfactory nerves and the anterior ethmoidal...
The cricoid cartilage is a ring shaped structure that sits just below the thyroid cartilage. It is the only complete cartilaginous ring of the whole airway.
The anterior portion is called the arch and the posterior quadrangular shaped portion is the lamina. It articulates with th...
The crista galli is a thick, midline, smooth triangular process arising from the superior surface of the ethmoid bone, projecting into the anterior cranial fossa. It separates the olfactory bulbs, which lie either side of it in the olfactory fossae of the cribriform plate. It serves as an anteri...
The crystalline lens (or simply, the lens) is in the ocular globe between the posterior chamber and the vitreous body. It is transparent and biconvex in morphology, and aids the focusing of light onto the retina.
The lens lies in the globe at the posterior aspect of th...
The cuneiform cartilage is a small, paired cartilage which resides in the aryepiglottic fold. It takes the form of a club-like nodule, visible as an elevation beneath the mucosa (the cuneiform tubercle) anterosuperior to the corniculate cartilages.
History and etymology
The word cuneiform deri...
The danger space is a potential space located behind the true retropharyngeal space, which connects the deep cervical spaces to the mediastinum.
anteriorly: alar fascia
posteriorly: prevertebral layer of the deep cervical fascia
The deep auricular artery is the first named branch of the maxillary artery and passes through the bony or cartilaginous wall of the external acoustic meatus to supply the skin of that canal and part of the tympanic membrane. It can sometimes contribute a small branch to the arterial supply of t...
The deep cervical fascia consists of 3 separate but related fascial layers that encircle structures in the neck and allow anatomic compartmentalisation. These layers cannot be visualized directly by cross sectional imaging. All 3 layers meet to form the carotid sheath. From superficial to deep, ...
The deep petrosal nerve transmits post-ganglionic sympathetic fibres from the internal carotid plexus to the Vidian nerve on its way to the pterygopalatine ganglion.
The nerve begins at the internal carotid plexus and runs alongside the lateral aspect of the internal carotid arte...
Head and neck anatomy is described in slightly different terms in the radiology literature reflecting the importance of fascia lined spaces in confining various pathologies. As such the neck has been divided into a number of 'deep spaces' which overlap with traditional anatomical description.
The deep temporal arteries (anterior and posterior) are branches from the second part of the maxillary artery. They ascend between the temporalis muscle and the pericranium supplying the overlying muscle.
The anterior branch communicates with the lacrimal artery by means of small branches which...
The deep temporal nerves are a pair of motor branches of the anterior division of the mandibular division of the trigeminal nerve. It should not be confused with the temporal branch of the facial nerve.
The two deep temporal nerves divide off the anterior division and course abov...
The Delphian (prelaryngeal/precricoid) node is one of the cervical lymph node groups that comprise level VI cervical lymph nodes and is not routinely excised in radical neck dissections.
It is located between the cricothyroid muscles, above the thyroid isthmus, lying directly ant...
The depressor anguli oris (triangularis) muscle is one of the muscles of facial expression.
origin: oblique line of the mandible
angle of the mouth
superficial fibres from both sides merge to form the transversus menti
innervation: facial nerve
The digastric muscle is composed of two bellies, anterior and posterior, connected by an intermediate round tendon. The two bellies of the muscle have different embryonic origins and hence are supplied by different cranial nerves.
anterior belly: digastric fossa on the deep sur...