Aberrant internal carotid artery is a variant of the internal carotid artery and represents a collateral pathway resulting from involution of the normal cervical portion (first embryonic segment) of the internal carotid artery 5.
There is consequent enlargement of the usually sma...
Accessory maxillary ostia are a common anatomic variant, and are usually found incidentally on CT scans of the paranasal sinuses. Accessory ostia of the maxillary sinus are common, occurring in up to 40% patients 1. No significant association has been found between the presence of accessory osti...
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 cave and the middle cranial fossa. It also usually supplies...
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 centers.
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...
The adenoid tonsils, or often just simply the adenoids (also known as the nasopharyngeal or pharyngeal tonsils), are paired foci of lymphatic tissue located on the superoposterior wall of the nasopharynx and form part of Waldeyer's ring.
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 alar fascia is a thin fibroareolar membrane separating the (anterior) true retropharyngeal space from the (posterior) danger space. It is the ventral component of the deep layer of the deep cervical fascia.
Notably, in the well patient, the alar fascia is not usually visible on cross-sectio...
Ampulla (plural: ampullae) is an anatomical term used for tubular structures with a short segmental bulbous dilatation:
ampulla (fallopian tube)
ampulla (lacrimal system)
ampulla (semicircular ducts)
ampulla of Vater
ampulla (vas defe...
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 artery is the terminal branch of the facial artery.
It becomes the angular artery after the lateral nasal artery branch from the facial artery. It courses superiorly along the lateral border of the external nose to the medial canthus. It is accompanied by the angular vein which drai...
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 can refer to:
annular ligament of the stapes
annular ligament of the proximal radio-ulnar joint
A mnemonic to remember the contents of the tendinous ring (also known as the annulus of Zinn) from superior to inferior is:
One Canal, Several Orbital Nerves In One Annulus
OC: optic canal
SO: superior division of oculomotor nerve
N: nasociliary nerve
IO: inferior division of ocu...
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 most of the infrahyoid (strap) muscles (excluding the thyrohyoid muscle).
It lies within the carotid triangle, s...
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 condylar confluence is an extracranial venous structure at the base of skull that communicates extensively with regional veins and dural venous sinuses.
It is located immediately anterior to the hypoglossal canal and medial to the jugular vein, just inferior to the jugular bulb an...
The anterior cranial fossa constitutes the floor of the cranial vault which houses the frontal lobes of the brain.
Structures present in the midline of the anterior cranial fossa from anterior to posterior are:
groove for superior sagittal sinus
groove for anterior meningeal v...
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 cog.
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 the 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 nerv...
The anterior ethmoidal notch contains the anterior ethmoidal artery and has significant rates of anatomic variation that put the artery during function endoscopic sinus surgery (FESS).
The anterior ethmoidal notch lies in the medial wall of the superomedial orbit, adjacent to the...
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 (or external) 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 focused, first described from early dissection-based anatomical studies which predated cross-sectional anatomi...
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 pneumatization of petrous apex is a frequent normal anatomic variant resulting in asymmetric fatty bone marrow within the petrous apex. It is a common incidental finding on brain and skull base MRI.
Asymmetric pneumatization of the pet...
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...
Barrow caroticocavernous fistula classification divides caroticocavernous fistulas into direct (type A) or indirect (types B-D). This classification was proposed by Barrow et al. in 1985 1 and at the time of writing (mid-2016) remains the most widely used system for describing caroticocavernous ...
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 ...
Bathrocephaly, also known as bathrocephalic occiputs, is a normal variation in skull shape, caused by an outward convex bulge of mid-portion of the occipital bone, often associated with a modification of the mendosal suture.
The true incidence of this disorder is unknown 1.
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 bar, in the anterior superior quadrant, are the facial nerve (CN VII) and nervus intermedius, and posterior to it, in the post...
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 branchial (or pharyngeal) apparatus is the complex region in the developing embryo between the head and chest that develops in the fourth week and provides bilateral ridges and valleys that subsequently develop into numerous anatomic structures of the head, face, palate and anterior neck. Th...
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 year 2 (typically around 18 months after birth).
It is one of the skull landmarks, craniometric...
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, also known as the buccinator space, is one of the seven suprahyoid deep compartments of the head and neck.
The buccal spaces are paired fat-containing spaces on each side of the face forming cheeks. Each space is enveloped by the superficial (investing) layer o...
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 buccinator muscle is a muscle of facial expression located in the cheek, between the maxilla and mandible, and functions chiefly as a muscle of mastication.
origin: outer surface of alveolar process of both maxilla and mandible, and anterior margin of the pterygomandibular raphe 1
The buccopharyngeal fascia is the component of the middle layer of the deep cervical fascia that invests the outside of the pharyngeal constrictors and buccinator muscles.
The term has been variably used to refer to the entire visceral component of the middle layer of the deep cerv...
The bulla lamella is a structure that, when intact, forms the posterior boundary of the frontal recess. When pneumatized, 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 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 carotid plate. The carotid canal is initially d...
The carotid plate, also known as the tympanic plate, is a thin (0.5 mm) bony plate that separates the carotid canal from the middle ear cavity.
The caroticotympanic artery perforates the carotid plate normally.
Disruption or dehiscence of the carotid plate may...
The carotid space, the suprahyoid portion of which is also known as the poststyloid parapharyngeal space, is a deep compartment of the head and neck bound by the carotid sheath.
The "carotid space" terminology was introduced by some radiologists to facilitate differential diagnosis...
The carotid triangle is one of the paired triangles in the anterior triangle of the neck. The triangles of the neck are surgically focused, first described from early dissection-based anatomical studies which predated cross-sectional anatomical description based on imaging (see deep spaces of th...
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 center of t...
The central base of skull is a region of the skull base centered 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 tumors of the ...
The cervical lymph node groups covers all the lymph nodes in the head and neck region. These named groups overlap with the cervical lymph node levels, which are numbered.
Groups described in the literature include but are not limited to the following:
superficial lymph node gro...
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 cervical thymus (plural: cervical thymi) refers to an ectopic location of the thymus in the neck above the level of the brachiocephalic veins.
A cervical thymus usually presents before adolescence as a painless unilateral midline or lateral neck mass.
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 choroid is part of the uveal layer of the eye along with the ciliary body and iris 1.
location: posterior aspect of the globe
function: vascularization of the outer retina
arterial supply: posterior ciliary arteries
innervation: short ciliary nerves, long ciliary nerves
The ciliary ganglion is one of four parasympathetic ganglia of the head and neck. It receives parasympathetic fibers from the oculomotor nerve.
smallest of the ganglia (2 mm in size)
located posterolaterally in the intraconal space of the orbit (towards the orbital apex) between...
Clival diploic veins are veins that travel through the body of the clivus connecting intracranial venous structures on the inner surface of the skull (e.g. basilar venous plexus, inferior petrosal sinuses, marginal sinus, internal carotid artery venous plexus of Rektorzik, inferior petro-occipit...
The clivus (of Blumenbach) is the sloping midline surface of the skull base anterior to the foramen magnum and posterior to the dorsum sellae 1. Specifically, it is formed by the sphenoid body and the basiocciput, which join at the spheno-occipital synchondrosis. At the clivus, the occipital bon...
The cloison sagittale (sagittal partition), also known as Charpy fascia, is a sagittally oriented fascia on either side of the neck that separates the midline deep neck spaces (retropharyngeal space, prevertebral space, and danger space) from the more lateral parapharyngeal space (including caro...
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.
History and etymology
The cochlea (plural: cochleae) is part of the inner ear osseous labyrinth found in the petrous temporal bone. It contains the cochlear duct, part of the membranous labyrinth which senses hearing.
The cochlea is a shell-shaped spiral that turns between two-and-a-half and two-and-t...
The cochlear aqueduct is a small narrow bony canal in the bony labyrinth of the petrous temporal bone. It contains the perilymphatic duct which arises from the scala tympani of the cochlea draining perilymph into the cerebrospinal fluid in the posterior cranial fossa near the lateral margin of t...
The cochlear cleft is a curvilinear radiolucent area of incomplete endochondral ossification in the otic capsule adjacent to the cochlea. It is a variant most prominent in children that may also be visible in adults 1.
The cochlear cleft is a C-shaped structure in the otic capsul...
The cochlear duct (also known as the scala media) is an endolymph-filled cavity located between the scala vestibuli (upper) and the scala tympani (lower) 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, itself fo...
The cochleariform process is the thin osseous projection in the anterior wall of the middle ear cavity that acts as the fulcrum for the tendon of the tensor tympani.
The cochleariform process is located 2,3:
at the posterior termination of the semicanal for tensor tym...
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 cog is a coronally oriented bony process in the middle ear cavity of the temporal bone that projects from the tegmen tympani, separating the anterior epitympanic recess from the posterior epitympanum. The cog ends anterosuperior to the head of the malleus and superior to the cochleariform pr...
The colliscalene triangle is an important anatomical region of the neck, situated medial to the scalenus anterior muscle.
It should not be confused with the scalene triangle which is located posterior to the scalenus anterior muscle.
medial: lateral border of longus...
The columella is the most anteroinferior portion of the nasal septum and forms the central fleshy portion between the two nostrils when looking at someone's nose. It is a single midline structure composed of cartilage and overlying skin, extending posteriorly from the tip of the nose. The latera...
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...
Compressor naris muscle forms the transverse component of nasalis muscle, and is one of the muscles of the nose, a subset of the muscles of facial expression.
origin: frontal process of maxilla
insertion: medial insertion into a transverse aponeurosis
innervation: facial nerve (V...
Concha bullosa (plural: conchae bullosae) (also known as middle turbinate pneumatization) 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. It is the largest of the emissary foramina of the skull 1.
location: in the condylar fossa of the posterior cranial fossa, posterior to the occipital condyles...
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...