The maxillary incisive canal runs through the maxilla in the midline. It connects the inferior nasal cavity with the superior oral cavity, opening at the incisive foramen posterior to the central maxillary incisor teeth. It contains the descending palatine artery and the nasopalatine nerve.
Incisive canal cysts, also known as nasopalatine duct cysts (NPDC), are developmental, non-neoplastic cysts arising from degeneration of nasopalatine ducts. These ducts usually regress in fetal life. The persistence of ductal epithelium leads to formation of cyst.
It is considered the most comm...
The incisive foramen (also known as nasopalatine foramen or anterior palatine foramen) is the oral opening of the nasopalatine canal. It is located in the maxilla in the incisive fossa, midline in the palate posterior to the central incisors, at the junction of the medial palatine and incisive s...
The incisive nerve is one of the two terminal branches of the inferior alveolar nerve, a branch of the posterior division of the mandibular division of the trigeminal nerve. It continues running anteriorly in the medullary cavity of the mandible after the mental nerve branches off and exits via ...
The incus is the middle of the ossicles articulating with the head of the malleus anteromedially and the stapes inferomedially.
a body which articulates with the head of the malleus, and to which the superior ligament of the incus is attached (to the roof of the middle ear cavit...
Infantile cervical ligament oedema can typically be seen when infants have suffered accidental or abusive head and neck trauma. The finding is best seen on sagittal STIR images.
The posterior ligamentous complex refers to the ligamentum flavum and interspinous ligaments. The anteri...
Infantile haemangiomas are benign vascular neoplasms that are the most common tumours of infancy. They can occur virtually anywhere, but the majority are found in the head and neck regions.
This article aims to be a generic discussion of the condition, for detailed and more specific imaging fea...
The inferior alveolar artery is a branch of the maxillary artery. It runs with the inferior alveolar nerve as it descends through the infratemporal fossa and enters the mandibular canal and supplies mandibular teeth. In the region of the first premolar it bifurcates into the incisive and mental ...
The inferior alveolar nerve or inferior dental nerve is a mixed sensory and motor branch of the posterior division of the mandibular division of the trigeminal nerve in the pterogomandibular space of the oral cavity.
The inferior alveolar nerve divides off the posterior division ...
Inferior labial artery (old name: inferior coronary artery) is one of the facial branches of the facial artery. It is smaller than the superior labial artery. It supplies the lower lip, including its labial glands, mucous membranes and muscles.
origin: facial branch of the facial arter...
The inferior longitudinal muscle of the tongue is one of the 4 intrinsic muscles of the tongue which alters the shape of the tongue mass, being entirely confined to the tongue without an attachment outside the tongue (like the extrinsic muscles of the tongue).
The muscles fibres ...
The inferior meatus is an air passage of the lateral nasal cavity located between the inferior nasal concha and lateral nasal wall. The nasolacrimal duct drains into the inferior meatus.
The plural of meatus is meatus (Latin noun of the fourth declension) or meatuses. Meati is inco...
The inferior median clival canal also known as the canalis basilaris medianus is a rare anatomical variant of the clivus, which passes in the sagittal plane from the intracranial surface of the clivus to its retropharyngeal surface. It is generally thought to represent a remnant of the notocord....
The inferior nasal conchae or turbinates are one of the pairs of conchae in the nose.
It extends horizontally along the lateral wall of the nasal cavity and consists of a lamina of spongy bone, curled upon itself like a scroll. The inferior nasal conchae are considered a pair of ...
The inferior oblique muscle is one of six extra-ocular muscles that control eye movements.
innervation: inferior branch of the oculomotor nerve (CN III)
origin: orbital surface of the maxilla
insertion: globe (posterior, inferolateral surface)
primary function: one of two ocular ext...
The inferior ophthalmic vein (IOV) is a vein of the inferior orbit and is smaller than the more well known superior ophthalmic vein.
The vein forms at the confluence of several veins within the anteroinferior orbit along the infraorbital margin from facial vein tributaries. It co...
The inferior pharyngeal constrictor muscle is one of the pharyngeal constrictor muscles. Its primary action is constriction of the pharynx (in coordination with the superior pharyngeal constrictor and the middle pharyngeal constrictor muscles) to deliver a bolus of food into the oesophagus.
The inferior rectus muscles is one of the 6 extra-ocular muscles that control eye movements.
innervation: inferior branch of the oculomotor nerve (CN III)
origin: Annulus of Zinn (tendinous ring)
insertion: globe (anterior, inferior surface)
primary function: one of two ocular depre...
The inferior thyroid artery is a branch of the thyrocervical trunk (85%) or subclavian artery (15%) and ascends to enter the thyroid gland on its posterior surface, as well as supplying both the superior and inferior parathyroid glands 1. The nerve is closely related to the ascending limb of the...
The infrahyoid muscles or strap muscles are a group of four paired muscles in the anterior neck below the hyoid bone, within the muscular triangle. They are responsible for depressing the hyoid during swallowing.
The four muscles are:
sternohyoid: superficial and medial
omohyoid: superficial ...
The infraorbital artery is a branch of the third part of the maxillary artery. It runs through the inferior orbital fissure, orbit, infraorbital canal then the infraorbital foramen. Here it gives off the anterior superior alveolar artery which supplies the anterior teeth and the anterior part of...
The infraorbital foramen is located in the maxillary bone. It is the anterior opening of the infraorbital canal, which is the anterior continuation of the infraorbital groove, which course through the floor of the orbit. The canal may reside entirely in the maxillary sinus, suspended from the si...
The infraorbital nerve is a branch of the maxillary division of the trigeminal nerve.
The infraorbital nerve divides off the maxillary division just after emerging from the foramen rotundum to enter the pterygopalatine fossa. It courses laterally over the palatine bone and maxi...
The infratemporal fossa is a complex space that lies posterolateral to the maxillary sinus and many important nerves and vessels traverse it.
The infratemporal fossa is the space between the skull base, lateral pharyngeal wall and the ramus of mandible. The fossa communicates w...
The infratrochlear nerve is an extraconal branch of the nasociliary nerve, a branch of ophthalmic division of the trigeminal nerve. Some authors describe it as the terminal branch of the nasociliary nerve. It courses through the medial aspect of the extraconal space of the orbit inferior to the ...
Ingested bones that become lodged in the throat or gastrointestinal tract are a common presentation to the emergency department. Recognition is important because these cases can be potentially fatal.
Patients may present with a 'foreign body' feeling in the throat after eating fish ...
The inion is the tip of external occipital protuberance, the midline bony prominance in the occipital bone where the ligamentum nuchae and trapezius muscle attaches. It is usually easily palpable.
It is the the surface marking of the internal attachment of the tentorium cerebelli.
It is one of...
The inner ear refers to the bony labyrinth, the membranous labyrinth and their contents. It is divided into three main parts:
A useful mnemonic to remember innervation of the muscles of the middle ear is:
S for Stapedius
T for Tensor Tympani
S: stapedius is supplied by a branch of the facial nerve - the Seventh cranial nerve. It is also the Smallest muscle in the body, and inserts onto the neck of Stapes.
Inspissated colloid (colloid crystals) in a thyroid nodule leads to focal hyperechogenic foci, which can potentially be confused with microcalcifications.
hyperechoic focus in a thyroid nodule
reverberation artifact / comet-tail artifact
this feature is the most reliabl...
Internal auditory canal (IAC) diverticulum are small focal outpouching arising from the anterolateral wall of the IAC.
In one study, they were identified in 5% of petrous temporal bone CT-scan 1. In the same study, it was coexisting with otosclerosis in 1% of cases 1.
A mnemonic to remember the relative position of nerves inside the internal auditory canal (IAC) is:
Seven up, Coke down
Four nerves pass through the IAC:
facial nerve (CN VII)
three components of the vestibulocochlear nerve (CN VIII)
cochlear nerve (CN VIIIc)
superior vestibular n...
The internal jugular vein (IJV) is the major venous return from the brain, upper face and neck.
Origin and course
It is formed by the union of inferior petrosal and sigmoid dural venous sinuses in or just distal to the jugular foramen (forming the jugular bulb). It descends in t...
A useful mnemonic to remember the branches of the internal jugular vein is:
Medical Schools Let Fun People In
From inferior to superior:
M: middle thyroid vein
S: superior thyroid vein
L: lingual vein
F: facial vein
P: pharyngeal vein
I: inferior petrosal sinus
The internal palpebral arteries, or medial palpebral arteries, are branches of the ophthalmic artery, with superior and inferior medial palpebral branches arising opposite the trochlear of the superior oblique muscle.
The internal palpebral arteries enter the superior and inferio...
The internasal suture is a single, midline cranial suture between the two nasal bones. It meets the frontonasal suture to form the nasion 1.
The interscalar septum is a thin bony plate that separates each turn of the cochlea 1.
It radiates from the modiolus laterally to the spiral ligament 2. Vessels (venules, arterioles and capillaries) run within the septum through bony canals 2.
Partial absence of the intersca...
The intraconal orbital compartment or intraconal space is the conical space within the orbit and musculofascial cone, the base of which is anterior and is formed by the posterior half of the globe. The sides are formed by the extraocular muscles and their surrounding fascia which pass posteriorl...
Intraconal orbital lesions are broadly divided into two main groups; those with or without involvement of the optic nerves:
Lesions with optic nerve involvement:
optic nerve glioma
optic nerve meningioma
lymphoma and leukaemia
Intracranial dermoid cysts are uncommon lesions with characteristic imaging appearances. They can be thought of as along the spectrum: from epidermoid cysts at one end (containing only desquamated squamous epithelium) and teratomas at the other (containing essentially any kind of tissue from all...
Intraductal papilloma of salivary gland (also known as an inverted ductal papilloma or sialadenoma papilliferum) is a benign relatively rare salivary gland tumour. '
They typically arise in adulthood and there may be a slight male predilection.
They may show a characte...
Intraosseous meningioma, also referred as primary intraosseous meningioma, is a rare subtype of meningioma that accounts for less than 1% of all osseous tumours. They fall under the subgroup of primary extradural meningiomas.
It is important to note that it has been argued by some ...
The intrinsic muscles of the larynx can be considered in two groups:
muscles that control the inlet of the larynx
muscles that move the vocal ligaments
Muscles of the inlet
aryepiglottic muscle: lies within the aryepiglottic fold, runs from the side of the epiglottis and inser...
The intrinsic muscles of the tongue are a group of 4 muscular bands in the tongue. In comparison to the extrinsic muscles of the tongue, they are entirely within the tongue with no external attachments. They act to alter the shape of the tongue where as the extrinsic tongue muscles alter the pos...
Inverted papillomas are a type of Schneiderian papilloma. They are uncommon with distinctive pathological and imaging features.
The term inverted papilloma is also used to describe a urothelial lesion. For a discussion of that entity, please refer to inverted papilloma of the urin...
Iodinated contrast-induced thyrotoxicosis is rare and may occur in patients with pre-existing thyroid disease and through complications of thyrotoxicosis (e.g. cardiac arrhythmia) may be fatal. Patients with a normal thyroid gland are unaffected.
Patients with existing thyrotoxicosis should no...
Iodine123 (I123) is a radioisotope of the element iodine (atomic number 53) used in nuclear medicine imaging including to scan the thyroid gland.
Uses, dosages, and time of Imaging
routine scan: 100-400 microCi po, image at 4-6 or 24 hours
thyroid cancer scan: 1.5 mCi po, image at 4-6 or 24 ...
An isolated cleft palate is a type of facial cleft. This is a much rarer occurrence than a cleft lip +/- palate and is thought to represent a different pathological entity.
The estimated incidence is at ~1 per 2000-2500 pregnancies 4-5. There may be a slight female predilection 4....
Jaffe-Campanacci syndrome is characterised by:
multiple non-ossifying fibromas of the long bones and jaw
café au lait spots
hypogonadism or cryptorchidism
giant cell granuloma of the jaw
Jod-Basedow phenomenon is hyperthyroidism following iodine intake in a person with long term underlying thyroid disease.
Jod-Basedow phenomenon occurs due to either overactivation of the entire thyroid gland or, more commonly, autonomous nodules within the gland after iodine repletio...
The jugular foramen courses anteriorly, laterally, and inferiorly as it insinuates itself between the petrous temporal bone and the occipital bone.
The jugular foramen is usually described as being divided into two parts by a fibrous or bony septum, called the jugular spine, into...
Jugular foramen schwannomas are a rare type of intracranial schwannoma that presents as a jugular fossa mass involving the jugular foramen.
In those without neurofibromatosis type 2 (NF2), they tend to present between the 3rd to 6th decades of life. There is a recognised female pr...
The jugular fossa is a depression situated on the inferior surface of petrous temporal bone posterior to the inferior opening of carotid canal. It lodges the jugular bulb. Anteriorly, lies the jugular foramen.
glomus jugulare is the most common tumour of jugular fossa
Jugular fossa masses comprise a range of pathological lesions that arise from or extend into the jugular fossa in the skull base. Although not a common location for tumours it is not unusual for jugular fossa lesions to be discovered incidentally on cross sectional imaging.
The jugular spine is a small sharp bony ledge which separates the two parts of the jugular foramen - pars nervosa anteriorly and pars vascularis posteriorly. It is an important landmark, as masses of the jugular foramen (e.g. glomus jugulare) will erode this spine, helping distinguish them from ...
Juvenile nasopharyngeal angiofibromas (JNA) are a rare benign but locally aggressive vascular tumour.
Juvenile nasopharyngeal angiofibromas occur almost exclusively in males and usually in adolescence (~15 years). They account for only 0.5% of all head and neck tumours 2, but are ...
Staging of juvenile nasopharyngeal angiofibromas is performed with cross-sectional imaging and relies on the identification of local tumour extent, and invasion of adjacent spaces. For a discussion of this entity please refer to the parent article: juvenile nasopharyngeal angiofibroma.
Kartagener syndrome is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterised by an abnormal ciliary structure or function, leading to impaired mucociliary clearance.
The prevalence of primary ciliary dyskinesia is approximately 1 in 12,000-60,000 ...
Keratocystic odontogenic tumours (KCOT or KOT), previously known as odontogenic keratocysts, are benign cystic neoplasms involving the mandible or maxilla and are believed to arise from dental lamina. They are locally aggressive and tend to recur after excision.
On imaging, they typically appe...
Keratosis obturans is a rare external auditory canal disease characterised by abnormal accumulation and consequently occlusion and expansion of the bony portion of the EAC by a plug of desquamated keratin. It can be confused by EAC cholesteatoma but they are completely different entities require...
The Keros classification is a method of classifying the depth of the olfactory fossa.
The ethmoid labyrinth is covered by the fovea ethmoidalis of the frontal bone and separates the ethmoidal cells from the anterior cranial fossa.
The very thin, horizontal cribriform plate (lamina cribrosa) of...
Kiesselbach's plexus (Kiesselbach's area or Little's area) is a vascular region of the anteroinferior nasal septum that comprises four arterial anastomoses:
anterior ethmoidal artery
a branch of the ophthalmic artery
a branch of the maxillary artery
greater palatine ar...
Kimura disease is a rare benign inflammatory disease that characteristically manifests as enlargement of cervical lymph nodes and salivary glands.
Kimura disease typically affects males (80%) between 20 and 40 years of age (80% of cases) 1-2, and is most frequently seen in Asia. S...
The term kissing carotids refers to tortuous and elongated vessels which touch in the midline. They can be be found in:
within the pituitary fossa
within sphenoid sinuses
within sphenoid bones
The significance of kissing carotids is two-fold:
may mimic intr...
Koerner's septum is a thin bridge of bone which divides the petrous and squamous portion of the mastoid air cells at the level of the mastoid antrum. It is commonly eroded by middle ear cholesteatomas.
Kuhn classification is an anatomical classification for the subtypes of frontal cells.
type 1 (~37%): a single air cell above the agger nasi cell
type 2 (~19%): two or more air cells above the agger nasi cell
type 3 (~7%): a single large cell above the agger nasi cell that extends into the fr...
Küttner tumour (KT) refers to a chronic sclerosing sialadenitis of the salivary glands. Despite the term tumour, it is a non neoplastic condition. It is classically described in relation the submandibular gland but less commonly can also affect other salivary glands 9 and occassionally as well ...
The labyrinthine artery, also known as the auditory artery or internal auditory artery, is a long and slender artery that is the main arterial supply to the vestibular apparatus and cochlea.
It usually originates from the AICA (~85%), although it can also branch from the basilar artery (~15%), ...
Labyrinthitis ossificans (LO), also known as labyrinthine ossification, represents pathological ossification of the membranous labyrinth as a response to an insult to the inner ear.
It is usually associated with profound sensorineural hearing loss.
It most co...
The labyrinth or lateral mass of the ethmoid bone consists of a number of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, anterior, middle, and posterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial, part...
The lacrimal apparatus consists of the lacrimal gland and the nasolacrimal drainage apparatus.
The gland produces tears secreted into the lateral aspect of the superior fornix. The serous fluid washes over the eye and is drained at the medial canthus by the superior and inferior lacrimal canal...
The lacrimal artery is a branch of the ophthalmic artery that supplies the lacrimal gland.
The lacrimal artery travels along the upper border of the lateral rectus muscle with the lacrimal nerve to supply the lacrimal gland as well as the eyelids and conjunctiva.
The lacrimal bones are paired craniofacial bones forming anterior aspect of the medial orbital walls.
The lacrimal bones have two surfaces and four borders. The lateral orbital surface is divided by a vertical posterior lacrimal crest with an anterior fossa for lacrimal sac and ...
The lacrimal canaliculi form the first part of the nasolacrimal drainage apparatus that drains tears produced by the lacrimal gland.
There are two lacrimal canaliculi - superior and inferior on each side. They commence at the superior and inferior lacrimal puncta, which drain te...
The lacrimal gland lies in the superolateral aspect of the orbit. It is part of the lacrimal apparatus and is responsible for tear production.
The lacrimal gland is roughly almond-sized and located anteriorly in the superolateral aspect of the extraconal space of the orbit. It h...
Lacrimal gland masses can be classified into two broad groups - inflammatory (~50%) and neoplastic, either lymphoma (25%) or salivary gland type tumours (~25%).
affects ~25% of patients with systemic disease
orbital inflammatory pseudotumour
The lacrimal nerve is the smallest branch of the ophthalmic division of the trigeminal nerve (V1).
The lacrimal nerve divides off the ophthalmic division of the trigeminal nerve (V1) just before entering the orbit through the superior orbital fissure outside and superolateral to ...
The lacrimal (or nasolacrimal) sac forms part of the nasolacrimal drainage apparatus. It is located in the preseptal part of the orbit.
The lacrimal sac lies in the lacrimal fossa on the inferomedial aspect of the bony orbit between the posterior and anterior lacrimal crests. Th...
The lacrimal sac fossa is an excavated fossa in the inferior aspect of the anteromedial orbital wall which contains the lacrimal sac. It is bounded by the anterior and posterior lacrimal crests of the maxillary and lacrimal bones, respectively. In adults, it measures approximately 8-9mm anteropo...
The lacrimomaxillary suture is a syndesmotic suture between frontal process of the maxilla and lacrimal bone in inferior aspect of anteromedial wall of the orbit approximately half way between the anterior and posterior lacrimal crests. It corresponds, internally, to the maxillary line in later...
Lagophthalmos refers to the inability of an individual to completely close the eyelids and can result in drying of the eyes and irritation and even permanent damage.
It is most commonly encountered in patients with facial nerve palsies (e.g. Bell's palsy) but can also result from scarring of th...
The lambda is the midline bony landmark where the lambdoid sutures and sagittal suture meet, between the occipital and two parietal bones. It may be a depression and therefore palpable. Accessory occiptal bones are common near the lambda, usually associated with the lambdoid sutures.
It is the ...
The lamdboid suture is the junction between the superior border of the occipital bone and the posterior borders of the right and left parietal bones.
The lamina papyracea, also known as the orbital lamina of the ethmoid bone, is the principal component of the medial wall of the orbit, and also the lateral surface of the ethmoid air cells.
superiorly with the orbital plate of the frontal bone
inferiorly with t...
Dehiscence of the lamina papyracea is an anomaly of the paranasal sinuses resulting a defect of the medial orbital wall.
There is some speculation that it might be caused by a hyperaerated ethmoid 1.
Almost all patient tend to be asymptomatic according to one...
Large vestibular aqueduct syndrome (LVAS) refers to the presence of congenital sensorineural hearing loss with an enlarged vestibular aqueduct. It is thought to be one of the most common congenital causes of sensorineural hearing loss (SNHL).
SNHL starts in childhood and...
The laryngeal cartilages form the "skeleton" of the larynx, of which there are a number:
arytenoid cartilage (paired)
cuneiform cartilage (paired)
corniculate cartilage (paired)
Laryngeal cysts can occur in any part of the larynx, but are more frequent in supraglottic locations, such as the epiglottis and vallecula. The prevalence of each location varies on different studies.
The laryngeal cysts represent a rare group, about 5%, of benign laryngeal lesio...
Laryngeal squamous cell carcinoma staging uses the TNM staging system and actual staging is subsite (see laryngeal subsites) specific for T1-3. A rough approximation for all subsites is
T1: limited to one subsite and normal cord mobility
T2: more than one subsite and impaired cord mobility (bu...
Laryngeal trauma is uncommon in the setting of external blunt or penetrating trauma. The larynx may also be injured internally, for example during endotracheal intubation.
Symptoms include hoarseness, laryngeal pain, dyspnoea, and/or dysphagia. Also, stridor, haemoptysis,...
Laryngoceles refer to dilatations of the laryngeal ventricular saccule located in paraglottic space of supraglottis.
On imaging, these lesions are generally characterised as well-defined, thin-walled, fluid or air-filled cystic lesions in the paraglottic space. The communication with the laryng...
The larynx is a continuation of the oropharynx, and extends from the epiglottis (namely the glossoepiglottic and pharyngoepiglottic folds) to the inferior aspect of the cricoid cartilage. Inferiorly, it continues as the cervical trachea.
The larynx consists of a cartilage "skele...
The lateralised internal carotid artery is an anatomic variation of the course of the horizontal internal carotid artery (ICA). It can be visualised on CT by its more posterolateral entrance to the skull base and protrusion into the anterior mesotympanum. It may result in pulsatile tinnitus.