Hyperparathyroidism-jaw tumor syndrome is an extremely rare condition where a gene mutation results in hyperparathyroidism in association with both benign and malignant tumors, most notably, tumors in the mandible or maxilla 2.
Approximately 200 cases have been reported in the med...
Hypertelorism refers to an abnormal increase in distance between any two organs although some authors use the term synonymously with orbital hypertelorism meaning an abnormal increase in distance between the two eyes. The article mainly focuses on the latter. The abnormality is similar to teleca...
Hyperthyroidism refers to increased production and secretion of thyroid hormone from the thyroid gland.
Hyperthyroidism is not synonymous with thyrotoxicosis, the latter referring to a clinical syndrome of excess thyroid hormone.
Hyperthyroidism may be acc...
Hypodontia refers to the congenital absence of one or more teeth.
Hypodontia is common, affecting ~15% of the population with a recognized variations in ethnicities, e.g. prevalence of 1% in indigenous Australians through to 30% in Japanese populations. There is a female preponder...
Hypoglobus refers to the inferior displacement of the globe in the orbit. It may or may not be associated with enophthalmos.
fracture of the orbital floor (most common)
silent sinus syndrome
orbital foreign bodies
The hypoglossal canal is located between the occipital condyle and jugular tubercle and runs obliquely forwards (posteromedial to anterolateral) allowing the hypoglossal nerve to exit the posterior cranial fossa.
Its proximal portion is often divided by a fibrous (sometimes ossified) septum, w...
Hypoparathyroidism results from reduced secretion of parathyroid hormone by the parathyroid glands. It results in hypocalcemia.
tetany: peripheral paresthaesia, carpopedal spasm, seizures
emotional lability, depression and anxiety, psychosis
Hypopharyngeal carcinoma staging refers to TNM staging of carcinomas originating in the hypopharynx. This system most commonly applies to squamous cell carcinomas but can also apply to rarer epithelial malignancies in the region. The following article reflects the 8th edition published by the Am...
Squamous cell carcinoma of the hypopharynx is relatively uncommon, carries the worst prognosis of any head and neck squamous cell carcinoma (HNSCC), and is a challenge to diagnose and treat.
Hypopharyngeal carcinoma is relatively uncommon representing only 10% of all proximal aerodigestive tra...
The hypopharynx or laryngopharynx forms the most inferior portion of the pharynx, being the continuation of the oropharynx superiorly and both the larynx and esophagus inferiorly.
The hypopharynx begins as the continuation of the oropharynx at the pharyngoepiglottic fold (which ...
Hypotelorism refers to an abnormal decrease in distance between any two organs although some authors use the term synonymously with orbital hypotelorism meaning an abnormal decrease in the distance between the two eyes (the eyes appear too close together). The article mainly focuses on the latte...
The clinical syndrome of hypothyroidism is marked by inadequate thyroid hormone production, resulting in a decreased rate of cellular metabolism. It may be primary, in which the dysfunction pertains to the thyroid gland itself, or secondary, due to hypothalamic or pituitary dysfunction 1.
The hypotympanum refers to the portion of the tympanic cavity lying inferior to the level of the inferior margin of the external acoustic canal (EAC).
The hypotympanum is the smallest of the three compartments that make up the tympanic cavity and is a shallow depression in the fl...
Hyrtl's fissure (also known as tympanomeningeal fissure) is a congenital infralabyrinthic fissure. It is a very rare cause of spontaneous CSF ottorhoea and meningitis.
This fissure is present in the developing fetal petrous temporal bone and is typically ossified by 24 weeks.
The ice cream cone sign may refer to:
the appearance of the head of malleus and the body and short process of the incus on axial CT scan: failure of this normal configuration suggests incudomalleolar dysarticulation
the ball of the ice cream is formed by the head of the malleus and cone is for...
Idiopathic orbital inflammation (IOI), also known as orbital pseudotumor and non-specific orbital inflammation, is an idiopathic inflammatory condition that most commonly involves the extraocular muscles. Less commonly there is inflammatory change involving the uvea, sclera, lacrimal gland, and ...
IgG4-related disease (IgG4-RD) is a systemic disease that is characterized by extensive IgG4-positive plasma cells and T-lymphocyte infiltration of various organs.
This condition has been known by many other names in the past, such as IgG4-related sclerosing disease, IgG4-related s...
Incidental thyroid nodules, sometimes called thyroid incidentalomas, are discrete lesions in the thyroid gland found on cross-sectional imaging performed for indications other than thyroid evaluation. They are common but occasionally represent thyroid cancer 1. This article discusses the epidemi...
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 incudomalleolar joint, also known as the incudomallear joint, is the joint between the incus and the malleus. The joint is part of the chain of ossicles sending vibrations from the tympanic membrane to the oval window.
dislocations of the joint result in hearing loss
The incudostapedial joint is the articulation between the incus and stapes bones in the middle ear. It is one of the three joints in the ossicular chain.
The incus (plural: incudes) is the middle of the three ossicles articulating with the head of the malleus anteromedially, forming the incudomalleolar joint, and the stapes inferomedially, forming the incudostapedial joint.
Named parts include:
a body which articulates with the head of the mall...
Infantile cervical ligament edema 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 anterio...
Infantile hemangiomas are benign vascular neoplasms that are the most common head and neck tumors 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...
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, located in the pteryogomandibular space of the oral cavity/masticator space.
The inferior alveolar nerve divides ...
Inferior alveolar nerve injuries are most common iatrogenic post third mandibular molar extraction although they can occur post dental implant or in mandibular fractures. This article is focused on iatrogenic injuries.
The incidence of inferior alveolar nerve injuries after third...
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 laryngeal artery accompanies the recurrent laryngeal nerve into the larynx, where it anastomoses with the superior laryngeal artery to supply the muscles and mucous membranes of the larynx 1.
origin: branch of the inferior thyroid artery
course: ascends the trachea to en...
The inferior longitudinal muscle of the tongue is one of the four intrinsic muscles of the tongue, which alter the shape of the tongue mass, being entirely confined to the tongue without any extraglossal attachment (cf. extrinsic muscles of the tongue).
The muscles fibers attach ...
The inferior meatus (plural: 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, and Woodruff plexus is located posteriorly.
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 extraocular 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 exte...
The inferior ophthalmic vein (IOV) is a vein of the inferior orbit and is smaller than the more well-known superior ophthalmic vein (SOV).
The vein forms from a plexus of several veins within the anteroinferior orbit along the infraorbital margin from facial vein tributar...
Mnemonic for the contents of the inferior orbital fissure (from medial to lateral) is:
Inferior Orbit Gets Infra-Orbital Nerves and VeinZ
Inferior Orbit Gets Infra-Orbital Nerves and VeinZ
IO: inferior ophthalmic vein (tributary to both pterygoid venous plexus and cavernous sinus)
The inferior pharyngeal constrictor muscle is one of the pharyngeal constrictor muscles. It has a sphincteric function, and physiologically is usually in a tonic state, constricting the distal end of the pharynx (in coordination with the superior pharyngeal constrictor and the middle pharyngeal ...
The inferior rectus muscles is one of the six extraocular 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 depr...
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 inferior thyroid vein, along with the superior and middle thyroid veins contribute to the drainage of the thyroid venous plexus on the anterior surface of the thyroid 1.
After arising from the venous plexus, the left inferior thyroid vein passes downwards to join the left bra...
Inferior turbinate hypertrophy is one of many causes of nasal obstruction and can be a contributing factor to obstructive sleep apnea.
allergic rhinitis (most common)
Treatment and prognosis
Pharmacological treatment (e.g. topic...
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 canal is a bony canal within the maxillary bone located at the anterior aspect of the orbital floor. It transmits the infraorbital nerve, which is a branch of the maxillary division of the trigeminal nerve (CN Vb), as well as the infraorbital artery and vein. The canal commences...
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 of the face 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 is...
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.
Fish bones are more commonly ingested than chicken or pork bones. Patie...
The inion (plural: inia/inions) is the tip of the external occipital protuberance (EOP), the midline bony prominence in the occipital bone from which the ligamentum nuchae and trapezius muscle attach. It is usually easily palpable.
It is the surface marking of the internal attachment of the ten...
The inner ear refers to the bony labyrinth, the membranous labyrinth and their contents. It may also be referred to as the vestibulocochlear organ, supplied by the vestibulocochlear nerve (CN VIII). It is divided into three main parts:
the cochlea housing the cochlear duct for hearing
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...
The internal acoustic canal (IAC), also known as the internal auditory canal or meatus (IAM), is a bony canal within the petrous portion of the temporal bone that transmits nerves and vessels from within the posterior cranial fossa to the auditory and vestibular apparatus.
An internal auditory canal (IAC) diverticulum or notch, also known as cupping of the internal auditory canal, is a small focal outpouching arising from the anterolateral wall of the internal acoustic canal (IAC). This is a benign normal variant and distinct from, although may occur in conjunctio...
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 carotid artery (ICA) is a terminal branch of the common carotid artery.
It arises most frequently between C3 and C5 vertebral level, where the common carotid bifurcates to form the internal carotid and the external carotid artery (ECA). Just superior to its ...
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 laryngeal nerve is one of the two branches of the superior laryngeal nerve and provides sensory innervation of the laryngeal mucosa down to the level of the vocal cords (supraglottic larynx).
origin: arises as the larger of the two branches of the superior laryngeal nerve...
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 interzygomatic line is a commonly used reference standard for the evaluation of proptosis due to various etiologies on CT/MRI scans.
A horizontal line should be drawn between the most anterior parts of the zygomatic bones in the axial plane.
The normal distance of the interzygom...
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 leukemia
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...
Intracranial lipomas are not tumors as such, but rather a result of abnormal differentiation of embryologic meninx primitiva. They are frequently associated with abnormal development of adjacent structures.
Intracranial lipomas are congenital lesions and as such are found at any a...
Intraductal papilloma of salivary gland (also known as an inverted ductal papilloma or sialadenoma papilliferum) is a benign relatively rare salivary gland tumor. '
They typically arise in adulthood and there may be a slight male predilection.
They may show a character...
Intralabyrinthine hemorrhage is bleeding within the labyrinth of the inner ear and is a rare cause of sudden onset sensorineural hearing loss and vertigo 1.
The incidence of intralabyrinthine hemorrhage is not known, and may be underdiagnosed due to its rarity and difficulty to d...
Intralabyrinthine schwannomas, schwannomas that arise within the membranous labyrinth (cochlea, vestibule, or semicircular canals), are uncommon compared to vestibular schwannomas and can be challenging to diagnose.
It should be noted that the term intralabyrinthine schwannoma is u...
Intraocular lens implants (IOLs) are used to replace the extracted lens as part of the standard surgical treatment for cataracts. The presence of a lens implant is known as pseudoaphakia.
Knowledge of the structure of an intraocular lens implant is required to ensure accurate identif...
Intra-ocular silicone oil has been used as a vitreous replacement and for internal tamponade of complex retinal detachments.
Some reported side effects include glaucoma and corneal decompensation 1.
Hyperatteunating on unenhanced CT with a reported average CT unit va...
Intraosseous meningioma, also referred to as primary intraosseous meningioma, is a rare subtype of meningioma that accounts for less than 1% of all osseous tumors. They are the most common type of primary extradural meningiomas 6.
It is important to note that it has been argued by ...
The intraparotid lymph nodes are groups of cervical lymph nodes located within the parenchyma of each of the parotid glands.
Among the salivary glands, only the parotid glands have their own internal lymph nodes due to the late encapsulation of the parotids during embryologic dev...
Intrasinus calcification is a phenomenon whereby calcification is formed within the paranasal sinuses. It can occur to varying extents, therefore leading to varying degrees of attenuation on CT. Such calcification may occur either concurrently within an opacified sinus or in an aerated sinus, de...
Intratonsillar abscesses, or simply tonsillar abscesses, are uncommon complications of tonsillitis in which pus accumulates focally in the parenchyma of the tonsil (within the capsule).
They can occur in both children and adults, but their incidence is not well-defined. In a recen...
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...
Iodide mumps is a rare delayed adverse reaction to iodinated contrast media.
It presents within 1 to 12 hours after contrast administration, with painless parotid and submandibular swelling. Both ionic and non-ionic contrast agents can cause these reactions, but about 90% of the cases occur wit...
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...
Iodine (chemical symbol I) is one of the trace elements. Its biological importance is its central place in the physiology of the thyroid gland and, in radiology, as the key chemical constituent of most of the radiographic, fluoroscopic, and CT contrast media.
Iodine-123 (I123 or I-123) 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
standard scan: 3.7-14.8 MBq (100-400 μCi) PO, image at 4-6 or 24 hours
thyroid cancer scan: 55.5 MBq ...
Iodine-131 (131I or I-131) is a radioisotope of iodine, which is used in the diagnosis and treatment of thyroid lesions. It is one of the oldest radiotracers used in nuclear medicine, in use for over 50 years. It is predominately used in thyroid ablation therapy, for patients post-thyroidectomy...
The iris (plural: irises or irides) is a pigmented muscular structure which modifies the amount of light entering the eye, by controlling the size of the pupil, its central aperture.
location: between the anterior and posterior chambers of the globe
function: controls the amount of l...
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....
Isthmus (plural isthmi) is an anatomical term and refers to a slender structure joining two larger components. Some of these uses of the word isthmus are now rarely used or only seen in older texts and articles:
isthmus (auditory tube)
isthmus (auricle of the ear)
Jacobson nerve is the eponymous name of the tympanic branch of the glossopharyngeal nerve (CN IX) and arises from the inferior ganglion of the glossopharyngeal nerve. It also carries preganglionic parasympathetic fibers, from the inferior salivary nucleus, which eventually enter the otic ganglio...
Jaffe-Campanacci syndrome is characterized by:
multiple non-ossifying fibromas of the long bones and jaw
café au lait spots
hypogonadism or cryptorchidism
giant cell granuloma of the jaw