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
Inner ear malformations are a spectrum of congenital anomalies involving the inner ear structures with an emphasis on the cochlea due to their implications for sensorineural hearing loss.
An imaging-based classification was first proposed in 1987 by Jackler et al. according to p...
A useful mnemonic to remember innervation of the muscles of the middle ear is:
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.
T: tensor tympani is supplied by a...
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 ...
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 ...
Internal carotid artery (ICA) dissection, like arterial dissection elsewhere, is a result of blood entering the media through a tear in the intima 1 and is a common cause of stroke in younger patients.
Dissection may occur at any age but is a common cause of stroke in young patien...
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.
International Frontal Sinus Anatomy Classification (IFAC) result from an expert consensus, developed to improve the ability of the surgeon to understand the possible variations of the frontal recess and frontal sinus anatomy.
anterior cells: push the drainage pathway of the fron...
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 pseudophakia (literally, "artificial lens").
Knowledge of the structure of an intraocular lens implant is requi...
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, representing an uncommon sinonasal tumor that mostly affects middle-aged men. On imaging, they classically demonstrate a convoluted cerebriform pattern seen on both T2 and contrast-enhanced T1 weighted MRI images.
The term ...
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
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...
Jugular bulb diverticulum refers to a protrusion of the jugular bulb with waist-like margin, which can occur with or without jugular bulb dehiscence.
The prevalence on imaging series ranges 1-8% 1,2.
Many patients are asymptomatic, but jugular bulb diverti...
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 recognized 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 tumor 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 tumors 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 anteromedially and pars vascularis posterlaterally. It is an important landmark, as masses of the jugular foramen (e.g. glomus jugulare) may erode the jugular spine, helping distingu...
The jugular trunks are small short paired lymphatic trunks, each one draining one side of the head and neck, forming an important terminal part of the lymphatic system 1-3.
the left and right jugular trunks are found in the root of the neck
the organs of the he...
The jugulodigastric lymph nodes, also known as subdigastric lymph nodes, are deep cervical nodes located below the posterior belly of the digastric muscle and anterior to the internal jugular vein.
They are located in neck node level IIa and receive lymphatic drainage from the tonsils, pharynx,...
Juvenile nasopharyngeal angiofibromas are a rare benign, but locally aggressive, vascular tumors that occur almost exclusively in young men.
On imaging, they present as a vividly enhancing soft-tissue masses centered on the sphenopalatine foramen. Given its vascularity, prominent flow voids ar...
Staging of juvenile nasopharyngeal angiofibromas is performed with cross-sectional imaging and relies on the identification of local tumor extent, and invasion of adjacent spaces. For a discussion of this entity please refer to the parent article: juvenile nasopharyngeal angiofibroma.
Juvenile recurrent parotitis (JRP) is a form of recurrent inflammatory parotitis occurring in childhood.
JRP is considered the second most common cause of parotitis in childhood and commonly begins between 3 and 6 years of age.
Multiple episodes of parotid...
Kartagener syndrome (also known as Kartagener-Afzelius syndrome) is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterized by abnormal ciliary structure or function, leading to impaired mucociliary clearance.
The prevalence of primary ciliary dyski...
Kayser-Fleischer rings, sometimes shortened to K-F rings, are caused by copper deposition in the cornea and are a specific, clinical sign of Wilson disease.
They are usually brown or dark reddish in color. Early on they may need a slit lamp to be visible before they becom...
Keratosis obturans is a rare external auditory canal (EAC) disease characterized 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 for EAC cholesteatoma but they are completely different entities ...
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...
Keutel syndrome is an extremely rare inherited condition characterized by
cartilage calcification which include
trachea - with resultant tracheobronchial stenosis
pulmonary arterial stenoses
brachytelephalangism (short fingers and nails that resemble drumsticks)
Kiesselbach plexus (Kiesselbach 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 artery...
The Killian dehiscence is a triangular-shaped area of weakness in the muscular wall of the pharynx, between the transverse and oblique bundles of the inferior pharyngeal constrictor 1. It is the most common site of pharyngeal diverticula 5.
It is located in the posterior wall of ...
Kimura disease, also known as eosinophilic hyperplastic lymphogranuloma, 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 ...
The term kissing carotids refers to tortuous and elongated vessels which touch in the midline. They can be found in:
within the pituitary fossa
within sphenoid sinuses
within sphenoid bones
The significance of kissing carotids is two-fold:
may mimic intrase...
Klaus height index is the distance between tip of the dens and the tuberculum torcula line (Twining's line) 1,2. A normal height is 40-41 mm.
A decreased Klaus height index is seen in basilar invagination.
The Koerner 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.
K-TIRADS is a reporting system designed by the Korean Society of Thyroid Radiology for ultrasound assessment of thyroid nodules and stratification of the requirement for FNA and malignancy. There is also stratification of indications for lymph node sampling.
This is a five-stage system using de...
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 tumor (KT) refers to a chronic sclerosing sialadenitis. Despite the term tumor, it is a non neoplastic condition. It is classically described in relation to the submandibular gland but less commonly can also affect the other salivary glands 9 and occasionally also the lacrimal gland 6.
This article lists a series of labeled imaging anatomy cases by system and modality.
CT head: non-contrast axial
CT head: non-contrast coronal
CT head: non-contrast sagittal
CT head: angiogram axial
CT head: angiogram coronal
CT head: angiogram sagittal
CT head: venogram axial
The labyrinth can refer to:
labyrinth of the inner ear
labyrinth of the ethmoid bone
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 also vascularizes the VII and VIII cranial nerves.
It usually originates from the AICA (~85%), althou...
Labyrinthitis is inflammation of the membranous labyrinth.
Labyrinthitis can be divided according to etiology.
Labyrinthitis is a potential complication of acute otomastoiditis with the spread of infection or of toxins from the middle ear to the inner ear via either th...
Labyrinthitis ossificans, 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, and may sometimes be associa...
The labyrinth or lateral mass of the ethmoid bone consists of a number of thin-walled cellular cavities, the ethmoidal air cells, arranged in two groups: anterior and posterior, and interposed between two vertical plates of bone; the lateral plate forms part of the orbit, the medial, part of the...
The labyrinth of the inner ear is the combined sensory organ of hearing and balance and its surrounding bony cavity located in the petrous temporal bone, consisting of two components:
the osseous labyrinth, the bony cavity, which houses
the membranous labyrinth, a tubular sac filled with endol...
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 tumors (~25%).
affects ~25% of patients with systemic disease
orbital inflammatory pseudotumor
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. It...
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 8-9 mm anterop...
Lacrimal sac masses are very uncommon and more commonly have a malignant (~80%) rather than benign (~20%) etiology.
granulomatosis with polyangiitis
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.
most common in facial nerve palsies (e.g. Bell palsy)
trauma/surgery: scarring of the eyelids 1 (cicatric...
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. It normally fuses at approximately 26 years of age.
The term lamellated (or laminated which means the same thing) is a radiopathological term used to describe the layered appearance of many calculi, including those of the renal tract, the salivary glands, and the biliary tree. The internal structure of these calculi has been likened to that of an...