Internal auditory canal (IAC) diverticulum, also referred to as cavitary plaque, is a 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 otos...
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).
Variations in origin...
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 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 schwannomas are uncommon compared to acoustic schwannomas and can be challenging to diagnose.
It should be noted that the term intralabyrinthine schwannoma is usually reserved for tumors that are entirely confined to the labyrinth. This, therefore, does not includ...
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...
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 ...
Intraparotid lymph nodes are a paired group of cervical lymph nodes located within the parenchyma of the parotid glands.
Among the salivary glands, only the parotid glands have their own lymphatics due to their late encapsulation during embryologic development.
Parotid nodes rec...
Intrasinus calcification is phenomenon whereby calcification is formed within the paranasal sinuses. It can occur to varying extent and lead to varying degrees of attenuation on CT. Such calcification may occur either concurrently within an opacified sinus or in an aerated sinus, depending on th...
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...
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 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 ...
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, ora...
Juvenile nasopharyngeal angiofibromas (JNA) are a rare benign but locally aggressive vascular tumor.
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 tumors 2, but are th...
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.
Kartagener syndrome is a subset of primary ciliary dyskinesia, an autosomal recessive condition characterized 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 ...
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...
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 located in the posterior wall of the laryngopharynx, slightly above the origin of the eso...
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 tumor (KT) refers to a chronic sclerosing sialadenitis of the salivary glands. Despite the term tumor, 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 as...
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
MR head: T2 axial
MR head: ...
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 usually originates from the AICA (~85%), although it can also branch from the basilar artery (~15%), ...
Labyrinthitis is inflammation of the membranous labyrinth.
Labyrinthitis can be divided according to etiology.
Labyrinthitis is a potential complication of acute otomastoiditis with spread of infection or of toxins from the middle ear to the inner ear via either the ro...
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 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 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.
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) 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 onion with multiple concen...
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, also known as large endolymphatic sac anomaly, refers to the presence of congenital sensorineural hearing loss with an enlarged vestibular aqueduct due to enlargement of the endolymphatic duct. It is thought to be one of the most common congenital causes of se...
Laryngeal carcinoma staging refers to TNM staging of carcinomas involving the supraglottic, glottic, and subglottic larynx. The vast majority of but not all applicable cases are squamous cell carcinomas. The following article reflects the 8th edition published by the American Joint Committee on ...
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...
The laryngeal saccule is a mucosa-lined sac or pouch that arises from the anterior aspect of the roof of the laryngeal ventricle. It is most prominent in newborn but involutes during childhood.
medial: false vocal cords
lateral: thyroid cartilage
Dilatation of th...
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, dyspnea, and/or dysphagia. Also, stridor, hemoptysis, s...
The laryngeal ventricle is a slitlike, mucosa-lined, space located between the true and false vocal cords. It is often seen on lateral radiographs of the neck as an air-filled space between the true and false vocal cords.
It should not be confused with the laryngeal vestibule.
The laryngeal vestibule is the part of the laryngeal cavity lying between the laryngeal inlet and vocal folds. It is found within the supraglottis. It has a wedge-shaped cross-section, its base lying anteriorly, with its apex tapering posteriorly.
anterior: tubercle of the epiglotti...
Laryngocele refers to dilatation of the saccule of the laryngeal ventricle.
On imaging, these lesions are generally characterized as well-defined, thin-walled, fluid or air-filled cystic lesions in the paraglottic space. The communication with the laryngeal ventricle is not always identified, a...
The larynx is an inferior continuation of the oropharynx. It 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 cartila...
The lateralised internal carotid artery is an anatomic variation of the course of the horizontal internal carotid artery (ICA). It can be visualized on CT by its more posterolateral entrance to the skull base and protrusion into the anterior mesotympanum. It may result in pulsatile tinnitus.
The lateral lamella is the name given to the lateral boundary of the cribriform plate. It runs vertically and joins the fovea ethmoidalis inferomedially. It is the thinnest part of the cribriform plate.
The lateral lamella needs to be assessed on pre-functional endoscopic sinu...
The lateral posterior inferior nasal nerve is a branch of the greater palatine nerve that supplies the posteroinferior nasal lateral wall.
The nerve branches off the greater palatine nerve in the greater palatine canal and exits the canal though a tiny un-named foramen in the pal...
The lateral pterygoid muscle, also known as pterygoideus externus or external pterygoid muscle, is one of the muscles of mastication.
The lateral pterygoid is a short, thick muscle, somewhat conical in form, which extends almost horizontally, posteriorly and laterally between th...
The lateral pterygoid nerves or nerves to lateral pterygoid muscle are a pair of motor branches of the anterior division of the mandibular division of the trigeminal nerve.
The two nerves divide off the anterior division and course along side the buccal nerve. Each nerve then pie...
The lateral rectus muscle is one of the 6 extraocular muscles that control eye movements. It is responsible for abduction and is the only muscle that is innervated by the abducens nerve (CN VI). It should normally measure 2.9 ± 0.6 mm.
innervation: abducens nerve (CN VI)
A mnemonic for the layers of the scalp is:
This is particularly helpful when considering the location of a scalp hematoma.
C: connective tissue
A: (galea) aponeurosis
L: loose connective tissue
Le Fort fractures are fractures of the midface, which collectively involve separation of all or a portion of the midface from the skull base. In order to be separated from the skull base, the pterygoid plates of the sphenoid bone need to be involved as these connect the midface to the sphenoid b...
Leiomyosarcomas (LMS) are extremely rare malignant neoplasms that originate from smooth muscle cells and may be considered the malignant counterpart of a leiomyoma. They are classified as a soft tissue tumor and account for ~8% of malignant soft tissue tumors 10.