The 2005 WHO histological classification of odontogenic tumors lays out a classification system for neoplasms and other tumors related to the odontogenic apparatus. At the time of writing (2016), it is still the most widely used classification system although a new revision is due to come up in ...
Aberrant internal carotid artery is a variant of the internal carotid artery (ICA) and represents a collateral pathway resulting from involution of the normal cervical portion (first embryonic segment) of the ICA 5.
There is consequent enlargement of the usually small collaterals...
Abscesses are focal confined collections of suppurative inflammatory material and can be thought of as having three components 1:
a central core consisting of necrotic inflammatory cells and local tissue
peripheral halo of viable neutrophils
surrounded by a 'capsule' with dilated blood vessel...
Accessory maxillary ostia are a common anatomic variant, and are usually found incidentally on CT scans of the paranasal sinuses. Accessory ostia of the maxillary sinus are common, occurring in up to 40% patients 1. No significant association has been found between the presence of accessory osti...
The accessory meningeal artery is a branch of the maxillary artery but can also branch from the middle meningeal artery.
The artery passes upwards through the foramen ovale to supply the trigeminal ganglion and the dura mater of Meckel cave and the middle cranial fossa. It also usually supplies...
Accessory parotid glands are a normal variant and represent ectopic salivary tissue separate from, but usually in close proximity to, the main parotid glands.
Accessory parotid glands are commonly picked up incidentally on ultrasound; seen in ~20% of the general population 2.
The parietal and occipital bones in particular are common regions for accessory sutures because of their multiple ossification centers.
It is important to know these anatomic variations, mainly on the head trauma image studies in children, where it could be difficult to differentiate non-depres...
Achondroplasia is the most common cause of short-limb dwarfism. (For a general discussion, see the generic article on achondroplasia.)
As the skull base forms by endochondral ossification whereas the skull vault by membranous ossification, there is a marked discrepancy in relative size as the s...
Acinic cell carcinomas of the salivary glands are rare malignant neoplasms that account for 1-3% of all salivary gland tumors.
Pathology may superficially resemble normal serous (acinar) cells of the salivary glands. It is considered a low-grade, indolent malignancy, but with a tend...
Acoustic neuromas, also known as vestibular schwannomas, are relatively common tumors that arise from the vestibulocochlear nerve (CN VIII) and represent ~80% of cerebellopontine angle masses. Bilateral acoustic schwannomas are strongly suggestive of neurofibromatosis type 2 (NF2).
On imaging, ...
Acquired cholesteatomas make up 98% of all middle ear cholesteatomas and are almost always closely related to the tympanic membrane, from which most are thought to arise.
The vast majority of acquired cholesteatomas develop as a result of chronic middle ear infection and...
Acrocephalopolysyndactyly (ACPS) syndrome is comprised of a rare group of disorders collectively characterized by:
calvarial anomalies: e.g. craniosynostoses
digital anomalies: syndactyly and polydactyly
While there can be some overlap in features, they can be primarily classified into the fo...
Acrocephalosyndactyly syndromes (ACS) are a rare group of disorders collectively characterized by:
calvarial anomalies, e.g. craniosynostoses
digital anomalies, e.g. syndactyly
While there can be some overlap in features, they can be primarily classified into the following maj...
ACR TI-RADS is a reporting system for thyroid nodules on ultrasound proposed by the American College of Radiology (ACR) 1.
This uses a standardized scoring system for reports providing users with recommendations for when to use fine needle aspiration (FNA) or ultrasound follow-up of suspicious ...
Acute invasive fungal sinusitis is the most aggressive form of fungal sinusitis. It is seen particularly in immunocompromised patients and is the source of significant morbidity and mortality. It should be distinguished from the other two forms of invasive fungal sinusitis, chronic invasive fung...
Acute mastoiditis refers to a suppurative infection of the mastoid air cells. It is the most common complication of acute otitis media.
In acute otitis media, an inflammatory middle ear effusion is present that can freely move into the mastoid air cells. Consequently, some authors ...
Acute otitis externa (AOE), also known as "swimmer's ear", is inflammation of the external auditory canal (EAC) that can involve the pinna as well. Bacterial infection, most commonly with Pseudomonas aeruginosa, is responsible for the overwhelming majority of cases. It is a common condition.
Acute sinusitis (rare plural: sinusitides) is an acute inflammation of the paranasal sinus mucosa that lasts less than four weeks and can occur in any of the paranasal sinuses. If the nasal cavity mucosa is also involved then the term rhinosinusitis may be used.
Adenocarcinoma of the lacrimal glands is rare, with few cases reported in the literature since it was first described in 1996 1. Primary adenocarcinoma of the lacrimal gland is extremely rare; only 9 cases have been reported in the literature 1,2. It can be classified into high- and low-grade ma...
Adenoidal hypertrophy or enlargement is common in childhood and is due to an increase in the size of the adenoids.
nasal congestion: adenoid facies
chronic or recurrent otitis media due to their proximity to the Eustachian tubes
Adenoid cystic carcinomas are a rare histological subtype of adenocarcinoma.
Adenoid cystic carcinomas are generally considered low grade 4. The tumors have a notable tendency for perineural spread.
They have a wide distribution and mainly occur in relation to the airways,...
Adenoid cystic carcinoma (ACC) of the lacrimal glands is an extraconal malignancy usually originating from the orbital lobe of the lacrimal gland.
It often presents with orbital pain and paresthesia, since this type of tumor is frequently associated with perineural spread...
Adenoid cystic carcinoma (ACC) of the salivary glands is the most common malignancy involving the minor salivary glands and the second most common malignancy involving the parotid gland.
Adenoid cystic carcinomas arise more commonly in the minor salivary glands (~55%) than in the maj...
Adenoid facies, also known as the long face syndrome, refers to the long, open-mouthed face of children with adenoid hypertrophy. Hypertrophy of the nasopharyngeal pad of lymphoid tissues (adenoids) is the most common cause of nasal obstruction in children. The mouth is always open because upper...
The adenoid tonsils, or often just simply the adenoids, (also known as the nasopharyngeal or pharyngeal tonsils) are paired foci of lymphatic tissue located on the superoposterior wall of the nasopharynx and form part of Waldeyer's ring.
Adenolipoma of the thyroid gland (also known as a thyrolipoma or a thyroid hamartoma) is a rare, benign fat-containing thyroid lesion. These lesions are usually well encapsulated and are composed of varying degrees of follicular thyroid tissue (thyroid adenoma) and mature adipose tissue; the amo...
Adenomatoid odontogenic tumors are rare and differ from most other dentition related lesions in that they more frequently occur in the maxilla.
They are also seen more frequently in females, most frequently in the second decade of life.
They present as an e...
Adhesive otitis media is a form of chronic otitis media where there is a adhesion of medial ear structures as a result of chronic inflammation. There are often complete or partial adhesions between the thin retracted and atrophic pars tensa and the medial wall of the middle ear.
Adrenal vein sampling (AVS) is a procedure where blood is collected from the adrenal veins via catheter to confirm autonomous hormone production, if it is unilateral or bilateral, and to guide further treatment.
AVS is commonly performed in primary aldosteronism, being indicated to ...
Cervical lymphadenopathy in an adult can result from a vast number of conditions. They include:
from head and neck tumors
other neoplastic lesions
Agger nasi air cells are the most anterior ethmoidal air cells lying anterolateral and inferior to the frontal recess and anterior and above the attachment of the middle turbinate. They are located within the lacrimal bone and therefore have as lateral relations the orbit, the lacrimal sac and t...
AIDS-defining illnesses are conditions that in the setting of a HIV infection confirm the diagnosis of AIDS, and do not commonly occur in immunocompetent individuals 2. According to the CDC surveillance case definition 1, they are:
bacterial infections: multiple or recurrent
The alar fascia is a thin fibroareolar membrane separating the (anterior) true retropharyngeal space from the (posterior) danger space.
Notably, in the well patient, the alar fascia is not usually visible on cross-sectional imaging, and the two spaces are typically identified as a single space....
Allergic fungal sinusitis is the most common form of fungal sinusitis and is common in warm and humid climates. On imaging, it usually presents as opacification and expansion of multiple paranasal sinuses, unilaterally or bilaterally, with content that is centrally hyperdense on CT. MRI shows T2...
Allgrove syndrome (also known as triple A syndrome) is an autosomal recessive condition that consists of three main findings:
Alport syndrome is an X-linked dominant disease characterized by progressive sensorineural hearing loss, renal disease and, at times, ocular lesions.
sensorineural hearing loss: typically high frequency 2
anterior lenticonus: most common ...
Amaurosis fugax is the transient monocular loss of vision, normally lasting a few seconds to a few minutes, secondary to vascular ischemia or insufficiency.
It has an incidence of 50,000 per year in the United States.
Patients present with transient monoc...
Ameloblastic fibromas appear as unilocular lucent mandibular lesions, most frequently in the posterior mandible, and are usually associated with impacted teeth, centered on the unerupted crown. They, therefore, appear very similar to unilocular ameloblastomas. They are composed of enamel and emb...
Ameloblastic fibro-odontoma (AFO) is a rare benign mixed odontogenic tumor that usually arises in the maxilla and mandible. According to the 2005 WHO classification of odontogenic tumors, it is defined as a benign tumor that resembles ameloblastic fibroma but contains enamel and dentin.
Ameloblastomas are locally aggressive benign tumors that arise from the mandible, or, less commonly, from the maxilla. Usually present as a slowly but continuously growing hard painless lesion near the angle of the mandible in the 3rd to 5th decades of life, which can be severely disfiguring if ...
The American Dental Association Universal Numbering System is a tooth notation system primarily used in the United States.
Teeth are numbered from the viewpoint of the dental practitioner looking into the open mouth, clockwise starting from the distalmost right maxillary teeth.
Anaplastic thyroid cancer staging refers to TNM staging of anaplastic thyroid carcinomas. Papillary, follicular, and medullary thyroid carcinomas are staged separately. The following article reflects the 8th edition manual published by the American Joint Committee on Cancer, which is used for st...
Anaplastic thyroid carcinoma is a highly aggressive form of thyroid cancer and accounts for ~1-2% of primary thyroid malignancies. Of all the subtypes, this carries the worst prognosis.
Typically occurs in the elderly (peak incidence in 6th to 7th decades). A significant proportio...
The anatomy curriculum is one of our curriculum articles and aims to be a collection of articles that represent the core anatomy knowledge for radiologists and imaging specialists.
Head and neck anatomy
Abdominal and pelvic anatomy
The angular artery is the terminal branch of the facial artery.
It becomes the angular artery after the lateral nasal artery branch from the facial artery. It courses superiorly along the lateral border of the external nose to the medial canthus. It is accompanied by the angular vein which drai...
The angular vein drains the anterior region of the scalp 1. It is formed by the union of the supratrochlear and supraorbital veins and becomes the facial vein 1,2,3.
The angular vein is formed at the medial canthus as the supratrochlear vein and supraorbital vein unite 1,2. The a...
Aniridia refers to either the clinical sign of a complete/partial absence of the iris, or more specifically to the disease entity classic aniridia. Rarely other genetic conditions may cause this sign.
Classic aniridia is inherited as an autosomal dominant condition and is seen in ...
Anisocoria is present when an individual's pupils differ in size. If a person's pupils are symmetric there is said to be isocoria.
The prevalence of transient physiological anisocoria of >0.4 mm is found in up to 20% population. However persistent anisocoria seems to be rarer, in ...
The annular ligament can refer to:
annular ligament of the stapes
annular ligament of the proximal radio-ulnar joint
Anorexia nervosa is a psychiatric disorder characterized by distorted self-perception of body weight leading to starvation, obsession with remaining underweight, and an excessive fear of gaining weight. One in five patients with anorexia dies, due to complications of the disease.
The ansa cervicalis (or ansa hypoglossi, an archaic synonym) is a component of the cervical plexus which gives muscular branches to the geniohyoid muscle of the suprahyoid group and most of the infrahyoid (strap) muscles (excluding the thyrohyoid muscle).
superior root: d...
The anterior cervical space is a small infrahyoid compartment of the head and neck. It is a fat containing space and is not enclosed by fascia 1.
posterior: carotid space
medial: visceral space
superior: submandibular space
The anterior commissure of the larynx is the anterior junction point of the true vocal cords. It is bounded anteriorly by the thyroid cartilage and is part of the laryngeal glottis.
The anterior cranial fossa constitutes the floor of cranial vault which houses the frontal lobes of the brain.
Structures present in the midline of anterior cranial fossa from anterior to posterior are:
groove for superior sagittal sinus
groove for anterior meningeal vessels
The anterior division of the mandibular division of the trigeminal nerve has four branches, which are all motor branches except one. The four branches are:
deep temporal nerves
lateral pterygoid nerves
The anterior epitympanic recess, also known as the supratubal recess, is a small discrete space in the epitympanum anterior to the malleus. It is separated from the epitympanum proper by the anterior attic bony plate, also known as the cog, which has its orientation in the coronal anatomical pla...
The anterior ethmoid artery is a branch of the ophthalmic artery. It supplies the anterior and middle ethmoidal sinuses, frontal sinus, the lateral nasal wall and the nasal septum (see nasal cavity).
It traverses the anterior ethmoidal foramen with the anterior ethmoidal nerve (w...
The anterior ethmoidal nerve is an extraconal branch of the nasociliary nerve, a branch of the ophthalmic division of the trigeminal nerve. Some authors describe it as either the terminal branch or a direct continuation of the nasociliary nerve. It branches off distal to the infratrochlear nerv...
The anterior jugular vein is a paired tributary of the external jugular vein.
It arises beneath the chin in the region of the hyoid bone or suprahyoid neck.
Origin and course
The anterior jugular vein has its origin as the confluence of several small superficial subma...
The anterior lacrimal crest is a bony projection on the frontal process of the maxilla continuous with the orbital rim which creates the lateral margin of the lacrimal sac fossa. The medial palpebral ligament is attached to anterior lacrimal crest.
Immediately anterior to the anterior lacrimal ...
The anterior (or external) nares (singular: naris) (or nostrils) form the entrance to the nose. Each naris is formed by a ring of structures:
medially the columella (soft tissue anteroinferior portion of the nasal septum)
laterally and superiorly the nasal ala
inferiorly the nasal sill
The anterior superior alveolar canal courses through the anterior wall of the maxillary sinus, and contains the anterior superior alveolar nerve, artery and vein. Usually, it shares a common channel with the infraorbital canal but when seen separately should not be confused for a fracture.
The anterior superior alveolar nerve, also known as the anterior superior dental nerve, is the third branch of the infra-orbital nerve, from the maxillary division of the trigeminal nerve. It is the largest of the superior alveolar nerves and contributes to the superior dental plexus.
The anterior triangle forms the anterior compartment of the neck and is separated from the posterior triangle by the sternocleidomastoid muscle. The triangles of the neck are surgically focused, first described from early dissection-based anatomical studies which predated cross-sectional anatomi...
The anterior tympanic artery is the second named branch of the first part of the maxillary artery. The vessel passes through the petrotympanic fissure to supply the lining of the middle ear and accompanies the chorda tympani in its course.
Antrochoanal polyps (ACP) are solitary sinonasal polyps that arise within the maxillary sinus. They pass to the nasopharynx through the sinus ostium and posterior nasal cavity, enlarging the latter two.
Similar, less common, polyps can arise in the sphenoid sinus extending into the nasopharynx:...
An antrolith is a calcified mass within the maxillary sinus. The origin of the nidus of calcification may be extrinsic (foreign body in sinus) or intrinsic (stagnant mucus, fungal ball).
Most antroliths are small and asymptomatic. Larger ones may present as a chronic maxillary sinusitis with sy...
Aphakia (less commonly aphacia) is the absence of the lens from the ocular globe.
surgical removal of a cataract (commonest cause)
Treatment and prognosis
Surgical insertion of an intraocular lens implant, in which case the aphakic appearance is calle...
Ariboflavinosis is the term given to riboflavin (vitamin B2) deficiency.
Ariboflavinosis has been seen in both developed and developing countries, and across the socioeconomic spectrum. It is usually present in the context of other hypovitaminoses.
It has been found to more comm...
Arnold's nerve is the auricular branch, also known as the mastoid branch, of the vagus nerve (CN X).
Origin and course
Arnold's nerve originates from the superior ganglion of the vagus nerve and also has a small contribution from the inferior ganglion of the glossopharyngeal nerve. It ascends ...
Arrested pneumatization of the skull base is an anatomical variant that most commonly occurs in association with the sphenoid sinus. It is known that the sphenoid bones undergo early fatty marrow conversion antecedent to normal pneumatization. However, for unclear reasons, some individuals exper...
The arteries of the head and neck are branches of the common carotid and subclavian arteries.
common carotid artery
internal carotid artery (segments)
persistent stapedial artery
AI TI-RADS (Artificial Intelligence Thyroid Imaging Reporting and Data System) is a data-driven analysis and revision of the 2017 ACR TI-RADS 1. Published in May 2019 2, this had the intention of simplifying categorization and improving specificity while maintaining high sensitivity. This system...
The aryepiglottic folds are two ligamentomuscular structures within the supraglottic larynx that function to protect the airway when swallowing.
Each aryepiglottic fold is comprised of the superior ligamentous edge of the quadrangular membrane and covering mucous membrane 1, the ...
The arytenoid cartilages are paired hyaline cartilages that articulate with the sloping upper border of the lamina of the cricoid cartilage by the cricoarytenoid joint. This joint allows movement of the arytenoid cartilages, which is vital in approximating, tensing and relaxing the vocal folds.
The ascending cervical artery is 1 of the 4 branches of the thyrocervical trunk (off the first part of the subclavian artery).
It is a small artery that ascends medial to the phrenic nerve on the prevertebral fascia. It contributes many small spinal branches into the intervertebral foramina of ...
The ascending pharyngeal artery, the smallest branch of the external carotid artery, is a long, slender vessel, deeply seated in the neck, beneath the other branches of the external carotid and under the stylopharyngeus.
origin: a branch of the external carotid artery
Aspergillus flavus is a fungus and one of the species of Aspergillus that is common in the environment and responsible for pathology in humans.
It is the second most common cause of pulmonary aspergillosis (after Aspergillus fumigatus) and can additionally cause corneal, otomycotic, and nasoorb...
Assessment of thyroid lesions is commonly encountered in radiological practice.
hyperplastic / colloid nodule / nodular hyperplasia: 85%
papillary: 60-80% of carcinomas
Ultrasound along with nuclear medicine, is an important modality for assessment of thyroid lesions, and it is also frequently used to guide biopsy. Diagnostic criteria for thyroid nodules continue to evolve with improving ultrasound technology.
The asterion is the junction on the side of the posteroinferior calvarium where three sutures meet:
It represents the site of the closed mastoid fontanelle. It is located at the posterior end of the parietotemporal suture, whereas ...
Asteroid hyalosis is a degenerative condition of the eye where there is an accumulation of calcium soaps in the vitreous chamber.
The prevalence increases with age from 0.2% in 43-54-year-olds to 2.9% in 75-86-year-olds. The overall prevalence is 1.2%. It is more commonly unilater...
Asymmetric pneumatization of petrous apex results in asymmetric fatty bone marrow within the petrous apex. It is a common incidental finding on brain and skull base MRI.
Asymmetric pneumatization of the petrous apex results in the presence of bon...
The American Thyroid Association (ATA) guidelines for assessment of thyroid nodules are meant to improve inter- and intra-reader consistency during assessment of thyroid nodules on ultrasound, and to facilitate communication with referring endocrinologists.
The 2015 guidelines stress the import...
The atlantodental interval (ADI), as the name suggests, is the horizontal distance between the anterior arch of the atlas and the dens of the axis, used in the diagnosis of atlanto-occipital dissociation injuries and injuries of the atlas and axis.
It is the distance (in mm) between the posteri...
This mnemonic helps when remembering the ascending order of structures that correspond to each waveform in an auditory brainstem response (ABR) tracing:
E: eighth nerve action potential (wave I)
C: cochlear nucleus (wave II)
O: olivary complex (superior) (wave III)
An auricular pseudocyst is a rare and benign cystic swelling resulting from intracartilaginous accumulation of fluid within the pinna.
While it can occur at any age and in either gender, it typically presents in middle aged males with a mean age of presentation being around 35-40 ...
The auriculotemporal nerve is a sensory branch of the posterior division of the mandibular division of the trigeminal nerve.
The auriculotemporal nerve divides posteriorly from the posterior division of the mandibular division before dividing into two roots separate to encircle t...
Autoatticotomy denotes extensive pathological (cf. surgical atticotomy) destruction of the attic (epitympanum), most commonly due to cholesteatoma. It is an early stage prior to a more extensive process of destruction known as automastoidectomy.
Autoimmune thyroiditis (plural thyroiditides) (AIT) refers to a group of conditions where there is inflammation of the thyroid gland secondary to thyroid autoantibodies.
They are the most common thyroid disease group in the pediatric population 5.
Entities that fall un...
Automastoidectomy denotes extensive bone destruction of the mastoid mimicking the appearance of surgery (mastoidectomy), most often caused by cholesteatoma.
Spontaneous evacuation of cholesteatoma can be seen with automastoidectomy 1. In these circumstances, it is often referred to as mural cho...
Autophony, also known as tympanophony, is the experience of finding that one's own voice sounds much louder than normal or is unpleasantly garbled.
Autophony has been described in several clinical entities including superior semicircular canal dehiscence syndrome and patulous Eustachian tube d...
Exudative tracheitis, also known as bacterial tracheitis, membranous croup or membranous laryngotracheobronchitis, is a rare, but potentially life-threatening cause of upper airway obstruction.
Typical age ranges from 6 to 10 years of age.
Clinically it pre...