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 is a frequent normal anatomic variant resulting 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 pet...
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...
Atlanto-occipital dissociation (AOD) injuries are severe and include both atlanto-occipital dislocations and atlanto-occipital subluxations.
The tectorial membrane and alar ligaments provide most of the stability to the atlanto-occipital joint, and injury to these ligaments results i...
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.
Alternatively, the term refers to spontaneous dra...
Autoimmune thyroiditis (plural: thyroiditides) (AIT) refers to a group of conditions in which 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 fal...
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...
This classification was initially proposed by Bailey in 1929 2 and remains the most widely used classification system at time of writing (July 2016).
Bailey classification of second branchial cleft cysts provides a structure for classing second branchial cleft cysts into four types. It is no lo...
The ballet sign refers to the paralysis of voluntary movements of the eyeball with preservation of the automatic movements. Sometimes this sign is present with exophthalmic goiter and hysteria.
Barosinusitis, also known as sinus barotrauma or aerosinusitis, refers to inflammatory changes that affect the paranasal sinuses due to alterations in atmosphere pressure, with uncompensated pressure changes within the sinonasal cavities.
Barosinusitis is most common in aviation t...
Barrow caroticocavernous fistula classification divides caroticocavernous fistulas into direct (type A) or indirect (types B-D). This classification was proposed by Barrow et al. in 1985 1 and at the time of writing (mid-2016) remains the most widely used system for describing caroticocavernous ...
Basal cell adenomas are uncommon salivary gland tumors, representing ~4% (range 1-7.5%) of benign parotid tumors. They can also occur in the other major salivary glands as well as the minor salivary glands.
Most commonly, a painless growing mass 1.
The basal lamella, also known as basal lamella of the middle turbinate, is an osseous lamella that separates the anterior from the posterior ethmoid sinuses 1.
Internal anterior to posterior partitions of the ethmoid sinuses are called basal lamellae. According to a concept propose...
The base of the skull (or skull base) forms the floor of the cranial cavity and separates the brain from the structures of the neck and face.
The base of the skull is a bony diaphragm composed of a number of bones - from anterior to posterior:
Basilar fractures of the skull, also known as base of skull fractures, are a common form of skull fracture, particularly in the setting of severe traumatic head injury, and involve the base of the skull. They may occur in isolation or often in continuity with skull vault (calvarial) fractures or...
The basion is the median (midline) point of the anterior margin of the foramen magnum. The apical ligament attaches to it.
It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.
Various lines and measurements using the ...
Bathrocephaly, also known as bathrocephalic occiputs, is a normal variation in skull shape, caused by an outward convex bulge of mid-portion of the occipital bone, often associated with a modification of the mendosal suture.
The true incidence of this disorder is unknown 1.
Battle sign is an eponymous term given to mastoid ecchymosis (bruising of the scalp overlying the mastoid process) and is strongly suggestive of a base of skull fracture, most commonly a petrous temporal bone fracture.
History and etymology
Mr William Henry Battle (1855-1936) was an English s...
A mnemonic used to remember the behavioral changes of obstructive sleep apnea (OSA) is:
P: poor school performance
L: lack of concentration
Behçet disease is a multisystemic and chronic inflammatory vasculitis of unknown etiology.
The mean age at which Behçet disease occurs is 20-30 years. The disease is most prevalent in the Mediterranean region, Middle East and East Asia. The highest incidence has been reported in T...
Benign enhancing foramen magnum lesions, also described as high signal lesions, have been anecdotally seen by radiologists for years but only recently described as an incidental finding on 3D FLAIR MRI in a typical location in the foramen magnum just posterior to the intradural vertebral artery....
Benign lymphoepithelial lesions (BLL or BLEL), also misleadingly known as AIDS-related parotid cysts (ARPC), are mixed solid and cystic lesions that enlarge the parotid glands, and are usually associated with cervical lymph node enlargement, and nasopharyngeal lymphofollicular hyperplasia.
There are a number of benign metastasizing tumors:
benign metastasizing meningioma 1,2
benign metastasizing leiomyoma 3
primary adenoma of thyroid 4
giant cell tumor of bone 5
Benign minor salivary gland pathology is a broad term that encompasses a number of relatively uncommon pathologies that affect the minor salivary glands of the head and neck:
salivary retention cysts
Benign paroxysmal positional vertigo (BPPV) is one of the most common causes of vertigo. It occurs secondary to change in posture and typically is associated with nystagmus. The etiology is thought to be due to changes of position of the otoliths in the inner ear, most commonly into the posterio...
Bethesda classification system for thyroid fine needle aspirates comprises of six (6) categories in pathological reporting of thyroid FNA's with each category is linked to a malignancy risk. They are as
category I: non diagnostic
category II: benign
category III: atypia of undetermined signif...
A Bezold abscess is a complication of acute otomastoiditis where the infection erodes through the cortex medial to the attachment of sternocleidomastoid, at the attachment site of the posterior belly of the digastric muscle, and extends into the infratemporal fossa. Due to it being deep to the i...
The Biffl scale or grade illustrates the spectrum of blunt cerebrovascular injury (BCVI) seen on angiography (both CTA and DSA). Some authors refer to the grading scale as the Denver scale, which is not to be confused with the Denver criteria, a series of clinical indications to screen for blunt...
A bifid premolar root is a normal variant there are two roots involving a premolar tooth. It is thought to present in aprroximately 2.5 % of population 1. They are mostly located in the buccal and lingual directions. In a very small proportion of people the premolar teeth can contain more than 2...
Bill bar is a bony anatomical landmark that divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment. Anterior to Bill bar, in the anterior superior quadrant, are the facial nerve (CN VII) and nervus intermedius, and posterior to it, in the post...
The bimastoid line has been described and used to evaluate basilar invagination on frontal skull plain film and coronal reconstructed CT image.
The bimastoid line is drawn between the inferior tips of the mastoid processes bilaterally. The tip of the odontoid process of C2 normally projects les...
The binocular distance (BOD) is a measurement between the two lateral (outer) canthi of each eye. It is sometimes used as a accessory fetal biometric parameter where it is often documented on both 2nd trimester anatomy scans on axial brain scans. The largest diameter of the orbit should be used ...
Biphenotypic sinonasal sarcoma, initially named low-grade sinonasal sarcoma with neural and myogenic features, is a rare and only recently described low-grade sarcoma of the nasal and paranasal sinuses. The tumor exhibits both neural and myogenic differentiation and thus can be problematic to di...
Black eyebrow sign is the description given on plain facial radiographs to intra-orbital air 1.
Air rises into the most superior aspect of the orbit, almost always in the context of a facial fracture, in a linear fashion, giving the appearance of an eyebrow. The fracture is usually an orbital b...
The black turbinate sign refers to the non-enhancement of nasal turbinates in a patient with acute invasive fungal rhinosinusitis.
Angioinvasive fungal infection (e.g. mucormycosis or aspergillosis) involves the nasal mucosa and causes infarction of the surrounding tissue. The infarcted tissue ...
Blepharophimosis is dysplasia of the eyelids, where there is horizontal shortening of palpebral fissure. It is often associated with ptosis.
Blepharophimosis is a feature of Dubowitz syndrome and Smith Lemli Opitz syndrome.
Blepharophimosis, ptosis, and epicanthus inversus syndrome (BPES) is c...
Blepharospasm is a type of focal dystonia where there is involuntary eyelid closure due to overactivity of muscles around the eyes, particularly orbicularis oculi.
It is categorized into:
cause unable to be identified
cause can be established such as 1
Blunt traumatic neck injury is uncommon because it is usually protected by the head, shoulders, and chest. This term is generally used to refer to injuries of the neck besides to cervical spine injuries, which are common.
Blunt injury to the neck is most commonly from motor vehicle ...
The body of the sphenoid bone is the midline cubical portion of the sphenoid bone, hollowed by the sphenoid air sinuses.
The body has superior, inferior, anterior, posterior, and lateral surfaces.
The superior surface features:
ethmoidal spine: prominent spine that articulates...
Bogorad syndrome also known as the syndrome of crocodile tears, is characterized by residual facial paralysis with profuse lacrimation during eating. This phenomenon is also known as paroxysmal lacrimation or the gustolachrymal reflex. It is caused by a misdirection of the regenerating autonomic...
The Bolger classification of maxillary sinus hypoplasia proposed by Bolger et al. in 1990 1 takes into account associated anomalies of the uncinate process, which are of utmost importance for planning functional endoscopic sinus surgery (FESS).
Maxillary sinus hypoplasia in itself is asymptomat...
The bony orbit refers to the bones that constitute the margins of the orbits, that is the roof, medial and lateral walls and floor. The orbital margin or rim refers to the anterior circular margin of the orbit. The orbital apex refers to the posterior confluence of the orbit, where the optic can...
Boogard's angle is measured by drawing a line from basion to opisthion and another line along the plane of the clivus to the basion intersecting the first line - the angle between these two lines is measured.
The normal angle is 126° +/- 6°. If the angle measures more than 136° it is indicative...
Alain Bouthillier et al. described a seven segment internal carotid artery (ICA) classification system in 1996 1. It remains the most widely used system for describing ICA segments.
A helpful mnemonic for remembering ICA segments is:
C'mon Please Learn Carotid Clinical Organizing Classificati...
Brachiocephalic vein stenosis refers to a narrowing of the brachiocephalic vein. It is commonly seen in chronic hemodialysis patients.
A study conducted in Chinese population shows a prevalence of stenosis in hemodialysis patients was 30-50% 3.
Brachycephaly refers to a calvarial shape where the bi-parietal diameter to fronto-occipital diameter approaches the 95th percentile. It can result from a craniosynostosis involving the coronal and lambdoid sutures.
Brachycephaly can be associated with numerous syndrome...
A mnemonic for remembering the branches of the maxillary artery is:
DAM I AM Piss Drunk But Stupid Drunk I Prefer, Must Phone Alcoholics Anonymous
D: deep auricular artery
A: anterior tympanic artery
M: middle meningeal artery
I: inferior alveolar artery
A: accessory meningeal ar...
Mnemonics for the branches of the external carotid artery abound. A few colorful examples include:
Some American Ladies Found Our Pyramids Most Satisfactory
Some Anatomists Like Freaking Out Poor Medical Students
She Always Likes Friends Over Papa, Mama, and Sister
There are many many many ...
Useful mnemonics to remember the four branches of the thoracoacromial artery are:
CAlifornia Police Department
Cadavers Are Dead People
B: breast (pectoral)
CAlifornia Police Department
The branchial (or pharyngeal) apparatus is the complex region in the developing embryo between the head and chest that develops in the fourth week and provides bilateral ridges and valleys that subsequently develop into numerous anatomic structures of the head, face, palate and anterior neck. Th...
Branchial cleft anomalies comprise of a spectrum of congenital defects that occur in the head and neck.
The anomalies result from branchial apparatus (six arches; five clefts), which are the embryologic precursors of the ear and the muscles, blood vessels, bones, cartilage, and mucos...
Branchio-oculo-facial syndrome (BOFS) is a very rare autosomal dominant genetic disorder that is characterized clinically by abnormalities affecting the eyes, craniofacial structures, and branchial sinuses.
More than 80 cases have been reported in the global literature since its f...
Branchio-otic syndrome (also known as BOS, BOS1, BO syndrome 1 and branchiootic dysplasia) is a rare autosomal dominant disease. It manifests as abnormalities of the second branchial arch, with predominant abnormalities of the ear. No renal disease is seen, in contradistinction to its close name...
Branchio-oto-renal (BOR) dysplasia, syndrome, or spectrum disorder is a rare syndromic disorder characterized by cervical branchial apparatus anomalies, ear malformations, and renal anomalies. If there are no renal anomalies, then it is more likely to be branchiootic dysplasia.
The bregma is the midline bony landmark where the coronal and sagittal sutures meet, between the frontal and two parietal bones.
It is the anterior fontanelle in the neonate and closes in the second year 2 (typically around 18 months after birth).
It is one of the skull landmarks, craniometric...
The broken heart sign, also known as the Y sign in older otorhinolaryngology literature 2,3, describes the appearances of incudomalleolar disarticulation.
This sign is identified on CT in the coronal plane, being formed by the widening of the incudomalleolar joint and lateral displacement of th...
The Brown syndrome refers to an inability of a patient to perform an upward gaze while the eye is adducted due to an abnormality of the superior oblique tendon sheath complex.
History and etymology
It was first described by Allan Brown in 1950 1.
The ultrasound "U" classification of thyroid nodules has been developed by the British Thyroid Association (BTA) as part of their 2014 guidelines on the management of thyroid cancer 1.
It allows for stratifying thyroid nodules as benign, suspicious or malignant based on ultrasound appearances t...
The buccal nerve is the only purely sensory branch of the anterior division of the mandibular division of the trigeminal nerve. It is not to be confused with the buccal branch of the facial nerve.
The buccal nerve divides off the anterior division and passes with the paired nerve...
The buccal space, also known as the buccinator space, is one of the seven suprahyoid deep compartments of the head and neck.
The buccal spaces are paired fat-containing spaces on each side of the face forming cheeks. Each space is enveloped by the superficial (investing) layer o...
The buccinator artery is a small branch from the second part of the maxillary artery. It runs obliquely forward, between the medial pterygoid and the insertion of the temporalis, to the outer surface of the buccinator, to which it is distributed, anastomosing with branches of the facial artery a...
The buccinator muscle is a muscle of facial expression located in the cheek, between the maxilla and mandible, and functions chiefly as a muscle of mastication.
origin: outer surface of alveolar process of both maxilla and mandible, and anterior margin of the pterygomandibular raphe 1
The buccopharyngeal fascia is the component of the middle layer of the deep cervical fascia that invests the outside of the pharyngeal constrictors and buccinator muscles.
The term has been variably used to refer to the entire visceral component of the middle layer of the deep cerv...
The bulla lamella is a structure that, when intact, forms the posterior boundary of the frontal recess. When pneumatized, it forms the ethmoid bulla.
It is frequently incomplete and often does not reach the roof of the ethmoid at the skull base. Under these circumstances, the fro...
Buphthalmos is a descriptive term which simply means an enlarged eyeball or ocular globe due to increased intraocular pressure (glaucoma), without deformation or and intrinsic mass lesion.
It typically manifests in infants and young children.
It usually indicates the p...
Calcification of the external ear (auricular cartilage) may arise from a number of causes, including:
gout and pseudogout
Calcification of the globe has many causes, varying from the benign to malignant. When calcification is seen of the posterior half of the globe, it could relate to any of the layers (scleral, choroidal or retinal), as it is not possible to separate them out on CT.
drusen: 1% population...
Calcific cervical lymphadenopathy is uncommon and has a limited differential diagnosis, including malignant and benign etiologies. The most frequent causes include 1:
malignancies (more common)
metastatic thyroid carcinoma (most common; papillary or medullary types) 2,5
Calcific tendinitis of the longus colli muscles is an inflammatory/granulomatous response to the deposition of calcium hydroxyapatite crystals in the tendons of the longus colli muscle. It is sometimes more generically known as calcific prevertebral tendinitis or, less accurately, as retropharyn...
Calcifying epithelial odontogenic tumor (CEOT), also known as a Pindborg tumor, (previously has been called adenoid adamintoblastoma, unusual ameloblastoma and cystic odontoma) is typically located in the premolar and molar region of the mandible, although up to a third are found in the maxilla....
Calcifying odontogenic cyst (COC) is a form of odontogenic cyst. There is some disagreement on the terminology and classification of this lesion.
It may represent around 0.3-0.8% of all odontogenic cysts 2.
It can show extreme diversity in its clinical and histopatholo...
The Caldwell-Luc operation uses an external approach for surgical treatment of the severely diseased maxillary sinus. It is an alternative to middle meatal antrostomy done via endonasal endoscopic surgery and was the primary approach used for accessing the maxillary sinus before the advent of en...
The Caldwell view is a caudally angled radiograph, with its posteroanterior projection allowing for minimal radiation to the orbits. This view may be used in imaging of the skull or facial bones depending on the clinical indications.
This view aids in visualizing the paranasal sinu...
Canadian C-spine rules are a set of guidelines that help a clinician decide if cervical spine imaging is not appropriate for a trauma patient in the emergency department. The patient must be alert and stable.
There are three rules:
is there any high-risk factor present that requires cervical s...
The canalis basilaris medianus (median basal canal), also known as clival canal, median clival canal, or inferior median clival canal, refers to a number of anatomic variant midline canals in the clivus, typically involving the basioccipital portion.
These canals are generally we...
A canal wall up mastoidectomy is one of the types mastoidectomies that can be performed. This involves exenteration of the mastoid air cells with preservation of the posterior wall of the external auditory canal, creating a mastoid bowl or cavity.
This procedure includes removal of Koerner’s ...
Capillary hemangiomas of the orbit, also known as strawberry hemangiomas, on account of its coloring, or orbital infantile hemangiomas, are the most common orbital tumors of infancy, and unlike orbital cavernous hemangiomas, they are neoplasms rather than vascular malformations.
The Capps triad refers to the constellation of clinical and imaging findings in patients with spontaneous retropharyngeal hematomas, and consists of:
tracheal and esophageal compression
anterior displacement of the trachea
subcutaneous bruising over the neck and anterior chest
History and et...
Carcinogens are substances known to cause cancer. They include:
Nasopharynx / nasal passage
ionizing radiation (not technically a substance)
polyaromatic hydrocarbons (PAH)
Carcinoma ex pleomorphic adenoma is the most common of three malignant mixed tumors of salivary glands, and are thought to arise from pre-existing pleomorphic adenomas (or benign mixed tumors) 1.
These tumors usually occur in older patients (6th to 8th decade), who have had a pleo...
Carcinosarcomas are highly malignant biphasic tumors with both carcinomatous (epithelial) and sarcomatous (bone, cartilage, or skeletal muscle) components.
It can arise in many organs:
lung 5: pulmonary carcinosarcoma
esophagus 1: esophageal carcinosarcoma
genitourinary tract 2
Caroticocavernous fistulas (CCF) represent abnormal communication between the carotid circulation and the cavernous sinus. They can be classified as direct or indirect which are separate conditions with different etiologies.
Direct CCFs are often secondary to trauma, and as such...
The caroticotympanic branch (tympanic branch) is a small branch from the C2 segment of the internal carotid artery. It is a vestigial remnant of the hyoid artery.
It passes posterolaterally into the middle ear cavity and anastomoses with the inferior tympanic artery (a branch of the ascending p...
Carotid artery stenosis, also known as extracranial carotid artery stenosis, is usually caused by an atherosclerotic process and is one of the major causes of stroke and transient ischemic attack (TIA).
This article refers to stenosis involving the carotid bulb and the proximal segment of inte...
The carotid bifurcation is the point at which the common carotid artery terminates. As it does so, it forms the internal and external carotid arteries which go on to supply the head and neck.
The height of the carotid bifurcation is noted to be highly variable in the literature. Most frequently...
The carotid body is located within the neck, and in close proximity to the carotid bifurcation. It is composed of a number of chemoreceptor cells and supporting matrix and detects changes in the composition of blood in the common carotid as it forms the internal and external carotid arteries.
Carotid body tumor, also known as a chemodectoma or carotid body paraganglioma, is a highly vascular glomus tumor that arises from the paraganglion cells of the carotid body. It is located at the carotid bifurcation with characteristic splaying of the ICA and ECA.