The carotid canal is a passage within the petrous temporal bone and transmits the internal carotid artery and sympathetic plexus. Its inferior opening is called the carotid foramen and is situated anteriorly to the jugular fossa and medially to the carotid plate. The carotid canal is initially d...
The carotid plate is a thin (0.5 mm) bony plate that separates the carotid canal from the middle ear cavity.
The caroticotympanic artery perforates the carotid plate normally.
Disruption or dehiscence of the carotid plate may be seen in
aberrant internal caro...
The carotid space, the suprahyoid portion of which is also known as the poststyloid parapharyngeal space, is a deep compartment of the head and neck bound by the carotid sheath.
The "carotid space" terminology was introduced by some radiologists to facilitate differential diagnosis...
The carotid triangle is one of the paired triangles in the anterior triangle of the neck. The triangles of the neck are surgically focused, first described from early dissection-based anatomical studies which predated cross-sectional anatomical description based on imaging (see deep spaces of th...
Carotid webs, also known as carotid intimal variant fibromuscular dysplasia, are rare vascular pathologies of the internal carotid artery that are an important cause of cryptogenic and recurrent ischemic stroke.
Carotid webs have had many different names in the literature, includin...
Carotidynia, also known as Fay syndrome, is a rare syndrome characterized by neck pain in the region of the carotid bifurcation.
It was classified by the International Headache Society (IHS) in 1988 as an idiopathic neck pain syndrome associated with tenderness over the carotid bifurcation with...
Castleman disease, also known as angiofollicular lymph node hyperplasia or giant lymph node hyperplasia, is an uncommon benign B-cell lymphoproliferative condition. It can affect several regions of the body but is commonly described as a solitary mediastinal mass.
There are two distinct subtype...
Cataracts are an opacification or thickening of the lens within the globe and are the leading cause of blindness in the world.
Visual deterioration occurs with increasing degrees of severity, and left untreated may present as complete blindness. The diagnosis is made cli...
Catel-Manzke syndrome is a digitopalatal syndrome initially described in 1961. Inheritance pattern is unknown. Radiographic findings include micronagthia and accessory ossicles at the bases of the metacarpals.
Cavernous sinus thrombosis (CST) is a rare condition, most commonly infectious in nature, and the diagnosis on imaging is not always straightforward. It has high mortality and morbidity rates.
Cavernous sinus thrombosis is rare with ~4.5 cases per 1,000,000 per year 5. It is the l...
Cebocephaly refers to a type of rare midline craniofacial anomaly where there is a single nostril (which usually ends blindly 6-7) with proboscis-like nose 8 and hypotelorism.
holoprosencephaly: particularly alobar holoprosencephaly
Cementoblastomas are one of many mandibular lesions is a rare tumor of the cementum, with only approximately 100 cases reported. The key to diagnosis, both radiologically and histologically, is an attachment to the tooth root.
Cementoblastomas have been previously described in the...
Cemento-osseous dysplasia (COD) is a benign condition affecting the jaw that may arise from the fibroblasts of the periodontal ligaments.
Three types have been described:
periapical cemental dysplasia
focal cemento-osseous dysplasia
florid cemento-osseous dysplasia
2005 WHO histo...
Cemento-ossifying fibroma (COF) are rare, benign neoplasms that usually arise from the mandible or maxilla. They most often arise from the tooth bearing areas of these bones.
In the 2005 WHO histological classification of odontogenic tumors, this tumor is referred to as "ossifying ...
The central artery of the retina or central retinal artery arises from the ophthalmic artery near or with the posterior ciliary arteries (either the lateral or medial branches) and supplies the retina 1,2.
The central artery of the retina courses anteriorly and inferior to the op...
The central base of skull is a region of the skull base centered on the pituitary fossa and includes surrounding structures.
Despite no single universally accepted definition of this region, it is frequently used clinically and is conceptually useful particularly when considering tumors of the ...
A cause of inner retinal infarction and profound, monocular vision loss, central retinal artery occlusion (CRAO) is most commonly caused by embolic occlusion of the central retinal artery.
The most common etiological associations with occlusion of the central retinal artery inclu...
The central retinal vein (CRV) or central vein of the retina, and sometimes shortened to the retinal vein, is the venous counterpart of the central retinal artery.
Each quadrant of the retina is drained by multiple minor retinal veins which coalesce to form a main retinal vein. T...
A leading cause of monocular vision loss, central retinal vein occlusion (CRVO) is most commonly caused by thrombosis of the central retinal vein, resulting in retinal edema and hemorrhage.
Occlusion of the central retinal vein is subclassified as ischemic and non-ischemic based on...
Cerumen, also known as earwax, is a natural secretion produced by and found within the external auditory canal (EAC). It has important roles as part of the first line of defense of the ear from micro-organisms and optimizing function of the tympanic membrane and EAC.
Cerumen is secre...
Cervical adenitis refers to the inflammation of lymph nodes in the neck.
Most common cause of a pediatric neck mass following non-specific infectious/inflammatory insults.
In the pediatric population, a child will present with a painful cervical mass.
The cervical lymph node groups covers all the lymph nodes in the head and neck region. These named groups overlap with the cervical lymph node levels, which are numbered.
Groups described in the literature include but are not limited to the following:
superficial lymph node gro...
Cervical lymph node metastases refer to regional nodal involvement by cancer in the head and neck, most commonly due to squamous cell carcinoma originating from the aerodigestive tract or skin. Radiologic detection of cervical lymph node metastases is important for clinical staging and planning ...
Cervical lymph node staging refers to evaluating regional nodal metastasis from primary cancer of the head and neck. The following article reflects the 8th edition of the TNM staging system published by the American Joint Committee on Cancer, which is used for staging starting January 1, 2018 1,...
The cervical plexus is formed by the ventral (anterior) rami of the C1 to C5 nerve roots and innervates the diaphragm, provides motor supply to some neck muscles and cutaneous sensation to the skin of the head, neck and chest.
anterior rami of C1 to C5 nerves
The cervical thymus (plural: cervical thymi) refers to an ectopic location of the thymus in the neck above the level of the brachiocephalic veins.
A cervical thymus usually presents before adolescence as a painless unilateral midline or lateral neck mass.
Chamberlain line is a line joining the back of hard palate with the opisthion on a lateral view of the craniocervical junction.
It helps to recognize basilar invagination which is said to be present if the tip of the dens is >3 mm above this line.
McGregor developed a modificatio...
Chandler classification is the most commonly used system for dividing the different types of orbital cellulitis. The system describes five stages 1,2 :
stage I: preseptal orbital cellulitis with inflammation and edema anterior to the orbital septum.
stage II: orbital cellulitis with extension ...
Charcot-Leyden crystals consist of collections of bipyramidal crystalloid made up of eosinophilic membrane proteins, which occur in:
other eosinophilic lung disease 2
certain cases of sinusitis (e.g. allergic fungal sinusitis)
They may be detected in the sputum or sinus secretions wi...
Cherubism has historically been considered a variant of fibrous dysplasia, but in reality is likely a distinct entity.
Cherubism is a rare disorder and the precise incidence is unknown. It is inherited in an autosomal dominant pattern 2 and has variable penetrance, with onset in ...
Choanal atresia refers to a lack of formation of the choanal openings. It can be unilateral or bilateral.
It frequently presents in neonates where it is one of the commonest causes of nasal obstruction in this age group. There is a recognized female predilection. The incidence is ...
Cholesteatomas are histologically-equivalent to an epidermoid cyst and are composed of desquamated keratinizing stratified squamous epithelium forming a mass.
They may be asymptomatic, or may present with conductive hearing loss, dizziness, or otorrhea.
Cholesterol granuloma (CG), also sometimes called a chocolate cyst of the ear or blue domed cyst, is a special type of middle ear granulation tissue which is particularly prone to bleeding and is a frequent cause of a hemotympanum. Cholesterol granulomas represent the most common cystic lesion o...
Chondromesenchymal hamartomas are rare, benign, tumor-like nasal masses in children that have been associated with DICER1 mutations.
The entity is rare: a systematic review of the literature in 2015 identified fewer than 50 reported cases 2. The mean age of presentation is 10 year...
Chondrosarcomas of the base of the skull are rare compared with other skull base tumors but are an important differential diagnosis as surgical resection and management are affected by the preoperative diagnosis.
Chondrosarcomas of the base of the skull make up only a small fracti...
The chorda tympani is a nerve that arises from the mastoid segment of the facial nerve, carrying afferent special sensation from the anterior two-thirds of the tongue via the lingual nerve, as well as efferent parasympathetic secretomotor innervation to the submandibular and sublingual glands.
Chorioretinal lacunae refer to punched out lesions in pigmented layer of retina, usually around the optic disc. It is a considered a consistent feature of Aicardi syndrome.
A choristoma is simply a collection of microscopically normal cells or tissues in an abnormal location. This is different to a hamartoma which is derived only from local tissues.
adrenal choristoma (myelolipoma)
facial nerve choristoma
Choroidal detachment is a detachment of the choroid from the underlying sclera due to the accumulation of fluid in the suprachoroidal space generally due to increased intraocular pressure (IOP), as observed in some settings:
exudative: fluid accumulatin...
Choroidal hemangiomas are benign vascular hamartomatous tumors of the choroid. They present in two forms based on the extent of choroidal involvement:
circumscribed choroidal hemangioma (CCH): solitary tumor with no systemic associations.
diffuse choroidal hemangioma (DCH): usually in associat...
Choroidal osteomas are rare benign calcific masses of the globe.
Choroidal osteomas are typically found in young Caucasian women 1. A number of familial cases have been reported 3.
These lesions are usually unilateral (75%), and result in painless and gra...
The choroid is part of the uveal layer of the eye along with the ciliary body and iris 1.
location: posterior aspect of the globe
function: vascularization of the outer retina
arterial supply: posterior ciliary arteries
innervation: short ciliary nerves, long ciliary nerves
Chronic invasive fungal sinusitis is a form of invasive fungal sinusitis.
The condition has a more prolonged course than acute invasive fungal sinusitis, usually more than 12 weeks 5. Patients are usually immunocompetent or have a milder level of immunocompromise. There ...
Chronic maxillary atelectasis is a descriptive term which is characterized by a persistent decrease in the maxillary sinus volume due to inward bowing of its antral walls. It is not considered synonymous with but can include the term silent sinus syndrome in special situations when there is al...
Chronic otomastoiditis is defined as persistent or recurrent inflammation of the middle ear (chronic otitis media) and mastoid, lasting usually for a minimum of 12 weeks, often resulting in permanent perforation of the tympanic membrane. It should be considered a separate entity from acute otoma...
Chronic otomastoiditis with ossicular erosions, also known as non-cholesteatomatous ossicular erosions or post-inflammatory ossicular erosions, is defined by the erosive changes involving the middle ear ossicles in the absence of cholesteatoma in a patient with a history of chronic otomastoiditi...
Chronic otomastoiditis with tympanosclerosis represents calcific foci within the middle ear or tympanic membrane secondary to suppurative chronic otomastoiditis.
Features include chronic otomastoidits findings such as middle ear soft tissue density and underpneumatised ma...
Chronic progressive external ophthalmoplegia (CPEO) is a rare mitochondrial ocular disorder.
Patients present with slowly progressive bilateral ophthalmoplegia (limitation of eye motion) and blepharoptosis.
The entity can manifest in isolation or as a syndrome with other...
Chronic sinusitis refers to ongoing long-term sinus infection-inflammation that often develops secondary to a prolonged/refractory acute sinus infection.
It most commonly affects young to middle-aged adults but can uncommonly also affect children.
Chvostek sign (also known as Chvostek-Weiss sign or Schultze sign 1) is the facial twitch obtained by tapping the distribution of the facial nerve in front of the tragus. It is caused by mechanical irritability of peripheral nerves. It is indicative of hypocalcemia and is the most reliable test ...
The ciliary ganglion is one of four parasympathetic ganglia of the head and neck. It receives parasympathetic fibers from the oculomotor nerve.
smallest of the ganglia (2 mm in size)
located posterolaterally in the intraconal space of the orbit (towards the orbital apex) between...
Cirsoid aneurysms are rare arteriovenous malformations of the scalp and extremities.
Patients often present with a slow-growing pulsatile mass and may also experience bleeding, tinnitus and/or a headache 3.
Cirsoid aneurysms develop due to an abnormal arteri...
Citelli abscesses are a suppurative complication of acute mastoiditis. The term may refer to extracranial abscesses in two different juxtamastoidal locations:
posterior to the mastoid involving/abutting the occipital bone
anteroinferior to the mastoid tip involving the digastric muscle or with...
Cleft lip and palate is one of the commonest of neonatal facial anomalies. In ~80% of cases, the two features tend to occur together 6.
It is estimated to occur with an incidence of ~1 in 700-to-1000 live births 1. This can increase to 4% for a sibling of a previously affected fet...
Cleft palate is a type of facial cleft. It can occur in two main etiologically different forms:
in association with a cleft lip: cleft lip +/- palate (much commoner)
on its own: isolated cleft palate (rarer)
Clival diploic veins are veins that travel through the body of the clivus connecting intracranial venous structures on the inner surface of the skull (e.g. basilar venous plexus, inferior petrosal sinuses, marginal sinus, internal carotid artery venous plexus of Rektorzik, inferior petro-occipit...
The differential of a mass involving or arising from the clivus is a relatively narrow one and can be divided into whether the lesion arises from the skull base itself, the intracranial compartment above or the base of skull below.
When evaluating the clivus it is important to compare the marro...
The clivus (of Blumenbach) is the sloping midline surface of the skull base anterior to the foramen magnum and posterior to the dorsum sellae 1. Specifically, it is formed by the sphenoid body and the basiocciput, which join at the spheno-occipital synchondrosis. At the clivus, the occipital bon...
The cloison sagittale (sagittal partition), also known as Charpy fascia, is a sagittally oriented fascia on either side of the neck that separates the midline deep neck spaces (retropharyngeal space, prevertebral space, and danger space) from the more lateral parapharyngeal space (including caro...
Cloquet's canal, also known as the hyaloid canal or Stilling's canal, is a transparent canal that runs from the optic nerve disc to the lens traversing the vitreous body. It serves as a perivascular sheath surrounding the hyaloid artery in the embryonic eye.
History and etymology
Cloverleaf skull, also known as kleeblattschädel syndrome or deformity, refers to a type of severe craniosynostosis which gives the skull a cloverleaf shape. It is very rare, with less than 130 case reports globally. It typically results from intrauterine premature closure of the sagittal, coron...
Coalescent mastoiditis is simply the term given to acute otomastoiditis when mucoperiosteal disease extends to involve the bone. The septae which normally separate one mastoid air cell from another are resorbed. This change is only easily appreciated on thin section bone-algorithm through the te...
The Coca-Cola bottle sign refers to the appearance of the muscles of the orbit in thyroid eye disease. The belly of the muscle enlarges with sparing of the tendinous insertion, giving the appearance of the traditional Coca-Cola bottle.
The enlargement of the muscles follows the I'M SLOW format...
Coccidioidomycosis refers to an infection caused by the dimorphic fungus Coccidioides spp, usually localized to the lungs. This disease is not to be confused with the similarly named paracoccidioidomycosis.
The most common forms of Coccidioides spp are Coccidioides immitis and Coc...
The cochlea (plural: cochleae) is part of the inner ear osseous labyrinth found in the petrous temporal bone. It contains the cochlear duct, part of the membranous labyrinth which senses hearing.
The cochlea is a shell-shaped spiral that turns between two-and-a-half and two-and-t...
Cochlear aplasia, or complete absence of the cochlea is a rare anomaly which accounts for only 3% of cochlear malformations.
complete absence of the cochlea. Dense otic bone is seen at the anatomical site of the cochlea 2
cochlear nerve canal and cochlear nerve are absen...
The cochlear aqueduct or canaliculus is a small canal in the bony labyrinth of the petrous temporal bone that contains the perilymphatic duct, which drains perilymph into the cerebrospinal fluid of the posterior cranial fossa subarachnoid space. It runs inferior and parallel to the internal audi...
The cochlear cleft is a curvilinear radiolucent area of incomplete endochondral ossification in the otic capsule adjacent to the cochlea. It is a variant most prominent in children that may also be visible in adults 1.
The cochlear cleft is a C-shaped structure in the otic capsul...
The cochlear duct (also known as the scala media) is an endolymph-filled cavity located between the scala vestibuli (upper) and the scala tympani (lower) in the cochlea which is part of the inner ear along with the vestibular apparatus 1,4. The cochlea is located in the bony labyrinth, itself fo...
Cochlear hypoplasia is a group of inner ear malformations defined by a smaller than normal cochlea with various internal architectural abnormalities such as having <2 turns.
Cochlear hypoplasia accounts for 15% of cochlear malformations 1.
According to the ...
The cochleariform process is the thin osseous projection in the anterior wall of the middle ear cavity that acts as the fulcrum for the tendon of the tensor tympani.
The cochleariform process is located 2,3:
at the posterior termination of the semicanal for tensor tym...
Cochlear implants (CI) are a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing. Unlike conventional hearing aids, the cochlear implant does not amplify sound, but works by directly stimulating any functioning audi...
Cochlear incomplete partition is a group of cochlear malformations associated with variable other inner ear architecture defects. These malformations have in common that the cochlea is clearly separated from the vestibule and the external contour of the cochlear is nearly normal in size, but the...
Cochlear incomplete partition type I (IP-I) is a type of cochlear anomaly associated with sensorineural hearing loss.
As with other types of incomplete partition, the cochlea is clearly differentiated from the vestibule and the external dimensions of the cochlea are n...
Cochlear incomplete partition type II (IP-II) is a type of cochlear anomaly associated with sensorineural hearing loss.
It should not be confused with Mondini anomaly, which is a historic term for a combination of IP-II and large vestibular aqueduct.
On CT, the coch...
Cochlear incomplete partition type III (IP-III) is the type of cochlear incomplete partition present in X-linked deafness, a rare, nonsyndromic, genetic cochlear anomaly associated with mixed conductive and sensorineural hearing loss.
The genetic disorder goes by many names 8:
The cochlear promontory is the name given to the bone that overlies the basal turn of the cochlea protruding into the middle ear cavity.
glomus tympanicum paragangliomas typically arise in the region of the cochlear promonotory
The cog is a coronally oriented bony process in the middle ear cavity of the temporal bone that projects from the tegmen tympani, separating the anterior epitympanic recess from the posterior epitympanum. The cog ends anterosuperior to the head of the malleus and superior to the cochleariform pr...
Cogan syndrome is a rare vasculitis of young adults that is primarily characterized by 1,4,6:
inflammatory eye disease (classically interstitial keratitis) 6
audiovestibular dysfunction (similar to Meniere disease) 6
Cogan syndrome is rare and can occur in people of any age and ...
COL4A1-related disorders are a group of autosomal dominant disorders caused by a mutation in the COL4A1 gene.
The exact prevalence is unknown, but the group of disorders is considered to be under-recognized, especially asymptomatic variants 1.
The clinical ...
Collet-Sicard syndrome, also known as condylar jugular syndrome, is a constellation of cranial nerve palsies due to neoplastic or non-neoplastic lesion at the jugular foramen 1,2.
Vernet syndrome, consisting of motor paralysis of
glossopharyngeal nerve (CN IX)
The colliscalene triangle is an important anatomical region of the neck, situated medial to the scalenus anterior muscle.
It should not be confused with the scalene triangle which is located posterior to the scalenus anterior muscle.
medial: lateral border of longus...
Colloid nodules are non-neoplastic benign nodules occurring within the thyroid gland. They form the vast majority of nodular thyroid disease.
Colloid nodules are composed of irregularly enlarged follicles containing abundant colloid. Some colloid nodules can be cystic (cystic colloid...
Coloboma is a collective term encompassing any focal discontinuity in the structure of the eye, and should not be confused with staphylomas, which are due to choroidal thinning.
Embryologically, colobomas are due to the failure of closure of the choroidal fissure. The most common si...
The columella is the most anteroinferior portion of the nasal septum and forms the central fleshy portion between the two nostrils when looking at someone's nose. It is a single midline structure composed of cartilage and overlying skin, extending posteriorly from the tip of the nose. The latera...
A simple mnemonic to recall a list of commonly calcifying metastases is:
B: breast cancer
T: papillary thyroid cancer
O: ovarian cancer (especially mucinous)
M: mucinous adenocarcinoma (especially colorectal carcinoma)
The common carotid artery is a paired structure that supplies blood to the head and neck.
left: branch of the aortic arch
right: branch of the brachiocephalic trunk
course: posterior to sternoclavicular joint, lateral to thyroid and trachea
supply: head and neck
Common cavity malformation is defined by the absence of the normal differentiation between the cochlea and vestibule, replaced instead by a cystic structure (i.e. the 'common cavity'). It accounts for about 25% of cochlear malformations 1.
confluence of the cochlea, vest...
The common facial vein is formed by the joining of the facial vein and anterior branch of the retromandibular vein. It is part of the venous drainage system of the face.
origin and termination: the facial vein (along with the facial artery) pierces the deep investing fascia of the neck...
Common variable immunodeficiency (CVID) is a condition that is associated with an impaired immune system. It is considered the most common symptomatic primary immunodeficiency and is characterized by recurrent respiratory tract infections.
The commonest presentation is th...
Complex midfacial fractures consist of multiple facial fractures that cannot be classified as any of the defined complex facial fracture (e.g. Le Fort fracture, zygomaticomaxillary complex fracture, naso-orbital-ethmoid fracture).
A handy mnemonic to recall the complications of transverse and longitudinal petrous temporal bone fractures is:
Listen Carefully To Something Funny
listen carefully = longitudinal / conductive hearing loss
to something funny = transverse / sensorineural hearing loss and facial nerve...
Compressor naris muscle forms the transverse component of nasalis muscle, and is one of the muscles of the nose, a subset of the muscles of facial expression.
origin: frontal process of maxilla
insertion: medial insertion into a transverse aponeurosis
innervation: facial nerve (V...