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...
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.
Retinal vein occlusion may occur in a venous tributary, deemed branch retinal vein occlusion...
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 secr...
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:
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) 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 of the petrous apex.
Cholesterol granulomas typically af...
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 otomastoiditis should be considered a separate entity from acute otomastoiditis, and is defined as persistent or recurrent inflammation of the middle ear and mastoid, lasting usually for a minimum of 12 weeks, and resulting in permanent perforation of the tympanic membrane.
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 ossicles in the absence of cholesteatoma in a patient with a history of chronic otomastoiditis.
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)
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 anomalies are a variety of congenital anomalies which, depending on the exact time at which an insult occurs during embryogenesis, may have different manifestations. Terminology is often used imprecisely leading to confusion not only among clinicians, but also in the literature.
Cochlear aplasia, or complete absence of the cochlea is a rare anomaly which accounts for only 3% of cochlear malformations.1
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 abse...
The cochlear aqueduct is a small narrow bony canal in the bony labyrinth of the petrous temporal bone. It contains the perilymphatic duct which arises from the scala tympani of the cochlea draining perilymph into the cerebrospinal fluid in the posterior cranial fossa near the lateral margin of t...
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 defined by small underdeveloped cochlea with < 2 turns.
a small cochlear bud of variable length (usually 1–3 mm). It has only one turn or a partial turn is seen
cochlear nerve often hypoplastic or absent
cochlear nerve canal: absent, narrow or no...
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 degree of inner ear architecture defects.
It is classified in three groups:
cochlear incomplete partition type I (IP-I)
a severe form of IP-I is known as cystic cochleovestibular malformation
Cochlear incomplete partition type I (IP-I) is a type of cochlear anomaly associated with sensorineural hearing loss.
The main findings on CT are:
absent interscalar septum
wide (most common) or normal cochlear nerve canal
Absence of these structu...
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), also termed X-linked deafness, is a rare type of genetic cochlear anomaly associated with mixed conductive and sensorineural hearing loss.
It is caused a mutation in the POU3F4 gene located on the X chromosome.
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 is a constellation of cranial nerve palsies due to a lesion at the jugular foramen such as a glomus jugulare tumor or schwannoma. It consists of :
Vernet syndrome, consisting of motor paralysis of
glossopharyngeal nerve (CN IX)
vagus nerve (CN X)
accessory nerve (CN XI...
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 failure of closure of the choroidal fissure. The most common site o...
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 t...
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...
Concha bullosa (plural: conchae bullosae) (also known as middle turbinate pneumatization) is a common finding and although associated with deviation of the nasal septum, it is usually of little clinical importance.
Concha bullosa is a normal variant and is one of the most common v...
Conductive hearing loss is a hearing loss where the ears' ability to conduct sound into the inner ear is blocked or reduced. It can be caused by a range of developmental, congenital or acquired pathology to the external, middle or inner ear.
Essentially any process that obstructs or ...
The condylar canal, or canalis condylaris, is a skull base canal in the posterior cranial fossa, located in the condylar fossa. It is the largest of the emissary foramina of the skull 1.
location: in the condylar fossa of the posterior cranial fossa, posterior to the occipital condyles...
Condylar process fractures are fractures of the condylar process of the mandible. The condylar process of the mandible is involved in around 30% of all mandibular fractures.
Condylar fractures are classified according to the location of the fracture and the direction displacement of the condyle...
Congenital absence of the internal carotid artery (ICA) is a rare anomaly that occurs in less than 0.01% of the population. It encompasses agenesis, aplasia, and hypoplasia 1.
The most common type of collateral flow is through the circle of Willis, through the anterior communicating artery (ACO...
Congenital calvarial defects are a group of disorders characterized by congenital calvarial bone defects that vary in severity.
CT with 3D shaded surface reformats is the best imaging tool as it demonstrates calvarial defects and bone margins:
Congenital cataracts are a major cause of blindness with early detection the most important factor in reducing impact on future vision.
Incidence is ~3 per 100,000 in the United Kingdom 1. Although the incidence tends to be higher in areas with increased rates of congenital infec...
Congenital cervical teratoma refers to a teratoma arising in the cervical region. They are thought to account for ~3% of teratomas in childhood/infancy 3.
The estimated occurrence in neonates is ~1:20,000-40,000 live births 8.
Most tumors are diagnosed at b...
Congenital cholesteatomas are identical to epidermoid cysts, differing only in name and location.
They are intraosseous inclusions of ectoderm, and are therefore comprised of keratin debris and cholesterol. Characteristically, they are located at the petrous apex. In contrast middle...
Congenital contractural arachnodactyly (CCA) (also known as Beals syndrome) is a rare connective tissue disorder that bears phenotypic similarities to Marfan syndrome, but is genetically distinct. Affected individuals have arachnodactyly, muscle contractures and ear anomalies, but without any oc...
Congenital goiter is a rare cause of neck swelling in neonates and is demonstrated as diffuse/nodular thyroid gland enlargement.
It is a common endocrine disease in newborns and affects approximately 1:2000-4000 live births.
There may be a difficult vaginal...
A congenital granular cell myoblastoma (also known as congenital epulis) is a very rare benign tumor which classically presents in the fetal-neonatal population.
It occurs almost exclusively in females when it presents in the fetal-neonatal population although no such predilection...
Congenital hypothyroidism (CHT), previously known as cretinism, can be of thyroidal or central (hypothalamic/pituitary) origin and can have a widely diverse molecular etiology.
Most children are asymptomatic at birth and are diagnosed after screening. In untreated congeni...
The features of an infant with congenital hypothyroidism can be recalled with the following mnemonic:
P: pot belly
P: puffy face
P: protruding umbilicus
P: poked out tongue
Congenital anomalies of the ossicles are most frequently associated with external ear abnormalities also, although they can occur in isolation.
These anomalies result in conductive hearing loss.
When bilateral, they are most frequently genetic with autosomal ...
The conjunctiva (plural: conjunctivas or conjunctivae) is a transparent membrane is attached at the margins of the cornea. It is loosely attached to the sclera and thence reflected over the inner surface of the eyelids. It is firmly attached to the tarsal plates and blends with the skin at the m...
A convoluted cerebriform pattern is a term used to denote the appearance of a sinonasal inverted papilloma on MRI. The appearance is seen on both T2 and post contrast T1 images and appears as alternating roughly parallel lines of high and low signal intensity.
This sign has been reported as pre...
The cornea forms the fibrous layer of the anterior portion of the eye. It functions to refract light entering the eye.
location: anterior one-sixth of the eyeball
blood supply: avascular
innervation: long ciliary nerves
relations: continuous with the sclera posteriorly and covered...
The corniculate cartilages are paired, elastic and accessory cartilages of the larynx that lie superior to and articulate with the apices of the arytenoid cartilages. They are components of the laryngeal cartilages. The word 'corniculate' comes from the latin word 'cornu' meaning horn-like.
The coronal suture is the cranial suture formed between the two parietal bones and the frontal bone. At the junction of coronal, sagittal and frontal sutures is the anterior fontanelle which is open at birth and usually fuses at around 18-24 months after birth.
Fusion of the coronal suture occu...